Distribution Of Zooplankton Research Articles

Influence of meromixia on the distribution of zoobenthos and zooplankton in the salt soda lake Doroninskoe

Meromictic soda lakes are considered models of reservoirs of the Early Proterozoic. Lake Doroninskoe belongs to a rare type of moderately salty alkaline soda lake with a carbonate type of salinity and pronounced meromixia. Studies and publications on the zoobenthos of the lake are rare. In 2005–2007, studies of zoobenthos and zooplankton of the lake were carried out. Meromixia of the water column caused the stable presence of zooplankton only in a layer up to 4 m. The distribution of the taxonomic abundance, quantitative development and structure of zoobenthos in the lake corresponds to the stratification of the water column into mixolimnion, chemocline and monimolimnion. Bottom biotopes and water column layers deeper than 4 m were uninhabited, which is probably due to the lack of oxygen and high hydrogen sulphide content in the bottom water layers due to meromixia. A similar distribution of zooplankton in Lake Doroninskoe and its mesocosm model was revealed.

A subsurface eddy associated with a submarine canyon increases availability and delivery of simulated Antarctic krill to penguin foraging regions

The distribution of marine zooplankton depends on both ocean currents and swimming behavior. Many zooplankton perform diel vertical migration (DVM) between the surface and subsurface, which can have different current regimes. If concentration mechanisms, such as fronts or eddies, are present in the subsurface, they may impact zooplankton near-surface distributions when they migrate to near-surface waters. A subsurface, retentive eddy within Palmer Deep Canyon (PDC), a submarine canyon along the West Antarctic Peninsula (WAP), retains diurnal vertically migrating zooplankton in previous model simulations. Here, we tested the hypothesis that the presence of the PDC and its associated subsurface eddy increases the availability and delivery of simulated Antarctic krill to nearby penguin foraging regions with model simulations over a single austral summer. We found that the availability and delivery rates of simulated krill to penguin foraging areas adjacent to PDC were greater when the PDC was present compared to when PDC was absent, and when DVM was deepest. These results suggest that the eddy has potential to enhance krill availability to upper trophic level predators and suggests that retention may play a significant role in resource availability for predators in other similar systems along the WAP and in other systems with sustained subsurface eddies.

芡实分区刈割试验对陈瑶湖后生浮游动物群落结构的影响

陈瑶湖流域是长江中下游重要的水禽省级自然保护区，近年来随着农业的发展，湖区存在芡实种植过密，汛期影响行洪的隐患，对湖区的水生态系统结构与功能的稳定性造成严重影响。为研究芡实分区刈割试验对陈瑶湖后生浮游动物群落结构的影响，于2019年8月期间对陈瑶湖后生浮游动物进行调查。共鉴定出后生浮游动物15科22属40种，其中轮虫12属26种，枝角类8属11种，桡足类2属3种，群落结构主要以轮虫为主，后生浮游动物种类分布时空上无显著差异（P>0.05）。共发现优势种8属10种，分别为萼花臂尾轮虫（Brachionus calyciflorus）、角突臂尾轮虫（Brachionus angularis）、剪形臂尾轮虫（Brachionus forficula）、螺形龟甲轮虫（Keratella cochlearis）、囊形单趾轮虫（Monostyla bulla）、蹄形腔轮虫（Lecane ungulata）、针簇多肢轮虫（Polyarthra trigla）、迈氏三肢轮虫（Filinia maior）、长额象鼻溞（Bosmina longirostris）和广布中剑水蚤（Mesocyclops leuckarti）。后生浮游动物密度和生物量平均值分别为（1681.49±205.73）个/L和（7.8±1.52） mg/L，密度和生物量峰值均出现在初期的未刈割区，最低值均出现在后期的河道。后生浮游动物密度的空间分布呈现未刈割区 > 刈割区 > 河道的特征，时间变化呈现刈割初期 > 前期 > 中期 > 后期的趋势，生物量的时空变化趋势与密度一致。ShannonWiener多样性指数、Margalef丰富度指数和Pielou均匀度指数变化范围分别为1.67-3.42、1.64-3.57和0.41-1.13.统计分析结果表明TN、TP、NH₄⁺-N、Chl.a、EC和SD是影响浮游动物群落结构的主要因子。综合生物和理化指标判别陈瑶湖水体已处于中污染状态；营养状态参数结果表明，陈瑶湖已处于中度富营养状态。;Chenyao Lake basin is an important waterfowl Provincial Nature Reserve in the middle and lower reaches of the Yangtze River,In recent years, with the development of agriculture, there are some hidden dangers in the lake area, such as planting too much Euryale ferox, affecting the flood discharge in flood season, and seriously affecting the stability of the structure and function of the aquatic ecosystem in the lake area.In order to study the effects of mowing experiment in different areas of Euryale ferox on the community structure of metazoan zooplankton in Chenyao Lake, the metazoan zooplankton was investigated in August 2019. A total of 40 species of metazooplankton belonging to 22 genera, 15 families were identified. Among them, 26 species belong to 12 genera of Rotifer, 11 species belong to 8 genera of Cladocera and 3 species belong to 2 genera of Copepoda,The community structure was dominated by Rotifers,There was no significant difference in the spatial and temporal distribution of metazoan zooplankton (P>0.05). A total of 8 genera and 10 species of dominant species were found,including Brachionus calyciflorus, B. angularis, B. forficula,Keratella cochlearis, Monostyla bulla, Lecane ungulata, Polyarthra trigla, Filinia maior, Bosmina longirostris and Mesocyclops leuckarti. The average animal density and biomass of metazoan zooplankton were (1681.49 +205.73) ind/L and (7.8+1.52) mg/L respectively,The peak values of density and biomass appeared in the initial stage of no mowing area and the lowest values all appeared in the later stage of channel.The spatial distribution of the density of metazoan zooplankton showed the characteristics of no mowing area > mowing area > river channel, while the temporal change trend was in the initial stage > early stage > middle stage > late stage. The trend of spatial and temporal variation in biomass and density was consistent. The Shannon Wiener diversity index, Margalef richness index and Pielou evenness index of the metazoan zooplankton community were 1.67-3.42, 1.64-3.57 and 0.41-1.13, respectively. The results of Redundancy analysis and Pearson correlation analysis showed that TN, TP, NH₄⁺-N, Chl a, EC and SD were the main factors affecting the community structure of zooplankton. According to the comprehensive biological and physical and chemical indicators, Chenyao Lake was in a state of moderate pollution. The results of nutritional parameters indicated that Chenyao Lake was in a state of moderate eutrophication.

Size-selective predation by three estuarine zooplanktivorous fish species

Context Zooplanktivorous fish are a key link between abundant zooplankton and higher trophic levels but the foraging behaviour of zooplanktivorous fish is not fully understood. Selective feeding behaviours have been observed, with many species of planktivorous fish targeting certain species and sizes of zooplankton for prey. However, why certain size classes of zooplankton are preferred remains unclear. Aim This study investigated prey selection by three zooplanktivorous fish species through the lens of optimal foraging theory. Methods We assessed the size structure of zooplankton in the environment and compared this with the size distribution of zooplankton in gut contents from three zooplanktivorous fish. Key results The targeted prey size of Atypichthys strigatus and Scorpis lineolata aligns with the prey size classes in the environment that contain the highest overall biomass. Trachurus novaezelandiae showed little evidence of targeting these size classes. Conclusions These prey sizes therefore represent the most efficient prey to target because the return on foraging effort is greatest. By contrast, T. novaezelandiae showed only an underselection of large and small prey. Implications By incorporating this information on this key trophic link between zooplankton and fish, ecosystem models could better resolve the size dependant predation, particularly in size-based models.

Hydrobiological Studies and Zooplankton Diversity of Sagar Talao District Bhandara Maharashtra

Air, water, land, flora and fauna are the natural resources of any ecosystem. Water is very important for existence of life. It is the medium, which gave birth to first primitive living molecules,as the living organisms found in water are reliable indicators of water quality. The distribution and diversity of zooplankton in aquatic ecosystem depends mainly on the physic-chemical properties of water. For the study of water quality, the limnological observation is needed. Most of the organisms are being extensively used as indicators of water pollution. The biological indicators provide a direct clue and quick information of the aquatic systems. In present study, the zooplankton of the Sagar Talao was studied for a period of one year with its physico chemical factors. In present study total of 09 species of zooplanktons belonging to Rotifera, Ostracoda Cladocera, Copepoda, were present..

Mesozooplankton community distribution on the Agulhas Bank in autumn: Size structure and production

The Agulhas Bank on the tip of southern Africa, like other shelf seas, is a relatively productive environment which plays a crucial role in the biology and success of many commercially valuable fish species. Fish and their larvae depend on zooplankton to feed on but, despite their importance, little is known about zooplankton distribution and production on the Agulhas Bank. Here we present results from a survey conducted in March 2019 on the East and Central Agulhas Bank, investigating mesozooplankton abundance, biovolume, taxonomic composition, size distribution (normalised biovolume size spectrum (NBSS) approach) and secondary production. A clear cross-shore gradient was observed with the inner-shelf having higher abundance and biovolume of mesozooplankton dominated by small-size organisms, most likely mirroring higher overall productivity of the coastal waters, while the outer-shelf showed the opposite trend (i.e., low abundance and biovolume; shallow NBSS slopes). This general pattern on the outer-shelf was, however, disturbed in one location (between 24 and 25°E) with a distinguishable mesozooplankton community, most likely linked to the passage of a meander on the inshore side of the Agulhas Current. The Central Agulhas Bank was typified by high mesozooplankton biomass (∼4 g C m-2), comparable to upwelling areas and dominated by copepods and doliolids. High copepod biomass was observed in this region before and was linked to a feature called the “Cold Ridge”. However, during our survey, no such ridge was observed. The mixed layer depth was relatively deep (>20 m) and high Chlorophyll a concentration was measured at depth, despite low net primary production rates. We suggest that this region is prone to other mechanisms such as retention due to cyclonic circulation or processes injecting nutrients in the upper mixed layer that require further research. Secondary production on the Agulhas Bank was in the same range as other shelf seas (0.03–1.55 g C m-2 d-1) and was correlated with mesozooplankton biomass. The comparison of primary and secondary production, measured simultaneously, suggested that mesozooplankton exert a significant control on net primary production, and can, in some areas, be food-limited (e.g., Central Agulhas Bank and inshore waters).

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.

Temporal and Spatial Distribution of Zooplankton Inhabiting Sandy and Muddy Shore Habitats at Jazan Coastal Area

Few studies were made about zooplankton distribution in Jazan coastal area. The present study dealt with the identification of zooplankton at the sandy shore (AlSalwa coast) and mangrove muddy shore (Turfa peninsula) at the Almarjan coast. Species richness and population density at different seasons were determined for both study areas between May 2016-April 2017. Conductivity, pH, water temperature, and salinity were measured. The relationship between water characters and the seasonal abundance of zooplankton seasons was examined through regression analysis. Ciliates, Rotifers, Nauplius larva, Gammarus sp., Veliger larva, Nematodes, Planaria, Copepods, and Kinorhyncha were recorded for both study areas. The highest species richness and population density were recorded during the summer season for Almarjan sandy shore and Turfa peninsula mangrove. Ciliates were the most abundant zooplankton on the sandy shore, while Kinorhyncha was the least abundant. The zooplankton Nematode was the most abundant at the Turfa Peninsula mangrove, whereas Gnathostomulida was the least abundant. Conductivity, salinity, and water temperature showed a significant regression relationship (P<0.05) with zooplankton abundance. Data was discussed to highlight the role of zooplankton abundance in the mangrove and sandy shore ecosystem.

Composition, Density and Spatial Distribution of Zooplankton in Inner Ambon Bay, Indonesia

Inner Ambon Bay is part of Ambon Bay; it is semi-closed area and a small pelagic fish fishing ground, especially anchovy. The anchovy is a zooplankton predator; therefore the existence of anchovy is affected by the abundance of zooplankton. The aims of the research are to obtain information on the composition, density, and spatial distribution of the zooplankton in these waters. Data of zooplankton composition were obtained from sampling by using plankton net at ten observation stations. Meanwhile, data of densities were collected using a scientific hydroacoustic system, BioSonic DTX supported with split-beam technology, on six parallel transect lines and one cross-parallel transect line. Geostatistical analyses technique was used to describe horizontal distributions of zooplankton, and vertical distributions pattern were plot in the graphs. The result shows that the zooplankton community is dominated by Copepod and meroplankton. The highest average density was found in August (9393 ind./m2),while the lowest density was in June (903 ind./m2).

Pelagic tunicates (Appendicularia and Thaliacea) of Sri Lanka: two first records with an annotated checklist.

In broadening the understanding of the diversity, distribution and seasonality of gelatinous zooplankton of Sri Lanka, a survey ('Waya-jel-Survey) was carried out in coastal waters of the country from 2016 to 2020, and the collected specimens of pelagic tunicates were taxonomically identified. Further, a comprehensive literature survey was conducted and the previous records on the occurrences of pelagic tunicates within the exclusive economic zone of Sri Lanka were cross-checked and listed in developing the first-ever annotated checklist. Among the samples collected in this study, Pyrostremma spinosum and Thalia sibogae were reported for the first time from Sri Lankan waters while two more thaliaceans, i.e., Doliolum denticulatum and Pegea confoederata, and six appendicularians, i.e., Fritillaria borealis sargassi, F. formica digitata, Oikopleura cophocerca, O. fusiformis, O. longicauda, and O. rufescens were re-recorded. In total, forty species (including two subspecies) in 19 genera, belonging to five families from four orders of the classes Appendicularia (n = 17 species) and Thaliacea (n = 23 species) were reported to be inhabited in Sri Lankan waters. Most of the records were from the Laccadive Sea region while the majority of the species have been reported during the northwest monsoon (December to February) period.

Environmental conditions drive zooplankton community structure in the epipelagic oceanic water of the southern Gulf of Mexico: A molecular approach.

Zooplankton plays a pivotal role in sustaining the majority of marine ecosystems. The distribution patterns and diversity of zooplankton provide key information for understanding the functioning of these ecosystems. Nevertheless, due to the numerous cryptic and sibling species and the lack of diagnostic characteristics for early developmental stages, the identification of the global-to-local patterns of zooplankton biodiversity and biogeography remains challenging in different research fields. The spatial and temporal changes in the zooplankton community in the open waters of the southern Gulf of Mexico were assessed using metabarcoding analysis of the V9 region of 18S rRNA and mitochondrial cytochrome oxidase c subunit I (COI). Additionally, a multiscale analysis was implemented to evaluate which environmental predictors may explain the variability in the structure of the zooplankton community. Our findings suggest that the synergistic effects of dissolved oxygen concentration, temperature, and longitude (intended as a proxy for still unidentified predictors) may explain both spatial and temporal zooplankton variability even with low contribution. Furthermore, the zooplankton distribution probably reflects the coexistence of three heterogeneous ecoregions and a bio-physical partitioning of the studied area. Finally, some taxa were either exclusive or predominant with either 18S or COI markers. This may suggest that comprehensive assessments of the zooplankton community may be more accurately met by the use of multilocus approaches.

Distribution and species composition of zooplankton (rotifers and crustaceans) in the Basin of the Middle Volga River, Russia.

BackgroundThe presented dataset contains information on the distribution and species composition of zooplankton (rotifers and crustaceans) registered in the Basin of the Middle Volga River, Russia. The studies have been performed in the Kuibyshev Reservoir (Samara Oblast and the Republic of Tatarstan), the Saratov Reservoir (Samara Oblast), in several lakes (Raifskoe, Gniloe, Krugloe and Lenevo) in the Volzhsko-Kamsky State Biosphere Reserve (Republic of Tatarstan) and in Lake Aslikul, one of the largest lakes of the Middle Volga River Basin, located in the Asly-Kul Natural Park (Republic of Bashkortostan). The hydrobiological data were obtained and published from 1957 to 2020. In total, the dataset includes 5141 records of 111 zooplankton species (including 17 subspecies), belonging to 45 genera. These are mainly native species - 98.5%, while the naturalised, including invasive species, accounts for less than 1.5%.New informationA total of 5141 records have been published on the taxonomic diversity and occurrence of zooplankton (rotifers and crustaceans) in the Middle Volga River Basin. Each record includes information about the place and date of finding the specimen, its taxonomy, occurrence and abundance and the collector. If the information about the find has been published, a link to the corresponding reference is provided. The presented dataset supplements the data on the distribution of zooplankton species in the European part of Russia. Data on zooplankton in the Middle Volga River Basin are published for the first time.

Investigation of the ecology of winter plankton of Lake Baikal using complex instrumental methods

Aim . The continuous monitoring of changes in ecosystems must be carried out in connection with global climate changes that affect the state of water bodies. Remote sensing methods have many advantages as a promising method for monitoring biocenoses in large water bodies. We carried out a comprehensive study comparing the results obtained using the latest instruments and methods to expand their further application to the continuous monitoring of water bodies. Material and Methods . The field research was undertaken using hydroacoustic sensors, submersible holographic camera and high‐resolution thermal sensors in addition to the classical methods of studying the zooplankton ecology – the Juday net and CTD probe. Water temperature, chlorophyll, photosynthetically active radiation and other parameters were measured with an AAQ‐Rinko probe. We provided data for one vertical up to a depth of 100 m. Results . The main components of mesozooplankton during the ice period are different age stages of the endemic crustacean Epischura baikalensis Sars 1900 and several rotifer species. The article discusses the heterogeneity of the environment and the distribution of plankton detected by various instruments. Conclusion . The experimental results obtained with the help of a set of devices show that the distribution of zooplankton is very strongly dependent on the physical parameters of the environment. The use of remote sensing methods is an important step towards the automation of basic monitoring of the ecosystem of Lake Baikal and other water bodies. The obtained field data will make it possible to further improve the pattern recognition algorithm in the software of the holographic installation for the specific conditions of Lake Baikal. The results of the vertical distribution and migrations of zooplankton in connection with environmental parameters are assumed to be processed using mathematical modeling methods.

Spatial variation and transport of abundant copepod taxa in the southern Gulf of St. Lawrence in autumn

Abstract The spatial distribution of zooplankton is influenced by complex interactions among population dynamics, vertical positioning and advection. We used empirical observations and particle tracking simulations to investigate variation in horizontal distribution of Calanus spp. and three neritic copepod taxa (Acartia spp., Pseudocalanus sp. and Temora longicornis) in the southern Gulf of St. Lawrence (sGSL) in October 2018. These copepods are potential prey for fish and the endangered North Atlantic right whale, Eubalaena glacialis. We quantified horizontal variation in abundance from a plankton survey, and obtained vertical distributions from a subset of locations and a process study conducted over ~1 day. Horizontal distributions of Calanus finmarchicus and Pseudocalanus sp. were widespread, whereas those of Calanus hyperboreus and C. glacialis were centred in the interior of the sGSL and those of Acartia spp. and T. longicornis were centred on the western side. Horizontal distributions of C. hyperboreus–C. glacialis and C. finmarchicus–Pseudocalanus sp. pairs were highly correlated. Contrasting distributions among C. finmarchicus and its congeners reflect interspecific differences in life history strategy and its interaction with ocean circulation. In autumn, a shift to increased current strength and flow-through circulation may lead to enhanced losses of Calanus spp. in the absence of upstream replenishment.

Autonomous Surface and Underwater Vehicles as Effective Ecosystem Monitoring and Research Platforms in the Arctic-The Glider Project.

Effective ocean management requires integrated and sustainable ocean observing systems enabling us to map and understand ecosystem properties and the effects of human activities. Autonomous subsurface and surface vehicles, here collectively referred to as “gliders”, are part of such ocean observing systems providing high spatiotemporal resolution. In this paper, we present some of the results achieved through the project “Unmanned ocean vehicles, a flexible and cost-efficient offshore monitoring and data management approach—GLIDER”. In this project, three autonomous surface and underwater vehicles were deployed along the Lofoten–Vesterålen (LoVe) shelf-slope-oceanic system, in Arctic Norway. The aim of this effort was to test whether gliders equipped with novel sensors could effectively perform ecosystem surveys by recording physical, biogeochemical, and biological data simultaneously. From March to September 2018, a period of high biological activity in the area, the gliders were able to record a set of environmental parameters, including temperature, salinity, and oxygen, map the spatiotemporal distribution of zooplankton, and record cetacean vocalizations and anthropogenic noise. A subset of these parameters was effectively employed in near-real-time data assimilative ocean circulation models, improving their local predictive skills. The results presented here demonstrate that autonomous gliders can be effective long-term, remote, noninvasive ecosystem monitoring and research platforms capable of operating in high-latitude marine ecosystems. Accordingly, these platforms can record high-quality baseline environmental data in areas where extractive activities are planned and provide much-needed information for operational and management purposes.

Biodiversity and Distribution of Zooplankton and Macrobenthic Invertebrates Communities in Lake Nasser, Egypt

Biodiversity and Distribution of Zooplankton and Macrobenthic Invertebrates Communities in Lake Nasser, Egypt

Seasonal Composition and Diversity of Zooplankton in Pichavaram Mangrove Forest, Southeast Coast of India

In the present study, the zooplankton diversity and distribution was studied in relation to seasonal variation of environmental parameters in the Pichavaram mangrove forest. Samples were seasonally collected (i.e., post-monsoon: January-2018 and monsoon: December-2018) from seven stations. A total of 48 zooplankton species belonging to two groups macro-zooplankton and micro-zooplankton were recorded during this study. A total of 48 species of zooplankton belonging to different groups were identified. Copepod was found to be the most dominant group and it contributed more than 50% of the total zooplankton collected in this study. The maximum number of zooplankton species (35) and diversity value (H’) 3.867 was recorded in the stations near coastal zone (P-7) during summer and minimum species number (24) and maximum species richness (d) 7.652 was recorded in stations near to freshwater zone (P-2) during monsoon. The species evenness (J') 0.866 was also recorded maximum at stations near river mouth (P-7). BIO-ENV (Biota-Environmental matching) and CCA results confirmed that the environmental parameters such as Temperature, Salinity, Dissolved Oxygen, Silicate, Chlorophyll, Primary Productivity, Total Biomass and Phaeopigments as the most influencing environmental parameters, which regulates zooplankton assemblage. The results of present study help to develop an understanding on the zooplankton distribution in mangrove forests, which will form a reliable tool in bio-monitoring studies

Zooglider‐measured association of zooplankton with the fine‐scale vertical prey field

AbstractWe use Zooglider, a low‐power optical zooplankton‐sensing glider, to test the covariability of the fine‐scale vertical distributions of six omnivorous zooplankton taxa with three different representations of their potential prey field: small suspended particles (equivalent circular diameter [ECD] between 0.25 and 0.45 mm), marine snow (ECD ≥ 0.45 mm), and chlorophyll a (Chl a), in the San Diego Trough. All three prey fields tend to be highly correlated from 100 m to the depth of the subsurface Chl a maximum layer (SCML), while correlations between the prey fields are weaker or nonexistent from the SCML to the surface. An index of spatial overlap (Local Index of Collocation) showed stronger overlap of zooplankton with marine snow or small particles than with Chl a in most cases. Moreover, generalized additive models revealed marine snow distributions or small particles as the primary explanatory variable, by percent deviance explained, for all zooplankton taxa tested. Chl a distributions were a secondary explanatory variable for four of the six taxa tested (small copepods, appendicularia‐Fritillaria, and both night and day large copepods), and an insignificant explanatory variable for the remaining two (appendicularia‐others and large protists). The distributions of suspended particles, during our year‐round study in the San Diego Trough, were more informative for explaining distributions of omnivorous zooplankton than Chl a alone.

Zooplankton of the low-oxygen waters of Bahia Callao (Central Peru) - with special reference to the reproductive activity of the copepod Acartia tonsa

Zooplankton distribution in the Bahia Callao, a low oxygen bay in Central Peru, was studied during surveys in March (austral summer) and September (austral spring) 2006. In March temperature was higher, but oxygen concentrations were much lower, especially near the sea floor. Zooplankton abundance at 14 repeated stations (March/September = 457/2356 ind. m−3), taxa number (35/97), and community composition changed drastically, but Acartia tonsa was dominant during both surveys. In contrast, abundance of meroplanktonic larvae did not change.The reproductive activity of A. tonsa was studied bi-weekly from November 2005 to August 2007 at a fixed station close to shore (9 m water depth). Population egg production rate ranged from 0.9 to 12.6 eggs female−1d−1 and was significantly related to Chlorophyll a, temperature, and dissolved oxygen. Individual clutch size ranged from 1 to 43 eggs. Egg hatching rate varied from 3.4 to 100%; the lowest values were associated with very low concentrations of dissolved oxygen in the surface layer and red tides. In feeding experiments at saturated oxygen concentrations >30 eggs female−1d−1 were produced, indicating continuous inhibition of egg production in the field. Oceanographic data demonstrate that the bay, and probably also the adjacent shelves, are exposed to frequent environmental changes, which challenge the survival and production of zooplankton and fish. The relationship between seemingly adverse environmental conditions and high biological productivity still needs to be understood.

Zooplankton Distribution in the Middle Volga River Reservoirs in Areas Under the Influence of Tributaries

Zooplankton Distribution in the Middle Volga River Reservoirs in Areas Under the Influence of Tributaries