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Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Cladocera represent an important zooplankton group because of their seasonal prominence in terms of abundance and their contribution in controlling primary production (phytoplankton). On a global scale, there are few studies on Cladocera in hypersaline environments. The present work aims to evaluate the spatio-temporal variation of the Cladocera assemblage across a salinity gradient in the habitats of the Araruama Lagoon. Samples were collected in random months over a period of four years at 12 fixed stations in the Araruama Lagoon using a WP2 plankton net equipped with a flow meter. Our results do not reveal significant influence of the tide and seasonal variation as factors affecting the Cladocera assemblage. Five Cladocera species were found in the Araruama Lagoon, only in stations 11 and 12 where they reached an average of 1,799 ± 3,103 ind. m-3. The mean of the Shannon Diversity Index was 0.45 ± 0.2. The species that stood out in terms of frequency and abundance were: Penilia avirostris (frequency of occurrence: 71%), followed by Pseudevadne tergestina (41%). The same species also stood out in terms of relative abundance, Penilia avirostris (87%) and Pseudevadne tergestina (11%). The absence of Cladocera in the innermost parts of the lagoon suggests that their entrance to these locations is possibly inhibited by the salinity and temperature gradient of the lagoon, being the main factors influencing the dynamics of the Cladocera assemblages.

The zooplankton community structure in bays fluctuates as a result of anthropogenic activities in such waters. We focused on the short-term variability of a zooplankton community and compared its differences at the outflow of a nuclear power plant (ONPP), in a marine cage-culture area (MCCA) and in unpolluted waters (UW) in the south-west part of Daya Bay from 28 April to 1 June 2001. Environmental factors and zooplankton abundance differed significantly among stations at ONPP, MCCA and UW: high temperatures and a high zooplankton abundance occurred at ONPP, while a high chlorophyll a concentration and a low zooplankton abundance prevailed in MCCA. Statistical analysis revealed that the zooplankton diversity and abundance could be reduced by the activity of the marine cage-culture in a short time. Penilia avirostris made up an important component of the zooplankton in the study area, its abundance ranging widely from 16 to 7267 indiv. m−3 from April to June and peaking at the ONPP outflow. The outbreak of P. avirostris probably resulted from the combined effects of favourable water temperature, food concentration and its parthenogenetic behaviour.

We studied the horizontal and vertical distributions of marine cladocerans across the Catalan Sea shelf (NW Mediterranean) in July and September 2003, and in June and July 2004. At the seasonal scale, Penilia avirostris appears first in June in the southern region, where temperatures are warmer, and its populations develop northward during the summer. Evadne - Pseudevadne did not show a clear pattern, likely because several species were pooled. In 2003 successive heat waves affecting southwestern Europe resulted in surface seawater temperatures about 2 °C higher than usual across the whole study region. These high temperatures were associated with much lower abundance of P. avirostris . Overall, the mesoscale distributions of cladocerans were associated with the presence of low salinity, productive and stratified waters of continental origin, and negatively linked to the intrusion of offshore waters. On the vertical scale P. avirostris was located within or above the thermocline, whereas Evadne - Pseudevadne was much shallower; no evidence of diel migration was detected in either group. Our study provides new insights regarding the environmental limits for marine cladocerans in the NW Mediterranean; in the particular case of P. avirostris that knowledge can define the likely boundaries of its new distributions as it expands poleward under climate change. [ABSTRACT FROM AUTHOR]

A 2-year survey of seawater chemistry and mesozooplankton abundance was carried out in Masan Bay, South Korea, one of the most eutrophic coastal ecosystems known. The study aimed to identify the major factors contributing to the seasonally persistent hypoxia in the bay, to characterise the Bay's mesozooplankton community and to examine the effects of low oxygen on the distribution of mesozooplankton. Hypoxia (<2 mg O2 L-1) was present only in summer, with ultrahypoxia (<0.2 mg O2 L-1) in the bottom waters of the inner bay in both years. Low summer oxygen can be attributed to high summer phytoplankton stocks, together with reduced oxygen solubility at high temperature and stratification of the water column that limits downward diffusion of oxygen. A seasonally and spatially distinct mesozooplankton community was identified in summer when there was greater influence of freshwater discharge in the inner bay. Marine cladocerans were very abundant, with a population outburst of Penilia avirostris in the inner bay (>4000 individuals m-3during summer. During hypoxic events, the abundance of Penilia avirostris was positively related to oxygen levels in the bottom water, suggesting that hypoxic conditions may cause mortality or have sublethal negative effects on population growth of this filter-feeding cladoceran. Low summer oxygen in a highly eutrophic and seasonally hypoxic coastal bay was attributed to high phytoplankton stocks, together with high temperature and stratification of the water column. A distinct mesozooplankton community was identified in summer of large freshwater discharge. The abundance of a marine cladoceran was positively related to oxygen levels, suggesting that hypoxic conditions may have lethal or sublethal effects. [ABSTRACT FROM AUTHOR]

Abstract: The cladoceran Penilia avirostris and three tunicate species, Oikopleura dioica, Dolioletta gegenbauri and Thalia democratica, form a mesozooplankton group which ingests a wide range of particles from pico- to micro- plankton, grows rapidly due to asexual reproduction, and thus can have major impacts on phytoplankton populations. These four zooplankton species were the most abundant tunicate and cladoceran species in a study where zooplankton were sampled biweekly at five stations across the inner continental shelf in the Mid-Atlantic Bight in 2005, 2006 and 2007. Vertical tows were taken at shallow stations and depth stratified vertical tows at stations >10m. P. avirostris and O. dioica had highly predictable seasonal cycles with peak abundances in July and August. D. gegenbauri also was present during this time period if upwelling favorable winds were present, which implies cross shelf transport from source populations in slope waters and the Gulf Stream. T. democratica only appeared in pulses when southerly winds were increasing in strength. The co-occurrence P. avirostris and the tunicate species with abundant Synechococcus and heterotrophic nanoflagellates during highly stratified summer conditions provide potential connections to microbial food webs as well as grazing opportunities on event scale blooms of dinoflagellate and diatoms species present in the area. [Copyright &y& Elsevier]

The average spatial distribution and interannual abundance patterns of the cladoceran Penilia avirostris are described from samples collected in the waters of the US Northeast continental shelf ecosystem. Integrated water column samples were collected with a bongo net from 1977-2009 on broad scale surveys of the shelf conducted approximately every two months. Collections were also made with a Continuous Plankton Recorder towed at 10 m depth along two routes; one that crossed the Gulf of Maine (1961-2009), and the other from New York City south-eastward toward Bermuda (1976-2009). P. avirostris was found to have a strong seasonal cycle in the southern half of the ecosystem. High coastal concentrations suddenly appear there in July-August, forming distinct onshore-offshore abundance gradients. The population slowly declines in the autumn months, essentially disappears from the zooplankton community during winter, and does not return again until its abrupt appearance in summer. Only low abundances in isolated patches were found in the northern half of the ecosystem and in the slope waters sampled by the CPR. Both samplers showed that annual abundance levels were variable with no long-term trend evident, nor were environmental measures or broad scale climate indices correlated to these variations. The cladocerans' summer population surge was significantly correlated with surface temperature and water column stratification indices. This is the first study to record the presence of P. avirostris in the Gulf of Maine region. [ABSTRACT FROM AUTHOR]

The ctenophore Mnemiopsis leidyi can consume large amounts of zooplankton prey. However, quantitative measurements of feeding rates, based on field data, are scarce. We measured the time required by the invasive M. leidyi to digest naturally occurring prey species in the Gullmar fjord, Sweden. Digestion times were related to prey size and type, number of prey in the gut and size of the predator. Large prey species or many prey in the gut resulted in longer digestion times compared with small or few prey, but digestion time also varied with the size of M. leidyi. The prey- and predator-specific digestion times were used together with in situ prey concentrations and gut contents of M. leidyi to calculate the clearance rates. Clearance rate as a function of ctenophore size is presented for the most abundant mesozooplankton: Acartia sp., Oithona sp., Oikopleura dioica and Penilia avirostris. On the basis of the relation between digestion time and the carbon content ratio between prey and predator, we discuss the possible effects of mixed prey assemblages on the estimates of clearance rates. [ABSTRACT FROM AUTHOR]

We studied the population dynamics and the reproductive biology of Penilia avirostris during three consecutive years on the inner shelf off Ubatuba, Brazil. Penilia avirostris individuals and its eggs and embryos were counted, measured, and classified into stages. The species occurred throughout the studied period, in a wide temperature range (14.8-28.2°C). Cladoceran densities were usually higher (>2,000 ind m) in warm seasons, when the water column was stratified as a consequence of bottom intrusions of the cold- and nutrient-rich South Atlantic Central Water. Juveniles, non-reproducing females, and parthenogenic females were the dominant developmental stages. Males and gamogenic females were rare and only occurred when females reached peak abundances. This suggests that in tropical and subtropical coastal seas gamogenesis in P. avirostris is not as common as in temperate seas, but may play a significant role in the density-dependent control of the population preceding unfavourable periods. [ABSTRACT FROM AUTHOR]

This paper describes the composition and abundance of zooplankton in the Bandırma Bay and the Erdek Bay. These bays are located in the southern Sea of Marmara, Turkey. Sampling was carried out during three cruises in summer (July 2006), autumn (October 2006), and spring (March 2007). Zooplankton abundance and biomass seasonally fluctuated and showed differences between the bays. Copepods were the most abundant component, and Penilia avirostris was the most important species during summer in the two bays. The fluctuations in zooplankton abundance, biomass, and community structure were determined by the physical environment. [ABSTRACT FROM AUTHOR]

The seasonal succession patterns of species of Cladocera with respect to changes in some environmental and biological parameters were examined in a harbour located at Kepez, Dardanelles from 11 April 2006 to 12 April 2007. For this study, environmental parameters and zooplankton data were analysed for one station and sampling trips were conducted every two weeks. Cladoceran abundance varied widely throughout the sampling period, exceeding ∼87% of total zooplankton, especially during the warmer seasons. The cladoceran community was mainly composed of Penilia avirostris, Pleopsis polyphemoides, and Evadne nordmanni, the first one occurring from late spring through early fall, and the latter two from early spring to early summer. Salinity and temperature seemed to have little or no effect on the distribution, abundance, and variability of the cladocerans in the system, indicating factors other than non-biological environmental parameters, such as competition with other groups of zooplankton, food availability and/or quality, have the greatest effects on cladoceran species composition. [ABSTRACT FROM AUTHOR]

Associations of pteropod, cladoceran, and chaetognath species were analyzed for the southern coast of Brazil in order to present a biological diagnosis of the oceanographic conditions in winter and summer. The density data from the different species were analyzed using nodal and ordination cluster techniques, linking the species associations with salinity and temperature and, consequently, with the water masses occurring in each period. Sagitta tenuis and Pleopsis polyphemoides were found to characterize the coastal water and, when associated with Evadne nordmanni and Pleopsis schmackeri, differentiated between the thermal characteristics of winter and summer, respectively. The Sub-Antarctic Shelf Water was characterized by the association of Sagitta tasmanica and Limacina retroversa in winter. The Tropical Water of the Brazil current presented several different associations, with Penilia avirostris, Sagitta enflata, and Creseis virgula dominating the shelf Tropical Water and Sagitta serratodentata, Limacina trochiformis, and Evadne spinifera characterizing the oceanic Tropical Water. The Sub-tropical Water, typical of upwelling processes, was characterized by the association of the chaetognaths Sagitta decipiens and Krohnitta subtilis, both in winter and summer. The species associations defined in this study agree with others carried out in neighboring areas and in previous sampling periods, characterizing the region as the southern transition zone. [ABSTRACT FROM AUTHOR]

Mesozooplankton community composition at the species/taxa level was investigated from January to December 2001, at eight stations in the northern Adriatic Sea. Annual dynamics, taxonomic composition and spatial diversity in relation to different trophic conditions are discussed as related to previous studies and to different conditions, such as the presence of mucilage events. Zooplankton communities all over the northern sub-basin were dominated by the cladoceran Penilia avirostris in summer, and by the calanoids Paracalanus parvus, Acartia clausi and the poecilostomatoids Oncaea spp. during the rest of the year. Whereas coastal communities were more variable with time and location, we were able to identify a group of offshore stations with a similar species/taxa composition and annual dynamics. Comparing the present results with previous studies, we observed significant changes in community composition in the time scale of 20 years, mostly due to a general decrease of A. clausi as the dominant species, being replaced by P. parvus. Also, P. avirostris swarms appear to have extended their temporal occurrence, and were present for longer periods of time when compared to past records. These changes might be related to the observed general increase of the average sea water temperature in the northern Adriatic Sea. [ABSTRACT FROM AUTHOR]

We examined the population genetics of six species of marine cladocerans, using a ~600 bp fragment of the cytochrome oxidase subunit I gene sequence. Phylogenetic analysis revealed significant intraspecific, semi-allopatric phylogenetic breaks in four out of five species belonging to the Podonidae, supporting an ancient radiation and oceanic expansion for this group. By contrast, Penilia avirostris (Sididae) displayed no phylogeographic structure across a global sampling, suggesting a recent worldwide expansion. Our results also show a transoceanic distribution of identical or very similar haplotypes in several species of marine Cladocera, which may be interpreted as either natural transport or evidence of recent anthropogenic transport. If the latter is the case, marine cladocerans represent one of the first genetically documented cases of exotic or invasive marine zooplankton, likely an underreported group. [ABSTRACT FROM AUTHOR]

The marine cladocerans Pseudevadne tergestina and Penilia avirostris use different strategies to avoid visual predators. Pseudevadne tergestina exhibited a pronounced diel cycle in reproduction, but did not perform diel vertical migration. Parthenogenetic females with fully developed embryos were absent during the day in both fishless enclosures and in the natural environment. This observation suggests that the diel cycle was due to nocturnal release of neonates and not the result of selective predation by fish. The need to use the compound eye to locate food would force P. tergestina to remain in the illuminated surface water during the day and release their offspring in darkness thus decreasing their visibility to fish. The diel cycle in reproduction in P. avirostris was not as pronounced as that in P. tergestina, but females with mature embryos were still more common at night than during the day. As a grazer of phytoplankton, P. avirostris performed diel vertical migration and retreated to dark, deeper waters during the day, avoiding visual predators. [ABSTRACT FROM PUBLISHER]

Marine cladocerans are important contributors to the zooplankton community of tropical and temperate coastal ecosystems during the warmer months, when they show explosive population growth. Despite this fact, little information is available on their ecology compared with the extensive studies on their freshwater relatives. The main objective of this study was to determine the in situ feeding and growth rates, and life history parameters of Penilia avirostris in São Sebastião Bay (Brazil) during austral summer 2004, as a premise to understand the advantages of this cladoceran in oligotrophic waters. Culture development experiments, monitored for a period of 12 days, showed that maximum juvenile release occurred after 2 days, and that the development duration of a complete cohort was around 9 days. From bottle incubation grazing experiments, significant ingestion rates upon flagellates, ciliates, dinoflagellates and diatoms were detected. Flagellates were the most important contributors to P. avirostris diet (ca. 80%). P. avirostris ingested between 28 and 97% of its own carbon biomass per day (daily ration) and individual growth rates of this marine cladoceran (0.10–0.24 d−1) increased with prey availability. The combination of ingestion rates of natural prey and growth rates provided gross growth efficiencies (GGE) of 15–53%, on a carbon basis. Our results suggest that P. avirostris has similar GGE to copepods, although at low food conditions the values for the marine cladocerans seems slightly higher. However, this characteristic alone does not explain the explosive growth and community dominance shown by P. avirostris. Therefore, other traits related to the reproductive biology of the species, such as short generation time, parthenogenetic reproduction, and continuous somatic growth, seems to be mostly responsible for the success of P. avirostris in many marine ecosystems during their seasonal occurrence. [ABSTRACT FROM AUTHOR]

In this work we studied the trophic ecology and feeding impact of the cladoceran Penilia avirostris and the cyclopoid copepod Oithona nana, the two dominant zooplankters in the summer communities of the coastal NW Mediterranean, on the naturally occurring microbial communities. In order to ascertain carbon surplus for growth and reproduction and the contribution to carbon and nitrogen recycling of these two species, we also determined their basal metabolism and excretion rates. The experiments conducted during summers 2002, 2003, and 2004 indicate that P. avirostris grazed mostly upon small flagellates, dinoflagellates, and diatoms, whereas O. nana had a narrower prey range, selecting motile organisms such as ciliates and occasionally dinoflagellates. The grazing impact of both species accounted, on average, for <10% of the standing stock of the microbial groups considered. In spite of the oligotrophic conditions, the feeding activity of P. avirostris is in general sufficient to compensate basal metabolism and allows a surplus for growth and reproduction. This was not the case for O. nana, its daily rations being often lower than the carbon basal demands. Regarding excretion rates, both species presented different N:P excretion ratios, the ones of O. nana falling within values typical for copepods, whereas the absence of detectable phosphorus excretion by P. avirostris implied an unbalance recycling with respect to typical Redfield ratio composition of marine seston. [ABSTRACT FROM AUTHOR]

The cladoceran, Penilia avirostris, was collected in zooplankton samples from Colville Bay, Prince Edward Island (46°N 62°W) in the southern Gulf of St. Lawrence, in the autumns of 2000 and 2001. This is the first report of the species from Canadian waters, and represents a northeasterly range extension of 5 degrees of latitude or approximately 1130 km. The most likely vector for this introduction was ballast water from international shipping. In October 2000, when the species was first detected, the observed population density of 0.073 individuals/m3 represented less than 0.3% of the zooplankton community. One year later, the density was 27.5 individuals/m3 and Penilia was the fourth most abundant zooplankter, accounting for 8% of the community. All females were parthenogenetic, but 0.3% of the individuals collected in 2001 were males, implying that sexual reproduction by resting eggs could occur in this population. The size of males (mean length 684 μm, range 591-773 μm) and parthenogenetic females (mean 840 μm, range 409-1000 μm) was similar to those reported in the literature. Three percent of the females were juveniles, and a reproducing population appeared to be well established. [ABSTRACT FROM AUTHOR]

Abstract: Food selection by the marine cladoceran Penilia avirostris was studied in the field by HPLC analysis of phytoplankton marker pigments and in the laboratory by microscopic measurement of cell removal. Comparison between pigment composition in natural phytoplankton and in P. avirostris showed that P. avirostris preferred diatoms, cryptophytes and chlorophytes, and ignored prymnesiophytes and dinoflagellates. Peridinin, the marker pigment for dinoflagellates was found in P. avirostris only when the dinoflagellate populations were dominated by Prorocentrum. Pigment degradation rates ranged from 13.73% for alloxanthin to 36.62% for chlorophyll a. Clearance rates measured in the laboratory provided further evidence of strong preference for diatoms and cryptophytes, and avoidance of dinoflagellates. Microscopic counts suggested that P. avirostris was feeding on prymnesiophytes, although ingestion of prymnesiophytes could not be confirmed by pigment analysis. [Copyright &y& Elsevier]

We conducted grazing experiments with the three marine cladoceran generaPenilia,PodonandEvadne, withPenilia avirostrisfeeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02-8.8 mm3 l-1, plankton assemblages grown in mesocosms at different nutrient levels), and withPodon intermediusandEvadne nordmannifeeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm3 l-1).P.avirostrisandP.intermediusshowed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively.E.nordmannipreferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were>2.5 µm, for all cladocerans.P.avirostrisshowed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits forP.intermediuswere 135 µm long and 60 µm wide; those forE.nordmanniwere 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment forP.avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher forP.intermediusthan forE.nordmanni. With increasing food concentrations, the clearance rates ofP.avirostrisshowed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates ofP.avirostris,P.intermediusandE.nordmanniwere 25.5, 18.0 and 19.3 ml ind.-1 day-1, respectively. Ingestion rates at similar food concentrations (0.4 mm3 l-1) were 0.6, 0.8 and 0.9 µg C ind.-1 day-1. [ABSTRACT FROM AUTHOR]

The diel cycle in the percentage abundance of parthenogenetic females carrying embryos of different developmental stages in the marine cladocerans Penilia avirostris, Pseudevadne tergestina, Pleopis polyphymoides and Pleopis schmackeri was studied at the edge of an artificial rocky shore area in a semi-enclosed bay in Hong Kong. Females carried embryos during both day and night, but females with fully-developed embryos were found predominantly at night. The diel cycle in the abundance of females with mature embryos was most pronounced in P. tergestina, and less prominent, but still clearly noticeable in P. avirostris, P. schmackeri and P. polyphymoides. The absence or scarcity of females with mature embryos during daytime could be caused by both selective predation by visual predators and nocturnal maturation and release of embryos. Juveniles of Acanthopagrus schlegeli (black seabream) were the most abundant planktivorous fish in the study area in spring. Stomach content analyses revealed that these daytime predators fed intensively on marine cladocerans and exhibited a strong selection for females with mature embryos. On the other hand, the gradual decline in the percentage of females with advanced embryos during the latter part of the night, when feeding by visual predators presumably had not yet begun, suggests that there was a tendency for nocturnal release of neonates in marine cladocerans. [ABSTRACT FROM AUTHOR]

The cladoceran Penilia avirostris is one of the more abundant and widespread members of the crustacean zooplankton in nearshore tropical and subtropical waters. Its abundance, biomass, fecundity, development rate and production were estimated in Kingston Harbour, Jamaica, during an 18 month period. Mean annual abundance of Penilia was 1821 m−3, while biomass (excluding eggs/embryos) was 2.87 mg ash-free dry-weight (AFDW) m−3 (43.1 mg AFDW m−2), accounting for 13% of the copepod community biomass. Fecundity increased with body size. There was no clear seasonal pattern of abundance, size or fecundity, nor were physical or biological variables correlated to these variations. Development time averaged 20.5 h for juveniles and 41.4 h for adult females during incubations; there was no clear evidence of a diel pattern to molting. Growth rate appeared to be exponential, with corresponding somatic growth rates, averaging 0.27 day−1 for juveniles, and 0.34 day−1 for somatic plus reproductive growth in adult females. Annual production was estimated as 173 kJ m−2 year−1, ∼10% that of the copepod community. Penilia avirostris production was similar to the third most productive copepod species. The importance of this species in tropical coastal waters would appear to be under-appreciated. [ABSTRACT FROM AUTHOR]

Selectivity-size spectra, clearance and ingestion rates and assimilation efficiencies of Acartia clausi (Copepoda), Penilia avirostris (Cladocera) and Doliolum denticulatum (Doliolida) from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluated in grazing experiments over a wide range of food concentrations (0.02–8.8 mm3 L−1 plankton assemblages from Blanes Bay, grown in mesocosms at different nutrient levels). Acartia clausi reached the highest grazing coefficients for large algae >70 μm (longest linear extension), P. avirostris for intermediate food sizes between 15 and 70 μm, and D. denticulatum for small sizes from 2.5 to 15 μm. Penilia avirostris and D. denticulatum acted as passive filter-feeders. Acartia clausi gave some evidence for a supplementary raptorial feeding mode. Effective food concentration (EFC) decreased linearly with increasing nutrient enrichment for D. denticulatum and followed domed curves for A. clausi and for P. avirostris with maximum values at intermediate and high enrichment levels, respectively. Clearance rates of crustacean species showed curvilinear responses with narrow modal ranges to increasing food concentration. Clearance rates of D. denticulatum increased abruptly and levelled into a plateau at low food concentrations. Mean clearance rates were 13.9, 25.5 and 64.1 mL ind.−1 day−1, respectively. No clearance could be detected for A. clausi at food concentrations <0.1 mm3 L−1 and for P. avirostris at food concentrations ≤0.02 mm3 L−1. Ingestion rates indicate a rectilinear functional response for A. clausi and for P. avirostris and showed a sigmoidal curve for D. denticulatum. Mean ingestion rates were 1.3, 2.8 and 7.7 μg C μg Cind.−1 day−1, respectively. Conversion of ingested carbon to tissue was 30–80% for the investigated crustaceans and 20–50% for doliolids. Food niche calculations suggest that food niche separation may explain the coexistence of the three species in summer in Blanes Bay. [ABSTRACT FROM AUTHOR]

The population dynamics of Penilia avirostris were studied in Guanabara Bay, southeastern Brazil. We determined birth rates according to the Edmondson-Paloheimo model, and analysed temporal variations in this parameter by the method of Polishchuk, which divides the birth rate into three components: egg development rate, mean brood size, and proportion of adults in the population. Considerations on the influence of major environmental factors such as food, predation, and temperature on changes in birth rates are made. The magnitude of the changes from parthenogenesis to gamogenesis alters the ratio of adults to juveniles, which may be a factor in determining the population peaks and valleys at certain times of the year. [ABSTRACT FROM AUTHOR]

Black seabream, Acanthopagrus schlegeli, and Japanese seaperch, Lateolabrax japonicus, are important commercial species in the coastal waters of western Pacific Ocean, including Japan, Korea and China. In Hong Kong, larvae and juveniles of these two species occur in bays and estuaries during late winter and spring. This study reports on the ontogenetic changes in food habits in larvae and juveniles of these species in an artificial rocky shore area. Copepods and cladocerans were the most numerous food items for black seabream. There was a shift to larger and benthic prey as the fishes grew. Japanese seaperch <2.1 cm fed predominantly on copepods and cladocerans, while larger prey were added as fish size increased. Japanese seaperch >6.0 cm were piscivorous. Maximum prey width increased with fish standard length and mouth gape width in both species. Overall, black seabream showed greater diet breadth than did Japanese seaperch. In black seabream, diet breadth increased with fish size. In Japanese seaperch, diet breadth increased with size for fishes <4.0 cm, then decreased as the fishes became piscivorous. Prey selectivity in black seabream was determined using information on prey availability in plankton samples. In general, preference was stronger for cypris larvae, Penilia avirostris and decapod larvae than for copepods and podonids. In recent years, overfishing and environmental degradation have led to the decline of fish populations in Tolo Harbour. Absence of fishes with empty gut indicates that inner Tolo Harbour is still an important nursery area for these two commercial species. [ABSTRACT FROM AUTHOR]

Examines the density of cladocerans Penilia avirostris and Evadne tergestina in Guanabara Bay, Brazil. Abundance of P. avirostris in summertime; Insufficiency of E. tergestina due to the relative increase of microphytoplankton density; Disappearance of P. avirostris and E. tergestina in winter.

Natural food items of five species of marine cladocerans, Evadne nordmanni, E. tergestina, Penilia avirostris, Podon leuckarti and P. polyphemoides, were investigated in the Inland Sea of Japan between April 1986 and May 1987. Gut content examination with SEM (scanning electron microscopy) revealed that feeding was largely limited to centric diatoms and a few exceptions of pennate diatoms and dinoflagellates. No animal remains were detected, and some unidentified materials were also found. Phytoplankton smaller than 35 μm in size (cell diameter in centric diatoms and longest dimension in others) was found most frequently in the gut of cladocerans. The role of grazing of marine cladocerans in trophodynamic pathways of the pelagic realm is discussed. [ABSTRACT FROM AUTHOR]

Development time of embryos in the brood pouch of the cladoceran Penilia avirostris Dana, 1852, was estimated by collecting zooplankton daily for 15 days in surface water of Guanabara Bay, Brazil. Each day the maturity stage of embryos of 90 parthenogenic females was noted. Total development time (egg to birth) varied from 2 to 3 days, the immature phase (stages I to IV) being generally longer (2 days) than intermediate and mature phases (1 day, stages V to XII). Similar results were obtained from Bottrell's equation, which takes water temperature into account.

The objective of this study was to report on some aspects of marine cladoceran reproduction in Guanabara Bay. Samples were collected during 1985 using a conical net with 200 mm mesh. Two species were identified: Penilia avirostris and Pseudevadne tergestina. Both species disappeared from the plankton in winter. Two months before this phenomenon, parthenogenetic females displayed reduction in brood size, while gamogenetic individuals appeared among the populations. This sequence of events is generally typical of marine cladoceran populations in temperate waters.

Penilia avirostris is a cosmopolitan marine cladoceran that inhabits coastal and shelf waters of most low and mid latitude ecosystems. In this study, we describe the life history and population dynamics of P. avirostris at a fixed coastal station in the NW Mediterranean Sea. This marine cladoceran was very seasonal, having population maxima in summer (2500–3000 ind m−3), and being practically absent from the water column for the rest of the year. The population typically collapsed in late summer–early autumn, and this decline was accompanied by a shift to gametogenetic reproduction, allowing the production of resting eggs to ensure the continuity of the species in the following season. Estimated birth rates of P. avirostris in the Catalan Sea ranged between 0.097 and 0.46 day−1 and seemed to be decoupled from changes in P. avirostris standing stocks. Birth rates were mainly dependent on the changes in abundance of embryo-carrying females and their brood size, because during the period of population plateau the temperature-dependent embryonic developmental time was rather similar (2.3–2.7 days). Neonates are like miniature adults and need a very short period of growth and moulting to reach the reproductive stage. This life-history trait can explain the fast blooming and dominance of plankton communities by P. avirostris under suitable conditions. Finally, the causes for the seasonal decline of P. avirostris populations are also discussed. [ABSTRACT FROM AUTHOR]

An ecological model for the simulation of the population dynamics of the cladoceran Penilia avirostris in Guanabara Bay, a tropical Brazilian bay, was developed. The simulated curve gave a good fit, in time and intensity, to the exponential increase and decrease in densities of P. avirostris during the March-July 2000 period. The densities of embryos, young individuals, males, and parthenogenic and gamogenic females were the state variables. Parameters of the model were varied within the range of field and literature data. Predation was considered as the main factor affecting mortality, the death rate being a function of the density of chaetognaths, the dominant invertebrate predator in Guanabara Bay. Input of resting eggs into the model as a “seed” source of embryos provided a good fit to the exponential increase of Penilia density. The observed sharp decreases and collapses of the population could not be explained by mortality or a shift from parthenogenic to gamogenic reproduction only. To provide an explanation, it was necessary to introduce an output forcing function, which probably represents physical factors such as water mass exchanges by tide- and wind-driven currents. [Copyright &y& Elsevier]

Populations of Penilia avirostris were studied in Guanabara Bay, southeastern Brazil, to assess temporal variations in the densities of parthenogenetic and gamogenetic individuals, length, and brood size. The abundance of P. avirostris varied widely during a brief 3-d period. These variations probably resulted from the combined action of water temperature, predation pressure by chaetognaths, and advection. Gamogenetic animals are found only during the peaks of population density of P. avirostris . To explain this phenomenon, we developed the hypothesis of constant population sex ratio : according to this hypothesis, the appearance of gamogenetic animals is a function, not of adverse environmental conditions, but rather of the low but constant rate of occurrence of males in the population. [Copyright &y& Elsevier]