Search

Bluegills Lepomis macrochirus R. provide popular sport fisheries but the quality of these fisheries has declined across much of their range. Factors that may influence bluegill demographics were examined in 18 Midwestern (USA) impoundments which contained largemouth bass Micropterus salmoides L., the main apex predator, as well as varying abundances of gizzard shad Dorosoma cepedianum L. and common carp Cyprinus carpio L., which can negatively influence the quality of bluegill populations. Regression models revealed that the relative abundance (catch-per-unit-effort [CPUE], number per hour of electrofishing) of bluegill was positively associated with largemouth bass CPUE and total phosphorous concentration. The total lengths (TL) and ages of the largest and oldest bluegills were negatively associated with common carp CPUE and total annual mortality of bluegills, and positively associated with the TL and age of bluegills when 50% were sexually mature and largemouth bass CPUE. Total annual mortality negatively influenced the TL and age at sexual maturity. Bluegills matured at larger sizes and older ages in impoundments with clearer water. This study revealed the strong influence of mortality on size and age structure and the onset of sexual maturity of bluegill, and the negative influence of common carp on these populations. Management strategies to improve bluegill populations should involve reducing bluegill mortality and common carp populations. [ABSTRACT FROM AUTHOR]

Comparative study of growth rate and size-age structure of gray sea urchin Strongylocentrotus intermedius is conducted for six its aggregations along Primorye coast on the data collected in diving surveys in 2015–2017. Some aspects of the method of the sea urchin individual age determination by concentric growth bands on interambulacral plates of its carapace are discussed (the plates are processed by M. Jensen method). The group growth is described with Bertalanffy equation. Considerable spatial variability of the growth rate is found between the aggregations that provides some distinctions in size structure of the sea urchins. The highest growth rate is observed for three habitats: Kreyser Rock Island — Cape Lisuchenko, Oprichnik Bay — Cape Grozny, and Cape Sosunov — Plitnyak Bay, where the sea urchins reach the commercial size mostly at the age from 3.5+ to 4.5+. On the contrary, 50 % of the sea urchins become large enough for commercial fishery at the age of 6+ in the Ezhovaya Bay, and the lowest growth rates are noted at Cape Yuzhny and Cape Nadezhda where the majority of sea urchins never reach the commercial size. The maximum age of S. intermedius (19 years) is registered for a specimen with size 73 mm caught at Cape Sosunov. Mean and maximum sizes of individuals in the aggregations of slow-growing S. intermedius are lower than in the aggregations with comparatively high growth rates; such aggregations are also distinguished by lack of commercially-sized individuals. Age structure of all aggregations shows strong irregularity of annual recruitment, particularly low portion of the sea urchins at the age of 1+ is noted. Anyway, the frequency goes down from the age of 7+...9+ that indicates mass elimination of elder animals.

Food web studies commonly ignore individual variation within a population and variation in the environment and assume these factors have insignificant effects on community dynamics relative to interspecific interactions. However, variation in body sizes within a population (size structure) and the physical structure of habitats (habitat complexity) can both affect interspecific interactions independently, with possible interactive effects. Using experimental mesocosms, we examined effects of predator size structure and habitat complexity on predation by two common predators in fishless ponds: larval aquatic beetles (Cybister fimbriolatus) and larval dragonflies (Anax junius). Cannibalism, intraguild predation, and predation on shared prey were measured at two levels of habitat complexity crossed with six size-structured pairs of predators. We found that highly complex habitats sustain a higher prey density because prey can take refuge from predators. Additionally, size structure had direct (size better predicted predation rate than did species identity) and indirect (IGP and cannibalism lowered predation rates) effects on consumptive interactions, which changed the composition and density of the predator guild. The identified size- and habitat-mediated mechanisms can change the frequencies of intraguild vs. interguild predation (a balance important in determining top–down control of predators), and therefore we argue that these sources of heterogeneity should be included in community ecology studies where possible.

Assessing the extant distribution of wildlife species is a crucial step towards promoting their protection and management in the light of global biodiversity decline, and even more so when threatened, vulnerable, rare, or endemic taxa are concerned. In this context, we present an overview of the biogeography of two freshwater turtle species, namely the Mediterranean pond turtle Mauremys leprosa and the European pond turtle Emys orbicularis, as a basis for Conservation Action Plans. Mauremys leprosa is widely distributed in the north and centre of Tunisia and has viable populations in most of the study sites. Based on the evaluation of its biogeography, the size, structure and genetics of four populations, it appears that this species is currently not threatened in Tunisia. In contrast, E. orbicularis, which is represented in eastern Algeria and Tunisia by an endemic, undescribed subspecies, was absent from 11 historical sites in Tunisia, and only isolated small populations and scattered individuals were present in the extreme north of the country. Our study thus suggests that this subspecies is declining in Tunisia and its status is probably close to Endangered (EN). Therefore, it needs special attention and urgent conservation measures. [ABSTRACT FROM AUTHOR]

The age or size structure of a population has a marked influence on its demography and reproductive capacity. While declines in coral cover are well documented, concomitant shifts in the size-frequency distribution of coral colonies are rarely measured at large spatial scales. Here, we document major shifts in the colony size structure of coral populations along the 2300 km length of the Great Barrier Reef relative to historical baselines (1995/1996). Coral colony abundances on reef crests and slopes have declined sharply across all colony size classes and in all coral taxa compared to historical baselines. Declines were particularly pronounced in the northern and central regions of the Great Barrier Reef, following mass coral bleaching in 2016 and 2017. The relative abundances of large colonies remained relatively stable, but this apparent stability masks steep declines in absolute abundance. The potential for recovery of older fecund corals is uncertain given the increasing frequency and intensity of disturbance events. The systematic decline in smaller colonies across regions, habitats and taxa, suggests that a decline in recruitment has further eroded the recovery potential and resilience of coral populations. [ABSTRACT FROM AUTHOR]

Assessing the extant distribution of wildlife species is a crucial step towards promoting their protection and management in the light of global biodiversity decline, and even more so when threatened, vulnerable, rare, or endemic taxa are concerned. In this context, we present an overview of the biogeography of two freshwater turtle species, namely the Mediterranean pond turtle Mauremys leprosa and the European pond turtle Emys orbicularis, as a basis for Conservation Action Plans. Mauremys leprosa is widely distributed in the north and centre of Tunisia and has viable populations in most of the study sites. Based on the evaluation of its biogeography, the size, structure and genetics of four populations, it appears that this species is currently not threatened in Tunisia. In contrast, E. orbicularis, which is represented in eastern Algeria and Tunisia by an endemic, undescribed subspecies, was absent from 11 historical sites in Tunisia, and only isolated small populations and scattered individuals were present in the extreme north of the country. Our study thus suggests that this subspecies is declining in Tunisia and its status is probably close to Endangered (EN). Therefore, it needs special attention and urgent conservation measures. [ABSTRACT FROM AUTHOR]

Copyright of Revista Mexicana de Biodiversidad is the property of Universidad Nacional Autonoma de Mexico, Instituto de Biologia 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.)

The current status of the red king crab population off western Kamchatka is considered based on data from bottom trawl surveys and fishery statistics since 2013. Some biological parameters of this crab species are provided; its commercial stock is estimated; some features of red king crab fishery and determination of total allowable catch for the past 7 years are analyzed. The red king crab fishing was resumed in 2013 after an 8-year ban imposed due to the population decline. During this period, the stock recovered and reached values greater than those recorded before the ban: the total estimated size of red king crab population in 2017 was almost 244 million ind., which is the highest value for the recent 17 years of research; the estimated number of commercial-sized males, 110 million ind., has not been recorded from the western Kamchatka shelf for at least past 4 decades. Recently, the Severny Zapretny and Khairyuzovsky areas of the shelf zone have yielded their role of main feeding grounds for pre-recruit crabs and juveniles to the Ichinsky area located south. For the 7 years of red king crab fishery, harvest values have been steadily high. In the past 3 years, the major part of the annual catch of live crabs has been exported to China and South Korea. As the analysis of size structure show, the body size of male red king crabs has been increasing each year all over the shelf. This may be explained by the strict sorting of caught crabs aboard vessels transporting live crabs with the release of the largest individuals; another possible explanation is the relatively low recorded number of pre-recruits in the past 2 years. For the 7 years past (including 2019), the fishing mortality rate is estimated within a range of 5–16% of the crab stock actually recorded from the permitted fishery areas, which is a highly cautious approach. In the nearest future, the crab commercial stock is expected to gradually decrease, which, nevertheless, should not fall below the reference target value of biomass. The current status of the red king crab population off western Kamchatka does not raise concern, and the ongoing intense harvesting of this valuable species within the recommended catch size will not have any negative effect on its commercial stock. [ABSTRACT FROM AUTHOR]

Historical comparisons of body size often lack pertinent details, including information on the sampling protocol and relevant ecological covariates that influence body size. Moreover, historical estimates of body size that rely on museum specimens may be biased towards larger size classes because of collector preferences, and thus size thresholds have been used to focus attention on maximum body size. We tested the consequences of sampling design, ecological covariates, and size thresholds on inferences of body‐size change using field‐contextualized historical records, rather than museum specimens. In 2014–2015, we revisited historical (1947–1963) size‐frequency distributions of three gastropods (Tegula funebralis, Lottia digitalis/L. austrodigitalis, Littorina keenae) in the context of population density and tidal height. In general, gastropods declined in size. However, our inferences regarding body‐size decline were tempered when the variation between sampling units was taken into consideration, resulting in greater uncertainty around the estimate of proportional change in body size. Gastropod size was correlated with population density and tidal height, and these relationships varied over time. Finally, the magnitude and direction of body‐size change varied with the amount of data available for analysis, demonstrating that the use of size thresholds can lead to incomplete conclusions. [ABSTRACT FROM AUTHOR]

Mussel beds are common in many intertidal and subtidal habitats, including sub-Arctic and Arctic regions. Despite their ecological importance, little is known about the demographic processes governing the development of mussel beds and particularly about the synchronization of these processes at different spatial scales. The development of a relatively compact, narrow littoral mussel bed of Mytilus trossulus, extending several hundred m along the shore of Koni Peninsula (Tauyskaya Bay, northern Sea of Okhotsk), was studied for four years during the period 2014–2017. This model bed was located along an exposed coast with a seasonal sea ice cover. It was used to test the hypothesis that small-scale synchronization exists, i.e., the changes in demographic structure of the population that occur simultaneously within a single mussel bed follow a similar pattern. This hypothesis was rejected. The size structure of the mussel population at the same tidal level changed from being uniform (2014) to being varied in 2015–2017. The course of development of the mussel population was different at the opposite ends of the bed. The cause of these differences may be unequal levels of recruitment of juveniles in the form of a gradient from one end of the bed to the other over the length of the bed. The gradient was associated with transition from one type of shore dynamic processes to another (accumulation vs. abrasion). Small-scale desynchronization may represent one of the reasons explaining the heterogeneity of mussel populations. The possibility of desynchronization of demographic processes should be taken into consideration when studying the spatial organization and dynamics of mussel beds. [ABSTRACT FROM AUTHOR]

Cities with great government capacity are expected to become more effective in mobilizing resources and promoting urban economic development than other cities. While urban government capacity is important in its own right, its size structure across nearby cities is crucial because multiple channels wherein local governments generate externalities beyond their jurisdictions are present. By quantifying urban government capacity and regional size structure across Chinese cities in 2010, I examine the direct effect of a city's government capacity on its economic performance and the indirect effect of the urban government capacity's size structure among neighboring cities. Our analysis confirms that urban government capacity has a positive and significant effect on urban economic performance, and cities exhibit better economic performance in regions that have a leading city in urban government capacity than in regions where urban government capacity is relatively evenly distributed. Further examination suggests that the effect of urban government capacity on economic performance is stronger for cities in monocentric regions than in other regions. [ABSTRACT FROM AUTHOR]

Although metamorphosis is widespread in the animal kingdom, several species have evolved life‐cycle modifications to avoid complete metamorphosis. Some species, for example, many salamanders and newts, have deleted the adult stage via a process called paedomorphosis. Others, for example, some frog species and marine invertebrates, no longer have a distinct larval stage and reach maturation via direct development. Here we study which ecological conditions can lead to the loss of metamorphosis via the evolution of direct development. To do so, we use size‐structured consumer‐resource models in conjunction with the adaptive‐dynamics approach. In case the larval habitat deteriorates, individuals will produce larger offspring and in concert accelerate metamorphosis. Although this leads to the evolutionary transition from metamorphosis to direct development when the adult habitat is highly favorable, the population will go extinct in case the adult habitat does not provide sufficient food to escape metamorphosis. With a phylogenetic approach we furthermore show that among amphibians the transition of metamorphosis to direct development is indeed, in line with model predictions, conditional on and preceded by the evolution of larger egg sizes. [ABSTRACT FROM AUTHOR]

For many fish taxa, trophic position and relative fecundity increase with body size, yet fisheries remove the largest individuals, altering food webs and reducing population productivity. Marine reserves and other forms of spatial protection can help mitigate this problem, but the effectiveness of these management tools may vary interspecifically and spatially. Using visual survey data collected on the Central Coast of British Columbia, for 12 species of exploited rockfish we found that body size responses to spatial fishery closures depended on interspecific variation in growth parameter k (the rate at which the asymptotic body size is approached) and on location. For two closures, relative body sizes were larger at protected than at adjacent fished sites, and these differences were greater for species with lower k values. Reduced fishery mortality likely drove these results, as an unfished species did not respond to spatial protection. For three closures, however, body sizes did not differ between protected and adjacent fished sites, and for another closure species with higher k values were larger at fished than at protected sites while species with lower k values had similar sizes in both treatments. Variation in the age of closures is unlikely to have influenced results, as most data were collected when closures were 13 to 15-years-old. Rather, the lack of larger fish inside four of six spatial fishery closures potentially reflects a combination of smaller size of the area protected, poor fisher compliance, and lower oceanographic productivity. Interspecific differences in movement behavior did not affect body size responses to spatial protection. To improve understanding, additional research should be conducted at deeper depths encompassing the distribution of older, larger fish. Our study--which was conceptualized and executed by an alliance of Indigenous peoples seeking to restore rockfishes--illustrates how life history and behavioral theory provide a useful lens for framing and interpreting species differences in responses to spatial protection. [ABSTRACT FROM AUTHOR]

Acer yangbiense Y.S. Chen & Q.E. Yang (Aceraceae) is a threatened tree species endemic to China, formerly presumed to have declined to only five extant individuals, restricted to Yangbi County, Yunnan Province. Our surveys in 2016, however, located 577 individuals in 12 localities, but only three localities (with a total of 62 individuals) are protected. Nine localities are on private forest land. The population's size structure is an inverse J-curve, but there is a scarcity of trees of the smallest size class and of seedlings. Our surveys also showed that the habitat of A. yangbiense is degraded as a result of the negative effects of agriculture, logging and wood harvesting. Assessment with the IUCN Red List categories and criteria indicates that A. yangbiense should be recategorized from Critically Endangered to Endangered. [ABSTRACT FROM AUTHOR]

Magnolia ovoidea is a narrowly endemic, Critically Endangered tree with a fragmented distribution in south-west Yunnan, China. We examined the size structure of this species, documented threats and assessed its extinction risk. We found the species in six locations, all in unprotected areas, in Maguan County. The largest subpopulations are in Donggua Lin and Youfang Po, with 17 and 50 living individuals, respectively. The distribution of the diameter at breast height of the M. ovoidea population has an inverse J-shape, indicating a stable size structure. However, the distribution of the height of seedlings is L-shaped, suggesting inhibited regeneration. The natural vegetation is severely fragmented in all six locations, surrounded by roads, farmlands, and Alnus nepalensis or Cunninghamia lanceolata plantations. We recommend that M. ovoidea should be categorized on the IUCN Red List as Critically Endangered based on criteria B2ab(iii) + C2a(i). [ABSTRACT FROM AUTHOR]

Harvest mortality typically truncates the harvested species' size structure, thereby reducing phenotypic complexity, which can lead to reduced population productivity, increased population variability, and selection on an array of life history traits that can further alter these demographic processes. Marine protected areas (MPAs) are a potential tool to protect older, larger individuals and therefore mitigate such ecological and evolutionary effects of harvest, depending on the degree of connectivity among areas. Such MPA protection relies on a shift in size‐dependent mortality, the measurement of which can therefore serve as an early indicator of whether MPAs might achieve the desired longer‐term ecological and evolutionary responses. We directly measured MPA effects on size‐selective mortality and associated size structure using mark–recapture data on European lobster (Homarus gammarus) collected at three MPA–control area pairs in southern Norway during one decade (n = 5,943). Mark–recapture modeling, accounting for variation in recapture probabilities, revealed (1) that annual mean survival was higher inside MPAs (0.592) vs. control areas (0.298) and (2) that significant negative relationships between survival and body size occurred at the control areas but not in the MPAs, where the effect of body size was predominantly positive. Additionally, we found (3) that mean and maximum body size increased over time inside MPAs but not in control areas. Overall, our results suggest that MPAs can rebuild phenotypic complexity (i.e., size structure) and provide protection from harvest selection. [ABSTRACT FROM AUTHOR]

The tropical Pacific Ocean supports many productive commercial fisheries. However, few studies of ecosystem structure in the tropical Pacific Ocean have been carried out. In this study, we analyzed the food web structure in the central and eastern tropical Pacific Ocean based on trophic relationships of 35 pelagic species collected by Chinese tuna longline observers from June to November in 2017. Topology indices (node degree, D; centrality indices, BC and CC; topological importance indices, TI1, TI3; keystone indices, K, Kt and Kb) and Key-Player algorithms (KPP-1, KPP-2) were used to select key species and construct a simplified food web combined with body size data. The Kendall rank correlation and hierarchical clustering analysis indicated that different topology indices resulted in consistent rankings of key species. Most key species were the same as those selected in other studies in the Pacific Ocean, such as Shortbill spearfish (Tetrapturus angustirostris), Swordfish (Xiphias gladius), Albacore tuna (Thunnus alalunga), cephalopods and scomber. The food web would be separated into many unconnected parts (F=0.632, FD=0.795, RD=0.957) after the removal of the five key species, indicating the key roles of these species in the food web structure and stability. Body size was considered an influential indicator in constructing the simplified food web. This study can improve our understanding of the food web structure in the tropical Pacific Ocean and provide scientific basis for further ecosystem dynamics studies. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is a semi-enclosed marginal sea. And in the northern SCS (NSCS), the Pearl River plume, mesoscale eddies and Kuroshio intrusion may influence the structure of pelagic ecosystems. Here, based on mesozooplankton samples collected in the NSCS from December 2014 to January 2015, spatial variations of mesozooplankton biomass, abundance, normalized biomass size spectra (NBSS), size structure and trophic structure were analyzed to study the response of mesozooplankton community to the influence of highly variable oceanographic environment. High biomass, abundance and intercept of NBSS for the mesozooplankton community were observed in highly productive regions (net primary production > 400 mg C m−2 day−1), such as river plume and cold eddy. No consistent spatial variation was observed for the slope of NBSS, probably because of highly dynamic marine environment in the NSCS. For the trophic structure of mesozooplankton community, the ratio of total chaetognaths biovolume to herbivores/omnivores biovolume (RTCH) was significantly high in river plume and Kuroshio intrusion. The high RTCH indicated unstable trophic structures, which may be due to extreme high proportion of smaller size individuals supported by discharge of river and transport of warm water species from the tropical western Pacific by Kuroshio intrusion, respectively. [ABSTRACT FROM AUTHOR]

Outbreaks of Acanthaster planci are one of the major contributors to coral reef degradation, particularly in Indo-Pacific region. Correct assessment of its impact on coral reef ecosystems requires an understanding to its biology and ecology. This present study was conducted to determine the abundance, size structure and preyed corals of A. planci in Lungui Island, Dimataling, Southern Philippines. Four replicates of 50 × 4 m belt transects were laid in each of three sampling stations. A total of 112 A. planci individuals were recorded, whose body sizes varied significantly between the three stations (H = 3.401; p = 0.0180 at a = 0.05) ranging from 120 to 270 mm. All detected A. planci individuals were observed foraging on corals. Five preyed coral genera were identified through morphology-based identification, where Pocillopora was the most preyed coral genus, foraged by 28.57% of total A. planci individuals. Although the number of A. planci individuals in Lungui Island has not reached the outbreak threshold level, its presence in the area should not be overlooked. In fact, this raises a need for continuous monitoring of its population level in these local reef areas of the coastal waters of Dimataling, Southern Philippines. [ABSTRACT FROM AUTHOR]

Skipjack tuna is a potential fish resource in the Makassar Strait, Bone Bay, and the Flores Sea waters, Indonesia. This fish is captured by fishermen using many kinds of fishing gear, and the most widely used is purse seine. The study was conducted from January to December 2018, aimed to compare the size structure of skipjack, productivity, and by-catch of purse seine inside and outside of Fish Aggregation Devices (FADs) areas. Fish length (cm, FL), annual production and trips data were collected from 10 ship owners in each fishing area, The main catch and by-catch weight data were obtained through direct observation of 30 trips each for 10 units, both of purse seines inside and outside of FADs areas in each study area. Comparative analysis of the catches of purse seines inside and outside of FADs areas included size structures using the Median Test (T test), productivity and by-catch using Mann-Whitney Test (T test). The results of the study explained that purse seiners inside FADs areas could increase business productivity, but caused an increase in small-sized skipjack and by-catch while purse seines outside of FADs areas caught less small size skipjack, low by-catch but low productivity. [ABSTRACT FROM AUTHOR]

This paper investigates the theoretical aspects for an optimal contraception control problem of a linear size-structured population model with extra mortality. The existence of a unique non-negative solution is established by using the Banach fixed-point theorem. The existence of a unique optimal strategy is derived by the Mazur theorem in convex analysis and the optimality conditions are obtained by means of normal cone and adjoint system techniques. Finally, some numerical results demonstrate the effectiveness of the theoretical results in our paper. [ABSTRACT FROM AUTHOR]

Haloxylon persicum is a desert shrub with economic and ecological importance for arid zones in Saudi Arabia. It has a vital role in the protection of Unaizah and Buraidah, two large cities, and their surrounding from the dangerous mobile sand dunes and without it, the area could be covered by these dunes in a few years. The current study aims to analyze the floristic, vegetation structure and size structure of H. persicum. Eighteen stands were selected along the north and south of the study area with 20 m² each. At each stand, the vegetation inventory including plant species abundance percentage and size structure for H. persicum were estimated. Three plant associations; H. persicum-Plantago boissieri, H. persicum-Stipagrostis plumose and H. persicum were identified. Analysis of H. persicum size structure frequency was skewed towards medium size classes in all populations and the early life stages such as juvenile and the seedling recruitment was extremely limited. These results indicated that the populations of H. persicum are threatened by aridity and human impacts. Therefore, efforts are required to minimize uncontrolled exploitation. Finally, in situ and ex situ conservation of H. persicum populations are strongly recommended. [ABSTRACT FROM AUTHOR]

Although analyses of species spatial distributions and genetic variation, creation of Red Lists and reserve design studies predominate in the plant conservation biology literature, in any conservation project they should be only a second step succeeding population demographic assessments. Demographic studies and analysis of the species regeneration niche are vital because only such studies can identify the factors that determine the population fate, the stages of the life-cycle that are most important for the population viability, and the regeneration niche parameters. Using published demographic data, we modelled a situation when either seed production or survival of emerging seedlings occur intermittently. We found that when recruitment occurs intermittently, the population size frequency distribution deviates from inverse J-curve, but no gaps in size classes are observed unless seed germination and/or survival of emerging seedlings are extremely rare events. Then we use these results to interprete population demography of ten threatened tree species from Wuling Mountains, China, and come to a conclusion that their demographic structure can not be a result of natural processes. Taken together, our results show how important even a single population census can be if it includes counting seedlings and saplings, for determining population viability and appropriate population management. Two types of populations must be recognized as requiring different managements strategies: with regeneration naturally occurring (even if limited) and with no seedlings/saplings present. Populations from the first category can be subjected to such management actions as reinforcement using plant material of appropriate origin. Planting conspecifics can boost regeneration through increased seed production. However, reinforcement will make no sense in populations in which lack of regeneration is due to reasons other than seed limitation. In such populations long-term monitoring and study program must be established to understand the reasons for lack of regeneration. [ABSTRACT FROM AUTHOR]

Many migratory species, from monarch butterflies to wildebeest, express partial migration, where only a subset of a population migrates. This intraspecific variation is likely to have large ecological consequences. We studied the ecological consequences of partial migration in a salmonid fish, Oncorhynchus mykiss, in coastal streams in California, USA. One ecotype, steelhead trout, migrates to the ocean, whereas the other, rainbow trout, completes its lifecycle in freshwater. Migration has a strong genetic basis in O. mykiss. In one stream, we found differences in the frequency of migration-linked genotypes below and above a waterfall barrier (migratory allele frequency of 60% below vs. 31% above). Below the waterfall, in the migratory-dominated region, the density of young fish (<1 yr old) was approximately twice that in the resident-dominated region above the waterfall (0.46 vs. 0.26 individuals/m2, respectively), presumably reflecting the higher fecundity of migratory females. Additionally, there were half as many older fish (>1 yr old) in pools downstream of the waterfall (0.05 vs. 0.13 individuals/m2). In a second stream, between-year variation in the dominance of migratory vs. resident fish allowed us to explore differences in fish density and size structure through time, and we found a consistent pattern. In brief, when migratory genotypes dominated, we found higher densities of young fish and lower densities of older fish, resulting in a simpler size structure, compared to when resident genotypes dominated. Moreover, large resident trout had a slightly higher trophic position than young fish (3.92 vs. 3.42 in one creek and 3.77 vs. 3.17 in the other), quantified with stable isotope data. The difference in fish size structure did not generate trophic cascades. Partial migration is widespread among migratory populations, as is phenotypic divergence between resident and migratory forms, suggesting the potential for widespread ecological effects arising from this common form of intraspecific variation. [ABSTRACT FROM AUTHOR]

The paper presents the results from a study of the population structure of alien snow crabs Chionoecetes opilio in the western Kara Sea near the Kara Strait using two methods: Sigsby trawling and video surveillance. The towed unmanned underwater vehicle Videomodule was used to estimate the population density of crabs: 0.55 ind/m2 in 2016, and 0.17 and 0.09 ind/m2 in 2017. No differences were revealed when comparing the size structure of the crab population based on the two methods. An exception is possible underestimation of younglings with a carapace width <20 mm when using the Videomodule. The minimum observed carapace size was ~10 mm, and the maximum, 127 mm. Both methods revealed the presence of all stages of crab growth, which indicates successful survival and growth of this crab in the western Kara Sea. An adequate assessment of the development of invasion of alien C. opilio in the Kara Sea requires annual video observations in the regions representing characteristic biotopes at different distances from the Kara Strait. [ABSTRACT FROM AUTHOR]

The results of a study of phytoplankton in Taganrog Bay in the Sea of Azov and the downstream reaches of the Don River carried out in January–November 2017 are presented. A total of 210 species of eukaryotic algae and cyanoprokaryotes are identified. An analysis of the taxonomic, ecological, and geographical composition of the plankton algal flora and seasonal dynamics of biomass of phytoplankton taxonomic and size structures has revealed no changes in the ratio of large taxonomic and ecological–geographic groups in the algal flora when compared with previous years (1980s to early 2000s). However, the proportion of myxotrophic phytophagellates, cyanoprokaryotes from the planktotrichet complex, and small species increased in algal communities. It is shown that the water salinity is the main factor influencing the formation of species richness and total biomass and structure of phytoplankton. The maximum diversity and biomass of phytoplankton are recorded in the horohalinicum zone. [ABSTRACT FROM AUTHOR]

Declines in predatory fish in combination with the impact of climate change and eutrophication have caused planktivores, including three-spined stickleback (Gasterosteus aculeatus), to increase dramatically in parts of the Baltic Sea. Resulting impacts of stickleback on coastal and offshore foodwebs have been observed, highlighting the need for increased knowledge on its population characteristics. In this article, we quantify abundance, biomass, size structure, and spatial distribution of stickleback using data from the Swedish and Finnish parts of the Baltic International Acoustic Survey (BIAS) during 2001–2014. Two alternative methods for biomass estimation suggest an increase in biomass of stickleback in the Baltic Proper, stable or increasing mean size over time, and larger individuals toward the north. The highest abundance was found in the central parts of the Baltic Proper and Bothnian Sea. The proportion of stickleback biomass in the total planktivore biomass increased from 4 to 10% in the Baltic Proper and averaged 6% of the total planktivore biomass in the Bothnian Sea. In some years, however, stickleback biomass has ranged from half to almost twice that of sprat (Sprattus sprattus) in both basins. Given the recent population expansion of stickleback and its potential role in the ecosystem, we recommend that stickleback should be considered in future monitoring programmes and in fisheries and environmental management of the Baltic Sea. [ABSTRACT FROM AUTHOR]

The summer monsoon shows a fundamental influence on the pelagic ecosystem of the South China Sea. Zooplankton are a major link for energy transfer between primary producers and upper trophic levels. Therefore, evaluating the energy transfer efficiency (ETE) of zooplankton is crucial to understand the function of pelagic ecosystem under the influence of monsoon. In this study, field surveys were conducted during May (intermonsoon) and August 2021 (summer monsoon) focusing on the variation of zooplankton size and trophic structures across the shelf and slope. The result showed that the summer monsoon reinforced the gradient of abundance, biovolume, and biomass from slope to shelf, and greatly intensified the role of environmental factors in driving spatial variation in most taxa. Both the results of size and trophic structures indicated that the ETE of zooplankton decreased from slope to shelf. The size structure also indicated that the ETE of zooplankton significantly increased under the influence of summer monsoon. These results were consistent with previous studies by different methods, suggesting that these approaches of size and trophic structures had important potential value in assessing changes in the function of marine pelagic ecosystem, especially when compared with sufficient historical data or reanalyzing historical samples. [Display omitted] • The effect of summer monsoon on ETE of zooplankton community was revealed. • The ETE of zooplankton significantly decreased from the slope to the shelf. • The ETE of zooplankton significantly increased during summer monsoon. • Size and trophic structure approaches can assess the function of pelagic ecosystem. [ABSTRACT FROM AUTHOR]

Urban lakes are important environmental assets that contribute significant ecosystem services in urbanised areas around the world. Consequently, urban lakes are more exposed to anthropogenic pressures. Zooplankton communities play a central role in lake processes and, as such, are very sensitive to the impacts of human activities both through in-lake and catchment processes. Understanding their ecological function in urban lakes and how they respond to urbanisation is essential for environmental sustainability. In this study, we investigated the reliability of zooplankton size structure as indicators of anthropogenic stressors in urban lakes. We examined the relationship between environmental variables and zooplankton community size spectra derived as mean body size, density, and biomass. Our study showed that the overall mean body size was within the small size group ranged from 416 to 735 µm equivalent spherical diameter (ESD). Despite no significant difference in total zooplankton density between lakes, there was variability in the total density of the five different size classes. Total biomass was characterised by a significant proportion of size >750 µm. As the specific parameter of normalised biomass size spectra (NBSS), the slopes of the NBSS varied from moderate (−0.83 to −1.04) for a community with higher biomass of the larger size zooplankton to steeper slopes (from −1.15 to −1.49) for a community with higher biomass of smaller size. The environmental variables, represented by total phosphorus (TP) and chlorophyll a (chl-a), had a strong effect on zooplankton biomass and NBSS, where TP and chl-a were significantly correlated with the increase of total biomass and corresponded well with a less negative slope. Our results indicated that the community metric was sensitive to nutrient input and that size-based metrics have the potential to serve as key indicators for the management of urban lakes.

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 (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.

Zooplankton inhabiting the Hornsund and Kongsfjorden fjords on Spitsbergen (Svalbard) were investigated in summer 2013. The goal of the study was to determine how the zooplankton communities vary in environments functioning under different oceanographic regimes. Sampling was conducted with nets of different mesh size and selectivity (56 μm WP-2, 180 μm MultiNet, and 1000 μm Tucker Trawl), which permitted comparing a wide size spectrum of zooplankton components. Species composition did not differ substantially between the fjords, but the zooplankton in Hornsund was almost two times less numerous, and it had lower biomass per unit volume. The highest abundance at both sites was in the smallest zooplankton size fraction found only in samples taken with 56 μm mesh WP-2 net. These comprised as much as 71% and 58% of the total zooplankton abundance in Hornsund and Kongsfjorden, respectively. The communities in both fjords had comparable contributions of Arctic and boreo-Arctic species biomass in the year of the study. However, the comparison of zooplankton characteristics over several years showed changes in abundance and biogeographic structure that corresponded with variations in the physical environments of the fjords. The results of the study permit predicting the possible effects of the increasing influence of Atlantic waters on zooplankton communities inhabiting Arctic marine pelagic ecosystems.

In the paper the statistical relationships between the size and production characteristics of phytoplankton and zooplankton of the Vistula and Curonian lagoons, the Baltic Sea, were investigated. Research phytoplankton and zooplankton within the Russian part of the area of the Vistula and the Curonian lagoon was carried out on the monthly basis (from April to November) within the framework of long-term monitoring program on evaluating of ecological status of the lagoons. The size structure of plankton is the basis for understanding of the development of production processes, mechanisms of formation of the plankton species diversity and functioning of the lagoon ecosystems. As results of the work it was found that the maximum rate of photosynthesis and the integral value of the primary production with a change in cell volume of phytoplankton are changed according to a power law. The result shows that the smaller the size of algal cells in phytoplankton communities the more actively occur metabolism and the more effective they assimilate the solar energy. It is shown that the formation of plankton species diversity in ecosystems of lagoons is closely linked with the size structure of plankton communities and with features of development of the production processes. It is proposed the structure of a spatially homogenous mathematical model of the plankton food chain for the lagoon ecosystems taking into account the size spectrum and the characteristics of phytoplankton and zooplankton. The model parameters are the sizedependent indicators allometrically linked with average volumes of cells and organisms in different ranges of their sizes. In the model the algorithm for changes over time the coefficients of food preferences in the diet of zooplankton was proposed. Developed the size-dependent mathematical model of aquatic ecosystems allows to consider the impact of turbulent exchange on the size structure and temporal dynamics of the plankton food chain of the Vistula and Curonian lagoons. The model can be used to study the different regimes of dynamic behavior of plankton systems depending on the changes in the values of its parameters and external influences, as well as to quantify the redistribution of matter flows in ecosystems of the lagoons.

Population of pale sea urchin Strongylocentrotus pallidus in Peter the Great Bay is investigated. The samples for its size structure and distribution were collected at the depth from 5 to 700 m in July 2013, 2014 and in April 2015 and the samples for the state of gonads, intestines and age structure - at the depths of 41, 69, 280, 346, and 670 m in early April 2015. The size structure at different depths is significantly different: the large individuals with average size of 70.0 mm (portion of commercial ones 98 %) occupy mainly the middle shelf area with the depths of 55-100 m, deeper at the depths of 100-200 m the portion of commercial urchins is lower (67 % in 2014 and 92 % in 2015), and the continental slope (depth > 200 m) is occupied by mainly (77-96 %) non-commercial individuals with average size of 35.5 mm. Age of sea urchins was determined by the growth zones on plates of their shells processed by Jensen method and varied from 3 to 12 years. The growth rate of sea urchins from the shelf areas was approximately in 1.5 times higher as compared with those from the continental slope, primarily due to different conditions of feeding. The gonads cellular composition was defined for the samples of 50 cells per female. The cells were differentiated in the categories of oocytes proliferation, oocytes differentiation, and mature eggs, and the gonad maturity stage was determined by domination of these categories, taking into accounts the S. pallidus reproductive cycle. In spring, the sea urchins from the shelf areas (depths of 41 and 69 m) were generally more mature as compared with those from the continental slope (depths of 280 and 346 m). However, correlation between the gonadal index and depth of habitat was not significant because the mature females were sampled in any depth. Composition of intestinal content and food components were determined visually, looking the bolus under binocular microscope. The sea urchins intestines were mostly filled with detritus at the depth of 41 m, sponges (Suberites sp.) at the depth of 69 m (70 % of cases), and unedible substances as silt and sand at the depth of 280, 346 and 670 m, minor fractions were the algal litter, remains of crustaceans, and detritus.

The litter macrofauna of 8 plantations of Populus italica (Du Roi) Moench, P. deltoides Marsh. and P. alba L. was studied in the city of Dnipro. The invertebrates were taken by manual sifting of litter from experimental plots of 8 m2. The total number of litter macrofauna in the poplar plantations varied from 8 to 187 specimen/m2, on average 53 specimen/m2. The greatest variety of species was obtained from a white poplar plantation with common hop and an elm-poplar plantation with bare soil and Amorpha fruticosa L. bushes (15 and 9 species correspondingly). The ma ximum readings on the Shannon–Weaver diversity index come from the abovementioned areas (3.2 and 2.9 bits respectively). The highest number of zoophages (40%) was obtained from the white poplar plantation with common hop. There was great consistency in the species composition across the plots, with the same 60 species (more than 50% of the total number of species of litter macrofauna recorded in the study) being found in 7 out of the 8 study plots. The share of species rare for any given ecosystem exceeded 10% in only 2 out of the 8 plantations studied. The dominant group in the size structure of the litter macrofauna of the poplar plantations (44–96%) was invertebrates of 4–7 mm length. In 5 out of 8 poplar plantations no species over 15 mm in length were found. This indicates the degraded size structures of the litter macrofauna communities. In taxonomic structure the dominant groups were Formicidae, Pulmonata, Porcellionidae, Lygaeidae, Julidae, Silphidae, Araneae, Carabidae, Staphylinidae. The results obtained indicate the low variety and degradation of the trophic and size structure of the litter macrofauna of these urban poplar plantations, which are subject to lack of moisture.

Chironomidae larvae may represent more than 70% of total Arthropoda numbers in hypersaline waters. Crimea, the largest peninsula of the Black Sea, has more than 50 hypersaline water bodies of marine and continental origin. Chironomidae larvae are common components of their ecosystems, but they still are poorly understood. This paper summarizes the results of a long-term study (2007–2016) of chironomids in Crimean hypersaline waters. More than 400 samples from 38 water bodies were used for analysis. The maximum salinity of water bodies containing Сhironomidae larvae was between 320 and 340 g/L. At first it was shown that Baeotendipes noctivagus (Kieffer, 1911) is the most halotolerant chironomid species in the world. Frequency of larvae occurrence varied and was negatively dependent on salinity. Four chironomid species were found: B. noctivagus, Cricotopus gr. cylindraceus (Kieffer, 1908), Tanytarsus gr. mendax Kieffer, 1925 and Paratanytarsus sp. Ceratopogonidae larvae were also found twice, at salinities of 150 and 270 g/L. B. noctivagus was the most common species, which occurred in 81% of samples with chironomids. Abundance of larvae fluctuated widely and reached high numbers: in plankton – to 8 thousand/m3, in floating green algae mats – up to 3 thousand/m2, and in benthos – up to 9 thousand/m2. Nonlinear dependence of chironomid abundance from salinity was observed; maximum abundance was at salinity levels of between 150 and 170 g/L. The average weight of larvae of 0.05–1.50 mm in length varied little in the samples; however, larvae of greater length had a significantly different average weight. Larvae of 8 mm in the samples had the average actual weight, which ranged from 0.750 to 2.203 mg.

Vatica cauliflora P.S. Ashton (Dipterocarpaceae) is a threatened tree species endemic to Kapuas Hulu District, West Kalimantan Province, Indonesia. The species is only known from the type specimen collected in 1953. After this first collection, there was no record confirming the presence of this tree in its natural habitat. Our recent surveys in 2019 and 2020 located 179 individuals of the species in six unprotected locations. The population's size structure is dominated (62.6%) by young individuals within the 0–5 cm diameter class. Our surveys also showed that the habitat of V. cauliflora is degraded as a result of the negative effects of agriculture and logging. Assessment with the IUCN Red List criteria indicates that V. cauliflora should be categorized as Critically Endangered. [ABSTRACT FROM AUTHOR]

Abstract The inverse relationship between size and abundance is a well‐documented pattern in forests, and the form of size–density relationships depends on the balance between growth and mortality rates in the community. Traditionally, studies of plant size distributions have focused on single‐species populations and forests, but here we examine diverse communities dominated by plants with varied life histories, including grasses, forbs, shrubs, and succulents. In particular, we test whether the parameters of the individual size distribution differ systematically across community types, whether they fit the contrasting predictions of metabolic or demographic theories, and whether they share a common cross‐community scaling relationship with forest communities and crop populations. All thirteen of our study sites better fit the predictions of demographic equilibrium theory, but interestingly, fits of both demographic and metabolic models showed little systematic variation across community types, despite large differences in environmental conditions and dominant life forms. Finally, analysis of the cross‐community scaling relationship demonstrates that natural and restored non‐forest communities conform to patterns of size and abundance observed among forest, plantation, and crop systems. Taken together, our results suggest that common ecological mechanisms govern plant community size structure across broad environmental gradients, regardless of the dominant plant life forms or limiting resources.

Large-scale macro-algal blooms of Ulva prolifera (also called green tides) have appeared each summer since 2008 in the western Yellow Sea. In this study, we investigated the temporal variability in zooplankton community in the western Yellow Sea and its possible links to green tides using data from a long-term plankton survey off the coast of Qingdao, China. Environmental conditions observed in the study area during the green tide period (GTP: June–August, 2008–2013) were compared to the non-green tide period (NGTP: June–August, 2005–2007), to support the contention that variations observed in zooplankton community may be attributed to the green tides, as opposed to natural climatic or environmental variations. Zooplankton assemblage structure observed during the GTP was then compared to the NGTP. Significant variations were detected both in zooplankton abundance and assemblage structure between the two defined periods. The abundance of zooplankton, mainly copepods, was significantly decreased during the GTP. Meanwhile, the relative abundance of copepods decreased by approximately 10% and that of gelatinous zooplankton, including appendicularians, chaetognaths, and medusae, almost doubled (ca. increased by 6.4%). The dominant species of meroplankton completely changed, specifically, polychaeta, and echinoderm larvae were more dominant than decapod and bivalve larvae. With regard to zooplankton size structure, the NGTP showed a higher size diversity with more small-sized organisms, while the GTP showed a lower size diversity in the community. According to general linear models, the interannual variation in summer zooplankton abundance was significantly correlated with green tides. These results indicate that the temporal changes in zooplankton community may have a close link to the green tides.

Marine Protected Areas have become a major tool for the conservation of marine biodiversity and resources. Yet our understanding of their efficacy is often limited because it is measured for a few biological components, typically top predators or species of commercial interest. To achieve conservation targets, marine protected areas can benefit from ecosystem-based approaches. Within such an approach, documenting the variation of plankton indicators and their covariation with climate is crucial as plankton represent the base of the food webs. With this perspective, we sought to document the variations in the emerging properties of the plankton to better understand the dynamics of the pelagic fishes, mammals and seabirds that inhabit the region. For the first time, we analyze the temporal variations of the entire plankton community of one of the widest European protected areas, the Parc Naturel Marin de la Mer d’Iroise. We used data from several sampling transects carried out in the Iroise Sea from 2011 to 2015 to explore the seasonal and inter-annual variations of phytoplankton and mesozooplankton abundance, composition and size, as well as their covariation with abiotic variables, through multiple multivariate analyses. Overall, our observations are coherent with the plankton dynamics that have been observed in other regions of the North-East Atlantic. We found that both phytoplankton and zooplankton show consistent seasonal patterns in taxonomic composition and size structure but also display inter-annual variations. The spring bloom was associated with a higher contribution of large chain-forming diatoms compared to nanoflagellates, the latter dominating in fall and summer. Dinoflagellates show marked inter-annual variations in their relative contribution. The community composition of phytoplankton has a large impact on the mesozooplankton together with the distance to the coast. The size structure of the mesozooplankton community, examined through the ratio of small to large copepods, also displays marked seasonal patterns. We found that larger copepods (members of the Calanidae) are more abundant in spring than in summer and fall. We propose several hypotheses to explain the observed temporal patterns and we underline their importance for understanding the dynamics of other components of the food-web (such as sardines). Our study is a first step toward the inclusion of the planktonic compartment into the planning of the resources and diversity conservation within the Marine Protected Area.

Pollution is one of the main anthropogenic threats to marine ecosystems. Studies analysing the accumulation and transfer of contaminants in planktonic food webs tend to rely on samples collected in discrete water bodies. Here, we assessed the representativeness of measurements at the chlorophyll-a maximum layer during the MERITE-HIPPOCAMPE cruise for the entire water column by investigating the vertical distribution of particles and plankton obtained by in-situ optical profilers at nine stations across the Mediterranean Sea. We identified specific conditions where the interpretation of results from contaminant analyses can be improved by detailing plankton size structure and vertical distributions. First, the presence of higher than usual plankton concentrations can result in sampling issues that will affect biomass estimation within each size class and therefore bias our understanding of the contaminant dynamics. Secondly, the presence of an unsampled water layer with high zooplankton biomass might imply non-resolved contaminant pathways along the trophic structure. This study lays the basis for optimizing sampling strategy in contaminant studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Liaodong Bay is one of the largest semi-enclosed bays located in Bohai Sea, in northeast China. It is an important feeding and spawning place, even wintering and breeding migration base for many marine organisms. The size structure of phytoplankton communities is a key feature of marine ecosystems and can be used as an indicator for algae disaster, but the methods to evalute is still challenging. Here, we compared the size-fractionated chlorophyll-a method with a high-throughout sequencing method in an evaluation of the size structure of phytoplankton assemblages in Liaodong Bay, China, in 2014. The proportion of picophytoplankton was estimated at just 19% according to the results based on size-fractionated chlorophyll-a, which likely represents a severe underestimation. The sequencing method confirmed that many kinds of phytoplankton species appeared in more than one size-fractionated filter membrane, with some even dominating where the filter membrane pore size was greater than the individual phytoplankton size. According to the sequencing method, the phytoplankton assemblages in Liaodong Bay were dominated by picophytoplankton (average proportion = 44%), followed by the nanophytoplankton (average 32%), a composition that is more consistent with other studies. The sequencing method provides a more robust way to assess the size structure and taxonomic diversity of marine phytoplankton communities. [ABSTRACT FROM AUTHOR]