Search

The distribution and abundance of hippoid zoeal stages offshore Veracruz, southern Gulf of Mexico, and the migration routes of these larvae in the western Atlantic, were analysed. Samples were collected with a Bongo net and larval dispersal was analysed applying the HYCOM hydrodynamical model; particles (virtual larvae) originating from 35 sites were tracked for 77 days. Larvae of Albunea paretii Guérin-Méneville, 1853 were the most abundant, and dispersal simulations indicated that older larvae occurring off Veracruz might originate from Texas. However, a substantial proportion of self-recruitment (7.8%) can occur, mainly due to the seasonal changes in direction of currents over the shelf as well as the high variability in weather conditions. Results also suggest that several generations of A. paretii are needed for the species to reach Veracruz from South America. A hypothetical model regarding the migration routes of A. paretii larvae in the western Atlantic is proposed.

The population ecology of luciferids has been scarcely studied. This study examined the distribution and population parameters of Belzebub faxoni and Lucifer typus in the western Gulf of Mexico. Samples were collected using a Bongo net at 82 sampling stations during three periods (July, January, and October–November). Abundance data of species were subjected to a regression tree analysis to determine the main factors affecting their distribution. In addition, total length data of individuals were fitted to a logistic equation to estimate the size at first maturity. Food availability was the key factor affecting the distribution of B. faxoni, which exhibited its highest abundance over the inner shelf. In contrast, L. typus avoided low salinity waters (&lt, 35.9 psu), and its highest densities were found over the slope and oceanic areas. The sex ratio in B. faxoni was always biased towards females, but L. typus showed variable sex proportions. Several hypotheses attempting to explain these disparities are discussed. Size structure in B. faxoni favored small individuals in summer, the reproduction peak. In contrast, the L. typus population was always dominated by large individuals, probably transported by currents from the main hatching sites. Size at first maturity was higher in L. typus (females: 8.16 mm, males: 8.63 mm) than in B. faxoni (females: 6.53 mm, males: 6.74 mm). Information here provided may help to better understand the population dynamics of these species.

espanolEn Costa Rica, los estudios sobre zooplancton que aborden los anfipodos pelagicos son escasos, la lista de especies previa a este trabajo incluye solo 41 especies del suborden Hyperiidea. El objetivo de este estudio fue actualizar la lista de especies de anfipodos pelagicos del Pacifico de Costa Rica y registrar especies previamente desconocidas en el pais. En julio de 2012, se realizo el muestreo del zooplancton de aguas cercanas a la isla del Coco, Costa Rica, en 26 estaciones oceanograficas. Un total de 13 especies de anfipodos pelagicos de los subordenes Amphilochidea (1), Hyperiidea (11) y Senticaudata (1) fue identificado para aguas del Pacifico costarricense. Los nuevos registros incrementan el conocimiento de la riqueza de anfipodos pelagicos para el Pacifico de Costa Rica a 54 especies, lo que sugiere la necesidad de explorar mas la diversidad de estos organismos en la region. EnglishFew studies of zooplankton have been carried out in Costa Rica that address pelagic amphipods; the species list prior to this work includes only 41 species from the suborder Hyperiidea. The aim of this paper was to update the species list of pelagic amphipods from the Pacific of Costa Rica, and record previously unknown species from the country. In July 2012, zooplankton sampling was carried out in the waters near Cocos Island, Costa Rica, at 26 oceanographic stations. A total of 13 pelagic amphipod species from the suborders Amphilochidea (1), Hyperiidea (11) and Senticaudata (1) were identified in the Pacific waters of Costa Rica. These new records increase the known total of pelagic amphipod species from the Pacific of Costa Rica to 54 species, which suggests a need to further explore the diversity of these organisms in the region. portuguesNa Costa Rica, os estudos sobre zooplâncton que abordam os anfipodes pelagicos sao escassos e a lista de especies previa a este trabalho inclui somente 41 especies da subordem Hyperiidea. Este estudo teve como objetivo atualizar a lista de especies de anfipodes pelagicos do Pacifico da Costa Rica e registrar especies previamente desconhecidas no pais. Em julho de 2012, foi realizada a amostragem do zooplâncton de aguas proximas a Isla del Coco, Costa Rica, em 26 estacoes oceanograficas. Um total de 13 especies de anfipodes pelagicos das subordens Amphilochidea (1), Hyperiidea (11) e Senticaudata (1) foi identificado nas aguas do Pacifico costarricense. Os novos registros aumentam o conhecimento da riqueza de anfipodes pelagicos no Pacifico da Costa Rica a 54 especies, sugerindo a necessidade de explorar mais a diversidade destes organismos na regiao.

Resumen Introducción: Clypeaster europacificus es una especie de galleta de mar que se distribuye de 0 a 200 m en el Golfo de California. Objetivo: Describir la morfología y el crecimiento relativo en la testa de C. europacificus. Métodos: Medimos 1 846 especímenes de museo de C. europacificus (N = 1 846) y analizamos el patrón de crecimiento en 32 especímenes de Baja California Sur, México (64 m de profundidad). Estudiamos cinco variables: radio mayor (R) (variable independiente), radio menor (r), longitud del pétalo anterior (LP), área total de prueba (A) y peso seco (P). Resultados: El área de cobertura del petaloide y el contorno de la testa son los caracteres taxonómicos importantes para C. europacificus: los especímenes van desde casi redondos en especímenes pequeños (≤ 3 cm de radio) a ondulados, enfatizando un contorno pentagonal, en organismos más grandes (≥ 3,1 cm de radio). Conclusiones: Existe un crecimiento alométrico negativo en las relaciones R vs. r, R vs. A y R vs. P; mientras que la relación R vs. LP tiene un crecimiento alométrico positivo. Abstract Introduction: Clypeaster europacificus is a species of sand dollar found from 0 to 200 m in the Gulf of California. Objective: Describe the morphology and relative growth in the test of C. europacificus. Methods: We measured 1 846 museum specimens of C. europacificus (N = 1 846) and analyzed growth pattern in 32 specimens from Baja California Sur, Mexico (64 m depth). We studied five variables: major radius (R) (independent variable), minor radius (r), length of anterior petal (LP), total test area (A) and dry weight (P). Results: The petaloid cover area and the outline of the test are the important taxonomic characters for C. europacificus: they range from almost round in small specimens (≤ 3 cm in radius) to wavy, emphasizing a pentagonal outline, in larger organisms (≥ 3.1 cm in radius). Conclusions: There is negative allometric growth in the relationships R vs. r, R vs. A, and R vs. P; while the relationship R vs. LP has positive allometric growth.

Tropical ophiuroid fauna belonging to the family Ophiolepididae are almost unknown. This study deals with the relative growth and morphometric traits of the ophiuroid Ophiolepis crassa from the Gulf of California, Mexico. Specimens examined in this study came from the Colección Nacional de Equinodermos, Universidad Nacional Autónoma de México, and were collected over soft bottoms off Punta Gorda. Thirteen anatomical features were measured in a total of 152 specimens, including disk diameter, arm length, as well as length and width of dorsal and ventral arm plates, and radial, oral, and adoral shields. Based on the range of values of the disk diameter, varying from 4 to 19 mm, we provided quantitative data on each anatomical measurement considering three size classes. Morphometric data were adjusted to a power equation to detect the degree of allometry in the growth of anatomical traits. Results indicated that all the ventral and dorsal plates, as well as the radial, oral, and adoral shields, suffer changes in shape during growth, but these changes are stronger in the plates. In addition, an analysis of symmetry applied to both right and left radial shields revealed that these structures remain nearly symmetrical during growth. The disk diameter vs arm/disk relationship indicated that the species is a surface dweller inhabitant of the seafloor. This study, based on a single sample collected in a restricted area of the eastern Pacific, provides useful quantitative information for further taxonomic, systematic, or biogeographic studies.

espanolResumen: El zooplancton dominante de la laguna La Mancha, Veracruz, Mexico, fue analizado con el objetivo de evaluar su variabilidad estacional y nictimera, asi como la influencia que sobre el ejercen las principales variables ambientales. De mayo 2012 a abril 2013, cada mes se realizo un ciclo de 24 h, tomando muestras cada 4 h, en la boca de la laguna. Simultaneamente a la toma de muestras de zooplancton, se registraron parametros ambientales in situ como la temperatura, oxigeno disuelto, salinidad, clorofila a y numero de celulas fitoplanctonicas. Se capturaron 54 taxa (principalmente del holoplancton) y 10 de ellos fueron considerados dominantes (abundancia total > 0,5%). La comunidad estuvo dominada por dos especies de copepodos (Acartia tonsa y Pseudodiaptomus pelagicus), asi como por larvas zoea de braquiuros (~85%). La abundancia total del zooplancton mostro pulsos significativos a lo largo del ano, uno en febrero-marzo dominado por copepodos y otro en septiembre-octubre, dominado por larvas de decapodos. A pesar de que la abundancia total del zooplancton fue mayor en la noche, solo P. pelagicus, anfipodos, megalopas y otras larvas de decapodo fueron significativas durante este periodo. De acuerdo con un Analisis de Correspondencia Canonica, el estado de la boca (abierta/cerrada), numero de cianofitas y precipitacion fueron los factores ambientales mas importantes en la determinacion de la abundancia del zooplancton dominante. EnglishAbstract: The dominant zooplankton of the La Mancha lagoon, Veracruz, Mexico, was analyzed with the objective of evaluating its seasonal and diel variability, as well as the influence of the main environmental variables on this variability. From May 2012 to April 2013, every month a 24-h cycle was completed, taking samples every 4 h, at the mouth of the lagoon. Simultaneously with zooplankton sampling, in situ environmental parameters such as temperature, dissolved oxygen, salinity, chlorophyll a and number of phytoplankton cells were recorded. We collected 54 taxa (mainly holoplankton) and 10 of them were considered dominant (total abundance > 0.5%). The zooplankton community was dominated mainly by two species of copepods (Acartia tonsa and Pseudodiaptomus pelagicus), as well as zoea larvae of brachyura (~85%). At seasonal level, the total abundance of zooplankton showed significant pulses throughout the year, one in February-March dominated by copepods and another in September-October, dominated by decapod larvae. On a diel scale, although total zooplankton abundance was significantly higher at night, only P. pelagicus, amphipods, megalopae, and other decapod larvae showed significant differences at this level. According to a Canonical Correspondence Analysis, the mouth stage (open/close), the number of cyanophytes and precipitation were the most important environmental factors in determining the abundance of the dominant zooplankton.

Immigration density magnitude and entry sizes of shrimp postlarvae to Terminos Lagoon were analyzed through sixteen fortnightly sampling from March to November in 2013, in three levels in the deepest channel of the Puerto Real inlet. Trapezium nets were used with 1.5 m length, 50 cm mouth diameter and 505 μm mesh, during each sampling 12 casts of 15 minutes/each were made. It was determined the presence of two species Litopenaeus setiferus and Farfantepenaeus duorarum, with total densities of 41.284 and 37.558 Pls 100 m-3 respectively. The annual cycle of immigration of postlarvae was very similar for both species, with a clear pattern of immigration throughout the year, linked to climatic variation, with the highest densities (88%) during rainy season. There were two periods of maximum density, related to the periods of greatest reproduction of these species. The density variation among cast reflects the presence of at least two and probably more postlarvae banks, located some closer than others to the mouth of the lagoon and with different densities in them. The average sizes of the two species were 7.9 mm total length of L. setiferus and 9.0 mm of F. duorarum. The differences in income sizes of both species seem to indicate the habitat preference of adult populations, L. setiferus occurring in more coastal areas than F. duorarum. Considering the variation in density and sizes throughout each sampling period, it is evident that the larvae on the banks belong to different cohorts and that have coincided in their location in front of the mouth.

En este estudio se analizo la fauna de moluscos holoplanctonicos en aguas neriticas de Mahahual, Reserva de la Biosfera Caribe Mexicano, bajo la hipotesis de encontrar una homogeneidad en la distribucion de la fauna en las plataformas interna y externa debido a la estrecha plataforma continental. Los muestreos de zooplancton se efectuaron con 2 redes conicas de apertura de malla de 333 y 505 μm en 33 estaciones de muestreo. En el laboratorio se estimo la biomasa de zooplancton en peso humedo y se separaron e identificaron los moluscos holoplanctonicos. Los valores de biomasa registrados (0.02 a 7.51 g 100 m-3) son tipicos de las aguas oligotroficas del Caribe. Se identificaron 8 especies de moluscos, que en orden decreciente de abundancia son: Creseis acicula, Heliconoides inflatus, Atlanta lesueurii, Diacavolinia longirostris, Limacina trochiformis, Limacina lesueurii, Firoloida desmarestia y Limacina bulimoides . Los resultados de la prueba estadistica Anosim mostraron que no hubo diferencias en la distribucion de la fauna entre las plataformas interna y externa, probablemente debido a la fuerte influencia de aguas oceanicas sobre las neriticas. La informacion aqui proporcionada es de gran importancia en la generacion de eventuales planes de conservacion de la biota pelagica de la reserva.

Many important phenomena in the plankton are driven by encounters among individuals. These encounters are mediated by the relative motion of zooplankters, either through the swimming ability of organisms, the small-scale hydrodynamic turbulence, or both. Through selected case studies, in this chapter, we illustrate how encounter rates influence the predator-prey interactions and reproduction, two of the major processes regulating the zooplankton population dynamics. Estimations on the encounter rates among zooplankters were made on the basis of the Gerritsen-Strickler and Rothschild-Osborn models, which consider non-turbulent and turbulent conditions, respectively. In a first case, we show how the predatory impact of siphonophores is over the fish larvae, in the southern Gulf of Mexico. In the absence of water turbulence, a predator encounters 38–40 prey in a day at surface waters, but under the influence of the wind, encounters can increase between 1.2 and 3.3 times depending on the wind velocity and prey speed. In a second case, we examined the encounters between a copepod predator and a cladoceran prey, the dominant groups in the meromictic lagoon of Clipperton atoll. Here, a predator can encounter a high number of prey (until 441) in a day, due to the high density of prey. Turbulence conditions enhance encounter rates, but even if encounters are high, it does not mean that a predator can ingest a high number of prey. In a third case, we analyzed the mate encounters of the holoplanktonic mollusk Firoloida desmarestia from the southern Gulf of Mexico, throughout an annual cycle. Results indicated that May is the high reproductive season, a period where a female can encounter 17 males in a day, under turbulent conditions. As F. desmarestia is a low abundant species, the role of wind-induced turbulence proved to be highly important in increasing encounters between mates. These case studies illustrate the importance of encounters among zooplankters in the growth and maintenance of populations in the plankton. Future field and experimental studies are needed to achieve a better understanding of the pelagic ecosystem dynamics.

espanolResumen: La costa sur del Golfo de Mexico es tipicamente una llanura costera que alterna con salientes rocosas. Este estudio tuvo como objetivo comparar la estructura comunitaria de los quitones del litoral rocoso de Montepio, durante los periodos meteorologicos de secas y nortes y proporcionar datos sobre el crecimiento relativo de las especies dominantes. Se muestreo sobre un transecto de 100 x 2 m en la zona intermareal y se recolectaron 83 individuos. Se identificaron 6 especies: Lepidochitona rosea, Chaetopleura apiculata, Ischnochiton kaasi, Lepidochitona pseudoliozonis, Lepidochitona liozonis y Acanthochitona andersoni. Las 2 epocas fueron muy similares en riqueza de especies (S= 4) y diversidad de Shannon (1,36 y 1,29 bits ind-1 en secas y nortes); sin embargo, solo 2 especies ocurrieron en ambos periodos, lo que indica un fuerte recambio estacional de especies (50%). Esta dinamica estacional se deberia a la discontinuidad del sustrato rocoso, que no permitiria una recuperacion rapida de las poblaciones despues del impacto de los nortes. La densidad de organismos fue baja ( EnglishAbstract: The southern Gulf of Mexico is typically a coastal plain where rocky shores are scattered distributed. The goal of this study was to compare the chiton community structure of the rocky shore of Montepio during the dry and ‘nortes’ (stormy) weather periods, and to gather data on the relative growth of the dominant species. Sampling was carried out along a transect of 100 x 2 m in the intertidal zone and 83 individuals were collected. Six species were identified: Lepidochitona rosea, Chaetopleura apiculata, Ischnochiton kaasi, Lepidochitona pseudoliozonis, Lepidochitona liozonis and Acanthochitona andersoni. Species richness (S= 4) and Shannon diversity (1.36 and 1.29 bits ind-1 in dry and stormy seasons) were very similar between the 2 seasons; however, only 2 species occurred in both periods, suggesting a strong seasonal exchange of species (50%). This seasonal dynamics could be due to the discontinuity of the rocky substrate, which would not allow a rapid recovery of the populations after the impact of storms. Density of individuals was low (

The immigration of white shrimp Penaeus setiferus (Decapoda: Penaeidae) postlarvae (Pls) into the Terminos Lagoon was studied to determine the annual pattern of abundance and its relationship with temperature, salinity, tidal current velocity, and river discharge. Zooplankton samples were simultaneously obtained fortnightly at surface, mid-water, and bottom. The nets used were 50 cm in diameter, 1.5 m in length and 505 μm mesh size. The results indicated a postlarval seasonal immigration pattern, with the lowest average density values from March to May and October to November, and significantly higher values from June to September; maximum peaks occurred in June and September. High Pls densities were obtained between one and three hours after the tidal inflow started. Temperature and salinity varied little during each sampling period and had no apparent effect on immigration, but did have an effect on the seasonal abundance cycle. The multiple regression models indicated that the tidal current velocity and the temperature explained 86% of the variation in Pls abundance during immigration to the Terminos lagoon. The larval migration varied at different levels, with highest densities occurring at a medium depth of 5 m. The Pls entered an optimal range of tidal current velocity (between 0.6 and 0.9 m3 s-1). The main entry mechanism was through the tide current of the Selective Tide Stream Transport, where the Pls could also select an optimum current velocity, avoiding the strata of higher turbulence that would imply higher energy expenditures.

This study examines the sexual differences in relative growth and morphometrical traits of the land crabJohngarthia planata(Stimpson, 1860). Individuals came from Clipperton, where an expedition was conducted in April 2015. A total of 275 individuals were captured manually, sexed and measured in seven dimensions from the carapace and chelae. Measurements were fitted to a power function to analyse the degree of allometry in growth. Results indicated that males had larger body and chelae sizes than females. For both sexes growth was negatively allometric for the carapace and positively allometric for the chelae. We hypothesize that stronger bodies in males confer advantages during intraspecific combats and their enlarged chelae are associated to their sexual behaviour. For each sex, measurements of both right and left chelae showed a homochelic condition. We suggest that these symmetrical features provide stability and balance to their body when feeding, fighting or excavating their burrows.

In order to study the segregated distribution of the three most abundant jellyfish species in the southern Gulf of Mexico, a total of 85 stations were sampled during an oceanographic cruise from 19 May to 18 June 2006. Trawling took place from surface to a maximum depth of 200 m, using a Bongo net with a 61 cm mouth diameter and 333 and 500 μm mesh sizes. Temperature and salinity were recorded. Samples were preserved in 4% formalin, neutralized with sodium borate, and changed to 70% ethylic alcohol after 24 hours for conservation. The jellyfish data were standardized to 100 m3 of filtered water. A total of 10,610 jellyfish were collected from the 333 μm mesh size net, of which eight species represented 88.49% of the total density: Aglaura hemistoma, Liriope tetraphylla, Nausithoe punctata, Clytia hemisphaerica, Persa incolorata, Obelia spp., Clytia folleata and Eutima gracilis. The former three species are the subject of this study. The results obtained indicate that the high density areas of these three species have a segregated distribution. Segregation values (White’s index) recorded between pairs of specie were very high: L. tetraphylla - A. hemistoma, 0.88; L. tetraphylla - N. punctata, 0.86 and A. hemistoma - N. punctata, 0.84. The spatial distribution of the high density areas of these species fits well with the three hydrodynamically different areas: A. hemistoma in Campeche Bank, L. tetraphylla on the Campeche and Tabasco shelves and N. punctata in Campeche Bay. This spatial distribution pattern corresponds to their main habitat and reproductive habits of the species, as well as the influence of the hydrodynamics that dominate each area.

Vertical distribution, sex ratio, size structure and mate encounters of Firoloida des- marestia in the southern Gulf of Mexico were analyzed during 4 seasons (in February, May, August and November). A total of 395 individuals were collected with an opening−closing net at 5 levels of the 105 m upper water column. Results indicated that the species reproduces throughout the year, with a reproductive peak in May and a low reproductive period from August to February. Length measurements indicated that females (as long as 30 mm) are larger than males (18 mm). Estimations of a 'spatial overlap' index showed a high overlap degree between sexes, suggesting that patterns in their vertical distribution are not a reproductive barrier. Sex ratio (F:M) at birth seemed to be 1:1, but during most of the year the adult sex ratio was dominated by females. We propose that larger dimensions and faster swimming speeds of females provide competitive advantages over males in searching for food and avoiding predators. Simulations of mate encoun- ters indicated that values during the low reproductive season were low under turbulent and non- turbulent conditions (< 4.9 males d −1 female −1 ), but enough to fertilize a high percentage of females. During the high reproductive season, encounters were as high as 17.2 males d −1 female −1 because the high density of adult population and the influence of wind-induced turbulence. We suggest that some biological features of females (seminal receptacle and exocrine gland) compen- sate for the low encounter rates. A conceptual model for the population dynamics of F. desmarestia is proposed.

The connectivity among subpopulations of Panulirus argus in the Gulf of Mexico is evaluated using a particle-tracking model coupled to a realistic hydrodynamic simulation generated with the Hybrid Coordinate Ocean Model. In 12 potential subpopulations of the Gulf of Mexico, virtual larvae were released daily from March 21 to June 18, 2006–2010. Virtual propagules were tracked for a maximum of 198 days and programmed to undergo vertical migrations and to eventually “die” according to an exponential decay function. The subpopulations that were the most inter-connected and had the highest values of self-settlement were those from the Bay of Campeche (Campeche, Southern Veracruz, Central Veracruz, and Northern Veracruz). This pattern can be explained by the recirculation resulting from the semi-permanent cyclonic gyre in the Bay of Campeche and the back and forth behaviour of the shelf currents at Veracruz. Self-settlement was low at Quintana Roo, Southern Florida, and Northwestern Cuba, because the Loop Current quickly transported the larvae away from those areas. Southern Florida received a considerable number of settlers coming from almost all other subpopulations mainly by means of the Loop Current. Larvae from Yucatan may be transported to subpopulations in the Bay of Campeche by means of both westward Loop Current Eddies and the westward inner-shelf current in the Campeche Bank. The continental shelf of the Bay of Campeche, particularly the islands and cays in the western edge of the Campeche Bank, emerged as both important settlement areas and larval dispersal pathways. A program for the protection of the species in these areas may help increase the population size of P. argus in the Gulf of Mexico, potentially favouring local fisheries.

This study simulated the connectivity patterns among 7 coral reef systems in the southern Gulf of Mexico. Two subgroups of reefs were considered: one near the mainland over the narrow western shelf, and the other over the wide Campeche Bank (CB). A particle-tracking mod- ule was coupled to a realistic simulation with the Hybrid Coordinate Ocean Model in order to study the transport and dispersion of particles in near surface waters. The simulation consisted of the launch of 100 passive particles (virtual larvae) from each reef, every 24 h over a 5 year period; it considered species lasting up to 35 d in the plankton and assumed no seasonality in reproduc- tion. On the western shelf, connection was northwards from March to August, and southwards from September to February; over the CB edge, the connection was northwestwards throughout the year. Over the western shelf, reefs showed a strong degree of interconnectivity and high par- ticle retention. Higher self-recruitment was most likely due to the passage of synoptic-scale atmospheric systems and their associated changes in wind and current direction. In contrast, CB reefs exhibited lower connectivity and less larval retention. Over the western edge of the Bank, connectivity was almost unidirectional because of the influence of the cyclonic gyre in the Campeche Bay, which causes particles to disperse over a wide area with low probabilities of self- recruitment. The main connection pathway was the confluence zone between neritic and oceanic waters over the outer shelf of the Bank. Connection between the 2 groups of reefs was weak.

The present study examines how the habitat type and food availability influence the small scale distribution and assemblages of opisthobranch species in the National Park Arrecife Alacranes, the largest coral reef system in the southern Gulf of Mexico. Samples were collected during December 2009, and April and September 2010 over different habitats (green, red, and brown algae, seagrass meadows, drifting Sargassum spp., rocks, corals, and sand). In total, 32 species were identified and a multidimensional scaling (MDS) analysis based on the Bray-Curtis similarity index was used to determine the main opisthobranch assemblages. The degree of association between the habitat type and the species composition was tested by a chi-square test and the significance of its value was determined by Monte Carlo randomizations. MDS results defined four faunal associations ("algal", "Thalassia", "Sargassum", and "rocky" assemblages), which showed a significant relationship between the composition of opisthobranch species and the habitat type. These results suggest that food supplies and feeding strategies play a dominant role in the coexistence of species and their small-scale spatial distribution within the reef. The algal assemblage, the group with the highest species richness, was mainly composed of herbivores inhabiting several types of benthic algal communities, whereas the Sargassum assemblage, was a less diversified group comprised of carnivores feeding on epibiont hydroids and was well adapted to the pelagic environment. The distribution of the opisthobranchs over the different habitats largely reflected the variety and availability of their food items.

The small-scale vertical distribution of five genera of holoplanktonic molluscs inhabiting the upper oceanic layer (0–105 m) was analysed to test whether evident distribution patterns could be attributed to habitat partitioning. Zooplankton samples were taken over neritic waters during the day and night using a 505-μm multiple closing net at five levels (0–6, 6–12, 12–18, 45–55 and 95–105 m) of the water column. Flowmeters were placed in each net to estimate the amount of filtered water. From the 55,654 identifiable specimens of holoplanktonic molluscs, only 6.2 % were in juvenile stage, and Cavolinia, Diacavolinia, Diacria, Oxygyrus and Clio were the most abundant genera. Adults of these genera comprised 3 % of the total abundance. The abundance data were examined using a spatial segregation index, and its significance was tested with null model methods based on Monte Carlo randomizations. Results indicated that adults showed a much more overlapped distribution in the water column than the in the earlier stages. Indeed, juveniles of Cavolinia, Diacavolinia and Oxygyrus were mainly found in the 0–18-m layer, whereas Diacria and Clio were recorded in the 45–105-m stratum. Null model arguments revealed a significant vertical segregation among them. Potential ecological factors involve preferential spawning areas of adults, avoidance of competition for feeding and spatial resources, use of visual capabilities in searching prey, brood protection and avoidance of strong turbulence conditions.

[Information on growth in hermit crabs is very scarce, possibly due to the inherent difficulties of extracting them from their shells. In this work we document the relative growth, sexual size dimorphism, and level of chelae asymmetry of the land hermit crab Coenobita clypeatus (Fabricius, 1787) collected on a coral reef island in the National Park Arrecife Alacranes, southern Gulf of Mexico, during December 2009 and September 2010. Specimens examined were anaesthetized in a clove oil-water solution to avoid unnecessary crab mortality. A total of 387 individuals was measured on six external variables: cephalothorax length and width, and both chelae in length and width. Taking the cephalothorax length as the reference dimension, the remaining measurements were fitted to a power function to examine the degree of allometry in growth and make comparisons between sexes. For each sex, an asymmetry index (AI) was calculated to determine the degree of heterochely, and the significance of its value was evaluated by means of null models. Numerically, males dominated the crab population in the largest size classes (>12.6 mm CL) in both seasons. As in most anomurans, C. clypeatus males attained larger body sizes than females, but their relative growth was most similar. For both sexes, the growth of chela width was positively allometric ( t -test, p p La informacion sobre el crecimiento de los cangrejos ermitanos es muy escasa, posiblemente debido a las inherentes dificultades para extraerlos de sus conchas. En este trabajo se documenta el crecimiento relativo, dimorfismo sexual y el nivel de asimetria de las quelas del cangrejo ermitano Coenobita clypeatus (Fabricius, 1787) recolectados en una isla coralina del Parque Nacional Arrecife Alacranes, sur del Golfo de Mexico, durante diciembre de 2009 y septiembre de 2010. Los especimenes examinados fueron anestesiados con una solucion de aceite de clavo para evitar la mortalidad innecesaria de cangrejos. Un total de 387 individuos se midieron en seis variables externas: largo y ancho del cefalotorax y largo y ancho de ambas quelas. Tomando la longitud del cefalotorax como la dimension de referencia, el resto de las medidas se ajusto a una funcion de tipo potencial para examinar el grado de alometria en el crecimiento y hacer comparaciones entre los sexos. Para cada sexo, se calculo un indice de asimetria (AI) a fin de determinar el grado de heterogeneidad entre las quelas y su valor de significancia fue evaluado por medio de modelos nulos. Numericamente, los machos dominaron la poblacion de cangrejos en las tallas de clase mayores (>12,6 mm CL) en ambas epocas. Como en la mayor parte de los anomuros, los machos de C. clypeatus alcanzan mayores tallas corporales que las hembras, pero su crecimiento relativo fue muy similar. Para ambos sexos, el crecimiento en el ancho de las quelas fue alometrico positivo ( t -test, p p , Information on growth in hermit crabs is very scarce, possibly due to the inherent difficulties of extracting them from their shells. In this work we document the relative growth, sexual size dimorphism, and level of chelae asymmetry of the land hermit crab Coenobita clypeatus (Fabricius, 1787) collected on a coral reef island in the National Park Arrecife Alacranes, southern Gulf of Mexico, during December 2009 and September 2010. Specimens examined were anaesthetized in a clove oil-water solution to avoid unnecessary crab mortality. A total of 387 individuals was measured on six external variables: cephalothorax length and width, and both chelae in length and width. Taking the cephalothorax length as the reference dimension, the remaining measurements were fitted to a power function to examine the degree of allometry in growth and make comparisons between sexes. For each sex, an asymmetry index (AI) was calculated to determine the degree of heterochely, and the significance of its value was evaluated by means of null models. Numerically, males dominated the crab population in the largest size classes (>12.6 mm CL) in both seasons. As in most anomurans, C. clypeatus males attained larger body sizes than females, but their relative growth was most similar. For both sexes, the growth of chela width was positively allometric ( t -test, p p La informacion sobre el crecimiento de los cangrejos ermitanos es muy escasa, posiblemente debido a las inherentes dificultades para extraerlos de sus conchas. En este trabajo se documenta el crecimiento relativo, dimorfismo sexual y el nivel de asimetria de las quelas del cangrejo ermitano Coenobita clypeatus (Fabricius, 1787) recolectados en una isla coralina del Parque Nacional Arrecife Alacranes, sur del Golfo de Mexico, durante diciembre de 2009 y septiembre de 2010. Los especimenes examinados fueron anestesiados con una solucion de aceite de clavo para evitar la mortalidad innecesaria de cangrejos. Un total de 387 individuos se midieron en seis variables externas: largo y ancho del cefalotorax y largo y ancho de ambas quelas. Tomando la longitud del cefalotorax como la dimension de referencia, el resto de las medidas se ajusto a una funcion de tipo potencial para examinar el grado de alometria en el crecimiento y hacer comparaciones entre los sexos. Para cada sexo, se calculo un indice de asimetria (AI) a fin de determinar el grado de heterogeneidad entre las quelas y su valor de significancia fue evaluado por medio de modelos nulos. Numericamente, los machos dominaron la poblacion de cangrejos en las tallas de clase mayores (>12,6 mm CL) en ambas epocas. Como en la mayor parte de los anomuros, los machos de C. clypeatus alcanzan mayores tallas corporales que las hembras, pero su crecimiento relativo fue muy similar. Para ambos sexos, el crecimiento en el ancho de las quelas fue alometrico positivo ( t -test, p p ]

Understanding the effects of regional processes on local community structure is a central issue of metacommunity studies. Here we examined the relative contribution of both regional and local processes to fish larvae community structure of seven brackish lagoons located along the Mexican Atlantic coast. The database analysed includes over 982 sampling stations. Partial Mantel tests were used to determine whether among lagoon differences in species composition were related to local, and/or regional-scale factors while controlling the effects of both geographical distances and lagoon environmental characteristics. Results indicate that regional processes had significant (P < 0.05) influence on the composition of the ichthyoplankton communities, with environmental characteristics either included (r 2 = 19.5%) or removed (r 2 = 23.7%), whereas local environmental characteristics were non-significantly associated (P= 0.917). Alongshore currents associated with larval duration appeared to be an important factor affecting connectivity among estuaries, whereas offshore currents seemed to represent an ecological boundary between the southern Gulf of Mexico and the Yucatan coasts. Also, regional terrestrial changes in freshwater sources between these regions appeared to be determinant for the presence of certain species. Metacommunity structure of the lagoons agrees with the "mass effects" model, in which patches are heterogeneous and regional phenomena represent the crucial spatial scales in community dynamics. There is an increasing need to model larval behaviour in relation to the physical scenario to evaluate the role of alongshore currents and oceanographic boundaries as they affect the extent of larval dispersal.

[Decapod metapopulation dynamics are better understood by confronting theoretical studies with empirical data. In this study, our goal was to analyse the morphometric characteristics and relative growth of the carapace of Trapezia bidentata (Forskal, 1775) and T. digitalis Latreille, 1828, crabs from the islands Clipperton and Revillagigedo, in order to assess the degree of inter- and intraspecific similarity of the four insular populations. We examined 325 specimens and identified four species: T. bidentata (72.9% of total abundance), T. digitalis (23.1%), T. formosa Smith, 1869 (3.4%), and T. corallina Gerstaecker, 1857 (0.6%). Three carapace measurements were taken for each specimen: carapace width (CW), carapace length (CL), and interocular distance (ID). The variables CL and ID were fit to a power equation taking CW as the reference dimension. As in other brachyurans, growth pattern analyses indicated an isometric type in all CW vs CL and CW vs ID relationships examined. Interspecific differences included a larger body size for T. bidentata and larger ID/CW for T. digitalis . Significant intraspecific differences in the two insular populations of T. digitalis were evidenced in the ID/CW ratio. In contrast, populations of T. bidentata were morphometrically closer. These results indicate a higher degree of connectedness of the parts of the T. bidentata metapopulation than of that of T. digitalis , probably due to differences in the duration of their larval stages. We think that the larger body size in T. bidentata might account for competitive advantages in food gathering and habitat selection over the remaining species. In turn, as a counteracting trait for its smaller size, the larger ID might allow T. digitalis a better ability to perceive 3D and to judge relative distances between objects, thus avoiding competitive combats and improving antipredatory or escape responses. La dinamica de las metapoblaciones de decapodos se comprende mejor confrontando estudios teoricos con datos empiricos. En este estudio, nuestro objetivo fue analizar las caracteristicas morfometricas y el crecimiento relativo del caparazon de Trapezia bidentata (Forskal, 1775) y T. digitalis Latreille, 1828, cangrejos de las islas Clipperton y Revillagigedo a fin de determinar el grado de similitud inter- e intraespecifica de las cuatro poblaciones insulares. Se examinaron 325 especimenes e identificaron cuatro especies: T. bidentata (72.9% de la abundancia total), T. digitalis (23.1%), T. formosa Smith, 1869 (3.4%) y T. corallina Gerstaecker, 1857 (0.6%). Para cada especimen, se tomaron tres dimensiones del caparazon: ancho (CW), largo (CL) y distancia interocular (ID). Las variables CL e ID se ajustaron a una ecuacion de tipo potencial tomando CW como la dimension de referencia. Como en otros braquiuros, los analisis del patron de crecimiento mostraron un tipo isometrico en todas las relaciones CW vs CL y CW vs ID examinadas. Las diferencias interespecificas incluyeron un mayor tamano corporal para T. bidentata y un mayor valor en el cociente ID/CW para T. digitalis . Se evidenciaron diferencias significativas intraespecificas entre las dos poblaciones insulares de T. digitalis en el cociente ID/CW. En contraste, las poblaciones de T. bidentata fueron morfometricamente mas semejantes. Estos resultados indican un mayor grado de conectividad en la metapoblacion de T. bidentata que en aquella de T. digitalis , debido probablemente a diferencias en la duracion de sus estados larvarios. Se piensa que la mayor talla corporal de T. bidentata representaria una mayor ventaja competitiva sobre el resto de las especies para atrapar alimento y seleccionar su habitat. A su vez, para contrarrestar su pequeno tamano, mayor ID permitiria a T. digitalis una mejor habilidad para percibir la 3D y juzgar la distancia relativa entre los objetos, evitando asi combates competitivos y mejorando sus respuestas de escape y antidepredatorias. , Decapod metapopulation dynamics are better understood by confronting theoretical studies with empirical data. In this study, our goal was to analyse the morphometric characteristics and relative growth of the carapace of Trapezia bidentata (Forskal, 1775) and T. digitalis Latreille, 1828, crabs from the islands Clipperton and Revillagigedo, in order to assess the degree of inter- and intraspecific similarity of the four insular populations. We examined 325 specimens and identified four species: T. bidentata (72.9% of total abundance), T. digitalis (23.1%), T. formosa Smith, 1869 (3.4%), and T. corallina Gerstaecker, 1857 (0.6%). Three carapace measurements were taken for each specimen: carapace width (CW), carapace length (CL), and interocular distance (ID). The variables CL and ID were fit to a power equation taking CW as the reference dimension. As in other brachyurans, growth pattern analyses indicated an isometric type in all CW vs CL and CW vs ID relationships examined. Interspecific differences included a larger body size for T. bidentata and larger ID/CW for T. digitalis . Significant intraspecific differences in the two insular populations of T. digitalis were evidenced in the ID/CW ratio. In contrast, populations of T. bidentata were morphometrically closer. These results indicate a higher degree of connectedness of the parts of the T. bidentata metapopulation than of that of T. digitalis , probably due to differences in the duration of their larval stages. We think that the larger body size in T. bidentata might account for competitive advantages in food gathering and habitat selection over the remaining species. In turn, as a counteracting trait for its smaller size, the larger ID might allow T. digitalis a better ability to perceive 3D and to judge relative distances between objects, thus avoiding competitive combats and improving antipredatory or escape responses. La dinamica de las metapoblaciones de decapodos se comprende mejor confrontando estudios teoricos con datos empiricos. En este estudio, nuestro objetivo fue analizar las caracteristicas morfometricas y el crecimiento relativo del caparazon de Trapezia bidentata (Forskal, 1775) y T. digitalis Latreille, 1828, cangrejos de las islas Clipperton y Revillagigedo a fin de determinar el grado de similitud inter- e intraespecifica de las cuatro poblaciones insulares. Se examinaron 325 especimenes e identificaron cuatro especies: T. bidentata (72.9% de la abundancia total), T. digitalis (23.1%), T. formosa Smith, 1869 (3.4%) y T. corallina Gerstaecker, 1857 (0.6%). Para cada especimen, se tomaron tres dimensiones del caparazon: ancho (CW), largo (CL) y distancia interocular (ID). Las variables CL e ID se ajustaron a una ecuacion de tipo potencial tomando CW como la dimension de referencia. Como en otros braquiuros, los analisis del patron de crecimiento mostraron un tipo isometrico en todas las relaciones CW vs CL y CW vs ID examinadas. Las diferencias interespecificas incluyeron un mayor tamano corporal para T. bidentata y un mayor valor en el cociente ID/CW para T. digitalis . Se evidenciaron diferencias significativas intraespecificas entre las dos poblaciones insulares de T. digitalis en el cociente ID/CW. En contraste, las poblaciones de T. bidentata fueron morfometricamente mas semejantes. Estos resultados indican un mayor grado de conectividad en la metapoblacion de T. bidentata que en aquella de T. digitalis , debido probablemente a diferencias en la duracion de sus estados larvarios. Se piensa que la mayor talla corporal de T. bidentata representaria una mayor ventaja competitiva sobre el resto de las especies para atrapar alimento y seleccionar su habitat. A su vez, para contrarrestar su pequeno tamano, mayor ID permitiria a T. digitalis una mejor habilidad para percibir la 3D y juzgar la distancia relativa entre los objetos, evitando asi combates competitivos y mejorando sus respuestas de escape y antidepredatorias. ]

Environmental factors determining the spatial pattern of the whole siphonophore community, as well as the hydrological occurrence ranges, small-scale vertical distribution, and spatial niche breadth and overlap of 23 siphonophore species collected off a riverine system in the southern Gulf of Mexico were analysed. A total of 149 zooplankton samples were collected in different strata of the water column (from 0 to 100 m) over a grid of 23 oceanographic stations during low (April) and high (October) rainy periods. Temperature and salinity measurements were taken with a CTD probe. Considering both seasons, salinity fluctuated between 30.7 and 37.0, and temperature between 18.2 and 29.0°C. Under these conditions, the hydrological occurrence ranges of species were analysed. Data on siphonophore biovolumes in the upper 30-m layer were subjected to a regression tree (RT) analysis taking the zooplankton biomass, the distance to the shore, the temperature, and the salinity as predictable variables. Results of the RT analysis showed that the distance from the shore, food availability, and temperature were among the most important factors affecting siphonophore spatial distribution. Food availability had a positive influence on the siphonophores distribution, whereas temperatures higher than 28.1°C seemed to depress most siphonophore populations. Diphyes dispar moderately dominated the community and represented 30% of the total biovolume. The calycophorans Abylopsis tetragona, A. eschscholtzi, Diphyes bojani, and Chelophyes appendiculata were the most generalist species as revealed by their niche breadth values, and Enneagonum hyalinum endured the widest salinity conditions (30.7–37.0) and was mainly distributed in coastal waters. The second most abundant species, the physonect Agalma okeni, exhibited a low mean niche overlap value with the calycophoran species. We hypothesise that differences in diet composition between physonects and calycophorans are the main cause of those low niche overlap values.

The existence of twoPisaster ochraceussubspecies has been proposed; one located northwards (P. ochraceus ochraceus)and the other southwards(Pisaster ochraceus segnis) from Point Conception. We used polymerase chain reaction–restriction fragment length polymorphism of the CO I and CO III mitochondrial genes to assess the degree of population structure from 126 samples collected along the western coast of North America, from Vancouver, Canada to Punta San Carlos, of Baja California, Mexico. The genetic structure was tested through molecular analysis of variance and by Monte Carlo simulations of the original data set. The phylogeographical pattern was deduced from a minimum spanning network analysis. No genetic structure was detected. Instead, a high degree of genetic homogeneity along the species distribution was evident from haplotype frequencies at each location. Two haplotypes,Po1andPo5, were predominant along the distribution and were considered ancestral because of their central position in the minimum spanning network. SincePisaster ochraceusdepicts a planktotrophic larval stage with very long duration before settlement, it seems to be able to surpass the biogeographical boundary that limits other species around Point Conception, thereby maintaining homogeneity of its genetic pool. Results of this study recognizeP. ochraceusas a single species.

The morphometric characteristics and relative growth of the swimming crab, Portunus spinicarpus collected in the southern Gulf of Mexico were examined. A total of 248 specimens was measured on 13 external variables, including measurements of carapace, chelae, and abdomen. For both males and females, each body character was adjusted to a power equation taking the carapace width as the independent variable, and comparisons in the growth parameter (b) between sexes were made. Discriminant Analyses (DA) were also applied to identify measurements characterizing sexes. The results obtained show the males to be larger than the females. The smallest individuals (

Selected cases of plankton studies were analyzed to illustrate the main types of relationships between the zooplankton and the ichthyoplankton abundance observed in the pelagic realm. Such relationships may exhibit a positive, a negative, or a random pattern. In the conceptual model here proposed, short-term oscillations among these patterns were attributed to small-scale biological processes, such as competition, predation, and intraguild predation, acting in conjunction with water turbulence. A negative relationship between zooplankton and ichthyoplankton abundance may be caused both by predation on fish eggs and larvae, and by detrimental competition and intraguild predation interactions for fish larvae. In contrast, positive relationships emerge from the absence or low abundance of major predators on the ichthyoplankton, and from food availability for fish larvae and competing species. The random pattern may appear as a gradual transitional stage between the negative and positive patterns, or be promoted by strong water turbulence – which generates random movements of individuals. The size of zooplankters greatly influences these small-scale phenomena. Hence, their role in the trophic web, the success in competition interactions and vulnerability to water turbulence depends on their size. Intra- and interspecific competition may be reduced by variability in body size within or among fish larvae populations. Owing to a strong interaction among phenomena at different scales, these small-scale processes are also influenced by larger scale features, such as seasonal changes in zooplankton biomass, water currents, or spawning periods of fish. At the space level, some theoretical studies have emphasized the role of water currents as a vector for fish larvae to reach the nursery grounds (migration triangle hypothesis), or to allow them to remain within their own population’s distributional area (member/vagrant hypothesis). At the temporal level, the match/mismatch theory insists in a synchrony between reproductive strategies of fish and cyclical changes in abundance and size spectrum of potential prey items for their larvae. In any case, a coincidence between favorable abiotic and biotic features during the whole life-cycle of fish would assure a success in survival of larvae and their subsequent recruitment to adult population.

Sanvicente-Anorve, L., Lopez-Sanchez, J.L., Aguayo-Lobo, A. and Medrano- Gonzalez, L. 2004. Morphometry and sexual dimorphism of the coastal spotted dolphin, Stenella attenuata graffmani , from Bahia de Banderas, Mexico. — Acta Zoologica (Stockholm) 85 : 223-232 External measurements and size differences between the sexes were examined in the coastal spotted dolphin, Stenella attenuata graffmani , in Bahia de Banderas, on the Mexican Pacific coast. The dolphins were collected by local fishermen and 29 external characteristics were measured by members of the Marine Mammals Laboratory, University of Mexico. The length of each characteristic with respect to total length was analysed through adjustment of the data to a power equation. A stepwise discriminant analysis was applied to the absolute values and to those expressed as proportions to analyse the differences between the sexes. Results indicate that growth in these dolphins is generally negatively allometric, and most of the characteristics measured were, in both absolute and proportional terms, greater in male dolphins than in female dolphins. As found in many species of odontocetes, the discriminant analysis showed that the main differences between the sexes for this coastal subspecies include the relative positions of the umbilicus, the genital aperture and the anus. The morphometric data provided by this study, corresponding to 29 specimens of S. a. graffmani collected in a restricted locality of the Mexican Pacific coast, are particularly interesting to studies documenting latitudinal morphological differences in the coastal spotted dolphin.

The salt-water intrusion into a lagoon system of the Sian Ka'an Biosphere Reserve was assessed during 1 year and related to the marine component of the larval fish assemblage. This system is environmentally complex because of the penetration of marine water and the discharge of surface and subterranean water. Biological samples were collected during four field expeditions from October 1996 to August 1997. Surface circular tows with 500-μm-mesh conical plankton nets with a flowmeter were made during the day. Position, depth, temperature and salinity were recorded at each sampling station. All fish larvae were removed from the samples and identified to the lowest possible taxon. Ichthyoplankton abundance was normalized to 100 m 3 of water. The distribution patterns of the carangiid Oligoplites saurus, the herring Opisthonema oglinum, the dragonet Diplogrammus pauciradiatus and members of the Tetraodontidae were related to the wind-driven circulation pattern of the lagoons obtained using a numerical model. The analysis of the distribution of ichthyoplankton showed that these species are good indicators of the spatial salinity variations controlled by the hydrodynamic characteristics of the system. The spatial use of these estuaries as a habitat for fish larvae is therefore strongly influenced by salinity distribution, itself modulated by annual variation of wind stress.

The diversity of benthic macrofaunal assemblages in the eastern English Channel is described from 707 samples collected with a Rallier-du-Baty dredge during 1971-1975. Four assemblages were primarily defined by means of multivariate data analyses and clustering methods: the 'Abra alba com- munity', the 'Ophelia borealis community', the 'pebbles community' and a 'mixed assemblage' of the first three communities. Spatial heterogeneity of these communities is significantly correlated with sedi- mentary characteristics, although local variability appears to be controlled by both physical and biological processes. Ecological diversity of these communities was analysed considering species richness (S), the Shannon diversity index (H � ), and rank-frequency diagrammes (RFD). These analyses were performed at two spatial scales: for a single sample, and for a 'site' of 10 pooled samples. Thus, several sites were chosen in order to compare diversity patterns and species quantitative structure among and within the communities. The greatest species richness was recorded for the pebbles (57-69) and the A. alba (63- 79) communities. In the former, high values may be due to the complexity of microhabitats and the large flux of food related to strong currents. In the latter, both organic matter and terrestrial inputs associated with the mud favour the presence of deposit-feeder organisms. No clear trend was observed among and within the community sites in terms of the species quantitative structure. Thus, convex RFD shapes were observed in three assemblages: the 'mixed assemblage' (offshore site), the A. alba (North Sea), and the pebbles (Normandy coast). 'Sigmoid' shapes were observed in the pebbles (Dover Strait) and A. alba (English coast) communities. Presumably, these shapes can be caused by the combined action of phys- ical (strong currents, substrate stability, mud content in the sediments) and biological factors (co-occur- rence of species from different communities, strong species recruitment, relative dominance of carnivorous species).

The aim of this study was to assess the leading physical and biological processes influencing the ichthyoplankton distribution in the Southern Gulf of Mexico at different scales. Data were obtained from previous studies focused on the analysis of environmental factors affecting ichthyoplankton distribution patterns in this region. We considered three observational scales: Bahia de Campeche (meso scale) the littoral zone adjacent to Laguna de Terminos (coarse scale) and one inlet between the lagoon and the sea (fine scale). At the fine scale, tidal- and wind-induced currents, bottom topography, and salinity gradients were among the main mechanisms controlling ichthyoplankton distribution. At the coarse scale, littoral currents, lagoon influence, spatial salinity variability, and meteorological conditions determined the structure and location of ichthyoplankton groups. At the meso scale, the main circulation pattern of the Southern Gulf, continental water discharges, mixing processes, and oceanic gyres were important processes explaining ichthyoplankton distribution patterns and community structure. These environmental features coupled with the life-cycle strategies of fishes, the periods and spawning areas of the adults, larval stages, dispersal capabilities of larvae, and the larval stage duration produce distinctive ichthyoplankton patterns. This multiscale study showed that every observational level gives key elements to understanding the dynamics of the system, and that physical and biological processes over similar ranges of time and length scales can explain ichthyoplankton distribution.

The Gulf of Tehuantepec, in the Mexican waters of the eastern tropical Pacific, is a very productive area with a high biological complexity, as the result of a wind-induced upwelling that occurs from November to February. The main assemblages of pelagic copepods in this region were identified and analysed in this study, during the final stage of the upwelling process. Samples were collected in oblique plankton hauls using a station grid that covered neritic and oceanic waters. Copepods were separated taking 10 ml aliquots from each sample. Data of copepod abundance were expressed as ind. m-3 and subjected to a Factor Correspondence Analysis, in order to determine the main copepod assemblages. Results indicate the presence of two main assemblages: neritic and oceanic. The neritic assemblage is located on shelf waters. Its characteristic species are Microsetella norvergica, Macrosetella gracilis, Nannocalanus minor, Centropages furcatus, Corycaeus speciosus, and Eucalanus subcrassus. The oceanic assemblage includes Copilia vitrea, Eucalanus inermis, Scolecithricella abyssalis, Haloptilus spp., and Rhincalanus spp. The composition of these assemblages corresponds to the physiography of the area, and this strong variation gradient from the coast to the ocean has been commonly observed in other assemblages of planktonic organisms as well. El Golfo de Tehuantepec, en aguas mexicanas del Pacifico Oriental Tropical, es una zona muy productiva y de alta complejidad biologica, debido a una surgencia eolica que ocurre de noviembre a febrero. En este trabajo, se identificaron y analizaron las principales asociaciones de copepodos pelagicos en esta region durante la etapa final del proceso de surgencia. Los muestreos fueron realizados mediante arrastres oblicuos en una red de estaciones que cubrio aguas neriticas y oceanicas. Los copepodos fueron separados de cada muestra a partir de alicuotas de 10 ml. Los datos de abundancia de copepodos fueron expresados como ind. m-3 y tratados por medio del Analisis Factorial de Correspondencias, a fin de determinar las principales asociaciones de copepodos. Los resultados indican la presencia de dos asociaciones principales: neritica y oceanica. La asociacion neritica se localiza sobre aguas de la plataforma continental. Sus especies caracteristicas son Microsetella norvergica, Macrosetella gracilis, Nannocalanus minor, Centropages furcatus, Corycaeus speciosus y Eucalanus subcrassus. La asociacion oceanica tiene como especies caracteristicas a Copilia vitrea, Eucalanus inermis, Scolecithricella abyssalis, Haloptilus spp. y Rhincalanus spp. La composicion de estas asociaciones corresponde con la fisiografia de la zona, y el fuerte gradiente de variacion en direccion costa-oceano es comunmente observado en otras asociaciones de organismos planctonicos.

Resume Une approche spatio-temporelle a ete adoptee pour comprendre l'influence des courants a long terme sur la repartition du zooplancton, de l'ichtyoplancton et des communautes ichtyoplanctoniques dans la Baie de Campeche, au Mexique. Pour cette approche, on utilise les resultats d'un modele numerique hydrodynamique et l'abondance zooplanctonique et ichtyoplanctonique. Trois communautes ichtyoplanctoniques, nommees « neritique d'influence fluvio-lagunaire a, « neritique a et « oceanique a ont ete identifiees en relation avec la physiographie de la zone. Un tourbillon cyclonique se forme dans la Baie de Campeche et derive vers l'ouest. La circulation induite par ce tourbillon facilite le transport et la distribution d'organismes planctoniques dans la baie. Le tourbillon induit le transport des larves, des eaux oceaniques vers la cote et vice-versa . La distribution saisonniere des larves de poisson est fortement influencee par la position du tourbillon. La repartition de l'abondance zooplanctonique et de la densite des larves de poisson pres de la cote, vers le delta du Grijalva-Usumacinta, est determinee par le front cotier.

The environmental factors that affect larval fish assemblages in the southern Gulf of Mexico were studied. Samples were collected with a Bongo net from the surface to a depth of 200 m, at 46 sampling stations, during spring 2006. The adult habitat was assigned to each larval fish taxon. Larval assemblages were defined by the Bray-Curtis index. A total of 182 taxa were found, of which most were oceanic, mid shelf and reef. Three assemblages were defined: Yucatan (YA), Tabasco-Campeche (TCA) and Oceanic (OA). The YA was located on the Campeche Bank, the wide Yucatan shelf where the most important hydrodynamic processes is a branch of Yucatan current. The TCA occupied the shelf of Tabasco and the southwestern shelf of Campeche, characterized by the continental freshwater discharge. The OA occupied the oceanic area of Campeche Bay, where the dominant hydrodynamic process is an almost permanent cyclonic gyre. As a result of the different hydrographic features, which are ocean currents, presence of gyres, freshwater discharge, and the topography; the Tabasco shelf, Campeche Bank (Yucatan shelf) and Campeche Bay constitute different regions. They are regions with clearly contrasting environmental scenarios. The geographic distribution of the 3 assemblages fitted well with these 3 hydrodynamically different areas. The structure and spatial distribution of the larval assemblages was determined first by the habitat of the adults and the spawning areas, and then being modulated by the hydrographic features that characterize each area. Se estudiaron los factores ambientales que afectan las asociaciones de larvas de peces en el sur del Golfo de México. Las muestras se obtuvieron con redes Bongo de superficie a 200 m, en 46 estaciones, en primavera 2006. A cada taxón de larvas se le asignó el hábitat de sus adultos. Las asociaciones de larvas se definieron por el índice de Bray-Curtis. Se registró un total de 182 taxones, la mayoría oceánicos, de plataforma media y arrecifales. Se definieron 3 comunidades, Yucatán (YA), Tabasco-Campeche (TCA) y Oceánica (OA). YA se ubicó sobre el Banco de Campeche, en la amplia plataforma de Yucatán, donde el proceso hidrodinámico más importante es una rama de la corriente de Yucatán. TCA ocupó la plataforma de Tabasco y suroeste de la plataforma de Campeche, caracterizada por la descarga de aguas continentales. OA ocupó el área oceánica de la Bahía de Campeche, donde el proceso hidrodinámico dominante es un giro ciclónico casi permanente. Como resultado de diferentes hechos hidrográficos, sean corrientes oceánicas, presencia de giros o descargas de aguas dulces, y la topografía; la plataforma de Tabasco, el Banco de Campeche (plataforma de Yucatán) y la Bahía de Campeche constituyen regiones con escenarios ambientales claramente contrastantes. La distribución geográfica de las 3 asociaciones de larvas se ajusta bien con estas 3 áreas de diferente hidrodinámica. La estructura y distribución espacial de las asociaciones de larvas está determinada en primer lugar por el hábitat y áreas de desove de sus adultos, siendo después modulada por las forzantes hidrográficas que caracterizan cada área.

Se analiza por primera vez la diversidad y distribucion de las apendicularias en la capa superficial de la columna de agua de la plataforma continental del sur del Golfo de Mexico. Las muestra se recolectaron en septiembre de 2003 usando una malla fina- Se identificaron 22 especies de las cuales Fritillaria venusta y Pelagopleura opresa tienen aqui su primer registro para el Golfo de Mexico. Las especies de Oikopleura ocurrieron en toda el area con sus mayores abundancias en aguas de surgencia que corren sobre la plataforma de Yucatan y Campeche. La mayor abundancia de las especies de Fritillaria y de los otros generos se registro en la plataforma media, externa y area oceanica de Campeche y Tabasco que estan influenciadas por las descargas de aguas continentales y un giro oceanico. La diversidad y abundancia varian en sentido contrario una de otra; alta abundancia y baja diversidad caracterizan a las areas costeras, en tanto baja abundancia y alta diversidad ocurren en la plataforma media, externa y area oceanica. La distribucion de las especies parece estar influenciada por las corrientes de la surgencia, giros, profundidad del area, descargas de aguas continentales, salinidad y temperatura. Sin embargo, puede asumirse que detras de estos factores fisicos estan la disponibilidad de alimento, el corto ciclo de vida y la alta eficiencia reproductiva, como los factores mas comunmente asociados a su distribucion

"The mesoscale spatial distribution of Oikopleura and Fritillaria in the southern Gulf of Mexico was analyzed to know the existence of segregation between them. Samples were taken on 97 stations in the 50 m upper layer. Temperature, salinity and turbidity were measured. The spatial segregation index 'D' was applied to Oikopleura and Fritillaria densities and its significance was tested with Monte Carlo method. Regression Tree (RT) analyses were performed to identify the main environmental factors affecting the distribution of genera. The D index value was 0.67, considered as a high value. RT analyses showed the water turbidity was the main factor affecting the spatial distribution of both genera. Fritillaria was found in turbid waters off the main fluvio-lagoon systems and Oikopleura was most abundant in the up welling waters over Yucatan Shelf. The segregation distribution of appendicularians in the study area appear to be strongly influenced by up welling and associated currents, and turbidity generated by continental water discharges. It could be assumed that food webs are an important associated factor. We hypothesize that a broad diet and higher filtration efficiency for larger particles (microfitoplankton) allows Oikopleura species to exploit the production in up welling areas, whereas Fritillaria species can not. It may explain its spatial segregation of these genera."

"El laboratorio de Zooplancton del Instituto de Ciencias del Mar y Limnología de la UNAM, ha estudiado por más de 25 años el ictioplancton del sur del Golfo de México. Los objetivos han sido determinar qué especies existen, dónde se distribuyen, cuál es su abundancia, qué comunidades forman, cuál es y a qué se debe su variación espacio-temporal. Se ha registrado la presencia de al menos 306 especies, 283 géneros y 120 familias de larvas de peces. La diversidad de especies y la abundancia de larvas aparecen como parámetros opuestos; la mayor densidad de organismos ocurre en áreas costeras y en plataforma media y disminuye hacia la zona oceánica; la diversidad en cambio es mayor en áreas oceánicas, al borde de la plataforma continental y se reduce hacia estaciones costeras. En general, la distribución de la abundancia de las larvas tiene un patrón recurrente y está determinada por las áreas y épocas de desove de las especies, por la disponibilidad de alimento y los procesos físicos, principalmente corrientes, descargas de agua continental y mezcla. La distribución de las larvas en la columna de agua parece depender del hábitat de sus adultos, aquellas cuyos adultos viven la zona costera se encuentran primordialmente en los primeros 30 m; las de origen oceánico ocupan generalmente capas con profundidades mayores a 50 m. Todas tienden a una mayor dispersión en la columna durante la noche. Se ha determinado la presencia recurrente de cuatro comunidades: a) Costera, b) Nerítica Interna, c) Nerítica Externa y d) Oceánica."

Se analizó estacionalmente la biomasa zooplanctónica (BZ) y la densidad ictioplanctónica (DI) en la columna de agua sobre la plataforma continental del sur del Golfo de México, para determinar sus patrones de distribución vertical y establecer si existe una relación entre ambos componentes. Se muestrearon cinco niveles de profundidad: 0-6 m, 6-12 m, 12-18 m, 45-55 m y 95-105 m. El patrón de distribución vertical de la BZ y de la DI fue similar en todas las épocas de muestreo, con la mayor concentración de organismos en los niveles superficiales y la más baja en los niveles más profundos. Estos resultados sugieren que la columna de agua en el área de estudio puede estar dividida en una capa superficial (0 a 18 m) y una capa profunda (45 a 100 m) y que las diferencias estacionales pueden ser atribuidas a los procesos de mezcla. Esta diferencia entre las capas superficiales y las profundas ocurre porque, en general, las capas superficiales de la columna de agua son las más productivas. La relación entre la BZ y la DI fue positiva y significativa (ANCOVA, P

Se estudiaron los patrones espacio temporales de la riqueza, diversidad, equidad y dominancia de la comunidad de peces de la laguna de Pueblo Viejo, Veracruz, México. El comportamiento ambiental del sistema estuvo definido por dos épocas climáticas: lluvias y secas. Se observó que la diversidad, equidad y dominancia de especies se correlacionaron significativamente (Ps0.05) con la temperatura. De las 66 especies colectadas, las que dominaron todo el año y en todas las localidades fueron Anchoa mitchilli, Bairdiella chrysoura y Membras martinica. Espacialmente, la riqueza y diversidad fueron significativamente (Ps0.01) mayores en las localidades con vegetación sumergida y en las localidades cercanas a la boca del sistema. En localidades con vegetación dominaron las especies Diapterus auratus y Lagodon rhomboides, mientras que en las localidades sin vegetación, dominaron Cathorops melanopus y Brevoortia gunteri. Estacionalmente, los pulsos de la riqueza y diversidad coincidieron con los máximos de la temperatura y la producción primaria del sistema. Además, las lluvias ejercieron un efecto significativo (P0.01) sobre la riqueza de especies, con un mes de desfasamiento. La dominancia de D. auratus y C. melanopus durante la época de lluvias, se relaciona con la disponibilidad de sus preferencias tróficas; mientras que la dominancia de L. rhomboides y B. gunteri durante la época de secas, se relaciona con sus patrones de reclutamiento de organismos juveniles a la población adulta dentro del sistema. En general, los parámetros de diversidad de la comunidad de peces tendieron a ser estables temporalmente y a variar espacialmente, lo que sugiere que la vegetación sumergida, puede ser más importante en la diversidad de la comunidad, que factores con influencia temporal, como la temperatura, precipitación y procesos de producción.

The composition, abundance, species richness and structural changes of the planktonic polychaete assemblages were analysed along a latitudinal transect in the California Current System (California, U.S.A. and Baja California, Mexico). The biological (species and abundance) and physical (temperature and salinity) data were analysed using Principal Component Analysis (PCA). The principal water masses in the survey area were determined. Twenty-four holoplanktonic species belonging to families Alciopidae, Iospilidae, Lopadorhynchidae, Tomopteridae and Typhloscolecidae were identified. Three clear species assemblages were discerned in the PCA results: 1. A ‘north group’ (from Oregon-California border to San Francisco), with relatively high species richness (11) and the highest mean abundance (121 ind. per 500 m3) was characterised byTomopteris septentrionalis, T. planktonis, Plotohelmis tenuis, and Travisiopis lobifera. California Current Water and Subtropical Central Water were present in the area occupied by this assemblage. 2. A ‘south group’ (from off Bahia Magdalena to Cabo San Lucas), with the highest species richness (16), but low mean abundance (37.8 ind. per 500 m3); it included tropical affinity species, such Lopadorhynchus henseni, Tomopteris nationalis, and Travisiopsis dubia. In concordance Surface Equatorial Water was identified in this region. 3. A ‘transition group’ (between the north and south regions) recorded the lowest mean abundance (2.3 ind. per 500 m3) and species richness (9). Only the California Current Water was detected in this area. The spatial pattern of species richness found along of this transect, was at least, partially due to the planktonic productivity distribution in the epipelagic region and the influence of several water masses coming from different directions.

Two specimens of Ophioderma ensiferum Hendler and Miller, 1984 were collected at 2 different localities in the Yucatán Peninsula, Mexico. The first one collected at Alacranes Reef, Yucatán, a transition zone between the Gulf of Mexico and the Caribbean, and the second one in an anchialine cave located in Cozumel Island, Quintana Roo. These records expand the known distribution of the species to the southern part of the continental shelf of the Gulf of Mexico. This finding represents the first record of this ophiuroid on the continental shelf of Mexico, and also the first record of this species in an anchialine cave.

"Changes in the composition and abundance of fish larvae in the water column were analyzed throughout an annual cycle (1994-1995) in the southern Gulf of Mexico, in order to establish the difference between the habitat of the larvae and the effect of oceanographic events on larval vertical distribution. The study area comprised the continental shelf off Tabasco and Campeche in the southern Gulf of Mexico. Samples were collected at five water column levels: 0-6, 6-12, 12-18, 45-55 and 95-105 m. A total of 118 taxa were identified, 52 were dominant species, 33 were larvae of neritic parents and 19 were larvae of mesopelagic parents. The results indicate that the water column presented two layers above the 105 m depth: a surface layer (0-18 m) and a deep layer (45-105 m). The greatest density of larval species that inhabit neritic areas as adults was recorded in the surface layer (0-18 m), while larvae of which the parents inhabit mesopelagic areas were found in the deep layer (45-105 m). The mixing of the water column was the most important physical factor regarding the variation in the vertical distribution of the larvae of both groups, particularly in winter. However, the biology of each species and the habit to occupy a particular depth was the most important factor that determined their distribution in the water column."