Zooplankton Composition Research Articles

Differential response of Bay of Bengal during deficit and normal monsoons.

Present study explains the disparity in biological production (primary and secondary) with respect to two distinct monsoonal regimes in the western Bay of Bengal, viz., deficit monsoon (DM) and normal monsoon (NM). A combination of in situ and satellite data during the years 2002 (DM) and 2003 (NM) was used to address the physico-chemical and biological responses. The basin was relatively warm (ΔSST = 0.55°C) and fresh (ΔSSS = -0.55) during DM than NM. Physical processes such as coastal upwelling and cyclonic eddy were prominent during NM. Variations of hydrography between DM and NM were reflected in the biological production as well. Chlorophyll a concentration (0.05 to 5.2mgm-2) was almost similar during both the periods; however, column production showed higher values during DM. Mesozooplankton standing stock was relatively less during DM than NM. Composition of zooplankton also showed pronounced variation between the periods. This can be attributed to the variability in biological response of the region to the varying environmental condition. Relatively high chlorophyll a and primary productivity observed during DM may be due to the increased light availability (less cloud cover) and extended euphotic depth. In addition, the low mesozooplankton standing stock (low grazing) observed during the period also might have helped in maintaining a relatively high rate of production. The seasonal production of the basin is influenced by duration and intensity of various atmospheric as well as oceanic processes.

Zooplankton Population and Community Structure Changes in Response to a Harmful Algal Bloom Caused by Prorocentrum donghaiense in the East China Sea

Blooms of the dinoflagellate Prorocentrum donghaiense have had adverse impacts on marine ecosystems. However, ecological details, particularly the impacts and processes of the P. donghaiense bloom on the zooplankton community structure are poorly known. We investigated the changes of zooplankton communities in situ within the whole process of a P. donghaiense bloom in the coastal waters in southern Zhejiang Province, China, in May 2016. Results showed that ecological changes during the blooms of P. donghaiense could be divided into three major phases, namely the growth, maintenance, and dissipation phases with regard to the cell abundance of P. donghaiense by bottle sampling of plankton. A total of 42 species of zooplankton were identified. The average abundance and species number of zooplankton in the growth phase were significantly higher than those in the maintenance and dissipation phases. It is shown that the top-two highest proportions of zooplankton in the growth phase were small jellyfishes and copepods, while small jellyfishes and chaetognaths, and copepoda larvae and chaetognaths were the top-two highest in the maintenance and dissipation phases respectively. However, the values of biodiversity index have no statistically significant differences between the three phases. The present results suggested that P. donghaiense bloom produced significant negative impacts on the abundance and species composition of zooplankton with particular reference to copepods.

Zooplankton of small reservoirs of the desert zone of Kazakhstan

The purpose of the work is to study the abundance and biomass of zooplankton communities of small reservoirs to assess the possibility of their use for fishery purposes. The article presents the results of a survey of 10 reservoirs of the middle desert and desert plains of the Central Asian type in September 2020. Small reservoirs and lakes of the region (0.01–0.52 km²) are freshwater, shallow (average depth 0.5–2.3 m), with a high degree of overgrowth of coastal (25–60%) and aquatic vegetation (60–90%). Eight of them are at the lower level of mesotrophy in terms of organic matter content. Lakes Mozgovoy and Kosmurat are mesoeutrophic and oligotrophic reservoirs. In most reservoirs at the time of the study, summer water temperatures were noted during the day (18.3–23.7 °C). A feature of the six reservoirs was the high content of phosphorus ions. The optimal level of this element was in the three upper reservoirs of the Kenes cascade due to the inflow of water from the mountains. The species composition of zooplankton in September is poor, the number of species ranged from 2 to 13. The basis of quantitative characteristics were planktonic and benthic Copepoda or Rotifera. The exception was oz. Cerebral, in which Cladocera prevailed at the expense of representatives of the Chydoridae. The biomass of zooplankton in the lakes was also quite low from 5.3 to 832.5 mg/m³. Thus, according to S.P. Kitaev’s trophic scale, reservoirs belong to the oligotrophic type. A comparative analysis of the zooplankton state in autumn and in other seasons shows a consistently low productivity of arid cenoses in conditions of low water and significant overgrowth. To improve the productivity of reservoirs and their further fishery use, it is necessary to optimize the habitat of aquatic organisms with an improvement in the water content regime and a decrease in the level of overgrowth in them.

Composition and distribution of zooplankton species in the subtropical areas of the Northwestern Pacific Ocean

Based on the investigation data of 44 stations in the area 28°－35° N, 147°－154° E of the Northwestern Pacific Ocean by the research ship 'Songhang' in March 2019, we analyzed species composition and distribution of zooplankton to understand zooplankton community structure in the subtropical areas of the Northwestern Pacific Ocean. The results showed that a total of 456 zooplankton species (including planktonic larvae and unidentified species) were recorded in the surveyed area, which were belonged to 8 categories and 14 groups. There were 163 species of copepods, as the dominant group. The dominant species included 9 warm-water species, Eudoxoides spiralis, Neocalanus gracilis, Pleuromamma gracilis, Sagitta enflata, Doliolum nationalis, S. hexaptera, Euchirella rostrata, Nannocalanus minor and Mesocalanus tenuicornis, and one temperate species, Calanus jashnovi. Both the warm current indicator species S. hexaptera and the cold current indicator species C. jashnovi occurred simultaneously in the subtropical area, indicating that the Kuroshio Current and the Oyashio Current had an important impact on the diversity and temporal-spatial distribution of marine zooplankton. The average biomass was (31.64±23.81) mg·m-3, and the average abundance was (22.2±17.6) ind·m-3. The average values of purity index (C), eveness index (J), Shannon diversity index (H) and richness index (D) were 0.09±0.10, 0.76±0.10, 4.88±0.71, and 23.53±8.08, respectively. The spatial distribution of the four indices were uneven and irregular. During the study period, species composition of zooplankton in the Northwest Pacific was rich, species distribution was uneven, and community structure was stable.

Seasonal and diel variations in the vertical distribution, composition, abundance and biomass of zooplankton in a deep Chilean Patagonian Fjord.

Comau Fjord is a stratified Chilean Patagonian Fjord characterized by a shallow brackish surface layer and a >400 m layer of aragonite-depleted subsurface waters. Despite the energetic burden of low aragonite saturation levels to calcification, Comau Fjord harbours dense populations of cold-water corals (CWC). While this paradox has been attributed to a rich supply of zooplankton, supporting abundance and biomass data are so far lacking. In this study, we investigated the seasonal and diel changes of the zooplankton community over the entire water column. We used a Nansen net (100 µm mesh) to take stratified vertical hauls between the surface and the bottom (0-50-100-200-300-400-450 m). Samples were scanned with a ZooScan, and abundance, biovolume and biomass were determined for 41 taxa identified on the web-based platform EcoTaxa 2.0. Zooplankton biomass was the highest in summer (209 g dry mass m−2) and the lowest in winter (61 g dry mass m−2). Abundance, however, peaked in spring, suggesting a close correspondence between reproduction and phytoplankton spring blooms (Chl a max. 50.86 mg m−3, 3 m depth). Overall, copepods were the most important group of the total zooplankton community, both in abundance (64–81%) and biovolume (20–70%) followed by mysids and chaetognaths (in terms of biovolume and biomass), and nauplii and Appendicularia (in terms of abundance). Throughout the year, diel changes in the vertical distribution of biomass were found with a daytime maximum in the 100–200 m depth layer and a nighttime maximum in surface waters (0–50 m), associated with the diel vertical migration of the calanoid copepod family Metridinidae. Diel differences in integrated zooplankton abundance, biovolume and biomass were probably due to a high zooplankton patchiness driven by biological processes (e.g., diel vertical migration or predation avoidance), and oceanographic processes (estuarine circulation, tidal mixing or water column stratification). Those factors are considered to be the main drivers of the zooplankton vertical distribution in Comau Fjord.

Application of artificial neural network to estimate the quality of little auks' potential foraging grounds on Spitsbergen

AbstractThe availability of food for the zooplanktivorous seabirds, such as an endemic High Arctic alcid, the little auk (Alle alle) is essential for its population status and in consequence for fertilizing nutrient‐poor Svalbard tundra. Since the zooplankton composition and concentration vary over time and space on foraging grounds, it is challenging to monitor these changes and it could be facilitated by using original machine‐learning methods. We propose to use supervised artificial neural network (ANN) with back‐propagation algorithm, in which we rank each zooplankton taxonomical category (ZTC) based on its share in biomass of little auks' diet. The highest rank was assigned to the largest and most frequent prey, for example, fifth copepodid stage (CV) of Calanus glacialis (0.75), amphipod Apherusa glacialis (0.17) and females of Calanus hyperboreus (0.12). In order to qualify the potential foraging grounds for little auks, zooplankton samples were collected at sea, in the vicinity of five West Spitsbergen fjords characterized by different oceanographic conditions. Consequently, the southern and middle fjords of Spitsbergen were described as the best foraging grounds, while the lowest quality was designated to the northernmost locations. ANN was validated with independent long‐term monitoring dataset from Hornsund and 78% of stations were classified correctly, which indicates that the presented method is reliable for quick estimation of little auks' foraging grounds qualities. This research proposes a new, automated approach for potential foraging grounds classification and delivers an open‐access application that allows following and predicting changes in an emblematic Arctic predator–prey relationship (little auk‐zooplankton).

Utilization of Live‐Food Enrichment with Polyunsaturated Fatty Acids (PUFA) for the Intensive Culture of Yellow Perch Larvae

AbstractChallenges associated with first feeding have impeded the intensive culture of larval Yellow Perch Perca flavescens. Live‐food enrichment with polyunsaturated fatty acids (PUFAs) can increase the growth and survival of larval fish, but this method has not been tested with Yellow Perch. This study includes two experiments that were meant to evaluate (1) the relative proportion of docosahexaenoic acid (DHA; 22:6[n‐3]) and arachidonic acid (ARA; 20:4[n‐6]) in enrichment emulsions and (2) the provision of PUFA emulsions in ethyl ester (EE) or triacylglycerol (TG) form on Yellow Perch growth and survival. Fish were provided with live rotifers Brachionus plicatilis and brine shrimp Artemia nauplii for the first 10 d of exogenous feeding within a specialized recirculating system (phase I). Fish were then transferred to flow‐through tanks and were fed Artemia nauplii for 3 d before gradually transitioning to a formulated starter diet (5–7 d; phase II). Fish size, growth, survival, swim bladder inflation rates, and lipid/fatty acid concentrations were evaluated after each phase. Overall, rotifers assimilated ARA in higher concentrations (23.3% of total fatty acids) than Artemia (0.6–0.7% of total fatty acids). Rotifers also tended to assimilate PUFAs better in EE form than in TG form (71.3% versus 66.5% Σn‐3 + n‐6 fatty acids). In the first experiment, fish from the ARA‐ and DHA‐enriched diet groups had greater swim bladder inflation rates (phase I) and growth rates (phase II) than the unenriched control group. In phase I of the second experiment, the EE enrichment group had a significantly faster growth rate than the TG enrichment group (specific growth rate: mean ± SD = 40.5 ± 0.9% and 36.6 ± 1.8%, respectively). Fatty acid composition of zooplankton was heavily influenced by enrichments, and fatty acid composition of larvae/juveniles reflected that of their live prey. The results of this study suggest that PUFA enrichment of live feeds can accelerate Yellow Perch growth and reduce the time spent in the critical period of early development.

Identification of zooplankton carbon sources using fatty acid biomarkers in lakes and reservoirs at different trophic states in Nanjing and surrounding areas

脂肪酸在生物的摄食活动中相对稳定，可用于辨别消费者的食物来源.不同营养水平的湖泊与水库中浮游动物的碳源组成有差异，因而可能具有不同的脂肪酸组成特征.本研究对南京市及其周边21个湖库的颗粒有机物（POM）、浮游动物的脂肪酸组成进行了对比分析.结果表明，南京市及其周边湖库21个湖库由中营养、轻富营养、中富营养、重富营养共4个营养水平组成.中营养湖库总氮（TN）、总磷（TP）、叶绿素a（Chl.a）、浮游植物生物量均低于富营养湖库，透明度（SD）则相反.中营养湖库中POM脂肪酸的必需脂肪酸（EFA）平均浓度低于富营养湖库；而细菌特征脂肪酸∑C15+∑C17含量高于富营养湖库.随着湖库富营养化，POM中多不饱和脂肪酸（PUFA）浓度逐渐增大，单不饱和脂肪酸（MUFA）浓度则逐渐减少.中营养湖库中浮游动物PUFA浓度普遍低于富营养湖库，∑C15+∑C17含量高于富营养湖库；且浮游动物体内主要来源于藻类的必需脂肪酸EFA/C16：0比值与细菌源脂肪酸（∑C15+∑C17）/C16：0比值均大于其他湖库，表明中营养湖库中浮游动物摄食了较多细菌.随着湖库营养水平升高，浮游动物饱和脂肪酸（SFA）逐渐增多，MUFA浓度逐渐减少，EFA浓度增多，表明浮游动物主要摄食藻类，而外源碳对浮游动物的碳源贡献较小.冗余分析（RDA）结果显示，EFA/C16：0、（∑C15+∑C17）/C16：0与透明度呈正相关，与Chl.a、总磷、磷酸盐呈高度负相关，表明透明度较高、营养水平相对较低的湖库中，浮游动物可能利用较多的藻类与细菌碳；此外，陆源碳转化指标∑C24/C16：0与TN、硝态氮呈正相关性，表明随着营养水平升高，陆源碳对浮游动物碳源贡献呈增加趋势.总体而言，浮游动物更倾向于利用高质量的内源碳，但在内源碳不足以供给水生生物生长需求的中营养水体中，外源碳对生态系统的物质循环和能量流动会产生重要作用.;Fatty acids are relatively stable in the feeding activities of organisms and can be used to identify consumers' food sources. The carbon source composition of zooplankton in lakes and reservoirs with different nutrient levels is different, so they may have different fatty acid composition characteristics. This study compared the fatty acid composition of POM (particulate organic matter) and zooplankton in 21 lakes and reservoirs in Nanjing and its surrounding areas. The results show that the 21 lakes and reservoirs are composed of four nutritional levels:medium nutrition, light eutrophication, medium eutrophication, and heavy eutrophication. The total nitrogen (TN), total phosphorus (TP), chlorophyll-a (Chl.a), and phytoplankton biomass of mesotrophic lakes and reservoirs are lower than those of eutrophic lakes and reservoirs, while the transparency (SD) is the opposite. The average concentration of essential fatty acids (EFA) of POM fatty acids in mesotrophic lakes was lower than that of eutrophic lakes, while the content of bacterial characteristic fatty acids ∑C15+∑C17 was higher than that of eutrophic lakes. With nutrient increase, the concentration of polyunsaturated fatty acids (PUFA) in POM gradually increases, while the concentration of monounsaturated fatty acids (MUFA) gradually decreases. The PUFA of zooplankton in mesotrophic lakes and reservoirs is generally lower than that of eutrophic lakes and reservoirs, and the content of ∑C15+∑C17 is higher than that of eutrophic lakes and reservoirs; and the ratio of essential fatty acids EFA/C16:0, which are mainly derived from algae, and bacterial fatty acids in zooplankton (The ratio of ∑C15+∑C17)/C16:0 is larger than that of other lakes and reservoirs, indicating that zooplankton in the middle-nutrition lakes and reservoirs ingested more bacteria. As nutrient increases, zooplankton saturated fatty acids (SFA) gradually increase, MUFA gradually decreases, and EFA content increases, indicating that zooplankton mainly feeds on algae, while exogenous carbon contributes little to the carbon source of zooplankton. Redundancy analysis (RDA) show that EFA/C16:0, (∑C15+∑C17)/C16:0 are positively correlated with SD, and highly negatively correlated with Chl.a, TP, and phosphate, suggesting that zooplankton consumed more algal and bacterial carbon; and ∑C24/C16:0 is positively correlated with TN, nitrate nitrogen, indicating that zooplankton utilized more terrestrial carbon. In general, zooplankton is more inclined to use high-quality endogenous carbon, but in mesotrophic water bodies where endogenous carbon is not sufficient to supply the growing needs of aquatic organisms. Exogenous carbon plays an important role in the material circulation and energy flow of the ecosystem.

Biofouling initial succession on offshore artificial substrate under subtropical conditions

This study presents the initial stages of the macrofouling community on artificial substrate exposed to the offshore subtropical marine environment, and the contribution of depth (3 and 22m), exposure time (1-2-4-7-10-13-weeks), UV-radiation, rainfall, temperature, pH, salinity, water chlorophyll-a, and zooplankton supply to organism establishment. Steel substrates were placed horizontally on the structure of a pipeline monobuoy off the southern shore of Brazil (Tramandaí beach), and the ecological succession was monitored by six random removals per depth during the summer-autumn of 2011. Approximately 88.5% of the quantified settled individuals comprised fouling fauna and 11.5% vagile and sedentary fauna, although the taxa richness was higher for non-sessile invertebrates. Species richness and organism density up to four weeks were significantly higher at 3m-depth. After this period, a higher density of organisms was found at 22m, while during the whole study the species richness and diversity remained higher at 3m-depth. Zooplankton composition did not show a simultaneous temporal relationship with invertebrate recruitment at any depth; however, increasing the exposure time, the similarity between the planktonic and benthic communities also increased. Meroplankton, tychoplankton, and holoplankton were recorded on the substrates. This study showed that the depth of available substrates affects the macrofouling establishment, which is mainly associated with UV-radiation, exposure time, and ecological interspecific interactions.

ASSESSMENT OF THE ECOLOGICAL STATE OF WATERS BY THE SPECIES COMPOSITION OF ZOOPLANKTON AND PHYTOPLANKTON

Presented the results of studies of macrophytes, zooplankton and phytoplankton and the chemical composition of water polluted by sewage from a livestock enterprise and a conditionally clean pond. It was established that changes in the chemical composition of water after entering the reservoir of wastewater from a livestock enterprise due to an increase in the concentration of mineral and ammonium nitrogen, sodium ions, a decrease in the content of calcium and magnesium ions and hydrogen carbonate ions, at constant values of the pH indicator, total mineralization, potas-sium ions, chlorides and sulfates. Compared to a conditionally clean reservoir, it became polluted with sewage and was characterized by the intensive development of higher aquatic plants, a smaller number of zooplankton species, and its abundance and biomass underwent changes due to a decrease in the number of rotifers (Rotatoria) and an increase in the number of spiny (Sladocera) and copepods (Copepoda) crustaceans. Studies of the species composi-tion, number and biomass of phytoplankton in a pond polluted with wastewater from a livestock enterprise estab-lished the predominance of euglena algae over other species in the reservoir, a significant increase in the number of blue-green (Cyanophyta) and diatom (Bacillariophyta) algae in biomass, the presence of small-celled flagellates with department of cryptophytic and bacterial-fungal accumulations, in contrast to a conditionally clean water body. A conclusion was drawn on the expediency of using the species composition of phytoplankton and zooplankton, as well as individual indicators of the chemical composition of water as criteria for assessing the ecological state of ponds located in the area of activity of livestock enterprises when polluted by sewage.

FEATURES OF THE HYDROBIOLOGICAL REGIME AND STRUCTURE OF ICHTHY-OFAUNA LAKES KARTAL AND KAGUL IN THE CONDITIONS OF FISHERIES USE OF RESERVOIRS

The results of hydrobiological monitoring of Danube lakes (Kagul and Kartal) are given. These lakes are currently used as reservoirs for growing commercial fish. For the study of phytoplankton, zooplankton, macrozoobentos and ichthyofauna, the material was collected in March, July and October 2019. The similarity of the species composition of phytoplankton between the two lakes was high, in March it was 73,0 % (according to the Serensen’s index), in July and October – 59,0 % and 86,0 % respectively. Quantitative indicators of phytoplankton of oz. Kagul and Kartal were almost no different in March and October. In July, biomass of fodder phytoplankton in oz. Kartal was an order of magnitude higher at 5303,676±2713,636 mg·m–3 than Kagul's 417,362±52,409 mg·m–3. The richest taxonomic composition of zooplankton was noted in July (16 taxa), the poorest was in October (8 taxa). In both lakes, the basis of the number and biomass of zooplankton was formed by Rotatoria and Copepoda. In the spring, the greater average biomass of fodder zooplankton (863,58±593,25 mg·m–3) is noted in the oz. Kartal, in summer and autumn was in oz. Kagul 8152,58±2257,41 mg·m–3 and 5609,25±1995,85 mg·m–3 respectively. As part of the macrozoobentos of the studied lakes, oligohetes and two-winged insects were the most massive. The average biomass of fodder benthos in the oz. Kagul (13,816 g∙m–2) was 2,2 times larger than in oz. Kartal (6,386 g∙m–2). Its basis (89,7 % in Kagul, 99,8 % in Kartal) was formed by oligohetes and larvae of two-winged insects. The species diversity of Lake Kartal fish in 2019 was represented by 32 species of fish. 4 species from this list are invasion species: amur chebachok, silver crucian carp, sunny fish, rotan head. It is established that a significant biomass of small short-cyclic species of fish in the lake is not mastered. In these conditions, the stocking of the lake by large aboriginal predators can have a good positive effect, since there is a significant unused fodder base in the reservoir.

A novel approach for discovering correlations between elemental and molecular composition using laser-based spectroscopic techniques.

Modern analytical techniques, including laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy, yield multidimensional data, which are most efficiently used in conjunction with chemometric techniques, including multi-block algorithms. In this study, we use several algorithms for the processing of laser-induced breakdown and Raman spectra of zooplankton organisms, which are found to accumulate lithium for an unknown reason. Correlations between elemental and molecular composition of zooplankton have been found. We studied 29 samples: crustaceans, arrow worms, and sea snails. The obtained spectra were examined by principal component analysis (PCA), non-negative matrix factorization (NMF), consensus PCA (CPCA), and analysis of common components and specific weights (CCSWA, or ComDim). LIBS spectra are more sensitive towards taxonometric differences than Raman spectra. All the algorithms gave similar results, although still differing in details. Data fusion revealed a number of relationships, including the correlation of Li with potassium (R = 0.83, n = 14), with Raman bands of carotenoids (R = 0.89, n = 11) and tryptophan (R = 0.94, n = 9). The correlations were most pronounced in light-coloured parts of the inhomogeneous biological material. Ratios of fatty acids are associated with Li concentration if above 200 mg kg-1. Valine is also related to the Li accumulation. Thus, it is shown that the combination of LIBS and Raman spectroscopy, followed by appropriate mathematical treatment, is a convenient tool for comprehensive studies of environmental objects.

Сукцессии зоопланктона малых мелководных озер после проведения мероприятий по экореабилитации

The need for eco-rehabilitation of water bodies affected by strong anthropogenic influence increases greatly with an increase in the area of urbanized territories. The effectiveness of such measures may be evaluated by studying successions of hydrobiont communities in a rehabilitated water body. In 2017, actions were taken to rehabilitate the Lebyazhye Lakes system (Kazan), which included deepening the basins of Bolshoe Lebyazhye Lake and Svetloe Lebyazhye Lake to 4 m, isolating the bed of future basins with bentonite mats, supplying water from Izumrudnoye Lake through a pressure conduit, filling the lakes with water, and improvement of the shores. Then, in 2018–2021, zooplankton indicators of these lakes were studied and models of its food webs were proposed. After the work was completed, the lakes were successfully colonized by zooplankton: in 2018, the identified assemblage included 106 species, with 51 species of rotifers (46%), 36 species of cladocerans (34%) and 19 species of copepods (18%). However, in the absence of higher aquatic plants, a strong “bloom” of water was observed with the predominance of blue-green algae in the composition of phytoplankton and low water transparency. In 2020–2021, the zooplankton composition showed a decrease in the total number of species and the number of species in the sample, a decrease in the production in communities, a change in the composition of dominant species towards representatives of the genus Brachionus, and an increase in the variability of biomass dynamics. All these suggested instability and the gradual simplification of the community. In 2021, obligate predators disappeared from one of the lakes, which led to the shortening of food chains.

Zooplankton composition and abundance from Nideban Reservoir, Udgir Dist. Latur

Zooplankton composition and abundance from Nideban Reservoir, Udgir Dist. Latur

Zooplankton composition and abundance from Nideban Reservoir, Udgir Dist. Latur

Zooplanktons are the microscope free swimming organisms of aquatic system. There are represented by a wide array of taxonomic groups of which the members belonging to protozoa, Rotifera, Cladocera and Copepoda are most common and often dominate the entire communities. They have many remarkable features which hamper their predation by higher organisms. The members of Zooplankton community are important for their role in trophic dynamics, energy transfer in the aquatic ecosystem. They provide food for fishes in the water bodies and play a major role in the fish production. The zooplankton community was studied by monthly samples taken from Oct. 2018 to Feb. 2019. The reservoir water is used for agriculture and fishery activities.

Acoustic correction factor estimate for compensating vertical diel migration of small pelagics

Differences in acoustic estimates of small pelagic fish biomass, due to data acquisition during daytime and nighttime surveys, have been recognized for many years as a problem in acoustic surveys. In the absence of a single rule for all species and for all locations, some expert groups identified specific time intervals for acoustic data acquisition in relation to the schooling behavior of the target species. In the Mediterranean Sea, the research groups working in the MEDIAS (Mediterranean International Acoustic Survey) agreed on the importance that acoustic sampling are conducted only during day-time. Only when available time does not permit to complete the survey during daytime, data collection might be extended. In this case, working on data collected during both daytime and nighttime, a bias may occur in the biomass estimates. In order to evaluate and correct such bias, specific experiments were performed in some geographical sub-areas of the Mediterranean Sea. The data analysis allowed the estimation of a mean correction factor for the Strait of Sicily, where five surveys were carried out in different years. The correction factor was estimated also for the Adriatic Sea, Tyrrhenian Sea and Northern Spain; the observed variability among areas highlighted the importance of the spatial and temporal coverage of the survey area in order to obtain reliable estimates of the correction factor. Further studies are necessary to improve the interpretation of the obtained estimates in relation to area-related peculiarities such as zooplankton composition and abundance along with small pelagic fish community structure.

Distribution and diversity of gelatinous zooplankton in the southern South China Sea

Although gelatinous zooplankton are widely distributed in many ocean ecosystems, they have been understudied due to their fragility nature, difficulties to sample or handle and a lack of expertise. This study gives an insight into the distribution and diversity of gelatinous species in the Southern South China Sea. Species composition, distribution and abundance of gelatinous zooplankton were investigated along the East Coast of Peninsular Malaysia. A total of 37 species were recorded from 10 locations along 4 transects at 5.10° N and 6.80° N extending from 103.2° E to 105.3° E in August 2016. Seven medusae, six siphonophores, four appendicularians, six chaetognaths, six salps, four doliolids and four pteropods were identified from the study area. Appendicularia with 201 ind/m3 was found to be the most dominant taxa recorded, followed by chaetognaths with 197 ind/m3. Scyphomedusae were the least represented group in the study, with an abundance of 8 ind/m3. Stations near the inshore region show higher abundance and diversity of gelatinous zooplankton compared to offshore regions. The evenness index between stations revealed that the gelatinous zooplankton were evenly distributed. According to Principal Component Analysis (PCA), the diversity and distribution of gelatinous zooplankton are driven by depth and temperature.

Study of physiological and biophysical processes of degradation of components of the Aral Sea biosystem

The article considers the results of practical measures to solve environmental problems arising from the fall in sea level and the components of the Aral Sea biosystem, and approaches to their development. A complete literature review of previously planned and identified new environmental problems and practical measures to address the degradation of components of the Aral Sea biosystem is carried out. The research methodology included field studies on changes in the hydrophysical, hydrochemical and hydrobiological state of the landscape, as well as the study of the reference zones of the landscapes and subsequent comparisons with the results of satellite images. The scientific study examines the characteristics of their current state against the background of progressive salinization of the Aral Sea by studying the nature of the horizontal and vertical distribution of bacterio-, phyto- and zooplankton, measuring the concentrations of Chl-а and pheopigments,and determining the taxonomic composition of phyto-and zooplankton. The novelty of the research work for the first time, the consequences of the implementation of new materials, performed scientific research, characterizing the period of development of the problem in 2010-2020, are determined. The results of scientific research can be used for specialists-hydrologists, biologists, ecologists in the formulation of research and scientific and practical work in various landscape zones of the island region, in the preparation of environmental forecasts for the future development of this process. Key words:Aral Sea, phytoplankton, Chl-a, ecological crisis, island degradation, biosystem components, geographical forecast, landscape.

Specific Features of the Species Composition of Zooplankton in Mineralized Waterbodies of Specially Protected Natural Territories in the Ulug-Khem Depression (Republic of Tuva)

Specific Features of the Species Composition of Zooplankton in Mineralized Waterbodies of Specially Protected Natural Territories in the Ulug-Khem Depression (Republic of Tuva)

ФОРМИРОВАНИЕ ЗООПЛАНКТОНА БОГУЧАНСКОГО ВОДОХРАНИЛИЩА В ПЕРИОД ЕГО ЗАПОЛНЕНИЯ

For the first time, we present the materials of the spatial distribution of qualitative and quantitative indicators of zooplankton in the first year of top water level (TWL) in the Boguchany Reservoir. We indicate the dynamics of the formation of the zooplankton community in the Upper section of the reservoir during its filling (from 2013 to 2015). The Irkutsk, Bratsk, and Ust-Ilimsk reservoirs influence the composition and structure of zooplankton in the Boguchany Reservoir that closes the cascade of the Angara HPPs, and there is a great similarity of the crustacean and rotifer fauna with the upstream artificial reservoirs. During the study period (from 2013 to 2017), the plankton fauna included 84 species from 49 genera and 23 families. The horizontal distribution of quantitative indicators throughout the water area of the reservoir had a mosaic pattern. The relative and absolute proportion of rotifers in the composition of zooplankton decreased from the Upper section to the Lower one, and the dominance of crustaceans was opposite. Due to this, the maximum number (129±97.8 thou ind./m3) of zooplankton was recorded in the Upper section, and the biomass (2080±676 mg/m3) – in the Lower section. The obtained unique data on the composition, structure and quantitative development of zooplankton in the Boguchany Reservoir during its formation and filling are important for further monitoring of its state, including the assessment of the feeding of planktonophagous fish and juvenilefish.