Crustacean Biomass Research Articles

Study on combustion characteristics of crustacean biomass derived fuel coupled with in-situ capture of SO2 based on pulsed microwave radiation

Crustacean waste has great potential as fossil fuel substitution and efficient desulfurization to reduce pollutant emissions, but high moisture and poor quality restrict broad-scale utilization. This study used microwave radiation on crayfish shell to investigate the combustion characteristics and desulfurization effect in different atmospheres/pulse microwave cycle. Meanwhile, the structure evolution mechanism and molecular reaction pathways were revealed. The results show that crayfish shell derived fuel has a pleasurable combustion performance and sulfur fixation ability after microwave radiation in flue gas. The heat release of derived fuel increased by 29.9 % after five microwave cycle in flue gas, and activation energy decreased by 3.7 %. By contrast, the heat release increased by 17.4 % after five microwave cycle in inert gas, and activation energy increased by 39.3 %. Subsequently, the effect of microwave cycle times in flue gas on crayfish shell combustion and desulfurization performance was studied. The results show that the heat release of derived fuel gradually increases with microwave cycle. After seven microwave cycle, the derived fuel heat release and SO2 removal efficiency increased by 34.9 % and 44.4 %, respectively. The results establish the foundation for expanding the utilization pathway of crustacean waste and realizing the low-carbon energy transition.

Habitat Provision Differs Across Subtidal Reefs Varying in Location Within the Estuarine Landscape

Although position within the estuarine landscape is known to influence structural characteristics and ecological functioning of many habitats, the influence of position on subtidal oyster reef characteristics and functioning is relatively understudied. This study assessed habitat provision by oysters and benthic macrofauna on subtidal bar and patch oyster reefs within the northwestern Gulf of Mexico estuary. Bar reefs had greater and more variable oyster density, biomass, and volume, as well as dead shell material, compared to patch reefs. Benthic macrofaunal community composition differed between reef types, with bar reefs hosting 11× and 30× higher biomass of Porcellanidae and Ampithoidae crustaceans, and patch reefs supporting 34× and 47× higher biomass of Eunicidae annelids and Leptocheliidae crustaceans. The environmental variables most highly correlated with macrofaunal communities on both bar and patch reefs were sediment chlorophyll-a, volume of dead oyster shells, and depth. Despite differences in structural characteristics and position within the estuarine landscape, subtidal oyster reefs are often managed as a single habitat type. Our findings emphasize the importance of considering location in oyster reef conservation and restoration efforts to better predict and optimize faunal provision outcomes.

Sustainable Production of Chitin Nanowhiskers from Crustacean Biomass Using Cost-Effective Ionic Liquids: Strategies to Avoid Byproduct Formation

Nanochitin, especially in the form of chitin nanowhiskers (ChNWs), represents a significant advance in biopolymer technology due to its high specific surface area, superior tensile strength, and excellent thermal stability. Derived from crustacean waste, which contains 15–40% of chitin, these materials provide a sustainable option that diverts waste from landfills and contributes to environmental conservation. Traditional methods of isolating nanochitin are energy-intensive and generate substantial waste. This study introduces a more sustainable method using inexpensive ionic liquids (ILs) such as [Hmim][HSO4] and [HN222][HSO4], which bypass the costly and destructive steps of traditional procedures. This study also identified the byproduct in IL-mediated chitin hydrolysis reaction as calcium sulfate dihydrate and presented a solution to circumvent the byproduct formation. The effectiveness of the [HN222][HSO4] IL in producing ChNWs from both purified chitin and crustacean biomass was assessed, showing a high yield and maintaining the purity and structural integrity of chitin, thereby demonstrating a significant reduction in the environmental footprint of ChNW production.

Energy utilization potential of crustacean biomass: comprehensive evaluation of co-combustion with coal

Energy utilization potential of crustacean biomass: comprehensive evaluation of co-combustion with coal

Ecosystem dynamics and hypoxia control in the East China Sea: A bottom-up and top-down perspective

Decades of overfishing have greatly altered the community structure in the East China Sea (ECS). The decrease of top predators in the food web has weakened the control exerted from higher trophic levels. As a result, the biomass of benthic crustaceans, representing the third trophic level, has increased. This has probably led to a restriction of the second trophic level, diminishing its ability to control primary producer biomass. Consequently, the ecological pyramid of trophic levels in the ECS has been altered, reducing the top-down control on the first trophic level. This has made algal blooms more susceptible to occur under nutrient loads, temperate temperatures, and light availability. The reduced abundance of the fourth trophic levels has caused a larger portion of primary productivity to sink directly to the benthic community, bypassing the food web. This influx of sinking organic matter has resulted in organic enrichment in the bottom waters, impacting the biomass and diversity of benthic organisms. Furthermore, it has intensified anthropogenic carbon storage in the sediment. Subsequently, intense decomposition processes occur, leading to the development of anoxia and even hypoxia. The seasonal hypoxia off the Changjiang Estuary can be attributed to the combined influence of top-down control and bottom-up control related to nutrient loading, and terrestrial inputs. In order to mitigate extreme hypoxia events, it is necessary to implement comprehensive fisheries policies that prioritize the maintenance of a healthy and functional ecosystem. This approach should go beyond relying solely on watershed management strategies to regulate riverine inputs. Plain language summaryDecades of overfishing changed the food web in the East China Sea and weaken the resistance of ecosystem to hypoxia. Commercial fishing on top predators decreases the fourth trophic level while relatively increases the third trophic represented by crab and shrimp, which enhances grazing on the zooplankton. The decrease of the second trophic level fails to control the biomass of phytoplankton, thus more primary productivities directly sink to the benthic community and cause organic enrichment. The elevated flux of organic matters to the bottom waters causes the thrive of the carbs and shrimps, as well as more remineralization processes and eventually low oxygen level. Unlike the bottom-up perspective of hypoxia mechanism off the Changjiang Estuary, which is from the nutrient load, phytoplankton bloom, quick sink, effective decomposition and eventually hypoxia, the top-down control focuses on the changes of ecosystem structure and thus derived hindered energy transfer, changed community structure, enhanced carbon sink, elevated remineralization and ultimately hypoxia. These two mechanisms combine with each other and control the seasonal hypoxia off the Changjiang Estuary and even other coastal regions around the world.

Design of anti-saponification Ca-based catalyst with porous-shell structure from crustacean waste for biodiesel production

The rapid development of the biodiesel industry is of significant importance for achieving carbon emission reduction in the transportation sector. However, the presence of trace amounts of water in the feedstock during biodiesel synthesis may lead to severe saponification reactions, thereby reducing the yield of fatty acid methyl esters. In this study, based on our exploration of the characteristic of porous carbon to absorb moisture from the environment, we synthesized a CaO catalyst with porous carbon coating via discarded shrimp shell biomass. Because the carbonization temperature of organic matter in shrimp shells is lower than the decomposition temperature of CaCO3, the CO2 generated during pyrolysis can erode the pyrolytic carbon and form porous structure. The mesoporous carbon shell facilitates the diffusion of oil and methanol molecules while adsorbing moisture in the alcohol phase. This structure effectively minimizes the interaction between CaO and water, thereby suppressing saponification reactions and ensuring the smooth progression of the desired transesterification reaction. Through a series of physicochemical characterizations, the structure and water absorption performance of the catalyst were confirmed. The as-prepared CaO@PC-900 catalyst demonstrated the ability to maintain a biodiesel yield of over 85% in a reaction system with a water content of 3%, significantly surpassing the performance of commercial CaO and previously reported Ca-based solid bases. This work provides a new approach to the design of anti-saponification transesterification catalysts, while also offering a novel pathway for the synthesis of porous carbon from discarded crustacean biomass.

Daily responses of the planktonic food web to environmental dynamics in the vegetated littoral zone of a large shallow lake

Littoral zones are the most productive areas of shallow lakes and make important contributions to energy transfer to higher trophic levels in aquatic ecosystems. Great habitat heterogeneity characterizes the littoral ecosystems, often encompassing macrophyte covered areas that provide microhabitats with diverse structural complexity, and several effects over the structure and function of biological communities. The effects of macrophytes on trophic interactions are more complex in subtropical lakes than in temperate lakes. The relationships between planktonic food web components and the effects of a highly dynamic environment in structuring plankton communities were studied in a large subtropical shallow lake. The study was conducted for twenty-five consecutive days in the summer of 2016 at two sites (Station 1 and Station 2) in the well-developed littoral zone of Lake Mangueira hosting different plant life forms. Strong spatial variation between sampling stations was evidenced in the density of most of the communities, with the highest means of bacterioplankton, phytoplankton, and ciliates density being recorded at the station surrounded mainly by submerged macrophytes (Station 1). These plants particularly modify microhabitat complexity by increasing the availability and functional diversity of niches. Furthermore, submerged macrophytes tend to accumulate more periphyton biomass, a quality food resource for many consumers. Important grazing relationships, nutrient demands, and trophic structure were assessed through carbon biomass of the communities. Phytoplankton accounted for a greater proportion of the entire plankton community than bacteria, while zooplankton had low carbon biomass of crustaceans and a high dominance of ciliates and rotifers, with a greater grazing impact on bacterioplankton than on phytoplankton. According to RDA and multiple-regression analysis, nutrients and humic substances were the main predictors of variability in the littoral food web components over a short-sampling interval. The carbon biomass of bacteria and metazooplankton were both positively related to humic substances and nutrients at Station 1, as well as the biomass ratio of metazooplankton to phytoplankton and metazooplankton to ciliates. This suggests that humic substances have been metabolized by bacteria and transferred to higher trophic levels through predation. On the other hand, humic substances negatively affected the carbon biomass of bacteria and cyanobacteria at Station 2, suggesting a mostly refractory DOC around the emergent plants. Results indicate that despite the greater importance of bacterial biomass in the energy transfer through zooplankton predation, the efficiency of carbon transfer in algal and bacteria-based food webs was both very low. The effects of macrophytes on the quantity and/or quality of nutrients and substrates for bacteria uptake and phytoplankton requirements, explained the spatial variability of plankton food web components, even over the short distance between stations, as well as the inefficient microbial loop found in the littoral zone inhabited by macrophytes.

Distribution of crustaceans (Malacostraca, Arthropoda) in rivers of the semi-desert zone (with the example of the Volgograd reservoir tributes)

As a result of our studies of the macro- and nectozoobenthos of the rivers of the semidesert zone (the Volgograd reservoir basin), 16 Malacostraca species were recorded, most of which are representatives of the Ponto-Caspian complex. Compared to the Volgograd reservoir, there is an increase in the quantitative indicators of mysids and isopods and a decrease in the number of species, abundance and biomass of amphipods and cumaceans in the semi-desert zone rivers. The average abundance and biomass of crustaceans in the surveyed rivers are approximately 2.5 times lower than in the Volgograd Reservoir. Crustaceans of the Ponto-Caspian and PontoAzov complexes, as well as the isopods Asellus aquaticus (Linné, 1758) inhabit fresh and oligohaline waters, while the gammarids Gammarus lacustris (Sars, 1863) live in oligohaline and polyhaline waters. Amphipods are characterized by the largest number of species, which, taking into account their morphology and the type of substrate which they live on, are assigned to three ecomorphs, namely: clingers, crawlers, and diggers. No symbionts in the Yeruslan basin rivers were found. The noted amphipod ecomorphs are distributed relatively evenly with a slight dominance of crawlers (45%). It has been revealed that two types of crustacean cenoses are formed in the surveyed rivers. The first type is formed mainly by consortium interactions of the edificatory mollusks Dreissena with amphipods Chelicorophium curvispinum Sars, 1895, Dikerogammarus haemobaphes (Eichwald, 1841), mysids Paramysis ullskyi Czerniavsky, 1882, P. lacustris (Czerniavsky, 1882), and associated species. The second cenosis in the rivers is represented by a complex of small coastal mysid species Katamysis warpachowskyi Czerniavsky, 1882, Limnomysis benedeni Sars, 1893, and amphipods Chaetogammarus warpachowsky (Sars, 1894), the relationships within which are based on common biotopic conditions and feeding patterns.

Winter dynamics of abiotic and biotic parameters in eutrophic temperate lakes

Winter conditions in lakes of temperate climatic zones, especially the duration and thickness of ice and snow cover, are strongly influenced by climate changes. The aim of this study was to follow the dynamics of abiotic (organic carbon, total phosphorus, total nitrogen) and biotic (chlorophyll a, cyanobacteria, algae, nanoflagellates, ciliates, rotifers, crustaceans) parameters during two consecutive winters in three eutrophic lakes of different mixing regime (northeastern Poland). Our results showed that dissolved organic carbon was highly stable during both winters and practically did not differ among the studied lakes. Total phosphorus and chlorophyll a concentrations differed significantly between the dimictic and meromictic lakes. The concentrations of nutrients and chlorophyll a and the biomass of phytoplankton, protists, rotifers and crustaceans reached higher values in late winter than in early winter, depending on the lake type (morphometry, mixing regime) and the year of the study. The composition of phytoplankton and ciliates was more or less similar throughout the study in all lakes during both years, but the share of individual groups in the total biomass differed between early and late winter. A high cyanobacterial biomass in January under the ice in the meromictic lake was probably a legacy of the summer/autumn community. Small prostomatid ciliates were the most important group in late winter in the shallow lake. Cladocerans (Bosmina coregoni and B. longispina) were an important component of winter crustacean community on some occasions, especially in the shallow lake. Phosphorus was the major factor determining phytoplankton biomass. Heterotrophic nanoflagellates and rotifers were negatively related to ice cover, while ciliates were positively related to the water temperature. Our study demonstrated that the dynamics, abundance, and structure of the phytoplankton and zooplankton communities in eutrophic lakes changed from one winter to the next despite similar environmental conditions.

Alteration of alpha and beta diversity in nekton community by extreme marine heatwave events: An example from the East China Sea

In the year of 2016 to 2017, record-breaking marine heatwave (MHW) events occurred along the Chinese coast, exerting severe impacts on coastal fishes and fisheries. However, the response of the nekton community to MHW events still remains poorly understanding. Thus, to investigate the influences of the MHW events on species composition dynamics, this study conducted a survey on nekton communities in the northern East China Sea in the summers during 2014 to 2017. The recently-developed “heatwaveR” package was adopted to describe the variation characteristics of heatwaves within the study area, based on high-resolution remote-sensing sea surface temperature products. We also compared variations in the community structures of different biological groups before (2014–2015) and during the occurrence of the MHW events (2016–2017). During the MHW events, temperature increased by approximately 2.3°C in both 2016 and 2017. Compared with those before the MHW events, the biomass and dominance of several important crustaceans decreased, and the biomass of warm water affinity species increased significantly, while their richness and diversity decreased; the biomass of warm temperature affinity species declined significantly, while their diversity increased slightly. These results show the difference in the response rates of species with different thermal preferences and different species compositions to the extreme climate change. Beta diversity analysis revealed that the inter-group variation before and during the MHW event exceeded the intra-group variation, proving that MHWs changed the community structure to a certain extent. PERMANOVA test showed that the species compositions of planktivorous fish (FG1) and small-omnivorous fish (FG2) in the feeding-functional groups were significantly different before and during the MHW event, which may be attributed to the impact of MHWs on oligotrophic fishes through thermal preference and the trophic cascade effect. There was no significant change in the species compositions of other functional groups, indicating that medium-trophic and eutrophic fishes possessed certain adaptability to MHWs. Regarding fisheries management under extreme warming events, it would be advisable to diagnose temperature anomalies in the early stage, monitor changes in species abundance in the early life cycle, and then rapidly develop suitable fishing strategies.

Active flux seasonality of the small dominant migratory crustaceans and mesopelagic fishes in the Gulf of California during June and October

The biological carbon pump is the process that transports carbon vertically out of the mixed layer in the ocean. Besides the sinking flux of organic particles, active flux due to the daily vertical migration of zooplankton and micronekton promotes a significant carbon transport not fully accounted for or understood in the world’s oceans. The diversity and abundance of epipelagic and mesopelagic species in the Gulf of California has been extensively studied, but the role of micronekton in carbon export has not yet been investigated. We studied the carbon flux promoted by juvenile and adult mesopelagic fishes and crustaceans (Decapoda and Euphausiidae) during the transition from the cold to warm period (June) and the onset of the warm season (October) in 2018. We provide the first estimation of migrant biomass and respiratory flux of the most abundant migratory species of mesopelagic fishes, decapods and euphausiids in the Gulf of California. The micronekton species collected accounted for a large biomass of mesopelagic fishes and pelagic crustaceans. The average migrant biomass estimates were 151.5 ± 101.2 mg C·m−2 during June and 90.9 ± 75.3 mg C·m−2 during October. The enzymatic activity of the electron transfer system (ETS) was measured as an estimate of their respiratory rates. Average specific ETS activity was significantly different between fishes and decapods, and between fishes and euphausiids (p < 0.05). The respiratory flux of fishes was predominant in the Gulf of California, followed by pelagic decapods and euphausiids. Seasonal changes in respiratory flux were observed for fishes (June: 6.1 ± 1.5 mg C·m−2·d−1; October: 3.2 ± 1.8 mg C·m−2·d−1) and decapods (June: 0.4 mg C·m−2·d−1; October: 0.7 ± 0.05 mg C·m−2·d−1). Respiratory flux estimation by crustaceans (decapods and euphausiids) and fishes together was 6.86 mg C·m−2·d−1 during June, and 4.21 mg C·m−2·d−1 during October 2018, suggesting a functional role of this large micronektonic fauna in the biological carbon export in this region.

Isolation of Chitin Nano-whiskers Directly from Crustacean Biomass Waste in a Single Step with Acidic Ionic Liquids

Isolation of Chitin Nano-whiskers Directly from Crustacean Biomass Waste in a Single Step with Acidic Ionic Liquids

Multidecadal changes in the demersal community structure in an urban bay: Shift from a bottom- to a top-heavy pyramid

Fish community structures in urban bays have changed over time as a result of anthropogenic activities, leading to changes in species richness, diversity, fish assemblage composition, and abundance. Tokyo Bay is one of the most eutrophic urban bays in Japan, and hypoxia occurs every summer in the bottom water of the bay. Accordingly, the demersal community in the bay has undergone drastic changes in taxonomic composition over the past several decades. We analyzed data from a bottom trawl survey spanning 35 years to characterize multidecadal changes in the slopes of body size spectra of the demersal community in Tokyo Bay, as a reliable index to represent shifts in community structure. We found that the community shifted from bottom-heavy pyramids in the past (1977–1995) to top-heavy pyramids in recent years (2003–2019) due to a decrease in the biomass of small-sized crustaceans and an increase in the biomass of large-sized elasmobranchs. Human-induced hypoxia can promote the formation of top-heavy pyramids, as it decimates the number of small-sized individuals. The existence of energy subsidies to large-sized individuals from the inner-shallow and outer bay areas as well as the pelagic community provides a possible explanation for the persistence of top-heavy pyramids.

Diversity of vascular plants and zooplankton communities in regard to the ecological assessment of the territory of the ecological park “Samara Venice”, Samara Region, Russia

The results of the floristic and hydrobiological studies performed in May - August 2020 on the territory of the ecological park Samara Venice (Samara Region, Russia) are presented. These data form the basis for the ecological assessment of the territory. The diversity of vascular plants is presented by 4 divisions, 65 families, 205 genera, and 309 species. Among them, 66 species (21.4%) belong to the alien plant species, including nine invasive. Habitats of the plants included in the regional Red List are found. The zooplankton diversity comprises 60 species and morphs. The zooplankton community has undergone significant transformation, manifesting by an increase in the total biomass and in the biomass of crustaceans and rotifers, and by a decrease in absolute and relative species richness. It is revealed that a number of the studied water bodies belong to the transitional type, and may be characterized as of middle position between the meso- to eutrophic type (moderately polluted and polluted waters).

Drivers of variation in crustacean zooplankton production rates differ across regions off the west coast of Vancouver Island and in the subarctic NE Pacific

Abstract The subarctic NE Pacific is comprised of several oceanographic regimes, in which regional variability in sea surface temperature (SST), satellite chlorophyll a, and crustacean zooplankton biomass influence the production rates of crustacean zooplankton. Traditional methods for estimating zooplankton production rates are labour/time intensive and restricted to select copepod species. A practical field alternative is the ‘chitobiase method’, which yields community-level biomass production rates (BPR) analogous to traditional moulting rate methods. BPR was measured along the west coast of Vancouver Island and in the subarctic NE Pacific during 2005, 2009–2011, and 2015–2018. Generalized additive modelling identified SST and the developing crustacean zooplankton biomass as key drivers of BPR variability. BPR varied positively with the proportion of developing copepod biomass relative to that of non-copepod crustacean zooplankton biomass. Our analysis indicates that BPR variation is associated with zooplankton community composition, but that high zooplankton biomass is not necessarily predictive of high BPR. Specifically, higher BPR is associated with a higher relative biomass of large-bodied, cold-water indicator species, and a lower biomass of non-copepod crustaceans.

POPULATIONS OF ARTEMIA CRUSTACEANS OF KARABASSKY FLOODS OF PRIBALKHASHYE

The article presents the analysis of biological parameters of parthenogenetics of Artemia crustaceans of the hypergaline reservoirs of Kazakhstan. In the lakes under study there are shown the changes of the total crustacean biomass decreasing from high-productive to low-productive. Most of the reservoirs with Artemia in Kazakhstan are characterized by the presence of Artemia parthenogenetic populations with the absence or extremely small presence of males. The aggregation of males in significant numbers may indicate the tension of the ecological situation in the reservoirs and the desire of the population to increase the survival and stability of the offspring. It has been stated that all age periods of crustacean maturation are found in the reservoirs. At the same time, the basis of Artemia populations in all studied lakes are the youngest stages - nauplius, which form 53-86% of the total number of Artemias. In lakes Artemia crustaceans are presented by bisexual parthenogenetic race, with all age stages of development during the summer - autumnal period of observations. The hydrochemical mode of hypergaline lakes of Karabassky floods is favorable for activity of Artemia Branchiopoda crustaceans. The size of crustacean biomass populations in Lake Balhash change on seasons ranging from low to very high. Lake No. 1 is highly productive in Artemias in the summer, and lake No. 2 - in the spring. Such difference in temporary aspect is caused by existence of various generations in the populations of the crustaceans on seasons. The data obtained prove the high potential of the studied small reservoirs of the Balkhash region in relation to autumn plankton cysts

Food-web modification in the eastern Gulf of Finland after invasion of Marenzelleria arctia (Spionidae, Polychaeta)

The paucity of data on non-indigenous marine species is a particular challenge for understanding the ecology of invasions and prioritising conservation and research efforts in marine ecosystems. Marenzelleria spp. are amongst the most successful non-native benthic species in the Baltic Sea during recent decades. We used stable isotope analysis (SIA) to test the hypothesis that the dominance of polychaete worm Marenzelleria arctia in the zoobenthos of the Neva Estuary after its invasion in the late 2000s is related to the position of this species in the benthic food webs. The trend towards a gradual decrease in the biomass of Marenzelleria worms was observed during 2014–2020, probably due to significant negative relationships between the biomass of oligochaetes and polychaetes, both of which, according to SIA, primarily use allochthonous organic carbon for their production. The biomass of benthic crustaceans practically did not change and remained very low. The SIA showed that, in contrast to the native crustacean Monoporeia affinis, polychates are practically not consumed either by the main invertebrate predator Saduria entomon, which preys on M. affinis, oligochaetes and larvae of chironomids or by benthivorous fish that prefer native benthic crustaceans. A hypothetical model for the position and functional role of M. arctia in the bottom food web is presented and discussed. According the model, the invasion of M. arctia has created an offshoot food chain in the Estuary food webs. The former dominant food webs, associated with native crustaceans, are now poorly developed. The lack of top-down control obviously contributes to the significant development of the Marenzelleria food chain, which, unlike native food chains, does not provide energy transfer from autochthonous and allochthonous organic matter to the upper trophic levels. The study showed that an alien species, without displacing native species, can significantly change the structure of food webs, creating blind offshoots of the food chain.

РЕТРОСПЕКТИВНЫЙ АНАЛИЗ СТРУКТУРНЫХ ПЕРЕСТРОЕК В СОСТАВЕ МАКРОЗООБЕНТОСА НА ЭТАПЕ ТРАНСГРЕССИИ КАСПИЙСКОГО МОРЯ

The article highlights the processes of lowering and raising the Caspian Sea level and its influence on the quantitative and qualitative characteristics of the aquatic bioresources, including zoobenthos. The development of macrozoobenthos in the Caspian Sea including the Northern Caspian is associated with various processes: chemical, physical and biological. The presence of macrozoobenthos determines the fish productivity in the sea, it is an integral part of the ecosystem of the northern part of the Caspian Sea. In this regard, the assessment of the composition and quantitative characteristics of bottom communities becomes important. One of the urgent tasks of modern hydrobiology is detecting the basic regularities in the biotic processes that affect the qualitative and quantitative changes in the aquatic organisms. This research is of a retrospective nature. On the basis of a long-term analysis of the dynamics of the species structure of bottom zoocenoses there have been revealed the changes in the macrozoobenthos of the western part of the Northern Caspian in the first and second periods of the sea level rise (1978–1988 and 1989–1995). Decreasing water salinity, increasing desalinated zones and areas with oxygen deficiency in the bottom horizon (in the extremely high-water years of 1990 and 1991) contributed to the significant changes in the quantitative and qualitative composition of the bottom fauna. From the first stage to the second there was recorded a decrease in the number and biomass of crustaceans and molluscs. The species Stenogammarus macrurus (G. O. Sars) and Stenogammarus similis (G. O. Sars), which are tolerant to the significant salinity fluctuations, as well as abra, which is resistant to oxygen deficiency were most abundant in the water complex with light salinity. Also, there has been considered the water content of the rivers of the Caspian basin and the type of soil as factors influencing changes in the concentration of macrozoobenthos.

Limnoecosystems of the Kurgan region with domination in the zooplankton of the species group Daphnia (Daphnia)

The paper presents data on the state of populations of species of the genus Daphnia in the ecosystems of small lakes in the forest-steppe zone of the south-west of Western Siberia, in which they are the highest trophic link. The research was conducted in 2017 on the territory of the Kurgan region. In total, 5 lakes (Lysanovo, Dolgoe, Golovka, Second Mogilnoye, Krutoyar) located between 66°30’ and 67°00 ‘ were studied.d. and 55°00’ and 55°30 ‘ s. The studied lakes are typical for the forest-steppe zone of Western Siberia. According to the chemical composition, the lake waters of the studied limnoecosystems can be attributed to the bicarbonate and chloride classes, the sodium group. 5 species of the genus Daphnia were found in the reservoirs: Daphnia (Daphnia) - D.(D.) pulex, D.(D.) obtusa, D.(D.) longispina, D.(D.) galeata, and Daphnia (Ctenodaphnia)- D. (C.) magna. Populations of D. (D.) pulex are found in all the studied reservoirs. The maximum density and biomass of crustaceans of this species is noted in Lake Mogilnoye of 51 thousand individuals/m² and 3.62 g/m², respectively. The minimum, in the lake Dolgoe – 3.8 thousand individuals/m² and 0.019 g/m². Of the other species, D. (C.) magna is most common-in three reservoirs. At the same time, there is a significant variability in the population density from 0.478 thousand. individuals/m² (Lake Krutoyar) up to 9,864 thousand. individuals/ m² (lake Dolgoe). D. (D.) longispina is found in two lakes – the Golovka (25,230 thousand. individuals/m²) and Krutoyar (6,428 thous. individuals/m²). The lowest occurrence is typical for D. (D.) obtusa (Lake Golovka) and D. (D.) galeata (Lake Lysanovo). The greatest species diversity of the genus Daphnia was observed in Lake Golovka (3 species) and Krutoyar (3 species). It is concluded that the studied limnoecosystems are characteristic daphnia reservoirs with the dominance of one or two species from the genus Daphnia.

Damage assessment and survival estimates in the wedge clam (Donax trunculus) caught by mechanical dredging in the northern Alboran Sea

ABSTRACT This paper describes the impact of dredging on populations of the wedge clam (Donax trunculus) at two sites along the northern Alboran coast. Damage was assessed by quantifying shell and foot damage on commercial clams caught with mechanical dredges. Survival experiments were carried out to assess their survival capacity after 24 h purification treatment and 72 h cold storage, which represents an issue of great interest for fisheries research, management and marketing. Overall, 2.4% of wedge clams suffered any type of damage, including chipped edges and scratched valves. Higher proportions of shell-damaged individuals were positively correlated to bottom features (e.g. gravel content in sediment). Moreover, higher towing speed significantly increased shell damage. Analyses of shell damage areas revealed that the anterior dorsal and ventral parts of the shell are the most vulnerable to dredging. A total of 15.9% of individuals showed damage on the foot, which seems not to affect their survival. The incidence of foot damage was mostly linked to sublethal predation, reflected in a positive correlation between the proportion of foot-damaged individuals and biomass of decapod crustaceans in the fishing ground. Finally, D. trunculus exhibited very low mortality rates after 24 h purification treatment (0.2–0.4%) and 72 h cold storage (0.3–3.2%). The survival rate at the end of the experiment was high (>96%), with the highest mortality observed 96 h after the fishing day. No correlations were found between mortality rates and bottom type or towing speed.