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Leaf litter decomposition is a key ecosystem process in headwater streams, influenced by physical fragmentation, microbial degradation and feeding activity by stream biota. In some tropical streams, feeding by freshwater shrimps can exert strong top-down control on leaf litter decomposition, however, variation in shrimp macroconsumer effects across small spatial scales or among years is not well-known. We ran 50-day macroconsumer exclusion experiments to measure shrimp effects on leaf decomposition in two adjacent headwater streams in Puerto Rico, in 2017 (immediately prior to two Category 4 and 5 hurricanes) and again in 2018 and 2019, to assess shrimp effects in the context of post-hurricane conditions that included reduced canopy cover and higher shrimp (Atya and Xiphocaris) counts. Leaf decomposition was faster when shrimp had access to leaf packs, but only in the study stream with larger pools, which also had higher overall shrimp counts. However, increased shrimp abundances following the hurricanes did not result in faster decomposition, potentially because shrimp diets shifted toward algae post-hurricanes when canopies were more open. We conclude that shrimp effects on leaf litter breakdown may vary between adjacent streams that differ in habitat conditions and that increasing local shrimp abundances may fail to accelerate decomposition. [ABSTRACT FROM AUTHOR]

Amphidromous atyid shrimps in the genus Atyopsis consist of two species, namely, A. moluccensis and A. spinipes. The geographical distribution of A. spinipes extends to the Pacific islands and is wider than that of A. moluccensis. Amphidromous shrimp populations are linked through marine larval dispersal. Therefore, A. spinipes larvae may have an ability to survive in the open sea. We tested this expectation through larval culture experiments under different temperatures (20, 24, 28 and 32 °C) and salinity (8.5, 17, 25.5 and 34 ppt) conditions, which are crucial abiotic factors affecting the larval performance of decapod crustaceans. The larvae of A. moluccensis died soon after hatching at 34 ppt and survived to the juvenile stage under 24–32 °C and 17–25.5 ppt conditions. The larvae of A. spinipes survived to the juvenile stage under 24–32 °C and 17–34 ppt conditions, and their moulting incidence and survival time to death at 20 °C were higher and longer, respectively, compared with A. moluccensis larvae. The larvae of A. spinipes adapted to lower temperature and higher salinity conditions, allowing this species to expand their northward distribution through the open sea with high salinity conditions. [ABSTRACT FROM AUTHOR]

Due to their life cycle shared between rivers and oceans, amphidromous organisms serve as intriguing models for studying biogeography. To investigate the implications of their unique life history, we examined the population structure of the amphidromous shrimp Caridina natalensis across its known range in the South Western Indian Ocean. A total of 118 specimens were collected from 7 islands (Mayotte, Mohéli, Mahé, Praslin, Silhouette, Mauritius and Madagascar) and the African mainland (South Africa), and their 16S rRNA and Cox1 mitochondrial genes were sequenced. Our findings reveal significant regional structure among archipelagos, suggesting complex patterns of dispersal involving successive events of extinction-recolonization. By conducting a comparative analysis with six other amphidromous species from the South Western Indian Ocean, based on literature sources, we were able to draw conclusions regarding the amphidromous biogeography of the area. Furthermore, we propose a novel classification of amphidromous species, considering their population structure and life history traits. We defined four categories of increasing dispersal abilities and decreasing genetic population structure: 1. Land-locked species; 2. Species with reduced or facultative amphidromy; 3. Species with common amphidromy; and 4. Super-amphidromous species. Lastly, we identified the Comoros Islands (namely Mayotte and Mohéli) as a critical area for the dispersal of amphidromous species, emphasizing the need for prioritizing conservation efforts in this region. [ABSTRACT FROM AUTHOR]

Very little is known about the feeding of naupliar and juvenile life stages of omnivorous fairy shrimps (Crustacea: Anostraca). Here, we aim to reveal whether the fairy shrimp Branchinecta orientalis is an ontogenetic omnivore and at which age and ontogenetic stage they gain the ability to feed on zooplankton. We assess how food uptake rates change with age until reaching maturity by providing algae (pico- and nanoplanktonic unicellular algae) and zooplankton (rotifers and copepod nauplii) as food in individual experiments. We found that the fairy shrimp B. orientalis started to feed on both types of algal prey immediately after hatching. Nanoplanktonic algae likely represented the most important food source until reaching maturity. Moreover, fairy shrimps started to feed on zooplankton already when they were 7 days old. Slow-moving rotifers gradually gained importance in the fairy shrimp diet with time. Our results reveal an ontogenetic change in the prey spectrum of fairy shrimp. The systematic shift towards omnivory likely affects both phyto- and zooplankton community composition, possibly contributing to temporal changes in food web dynamics in fairy shrimp habitats, and temporary ponds, which may warrant more detailed investigations in future studies. [ABSTRACT FROM AUTHOR]

Amphidromous freshwater shrimps require saline environments for larval development. Lecithotrophic larval development trait may be selected in amphidromous shrimp species that inhabit the upper portions of rivers or streams, in which breeding and larval hatching occur. Thus, the newly hatched larvae require a relatively longer period for downstream transport in food-limited freshwater environments until they reach the sea. We tested this hypothesis through laboratory experiments using first stage zoeae of five Caridina species with different longitudinal distributions in the rivers or streams. The first stage zoeae were cultured without foods under 25 combinations of different salinity (0, 8.5, 17, 25.5, and 34 ppt) and temperature (20, 23, 26, 29, and 32 °C) levels. The first stage zoeae of C. leucosticta, C. serratirostris, and C. typus that inhabit lower reaches did not moult, whereas those of C. multidentata and C. prashadi that inhabit middle and upper reaches or headwaters moulted to the second stage zoeae at above 8.5 or 17 ppt salinity conditions. Thus, our findings highlight the salinity-dependent lecithotrophic development in amphidromous shrimps inhabiting the upper portions of rivers or streams. Larval survival and development strategies are discussed in terms of salinity- and temperature-dependent metabolism. [ABSTRACT FROM AUTHOR]

The patchy distribution of the ditch shrimp Palaemon varians (Palaemonidae) in small-scale habitats with low salinity may hint at isolation and fragmentation processes. In order to evaluate the extent to which gene flow barriers exist and salinity has an influence on this dispersal pattern, the genetic diversity and differentiation of Baltic and North Sea populations were investigated and set in context with sequence data from the Mediterranean Sea. Therefore, 133 sequences of a fragment of the cytochrome oxidase subunit 1 (COI) from 13 different populations from the Baltic Sea and North Sea were generated and complemented with publicly available sequences to estimate a haplotype network and calculate genetic differentiation and diversity. The results show that genetic differentiation correlates with geographic distance and the populations of the different basins are differentiated from each other. In contrast to the expectation, genetic differentiation was generally weak within basins. However, different clusters of differentiated populations could be revealed, indicating two migration events into the Baltic Sea. [ABSTRACT FROM AUTHOR]

The blue and red shrimp Aristeus antennatus has been intensively exploited by trawling fishery in the Western Mediterranean Sea. Implementation of an adequate management plan needs complete genetic data of the non-spawning and spawning grounds of the species. During the reproductive period, the species forms spawning aggregations in the middle slope, mainly constituted of mature females carrying spermatophores. Seven spawning females' grounds in the Western Mediterranean Sea from Gulf of Lions (France) to Cabo de Palos (Spain) were sampled during two consecutive years, 2016 and 2017. This study assessed for the first time the levels of genetic diversity within spawning grounds, the genetic divergence among them and estimated the degree of temporal genetic stability using multilocus genotyping. Our results showed a high connectivity of the spawning females' grounds that remains stable during the two analysed years, explained by passive larval dispersal, together with juveniles and adults' migration. We advise that a future management plan for A. antennatus fishery should consider the Mediterranean Subarea GSA6 as a single unit, but it should be combined with local monitoring in order to ensure the sustainable exploitation of the populations. [ABSTRACT FROM AUTHOR]

The freshwater opossum shrimp Mysis diluviana can undergo extensive diel vertical migration (DVM) to feed in shallow, prey rich strata at night. Bright moonlight limits their night-time migration presumably due to predator avoidance. Using a linked, foraging-bioenergetics model, we evaluated the cost of avoiding predators by simulating the effects of prey density, water temperature, and light intensity on daily feeding and growth of M. diluviana in Lake Pend Oreille, Idaho, USA. We found that when mysid distribution was not limited by moonlight intensity, simulated food consumption (10.3 J day−1) increased 1.6-fold compared to estimated consumption (6.1 J day−1) based on their observed, vertical distribution. Moreover, simulated growth of mysids (0.61 mg day−1) increased 74% compared to that estimated from observed distribution patterns (0.35 mg day−1), when they were located in deeper, darker strata. Given recent insights into partial DVM by M. diluviana, we note that proximate factors associated with predator avoidance in pelagic (light availability) and benthic (hunger level, body size and reproductive status) habitats may convey complimentary benefits to M. diluviana fitness by reducing predation mortality and increasing metabolic efficiency. [ABSTRACT FROM AUTHOR]

Salinity changes in transitional water ecosystems are a natural feature, but anthropogenic direct or indirect impacts are drastically altering their equilibrium and, therefore, their biological communities. Females of three species of Palaemonidae shrimps (the invasive Palaemon macrodactylus and the native P. adspersus and P. elegans) were collected in nature and kept in laboratory at salinities 20 and 30. For each species, the reproductive strategy (investment devoted to reproduction) and the reproductive performance (larval output and hatching success) were determined. Significant differences were observed comparing the three species, highlighting an opportunistic r-strategy in P. macrodactylus and P. elegans, while P. adspersus resulted to produce fewer and larger eggs. Palaemon elegans showed a lower hatching success than the other two species, and the size-adjusted larval output appeared to be highly sensitive to salinity variations, with a strong increase under euhaline conditions (salinity 30), while this increase was limited in the other two species. The selected species were used as model organisms to understand which could be the shift in biological communities due to salinity variations. Data suggest that a shift towards euhaline conditions will favor the native populations, while a shift towards mesohaline waters could determine an increase of the invasive shrimps. [ABSTRACT FROM AUTHOR]

Harmful effects of the toxic cyanobacterium Nodularia spumigena were observed in experimental marine shrimp production ponds in Brazil. Strains of this cyanobacterial species were isolated and cultured, and in the present study, we evaluated the influence of light intensity and the concentration of dissolved inorganic nitrate and phosphate on the growth, toxin concentration, heterocyte formation and akinete germination of N. spumigena. A factorial experiment (3 × 3) was performed to test three light intensities and nutrient concentrations with a reduced nitrate concentration, a reduced phosphate concentration and a nutrient-replete f/2 medium. The influence of light intensity on growth and akinete formation was varied: the highest cell density and chlorophyll a were recorded at the lowest light intensity, while the high light treatment stimulated akinete formation. The availability of phosphate was the main factor favouring the growth of N. spumigena and the formation and germination of akinetes, while the concentration of nodularin per cell was highest under phosphate deficiency. This information is useful in the management of aquaculture ponds and other brackish and marine environments where the goal is to reduce N. spumigena blooms. [ABSTRACT FROM AUTHOR]

Fairy shrimp are the most divergent taxon of large branchiopod crustaceans and have a worldwide distribution. Yet the diversity and distribution of fairy shrimps in the "Roof of the World" remain poorly known. Here, based on morphology, we identified three species of fairy shrimp (Branchinecta orientalis, Chirocephalus graziellae and Branchipodopsis affinis), among 14 fairy-shrimp populations from the Tibetan Plateau, China. Their phylogenetic relationships were verified based on mitochondrial DNA sequences (cytochrome c oxidase subunit I gene) and two nuclear markers (18S ribosomal RNA gene and internal transcribed spacer 2). Syntopy of different species of fairy shrimp was observed. Some haplotypes were shared among populations, and sequences from B. affinis exhibited a star-like pattern in haplotype networks, suggesting a recent rapid expansion. Finally, a high genetic diversity of fairy shrimp was detected on the Tibetan Plateau. Obtained results contribute to a better knowledge of the diversity of high-altitude fairy shrimps. [ABSTRACT FROM AUTHOR]

Peacock basses (genus Cichla) are a group of Amazonian predatory fishes that invaded many systems worldwide. Severe ecological impacts have been reported, but no study investigated the functional response of these fishes to variations in prey abundance, a crucial information to determine predator consumption and impact. In this study, we evaluated the functional response of the highly invasive Cichla kelberi toward prey species of different taxonomic groups, and compared it to the response of the wolf fish Hoplias malabaricus, a voracious predator used as baseline. We hypothesized that higher feeding rates drive the predatory impact of the invasive predator. Using a non-replacement experimental setup, we manipulated prey densities (fish and shrimp) in 1000-L mesocosm tanks to quantify the consumption response of each predator during 24 h. Both predators consumed more fish than shrimp, but C. kelberi consumed significantly more than H. malabaricus. We found that C. kelberi consistently displayed higher Type-II functional response than H. malabaricus toward both prey species. There was a non-significant effect of predator species on attack rates, but C. kelberi presented significantly lower handling time values and higher maximum feeding rates. Our findings provide empirical evidence that high individual consumption rates explain the predatory impact of the highly invasive C. kelberi, and predict strong effects on invaded communities. [ABSTRACT FROM AUTHOR]

Temporal variation in the density and distribution of the burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis, were compared in two estuaries along the West coast of the United States (USA) where they are recognized as important ecosystem engineers. Since these shrimp construct deep burrows in the sediment, we quantified the relationship between burrow openings and shrimp density (1.5 and 1.7 burrow openings per shrimp for N. californiensis and U. pugettensis, respectively) to permit population abundance estimates to be made over broad landscape scales. Neotrypaea californiensis populations estimated from burrow counts collected using a gridded survey design across representative tide flats declined by 25% between 2008 and 2010 in Yaquina Bay, Oregon and by 67% in Willapa Bay, Washington from 2006 to 2011, but increased again in Willapa Bay by 2014. Upogebia pugettensis had mostly disappeared from Willapa Bay by 2006 and declines were observed in Yaquina Bay, but the magnitude and long-term trajectory of U. pugettensis in this estuary was less clear. These species population fluctuations mirrored those observed in density collected at discrete sampling locations over the same period, equate to large changes in secondary production, and have likely resulted in substantial changes to estuarine habitat and food webs. [ABSTRACT FROM AUTHOR]

Fishers' ecological knowledge (FEK) has contributed to a better understanding about the reproduction of fishery resources, especially where biological data are scarce or unavailable. We analyzed FEK on the reproduction of five fishery resources in the Paranaguá estuarine complex and adjacent coastal area, Brazil, including fishes (Genidens barbus, Centropomus parallelus, Chaetodipterus faber, Pseudobatos sp.) and shrimp (Litopenaeus schmitti). We also sought to compare FEK with biological data and investigate which characteristics (age, fish evisceration and fishers' location) influence fishers' knowledge. We interviewed 132 artisanal fishers. FEK indicated reproductive peaks in the spring and summer for the fish species and in late winter and early spring for the shrimp. The maturation sizes according to FEK did not differ from sizes at first maturity (L50) as reported by biological studies for G. barbus and L. schmitti. Fishers' residence sites and fish evisceration influenced more their knowledge related to species reproduction than age. Fishers showed a detailed ecological knowledge about some reproductive aspects, including size at first maturity of females, site of occurrence and reproductive peaks. Furthermore, fishers were able to identify sexual dimorphism, parental care and ovoviviparity. These results can be applied to improve fisheries management in the context of data poor fisheries. [ABSTRACT FROM AUTHOR]

Diet has been linked to lifespan in a broad range of animals. In particular, pronounced caloric restriction has been associated with increased longevity. Herein, the relationship of feeding environment and longevity is examined experimentally using Spinicaudatan crustaceans ("clam shrimp") from the geographically widespread genus Eulimnadia. Two projects examine the effects of food differences on longevity, one comparing food environment early vs later in life and one comparing the effects of dietary restriction on longevity, growth, and reproduction. In the former, dietary restriction increased longevity, but only when diets were reduced later in life. A closer examination of the effects of dietary restriction in the second experiment did not find the expected trade-off of increased longevity and reduced reproductive output in the lowest-food treatment, but instead found an overall increase in both longevity and egg production on the low compared to the high food diet. Finally, a detailed analysis of the relationship of size (carapace length) with egg production was presented. This relationship could serve to obtain a rough estimate of reproductive output potential of fossil clam shrimps, of which typically only the carapace size can be assessed. [ABSTRACT FROM AUTHOR]

Aquatic ecosystem community dynamics are affected by anthropogenic pressures and subsequent environmental change. This study investigated the influence of land use in the Richmond River Catchment (New South Wales, Australia) on dietary sources for the freshwater Atyid shrimp Paratya australiensis. Carbon and nitrogen stable isotopes and Bayesian modelling determined the contribution to shrimp diets of two autochthonous sources (microphytobenthos and macrophytes) and two allochthonous sources (C3 and C4 plants) across sites characterised by five different land uses: forest, macadamia, grazing, sugar cane and urban. It was hypothesised that allochthonous sources would contribute more to shrimp diets at sites with more extensive riparian zones, but this was not substantiated. Autochthonous sources dominated shrimp diets across all land uses, although their dietary contribution varied with land use, likely reflecting changes in riparian and in-stream habitats and source availability. Autochthonous contributions were lowest and allochthonous contributions were highest, for shrimp at grazing and sugar cane sites, despite minimal riparian vegetation. A complex array of interactions may influence diets of in-stream consumers. This micro-catchment scale study demonstrated that land use changes play a key role in affecting carbon and nitrogen sources for P. australiensis and have the potential to change community dynamics in freshwater streams. [ABSTRACT FROM AUTHOR]

Species proliferate through evolutionary mechanisms but coexist through ecological dynamics. As such, it might be expected that mechanisms of speciation and species maintenance jointly influence the settlement of ecological communities, a process called community assembly. Disentangling the relative contribution of evolutionary and ecological dynamics might be a difficult task, particularly so for the tropical biotas due to their extreme diversity and large knowledge gaps. Here, we explore genetic diversity and distribution of 23 freshwater shrimp species of the genera Caridina and Macrobrachium in Sundaland to examine patterns of species co-occurrence based on 1583 observations across 19 sites in Java and Bali islands. DNA-based species delimitation methods applied to 204 cytochrome oxidase I sequences detected 30 operational taxonomic units and a few cases of deep intraspecific divergence. Species co-occurrence and phylogenetic community structure show no departure from expectations under a random distribution of species in landscapes and support a lottery model of community assembly. Species age estimates expand beyond the geological settlement of Sundaland, suggesting that species proliferation and community assembly are driven by mechanisms acting at distinct spatial and temporal scales. [ABSTRACT FROM AUTHOR]

Siblings often compete for limited resources, particularly food provided by their parents. Such competition is usually nonviolent, but direct aggression has evolved in some species. However, there is little knowledge about sibling aggression in species without parental provisioning. Here, we investigated sibling aggression in the cichlid Neolamprologus furcifer in Lake Tanganyika, Zambia. In this species, females guard their broods in the nest but do not provide any food. Early-stage fry did not show any sibling aggression while foraging on plankton, but began to show nonlethal aggression once they started to forage on small benthic shrimp at 2 weeks of age. The frequency of sibling aggression decreased at week 7, when the density of fry decreased remarkably. Sibling aggression also decreased following a short-term increase in food through supplemental feeding. The aggression was higher in the morning than in the afternoon despite higher abundance of shrimp at that time, and decreased when the number of shrimp in the nest was experimentally reduced. These results indicate that food availability affects sibling aggression of animals that do not exhibit parental provisioning. [ABSTRACT FROM AUTHOR]

Litter decomposition plays a crucial role in aquatic food webs. In the present study, we used a specially designed bucket, at the middle height of which a 1-mm nylon mesh was set, to investigate the direct (grazing) and indirect (feces) effects of shrimp Neocaridina denticulata on the decomposition of Typha angustifolia litters. During the 140-day decomposition period, the net overall effects of shrimp enhanced decomposition by 63.5%, which amounted to 32.8% of mass loss. Shrimp grazing contributed 81.7% of the enhanced decomposition, whereas feces contributed 18.5%. The early stage displayed the net effect of feces, whereas in the final days, it was mainly attributed to intensive grazing, which maintained litter breakdown at high speed. The presence of shrimp greatly improved the hydrolytic extracellular enzyme activities, especially peroxidase and phenol oxidase. Meanwhile, the presence of shrimp greatly enriched the water nutrients, total phosphorus in particular. However, selective absorption of NH4+-N by microorganisms caused its shortage for decomposers, suggesting their great demands for NH4+. Redundancy analysis showed that water physical and chemical properties could explain 73.5% of the variation of enzymatic activities. Besides directly grazing of shrimp, the main factors affecting decomposition were enzymatic activities in the absence of shrimp, while in the presence of shrimp, the factors changed to water physical and chemical properties (mainly pH, total nitrogen, and phosphorus, and NO3−-N). Our results demonstrated that some aquatic animals, like shrimp, not only breakdown leaf litters by grazing, but also stimulate the microbial activities by their byproducts such as feces. [ABSTRACT FROM AUTHOR]

The banana shrimp, Fenneropenaeus merguiensis, is a commercially important species of marine crustacean that, like other penaeids, exhibit a female-superior sexual dimorphism with respect to growth rate, making this species an attractive candidate for all-female (monosex) culture. To gain insight into the molecular mechanisms underpinning this characteristic, an analysis of gene expression was performed to compare digestive gland tissue from 14 male and 14 female banana shrimp (n = 28) larger than 10 g body weight. Female banana shrimp samples were found to have an increased expression of transcripts coding for chitin catabolism and binding. A novel transcript was also identified that displayed a distinct female-specific expression. Weighted gene co-expression network analysis (WGCNA) from female samples revealed that this novel transcript was highly connected within a gene module containing an abundance of transcripts with homology to transcription factors and genes associated with growth regulation. [ABSTRACT FROM AUTHOR]

In this study, we investigated the relative gene expression pattern of 12 candidate genes from giant freshwater prawn (GFP) using hepatopancreas, eyestalk and testis tissues to compare expression profiles among adult male morphotypes [blue claw (BC), orange claw (OC) and small males (SM)] that reflect a social hierarchy. In particular, we focused our analysis on genes documented in other invertebrate taxa that are known to influence (i) inter-male aggressive behaviour, (ii) visual systems and (iii) olfactory genes. Genes examined here were normalised to 18S rRNA as a reference. Differences in gene expression patterns among male morphotypes and tissues were highly significant (P < 0.0001) with higher expression levels in eyestalk tissue compared with testis and hepatopancreas in all morphotypes. This might imply that differences in expression pattern of key candidate genes in the eyestalk can potentially provide cues to directly influence the formation of the male social dominance hierarchy. Expression stabilities of genes were evaluated using the RefFinder analytical tool, which revealed that STRPC-short transient receptor and BDP-beadex dlmo protein showed relatively similar expression levels. LW OPSIN, a visual system gene, appeared to be directly involved in suppression of subordinate male gene expression related to the social dominance hierarchy in male GFP. This finding could potentially be important for developing technologies that allow male morph frequencies to be manipulated at harvest in farmed stocks. [ABSTRACT FROM AUTHOR]

In this study, we used a comparative transcriptomic approach using 35nt paired-end reads from three individuals each from two highly divergent lineages of the Australian freshwater shrimp, Paratya australiensis. The two lineages are widespread and largely sympatric in many regions; however, they occupy slightly differing habitats within respective river systems. From BLAST searches, we were able to identify 50 genes, based on gene ontology, involved in temperature tolerance, egg size control and more broadly osmoregulation, as well as genes associated with reproduction and life history characteristics predicted to be associated with adaptation to local aquatic environments. Differential gene expression analysis revealed 660 highly differentially expressed transcripts between the populations. Divergence in SNPs detected in the two lineages was consistent with the level of neutral divergence found in previous studies, but they appear not to correlate with differentially expressed candidate genes. However, we hypothesise that the 2554 filtered SNPs identified in this study will continue to further our understanding of how these lineages have evolved and adapted to their respective habitats and will contribute to further our interpretation of the enigmatic biogeographical history of the species. [ABSTRACT FROM AUTHOR]

The amphipod Eogammarus possjeticus is used as a potential living food in shrimp culture. Nevertheless, the productivity of the amphipod has been poorly studied. We conducted laboratory experiments to investigate the effects of temperature on the individual development and biomass production of E. possjeticus. The results revealed that the embryonic development time of E. possjeticus was shortened when temperature increased from 15 to 27°C, and the shortest juvenile development time appeared at 21°C. The survival rate of juveniles decreased with increasing temperature, and the maximum specific growth rate was found at 21°C. Thus, a temperature of 21°C was found to be the optimum temperature for biomass production of E. possjeticus in the laboratory. A population growth model was constructed with the experiment data based on the continuous population growth determination assumption. The longest survival time of E. possjeticus was about 260 days, and the optimal output quantity was up to 3.27 × 108 individuals, which was 1.60 × 106 times of the initial cultured individuals under the ideal indoor experiments conditions. Our research shows that E. possjeticus has potential to be cultured under controlled conditions at a commercial scale and serve as a food for intensive shrimp aquaculture. [ABSTRACT FROM AUTHOR]

In marine ecosystems, the most significant migration observed in terms of biomass distribution is the one connected with the vertical movements in the water column. In the present study, the vertical profiles of the mesopelagic shrimps Gennadas elegans, Eusergestes arcticus, Sergia robusta, and the epipelagic Parasergestes vigilax in the Balearic Sea (western Mediterranean), during the stratified (summer) and non-stratified (autumn) hydrographic conditions, were investigated through their ontogeny, from the larval to adult stages. The mesopelagic adults were observed to move down to the deeper layers during the night more than during the daylight hours. Most larvae aggregated within the limits of the upper water column. The P. vigilax larvae were collected only during the stratified period. The first two larval stages vertical distribution indicates that the mesopelagic crustacean spawning could occur at greater depths. During the non-stratified period, the larvae of the mesopelagic species tended to remain at about 500 m depth at night, rising towards the upper layers at sunrise. Vertical patterns are discussed, as strategies associated with predator–prey trade-offs. To our knowledge, the present study is the first such attempt to jointly analyze the vertical migrations of the developmental stages of the pelagic shrimps in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

The seabob shrimp Xiphopenaeus kroyeri ranks third in commercial importance among fisheries in southeastern Brazil. An important management question is whether the same offseason can be applied to different regions. The population dynamics of the seabob shrimp was compared in two regions of southeastern Brazil: Macaé, state of Rio de Janeiro and Ubatuba, state of São Paulo. All demographic categories of shrimp in the Macaé region were larger than those in the Ubatuba region. Lower temperatures and greater longevities in the Macaé region may account for this difference in size from Ubatuba. In Macaé, number of reproductive females and juveniles correlated with organic-matter content. In Ubatuba, only chlorophyll-a showed a correlation with reproductive females. The reproductive period and recruitment were correlated in both populations. The difference in environmental factors between these regions, resulting of the Cabo Frio upwelling, although they are located close together, directly influences the population dynamics of X. kroyeri. The Cabo Frio upwelling may be acting as a physical barrier, preventing gene flow and differentiating the seabob shrimp stocks in the two regions. These data suggest that different offseason periods for different regions could increase the sustainability of shrimp harvesting along the Brazilian coast. [ABSTRACT FROM AUTHOR]

Despite the biological and economic importance of the freshwater shrimp Macrobrachium amazonicum, a role for biogenic amines in the osmoregulatory capability of this diadromous species remains unstudied. This investigation provides an extensive kinetic characterization of the effects of the exogenous polyamines spermine, spermidine, and putrescine on (Na, K)-ATPase activity in gill microsomal preparations from juvenile and adult shrimps at varying concentrations of ATP, Mg, Na, and K, and on inhibition by ouabain. (Na, K)-ATPase activity in both juvenile and adult shrimps is inhibited by spermidine (60-95%) and putrescine (40-70%) while spermine has a negligible inhibitory effect (<10%). Putrescine affects the kinetics of ATP hydrolysis and enzyme affinity ( K ) for ATP in both enzymes, while spermidine alters specific activity only. Spermidine increases Mg affinity of the adult (Na, K)-ATPase while putrescine decreases Mg affinity in both enzymes. Spermidine decreases Na affinity by ≈50% in both enzymes, while putrescine increases affinity of the juvenile enzyme twofold. These biogenic amines cause slight changes in K values in both enzymes. These findings suggest that the effect of biogenic amines on gill (Na, K)-ATPase activity and kinetics may be species and stage specific. [ABSTRACT FROM AUTHOR]

Waterfalls are geomorphic features that often partition streams into discrete zones. Our study examined aquatic communities, litter decomposition and periphyton growth rates for above- and below-waterfall pools in Ulu Temburong National Park, Brunei. We observed higher fish densities in below-waterfall pools (0.24 fish m vs. 0.02 fish m in above-waterfall pools) and higher shrimp abundance in above-waterfall pools (eight shrimp/pool vs. less than one shrimp/pool in below-waterfall pools). However, macroinvertebrate densities (excluding shrimp) were similar among both pool types. Ambient periphyton was higher in below-waterfall pools in 2013 (4.3 vs. 2.8 g m in above-waterfall pools) and 2014 (4.8 vs. 3.4 g m in above-waterfall pools), while periphyton growth rates varied from 0.05 to 0.26 g m days and were significantly higher in below-waterfall pools in 2014. Leaf litter decomposition rates (0.001 to 0.024 days) did not differ between pool types, suggesting that neither shrimp nor fish densities had consistent impacts on this ecosystem function. Regardless, this research demonstrates the varied effects of biotic and abiotic factors on community structure and ecosystem function. Our results have highlighted the importance of discontinuities, such as waterfalls, in tropical streams. [ABSTRACT FROM AUTHOR]

The mysid shrimp Mysis salemaai is a key component of many lake food webs. However, despite its strong declines in some systems, information on its life history is rudimental. We explored variation in life history patterns of M. salemaai and how this varies with key environmental gradients at the southern range of its distribution. We found that body mass of reproductive females and individual larvae varied among lakes and increased with phosphorus concentrations, whereas growth rates were associated positively with temperature. However, even across strongly contrasting nutrient conditions, M. salemaai had invariant life history timing with a single, synchronised winter recruitment followed by parent mortality. This contrasts with variable reproductive timing of the species reported across the Baltic Sea, probably owing to differences in ambient conditions or genotypes. The highly variable body size at maturity likely facilitates matching of reproduction with seasonal pulses of planktonic food across a broad range of growing conditions. We conclude that current population declines of M. salemaai warrant further investigations into the temporal plasticity of environmental matching. [ABSTRACT FROM AUTHOR]

The sea-bob shrimp is a shallow-water species whose population dynamics along the southern and southeastern coasts of Brazil is influenced by the upwelling of the South Atlantic Central Water (SACW). Since the SACW does not reach our study area, we hypothesize that life cycle and distribution patterns are dominated by the local regime of estuarine plumes. Also, we would expect higher biomasses and larger individuals in autumn due to the closed fishing season. We conducted a survey for a year, consisting of 20 monthly trawling hauls. Spawning peaks occurred in spring and autumn, related to rainy periods with greater estuarine loads of particulate material and phytoplankton production. The relative abundance of larger individuals increased with depth, while juveniles concentrated at shallower sites. Size classes prior to the closed season were affected by increased fishing during summer due to tourist demand. Water transparency and bottom temperature were the main factors controlling the distribution and life cycle of sea-bob shrimp. Seasonal changes in biomass could be related to the inshore-offshore migrations of the type-3 life cycle, compounded by the impacts of fishing. Thus, fishing and local hydrography can drive life cycle and distribution patterns of the species, with important management implications. [ABSTRACT FROM AUTHOR]

Anchialine pools are unique localized brackish water ecosystems, comprised of fresh groundwater and saltwater from the ocean mixing through subterranean pathways. This study characterized physicochemical properties, biological communities, and food web structures in anchialine pools on Hawaii Island, hypothesizing pronounced differences between pools with and without introduced fishes. Pools varied greatly in size, temperature, salinity, and dissolved oxygen saturation. On average, 46% of observed species were introduced. Native species of high conservation concern such as the shrimp Metabetaeus lohena and Halocaridina rubra were not observed in pools with introduced fishes, where periphytic algal biomass was lower. δC and δN analyses revealed an unusual food web structure where all animal species (except Gambusia affinis) occupied the same trophic niche, independent of species, size, and sex. These findings illustrate that simple food web structures with opportunistic feeding patterns in all species can occur in ecosystems that have greatly variable physicochemical properties and diverse biological communities. The wide variation in biological communities even in adjacent pools indicates that individual anchialine pools are unique. The high proportion of introduced species and their observed effects on these fragile ecosystems suggest that they pose a serious threat to native biota in Hawaiian anchialine pools. [ABSTRACT FROM AUTHOR]

Two coastal locations situated inside and outside an upwelling area were investigated to assess the influence of environmental factors on the structure of marine shrimp assemblages. The locations were Macaé in the state of Rio de Janeiro (RJ), influenced by upwelling from Cabo Frio (RJ), and Ubatuba in the state of São Paulo, with no upwelling. Samples were collected monthly with trawl nets, in three sites in each location at depths of 5-20 m. The relationship between species abundance and environmental factors was tested by redundancy analysis. The total of 148,266 shrimp captured (102,832 from Macaé and 45,434 from Ubatuba) included 15 species, 13 genera, and 7 families. The caridean Periclimenes paivai was collected for the first time on the RJ coast, expanding its known geographical distribution. Higher richness and J′ and H′ values were obtained in the location under upwelling influence (Macaé). Environmental variables (granulometric composition and organic-matter content of sediment, bottom temperature, and salinity) were associated with the abundance of shrimp. Our results suggest that sediment type and temperature are among the most important variables affecting seasonal distribution of the species. However, other factors such as intraspecific migration might have also influenced the observed patterns. [ABSTRACT FROM AUTHOR]

In an 8-month mesocosm experiment, we examined how a simulated Everglades aquatic community of small native fishes, snails, and shrimp changed with the addition of either a native predator (dollar sunfish Lepomis marginatus) or a non-native predator (African jewelfish Hemichromis letourneuxi) compared to a no-predator control. Two snail species ( Planorbella duryi, Physella cubensis) and the shrimp ( Palaemonetes paludosus) displayed the strongest predator-treatment effects, with significantly lower biomasses in tanks with Hemichromis. One small native fish ( Heterandria formosa) was significantly less abundant in Hemichromis tanks, but there were no significant treatment effects for Gambusia holbrooki, Jordanella floridae, or Pomacea paludosa (applesnail). Overall, there were few treatment differences between native predator and no-predator control tanks. The results suggest that the potential of Hemichromis to affect basal food-web species that link primary producers with higher-level consumers in the aquatic food web, with unknown consequences for Florida waters. [ABSTRACT FROM AUTHOR]

Fairy shrimp (Crustacea: Anostraca) are specialist inhabitants of temporary aquatic habitats. In many parts of the world and particularly in Western Europe, however, populations are declining while the development of adequate conservation strategies is impeded by a poor knowledge of the genetic structure and taxonomic status of remaining lineages. We reconstructed a phylogeography of the species Chirocephalus diaphanus Prévost, 1803 using partial sequences of the mitochondrial COI gene and discuss the importance of different Pleistocene refugia to explain current diversity patterns. In addition to 20 C. diaphanus populations, we also included populations of six presumably closely related chirocephalids to evaluate their taxonomic status. Based on molecular data, the Eastern European subspecies C. diaphanus romanicus deserves species status while the species status of two Italian chirocephalids, C. salinus and C. ruffoi is questionable. Results indicate European C. diaphanus lineages diverged well before the last glacial maximum and survived the Pleistocene glaciations in multiple (sub)refugia along the Iberian, Italian, and Balkan peninsula. Northern Europe was subsequently recolonized from Southern France, resulting in high levels of cryptic diversity around glacial refugia but also in more widespread haplotypes in mainland Europe. [ABSTRACT FROM AUTHOR]

The river shrimp Athyaephyra desmaresti is a Mediterranean species which in recent years expanded its distribution, colonizing rivers of central Europe. The purpose of this study was to investigate the possibility of passive external dispersal of the river shrimp Athyaephyra desmaresti by waterfowl. We performed experiments testing shrimp desiccation survival, probability of attachment to waterfowl, and probability of successful transport. We found that in the laboratory 10% of the river shrimps can survive out of water for up to 90.1 min, but this period was reduced to 18.5 min under simulated bird flight conditions. Two different outdoor experiments simulating bird flight conditions indicated a 50% probability of successful transport on flight distances over 15 km. Our results using dead ducks show evidence that small, large or ovigerous river shrimps can attach to and be transported by ducks and that this capacity is affected by water depth. This study demonstrated that waterbird-mediated passive dispersal of river shrimps can occur and may be important for genetic flows between populations and for the colonization of new sites. [ABSTRACT FROM AUTHOR]

Structurally complex mangrove roots are thought to provide foraging habitat, predation refugia, and typhoon protection for resident fish, shrimp, and crabs. The spatially compact nature of Micronesian mangroves results in model ecosystems to test these ideas. Tidal creek nekton assemblages were compared among mangrove forests impacted by Typhoon Sudal and differing in stand structure. Structurally complex Rhizophora spp. stands were predicted to support higher densities and different communities of nekton and to provide greater protection from typhoons compared to less complex Sonneratia alba/ Bruguiera gymnorrhiza stands. Lift net data revealed that structural complexity did not support greater nekton densities, but did support significantly different nekton assemblages. The cardinalfish Apogon ceramensis and goby Oxyurichthys lonchotus had significantly higher densities in S. alba/ B. gymnorrhiza mangrove creeks, whereas the silverside Atherinomorus lacunosus and diogenid crabs had significantly higher densities in Rhizophora spp. creeks. Similar nekton densities 17 and 4 months after the typhoon in Rhizophora spp. creeks provided indirect evidence that structural complexity increased protection for resident nekton from disturbances. Findings indicate that studies of structural complexity and nekton densities may be better served when individual species are compared and that diverse mangrove tree assemblages will support diverse nekton assemblages that may be more resilient to disturbance. [ABSTRACT FROM AUTHOR]

In aquatic ecosystems, microorganisms and invertebrates provide critical links between plant detritus and higher trophic levels. Atyaephyra desmarestii is an omnivorous decapod that inhabits freshwaters and exhibits high tolerance to temperature oscillations and high ability to colonize new habitats. Although A. desmarestii is able to ingest a variety of foods, few studies have been conducted to elucidate the role of this freshwater shrimp on detritus breakdown in streams. In this study, A. desmarestii was allowed to feed on conditioned or unconditioned alder and eucalyptus leaves in microcosms with or without access to its fecal pellets. At the end of the experiment, total body length of the animals was measured, and the remaining leaves and fecal pellets were used for dry mass quantification and assessment of bacterial and fungal diversity by denaturing gradient gel electrophoresis (DGGE). Cluster analyses of DGGE fingerprints indicated that the major differences in microbial communities on leaves were between leaf types, while on fecal pellets were between conditioned and unconditioned leaves. However, the consumption rate by the shrimp did not differ between leaf types, and was significantly higher on leaves conditioned by microorganisms and in treatments without access to feces. In treatments without access to feces, the production of feces and fine particulate organic matter was also significantly higher for conditioned leaves. Overall, our results support the feeding plasticity of A. desmarestii and its potential role in plant litter breakdown in streams. This might have implications for maintaining stream ecosystem functioning, particularly if more vulnerable shredders decline. [ABSTRACT FROM AUTHOR]

Macrobrachium asperulum is a land-locked macroinvertebrate species of freshwater prawn, which inhabits a wide range of freshwater bodies and has an abundant pan-island distribution in Taiwan. In this study, we used mitochondrial (mt) DNA fragment sequences of the large subunit ribosomal RNA (16S rRNA) gene and the cytochrome oxidase subunit I (COI) gene to examine the phylogeographical pattern and the genetic structure of M. asperulum in Taiwan. Genealogic reconstructions present four lineages distributed in three geographical regions. Analysis of molecular variance (AMOVA) shows a significant genetic structure across all hierarchical levels, indicating that genetic variance is geographically subdivided. The high genetic structure of within-catchment or within-river populations implies that the freshwater prawn M. asperulum with a land-locked life cycle has a more-limited dispersal ability. The spatial divisions are probably correlated with two dispersal routes from the Asian mainland during the tectonic evolution of Taiwan. Subsequently, the population genetic structure is deeply influenced by the periodic oscillation of glaciations, followed by fragmentation due to the formation of geographical barriers, which resulted in rare contemporary gene flow. Population divergences indicate coalescent events between populations of China (Ming River) and Taiwan, dated to between the late Pliocene and early Pleistocene (2.63-1.78 myr). The high diversity of the genetic structure of eastern populations suggested multiple artificial introductions mainly from rivers of west-central Taiwan, and this has permitted lineage sorting and random drift. [ABSTRACT FROM AUTHOR]

The Anostracan genus Artemia is composed by several sibling species reproductively isolated, but identical or very similar in outward appearance. The genus shows also an underlying striking variability from the biochemical point of view, regarding especially the fatty acid profile of the cysts and nauplii. In Argentina, Artemia is represented by two bisexual species: A. franciscana and A. persimilis. Former studies have shown that A. franciscana is present in northern of 36º and that A. persimilis is constrained southwards of 37° S. In general, there is good agreement between morphological and cytogenetic comparisons of Argentinean populations with respect to species discrimination. However, new Argentinean Artemia populations are being analyzed morphologically and it becomes necessary to further investigate if the genetic adscription of these populations is congruent with the results obtained from the current morphological analyses. Restriction fragment length polymorphism (RFLP) analysis of a fragment of the 16S rRNA mitochondrial gene was used to investigate the genetic diversity and population structure of 10 new Artemia populations from Argentina. The mitochondrial DNA (mtDNA) results showed a similar pattern to that of previous cytogenetic and morphological analyses with the two Argentinean species appearing as highly divergent. The presence of A. persimilis in southern Argentina and the southernmost Chilean population was confirmed unveiling a novel picture of species distribution in the country. A. franciscana showed a unique haplotype. Populations of A. persimilis appeared highly structured, although their clustering did not follow a clear geographic pattern. The different Argentinean Artemia populations analyzed were characterized by high variability in their fatty acids, showing both marine- and freshwater-type profiles. For the first time, the investigation of the relatedness between the fatty acid composition in Artemia and genetic markers was attempted. The study aimed at the putative association of molecular markers with marine versus freshwater-type populations. A lack of correlation between RFLP patterns at mtDNA and the fatty acid (FA) profiles was found in the A. persimilis populations which was discussed from the point of view of two main genetic hypotheses and/or phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Large areas of uncompacted cyanobacterial accumulations (or “gyttja”) have been observed in Myall Lake, New South Wales, Australia. To determine whether the cyanobacterial accumulations were assimilated into the local food web, carbon and nitrogen stable isotopes were used to identify the primary food sources of a primary consumer in Myall Lake, the freshwater atyid shrimp Paratya australiensis. Suspended particulate organic matter (POM) and the macrophyte Myriophyllum salsugineum were identified as major dietary sources of P. australiensis. Enriched stable isotope signatures (δ13C and δ15N) of shrimp from gyttja-affected sites, relative to shrimp from unaffected locations, also indicated that P. australiensis were deriving a considerable portion of their dietary carbon and nitrogen requirements from gyttja. Stable isotope mixing models estimated that cyanobacterial accumulations might constitute up to 69% of P. australiensis biomass carbon and nitrogen requirements at gyttja-affected locations. To our knowledge, this is the first study to use stable isotope analysis to trace the assimilation of potentially toxic cyanobacterial accumulations into the trophic pathways of an affected system. [ABSTRACT FROM AUTHOR]

In this study, benthic decapods were sampled approximately for every three months between September 2000 and June 2002 in a heavily used subtropical lagoon and its vicinity waters in southwestern Taiwan. Seventeen shrimp species (dominated by Metapenaeus ensis and Penaeus semisulcatus) and 19 crab species (dominated by Thalamita crenata) were recorded within the lagoon, whereas a combined total of 32 shrimp species (mainly Metapenaeopsis barbata and M. palmensis) and 50 crab species (dominated by Portunus hastatoides) were recorded at 10, 20, 30, and 40-m depths outside the inlet–outlet of the lagoon. The decapod community in the lagoon varied little temporally, and was significantly different from those in the nearby waters. The results of this study document a decapod fauna in a lagoon subjected to decades of aquaculture activities and revealed that these activities benefited a distinct decapod assemblage, yet may have prevented the potential use of the lagoon by other species as a nursery or refuge. Aquaculture activities have since been prevented and dredging of the benthic sediments in the lagoon has been underway; thus the results of present study will provide a valuable and rare baseline data set to be used for future studies to determine how decapod communities shift in response to habitat change. [ABSTRACT FROM AUTHOR]

The aim of this article is to evaluate whether alterations in flood pulses differentially affect diet composition, feeding niche breadth, and diet overlap of piscivorous fish. Species examined were Acestrorhynchus lacustris, Hoplias aff malabaricus, Plagioscion squamosissimus, Rhaphiodon vulpinus, and Salminus brasiliensis. These species were collected with gillnets (different mesh sizes) in the upper Paraná River floodplain, during four distinct flood events (four periods; A = 1992/1993; B = 2000; C = 2001; and D = 2002). The volumetric method was chosen to express diet results. Feeding niche breadth was calculated using Levins measure, and diet overlap was evaluated by the Pianka’s Index. Flooding was more intense and lasted longer in the first period (1992/1993—A). Diet composition of the studied species was broad (47 total items consumed). For period A, Prochilodus lineatus was the main item taken by four out of five species. In the other periods, there were relevant alterations in diet, since P. lineatus was not recorded in any stomach of the five species; rather, it was replaced by the shrimp, Macrobrachium amazonicum. Diet overlap was low in all periods. The greatest overlap was obtained in period C for P. squamosissimus and R. vulpinus, due to high consumption of shrimps. There were no significant differences in niche breadth among species. However, the species presented distinct variation patterns in niche breadth. For example, H. aff. malabaricus showed a tendency toward increasing niche over the period, but the other species presented larger niches only during period A. Therefore, it can be concluded that the intensity and duration of the flood pulse influences: (i) the diet composition of piscivores; (ii) the breadth of their niches; and (iii) feeding overlap among species. [ABSTRACT FROM AUTHOR]

This study aims at analyzing morphological deformities in Palaemon population in the Gironde estuary. The most frequent abnormalities affected cephalothorax and rostrum, and to a lesser extent scaphocerites and uropods (with spectacular dissymmetry), whilst only few cases of antenna and telson deformities were observed. References on morphological abnormalities of crustaceans can be found in the literature, but dealing with only isolated individuals and not for Palaemonids species, whilst in the Gironde estuary up to 40% of adult individuals are affected. Deformities likely depend on water pollutants, among others heavy metals and PCBs. This hypothesis should be tested considering other European estuaries with similar features. [ABSTRACT FROM AUTHOR]

Trophic patterns of omnivorous freshwater shrimps, Exopalaemon modestus and Macrobrachium nipponensis, were investigated in two shallow eutrophic lakes by using stable isotope analysis. δ15N and δ13C of M. nipponensis and E. modestus increased with increasing body weight, which might be attributed to larger individuals ingesting organisms that feed higher up the food chain and/or increased assimilation of benthic food items with enriched isotopic signatures. Of the freshwater shrimps occurring in the studied lakes, those from Lake Taihu had significantly elevated δ15N and δ13C values (4.3‰ and 1.8‰, respectively) compared with those from the less eutrophic Lake Chaohu, indicating that the isotopic signature might partially reflect the trophic states of their habitats. Mixing model results suggested that the benthic food web provides the primary carbon source for both shrimp species, and that E. modestus assimilated relatively more pelagic food sources than M. nipponensis in these lakes. [ABSTRACT FROM AUTHOR]

Freshwater caridean shrimps account for approximately a quarter of all described Caridea, numerically dominated by the Atyidae and Palaemonidae. With the exception of Antarctica, freshwater shrimp are present in all biogeographical regions. However, the Oriental region harbours the majority of species, whilst the Nearctic and western Palaearctic are very species-poor. Many species are important components of subsistence fisheries, whilst the Giant River Prawn forms the basis of an extensive aquaculture industry. A total of 13 species are threatened or endangered, with one species formally extinct. [ABSTRACT FROM AUTHOR]

With about 500 known species worldwide, the large brachiopods are a relatively small group of primitive crustaceans. With few exceptions they live in temporary aquatic systems that are most abundant in arid and semi arid areas. As many regions remain unexplored and as especially the number of species in clam shrimps and tadpole shrimps is underestimated due to difficult identification, the species list will increase with future surveys. The Branchiopoda are monophyletic, but inter-ordinal relationships, as well as many evolutionary relationships at lower taxonomic levels are still unclear. Ongoing molecular studies will more accurately depict species diversity and phylogenetic patterns. With the exception of some anostracan families, most families are not restricted to the northern or southern hemisphere or specific zoogeographical regions. Large branchiopods are used for the assessment of the quality and function of temporary wetlands. Due to the reduction in number and quality of temporary wetlands, several species became endangered and are red listed by the IUCN. [ABSTRACT FROM AUTHOR]

In the early 1990’s a conspicuous shift took place in the density of two key macrofauna species at the Frisian Front (SE North Sea). The density of the formerly dominant brittlestar Amphiura filiformis showed tenfold reduction and remained low throughout the observation period (1986–2000). In the same period, the burrowing mud shrimp Callianassa subterranea showed a fourfold increase in density. Since the Frisian Front is a transition area where tidal currents fall just below the erosion threshold of silt and bioturbating mud shrimps can potentially affect the sediment erosion threshold, we examined the effects of the species on sediment erodibility. Two experiments were conducted in laboratory annular flumes. In the first experiment we compared the effects of pre-shift and post-shift combinations of the two species on the erodibility of Frisian Front sediment. The results indicated that the erosion was facilitated by a combination of high densities of C. subterranea and low densities of A. filiformis, representing the situation in the late 1990s. The difference in erodibility was already apparent at velocities equal to the critical near-bed current speed measured at the Frisian Front. In the second experiment the effects of pre- and post-shift densities of A. filiformis on sediment erodibility were compared . This showed that low A. filiformis densities as found in the late 1990’s facilitate erosion, but the effect is only significant at velocities above the critical near-bed velocity in the field. At the latter velocity, no significant difference in erodibility was found between the two A. filiformis densities. This implies that the difference in turbidity in the first experiment was mainly due to the activity of C. subterranea. The experimental results indicate that resuspension at the Frisian Front may occur more frequently as a result of the shift towards a Callianassa dominated community. More frequent resuspension of bottom sediment, most likely amplified by the climate induced increase of wind strength in the North Sea, may hamper the recovery of the A. filiformis adult population. [ABSTRACT FROM AUTHOR]

The identification of the environmental conditions inducing different ecophysiological responses in the different strains and populations of the brine shrimp Artemia should improve the understanding of their biogeographic distribution. Nauplii from two Argentinean brine shrimp populations, Artemia persimilis from Salinas Grandes de Hidalgo (province of La Pampa) and Artemia franciscana from Laguna Mar Chiquita (province of Cordoba), were grown up until adulthood at different salinities (30, 60, 90, 120 gL−1) and temperatures (12, 21, 28°C). The aim was to assess the effects of these different conditions on prereproductive life span and reproductive traits. Results evidenced that at 21 and 28°C, at any salinity, A. franciscana from Laguna Mar Chiquita attained higher survival and fecundity, after a shorter prereproductive period, than A. persimilis from Salinas Grandes de Hidalgo. These data support that A. franciscana, considered a superspecies, exhibits higher phenotypic plasticity than A. persimilis, and that A. persimilis is better adapted to lower temperatures than A. franciscana. These differences in temperature and salinity tolerance could explain the present distribution of these two species in the South Cone in South America. [ABSTRACT FROM AUTHOR]

Oxygen consumption rates of nauplii of the brine shrimp Artemia franciscana Kellogg 1906 were determined over a range of salinities from 10 to 110 ppm, in temperatures from 0 to 30°C, using a multi-factorial design. The oxygen micro-sensors employed have a fast response time and are capable of accurately measuring oxygen concentrations at temperatures well below 0°C. Oxygen uptake rate ranged from 0.03 to 0.66 μmol O2 mg−1 h−1 and was sensitive to changes in both salinity and temperature. Temperature was the dominant factor affecting oxygen consumption rates, which showed a significant increase with increasing temperature. A slight decrease was measured in oxygen consumption with increasing salinity related to differential solubility of oxygen in waters of different salinities. Thermal sensitivity of oxygen consumption determined from calculations of Q 10, indicated physiological adaptation of Artemia nauplii to the ranges of temperatures tested. [ABSTRACT FROM AUTHOR]

Flexibility in the feeding habits of juvenile Nile perch (1–30 cm total length) was studied from September 1988 to September 1989 at four sites (depth range: 1–25 m) in the Mwanza Gulf of Lake Victoria. During this period haplochromine cichlids were virtually absent in the area. We looked at the combined effects of predator size, season and habitat. Stomach content analysis showed that with increase in size, the diet of Nile perch shifted from zooplankton and midge larvae, to macro-invertebrates (shrimps and dragonfly nymphs) and fish. At a size of 3–4 cm Nile perch shifted from size-selective predation on the largest cyclopoids to predation on the largest, less abundant, calanoids. Zooplanktivory ended at a size of ca. 5 cm. Although an ontogenetic shift in the diet of juvenile Nile perch was obvious at all sampling stations, the contribution of prey types appeared to be habitat related. With increasing water depth the frequency of occurrence in the diet of most prey types decreased, but that of shrimps increased. At the entrance of the gulf (20–25 m deep) shrimps were the main food source throughout the year. Halfway the gulf (12–16 m), Nile perch showed seasonality in their feeding behaviour. Shrimps were taken there especially during the rainy season (January to May) when their densities at this station were high, whereas cannibalism prevailed during the rest of the year. In an environment with Nile perch and dagaa as alternative prey, shrimps were taken almost exclusively. They could be regarded as a key prey for Nile perch between 5 and 30 cm. [ABSTRACT FROM AUTHOR]

Atyid prawns from Lake Tanganyika are still poorly understood. There are at least 11 species sharing an exceptionally small size and a reduction in the number of branchiae. The majority are benthic although some are pelagic. This is reflected in different morphologies of the body and walking legs. Morphological adaptions of the denticles on the chelipeds are adaptive as they relate to different ways of feeding. Pelagic fish from Lake Malawi do not represent an example of sympatric speciation as suggested by Shaw et al. (2000). It is more likely that several, independent radiations started from inshore generalists, which gradually adapted to the openwater. [ABSTRACT FROM AUTHOR]