High Zooplankton Abundance Research Articles

Mesozooplankton community variability in the Seychelles–Chagos Thermocline Ridge in the western Indian Ocean

The Seychelles–Chagos Thermocline Ridge (SCTR), is formed by strong air-ocean interactions that cause open-ocean upwelling in the western Indian Ocean (WIO). The SCTR enhances upper-ocean nutrient levels, which promotes phytoplankton growth, leading to high zooplankton abundance and a strong nursery habitat for fish. To evaluate the evidence of significant upwelling in the SCTR, upwelling indicators associated with variability in the mesozooplankton community and other environmental factors were compared between SCTR and non-SCTR regions. We investigated mesozooplankton and physicochemical factors using multiple opening/closing net and environmental sensing system at three epipelagic (0–200 m) depth strata along 67°E (16°S–5°N) in the central and WIO. Survey stations were clustered into six environmental regions, including SCTR regions (I and II) and non-SCTR regions of the Southwest Monsoon Currents (SMC), Cold-Core Eddy (CCE), and the South Equatorial Current regions North(N) and South(S). Higher abundances of mesozooplankton were observed in the surface mixed layer (SML) (mean: 1275 inds. m−3). In the SML, Noctiluca scintillans were distributed ubiquitously, regions in the CCE were significantly different (p < 0.05). The middle layer (ML) of SCTR-II, there were significant peaks (p < 0.05) in abundance (962 inds. m−3) with significantly lower temperatures (mean: 17.7°C), and N. scintillans and Oncaea copepodites were numerically dominant. At the non-SCTR sites in the ML, there were significantly lower abundances, with a dominance of copepodites of Scolecithricella and Scolecithrix. Mesozooplankton abundance (mean: 57 inds. m−3) was significantly variable in the bottom layer (BL). The BL was dominated by either ostracods or Scolecithricella copepodites. Opportunistic copepods such as Oncaea spp. peaked in upwelled waters due to enhanced nutrients and associated high chlorophyll-a concentrations. A principal component analysis of the environmental factors and numerically dominant mesozooplankton groups showed that the dominant groups were affected by significantly elevated temperatures (25.3–29.8°C, p < 0.05) in the SML and by high salinity (34.8–35.7) in the ML. In the BL, there was no significant association between the mesozooplankton groups with any environmental factors. These results suggest the middle layer of the SCTR acts as a hotspot for opportunistic Oncaea spp., and is associated with open-ocean upwelling in the western Indian Ocean.

Variation in larval Gulf Menhaden diet, growth and condition during an atypical winter freshwater-discharge event in the northern Gulf of Mexico

In January 2016, historic levels of rainfall in the upper Mississippi River Basin prompted the earliest opening of the Bonnet Carré Spillway, a water control structure on the Mississippi River that diverts flood-stage river water through an alternate pathway (Lake Pontchartrain) into the northern Gulf of Mexico. This unprecedented winter opening of the spillway coincided with the spawning season and larval ingress period for Gulf Menhaden, a forage fish species that supports the largest commercial fishery in the region. Oceanographic observations and plankton samples were collected in the Mississippi Bight region shortly after the Bonnet Carré Spillway winter opening to examine the impacts on larval Gulf Menhaden feeding, growth and condition. Three distinct water masses were identified based on temperature, salinity, and particle scattering (proxy for turbidity) characteristics. Larval Gulf Menhaden with the highest growth rates and body condition were collected in a water mass defined by relatively high temperature and salinity and relatively low turbidity and zooplankton (prey) abundance. In contrast, larvae with the slowest growth rates and poor body condition were collected in a water mass with the highest zooplankton abundance, but also highest turbidity and lowest temperature and salinity. This water mass was nearest the diversion outflow and most impacted by the spillway opening. Our results indicate that the anomalous freshwater discharge event resulted in hydrographic conditions that diminished otherwise favorable larval fish foraging habitat with abundant zooplankton prey. These findings suggest that the recent trend of Bonnet Carré Spillway openings may result in negative consequences for larval fish survival and subsequent fishery recruitment.

A Study on Seasonal Variation in Zooplankton Abundance in Kadasgatti Minor Irrigation Tank of Bailhongal Taluk, Belagavi District, Karnataka State, INDIA.

Objectives: A study on seasonal variation in zooplankton community was undertaken to evaluate the present status of water quality at Kadasgatti minor irrigation tank (MIT) located in the northern transitional zone of Belagavi district. Methods and Statistical Analysis: Water samples were collected from January 2017 to December 2017. Physico-chemical parameters and qualitative and quantitative analysis of zooplankton were carried out. Pearson correlation was calculated using SPSS, IBM Version 21 software to find out interrelationships between water quality and zooplankton groups. Findings: A total of 52 species of zooplanktons were recorded during the study period with a total zooplankton abundance of 14327 individuals with a relative abundance of 35.42%. Rotifera was the dominant group with 27 species, followed by Cladocera, Copepoda and Ostracoda. The highest zooplankton abundance was observed in summer while minimum in post-monsoon season. Copepoda was highest abundant group during the entire study period with its maximum abundance during winter and gradually declined and reached to its minimum in post-monsoon. The presence of eutrophic indicator species like Brachionus calyciflorus, Brachionus angularis, Filina longiseta suggests eutrophication of the tank. Novelty: The study provides baseline data on the present status of the water body indicating that, anthropogenic activities, agricultural runoff are the main cause of eutrophication. Sustainable and holistic conservational strategies have to be adopted to protect the water body. Keywords: Cladocera; Copepoda; Eutrophication; Rotifera; Seasonal variation; Zooplankton abundance

ОСОБЕННОСТИ СТРУКТУРЫ И ДИНАМИКИ ЗООПЛАНКТОНА ОЗЕРА НЕРО (ЯРОСЛАВСКАЯ ОБЛАСТЬ) В ПЕРИОД ПОТЕПЛЕНИЯ КЛИМАТА

Data on the abundance, biomass, and composition of the dominant complex of zooplankton in the shallow hypertrophic lake Nero (Yaroslavl region) from 2007 to 2017 are present. The spatiotemporal distribution of zooplankton is analyze. The high zooplankton species richness is characteristic of Lake Nero (&gt;100 species in the general list and up to 22–27 species in the sample). 2007 to 2011, a low amount of zooplankton was noted (&lt;37.9 thous. ind./m3 and 0.15 g/m3), with a relatively high proportion of copepods (up to 83%). Since 2012, the abundance of planktonic animals has increased (313 thous. ind./m3 and 1.20 g/m3). In 2007–2017 the composition of dominants remained close to that in previous years; small crustaceans (Bosmina longirostris, Chydorus sphaericus, Mesocyclops leuckarti), rotifers (genera Asplanchna, Brachionus, Keratella, Trichocerca and Anuraeopsis) dominated the zooplankton community. Rotifer-dominated communities (with a high abundance of thermophilic Brachionus diversicornis) formed during abnormally warm summers. Two species groups are determined: the first dominates in spring, early summer, and autumn, and the second in the second half of summer. The high abundance of zooplankton (&gt;5 mil. ind./m3 and 10 g/m3) is in the thickets of macrophytes, which is 8–9 times higher than in the open littoral and pelagic zones. In the western littoral zone, the low abundance of zooplankton (&lt;1 g/m3) may be associated with local pollution, high concentration of chlorophyll a, high phytoplankton biomass, represented by low food cyanobacteria. The center part and the adjacent open littoral zone differed in composition and abundance of dominant species from the southern bays occupied by macrophytes. The trophic status of the lake ecosystem in terms of zooplankton is hypertrophic since the 1980s. The abundance, composition and structure of the community in the long-term aspect are stable with interannual fluctuations common for a high-trophic shallow lake.

Geoenvironmental Implications and Biocenosis of Freshwater Lakes in the Arid Zone of East Kazakhstan

Steppe and semi-desert lakes of Central Asia represent unique and still poorly known aquatic ecosystems. The paper provides summaries of multi-proxy environmental and biological investigations of the previously unexplored ground of Sibe lakes in the naturally pristine zone of East Kazakhstan, and of their contributions to people. Data on the taxonomic composition of zooplankton and zoobenthos of these freshwater lacustrine basins are presented in terms of the species’ frequency of occurrence; the abundance of the aquatic biomass and the analyzed water geochemical variables insofar as they are dependent and correlative. The qualitative and quantitative records display variability in the biocenosis diversity due to the lakes’ geochemistry and hydrology differences—some lakes being oligotrophic and others being moderately trophic. In the latter case, the lakes characterized by an increased macrozoobenthos biomass are favourable for local ichthyofauna. Sapro-biological analysis reveals the predominance of β-saprobic species in the zooplankton composition pointing to slight or moderate pollution of surface waters due to natural biotic substances. This observation is in agreement with differences in the water quality of solitary lakes. The uneven distributions of benthic invertebrates (in terms of taxonomy and species populations) in the water bodies suggest specific hydro-ecological conditions that predetermine the structure of the lakes’ biocenosis. The littoral part of the lakes is characterized by the highest abundance of zooplankton and benthic fauna. The Sibe lakes are an example of an autonomous functioning of the lacustrine basins in the upland arid steppe zone, which is characterized by pronounced climate “continentality” and a high level of the sub-aquatic flora and fauna endemism. The present results are relevant to the understanding of the ecosystems’ dynamics and the modern anthropogenic impacts upon the pristine parkland-steppe landscapes of Central Asia, with implications for regional nature protection and sustainable eco-recreation.

Нетипичное вертикальное распределение зоопланктона и рыб в пелагиали оз. Севан в период летней стратификации

Previous studies in Lake Sevan during summer stratification have shown that the highest zooplankton abundance and biomass was found at the lower boundary of the epilimnion. At the same time, whitefish (Coregonus lavaretus), being main planktivorous species in the lake, preferred the hypolimnion, but was leaving this layer if dissolved oxygen concentrations decreased to 1–5 mg/L. The study was conducted in Bolshoy Sevan (the southern part of Lake Sevan) on July 29–30, 2019. The vertical profiles of water temperature and dissolved oxygen concentration, as well as distribution of major taxonomic groups of aquatic organisms were assessed four times a day: in the dark (night time), in the light (day time), and in twilight (morning and evening). Fish population density was assessed using a “Simrad EK80” echosounder. Vertical distribution of zooplankton and fish observed within the study period did not correspond to that described earlier. Maximal zooplankton biomass during the study was recorded in the hypolimnion, and minimal biomass, in the epilimnion. Most of fish (89–100%) located in the metalimnion. At night, about 10% of the fish population descended to the hypolimnion, despite the low dissolved oxygen concentrations found there (3.0–3.1 mg/L). At dawn, about 7% of the fish ascended to the epilimnion, reaching a 7-m depth, where the water temperature was 20.8 °C. The water temperature range preferred by most fish individuals varied during the observation period and did not correspond to previously reported ranges.

Seasonal Changes in Zooplankton Community Structure and Distribution Pattern in the Yellow Sea, China

Changes in zooplankton community and distribution have significant influences on fishery resources due to their vital role in the marine food web. Seasonal variations in zooplankton community structure, abundance and biomass of major taxa and distribution pattern in the Yellow Sea, China were analyzed to obtain the current status of secondary production. A total of 73 taxa (mostly at the species level) were recorded with the highest species richness in summer and lowest in spring. The most abundant zooplankton species in all seasons were copepods Oithona similis, Paracalanus sp. and Calanus sinicus. The mean total zooplankton abundance was the highest in spring and followed a declining trend till winter. Cluster analysis identified two distinct zooplankton assemblages geographically found in the deep (> 50 m depth) and shallow regions. Zooplankton in the shallow region had higher abundance and species richness with the exception of winter season. Small copepods exhibited higher biomass in the shallow region but few abundance differences between the two domains. Large copepods (LC) and giant crustaceans (GC) usually had higher biomass in the deep region with the exceptions of LC in spring and GC in summer. Both the abundance and biomass of chaetognaths were significantly higher in the shallow region, where cnidarian abundance was also higher from spring to autumn. Water currents contributed to the transport of zooplankton between the two domains. The high abundance of copepods in the shallow region satisfied the requirements for the larval fish survival from spring to autumn. However, the high abundance of carnivorous zooplankton in summer–autumn may compete with larval fish for prey, and may directly feed on fish larvae.

Close Encounters - Microplastic availability to pelagic amphipods in sub-Antarctic and Antarctic surface waters

This study investigated the distribution of plastic debris from the Atlantic portion of the Sub-Antarctic to the Antarctic Peninsula. This region is home to some of the highest concentrations of zooplankton biomass but is also threatened by increasing shipping traffic from fishing and the growing tourism market. Samples were collected using a surface-towed neuston net during the Austral summer 2018, aboard the RRS James Clark Ross. Using Fourier Transform Infrared Spectrometry it was found that 45.6% of the plastic particles isolated from seawater samples were sampling contamination, originating predominantly from the ship. Of the remaining particles, both low density (polyethylene, polypropylene) and high-density (phenoxy and epoxy resins) polymers were found in the surface water suggesting both long-range and local sources of origin. Whilst we found that micro and mesoplastic concentrations in seawater were significantly low (0.013 ± 0.005n/m3) compared to global averages, they were higher along the Antarctic Peninsula than the open ocean (Sub-Antarctic) stations. The potential availability of micro and mesoplastics (MP) to pelagic amphipods was explored, using an observed encounter rate (OER) and a possible encounter rate (PER). The total OER (0.8%) was higher than the PER (0.15%), suggesting that even at low concentrations, microplastics are encountered, and potentially consumed, by amphipods. This study highlights the need to prioritise regions of high zooplankton abundance and to investigate both water and biota to build up a picture of plastic pollution and its potential interaction with the Antarctic Ecosystem.

Unravelling the spatio-temporal variation of zooplankton community from the river Matla in the Sundarbans Estuarine System, India

Zooplankton is an important bioindicator of ecosystem functioning. Knowledge of the seasonal fluctuation in the zooplankton population in estuarine waters of the Indian Sundarbans is rather limited. In the present study, we analysed the community structure of zooplankton assemblages and their spatio-temporal variations based on different multivariate statistics and indicator value analysis. A total of 56 taxa were identified and the density was primarily dominated by planktonic copepods and few meroplankton communities during four sampling seasons. The most abundant species were: Acartia spinicauda, Acartia sp., Bestiolina similis, Euterpina acutifrons, Labidocera acuta, Paracalanus aculeatus, Paracalanus parvus and Paracalanus indicus. Canonical Correspondence Analysis highlighted that temperature, pH, DO, salinity and nutrients were the prevailing environmental parameters associated with significant spatio-temporal changes of zooplankton distribution in this area. The highest abundance of zooplankton was recorded in winter, followed by monsoon, summer and spring. Throughout the study period, different zooplankton indices were observed in good condition. Seasonal occurrence of dominant zooplankton with high IndVal index was markedly observed and it might be used as a potential bioindicator for a particular season and environmental condition in this estuarine complex. The results of this study provide evidence for the presence of warm water species in the estuarine waters of the Indian Sundarbans and can be a clear indication of climate change-mediated elevated temperature in the estuarine system. Our results underscore the high diversity of zooplankton from mangrove dominated estuarine complex and emphasize the need for long-term monitoring in ecologically fragile ecosystems like the Sundarbans Estuarine System.

Nocturnal variation of the zooplankton community in coral reef substrates at Isla del Coco National Park (Eastern Tropical Pacific)

Introduction: Zooplankton is a major link in coral reef food webs and a source of nutrients for corals. Demersal zooplankton in coral reefs makes diel migrations at night to avoid predation by fish and corals, increasing abundance and biomass at night. Objectives: To study the composition and variation of the demersal and pelagic zooplankton community at night and to increase the taxonomic knowledge of the benthic copepod fauna over different substrates of a coral reef. Methods: Traps made of plastic, with a 100 μm mesh size collector cup attached, were placed for 12 hours between 5-10 m depth over four substrates: (1) sand, (2) small and (3) big colonies of Porites lobata, and (4) dead and alive corals. Sampling started at dusk (1800 h), and the collector cups were collected and replaced at 2100 and 0000, and the last samples removed at down (0600 h). Results: The highest abundance of zooplankton was capture over P. lobata colonies between 0000 to 0600 h. Copepods (adults, copepodites, and nauplii) dominated the community structure and were more abundant during all the time intervals and substrates. Pelagic copepods were more abundant than the benthic, however, not more diverse. Among the benthic copepods, 20 new records of harpacticoids and calanoids were registered for Isla del Coco and Costa Rican waters. Appendicularians and decapod larvae were also abundant. Changes in coral reef community structure were related with time and not with the kind of substrate, although some taxa were found only in a specific time interval or substrate. Conclusions: Community structure and abundance of demersal and pelagic coral reef zooplankton in Chatham Bay were dominated by copepods, larvaceans and decapod larvae, similar to other coral reefs around the world. The highest abundance peak of organisms in the water column between 0000 to 0600 h could be related to diel migration.

Distribution of zooplankton in the Indian sector of the Southern Ocean

AbstractThe community composition of zooplankton with an emphasis on copepods was assessed in the frontal zones of the Indian sector of the Southern Ocean (SO) during summer 2013. Copepods were the dominant group in both the bongo net and multiple plankton sampler across the entire region. High zooplankton abundance was recorded along each transect in the Polar Front (PF). Community structure in this front was dominated by common taxa, includingCtenocalanus citer,Clausocalanusspp.,Calanoides acutus,Calanus propinquus,Calanus australisandRhincalanus gigas, which together accounted for &gt; 62% of the total abundance.Calocalanusspp.,Neocalanus tonsusandC. propinquuswere indicator species in the Sub-Tropical Front (STF), Sub-Antarctic Front and PF, respectively. A strong contrast in population structure and biovolume was observed between then PF and the STF. The community structure of smaller copepods was associated with the high-temperature region, whereas communities of larger copepods were associated with the low-temperature region. Thus, it seems probable that physical and biological characteristics of the SO frontal regions are controlling the abundance and distribution of zooplankton community structure by restricting some species to the warmer stratified zones and some species to the well-mixed zone.

Relationship between distribution of dimethyl sulfide (DMS) and plankton community structure in Spermonde, Indonesia

Dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSP) and phytoplankton abundance are measured on the surface of the sea and sub-surface in the spermonde area, the Makassar Strait in January 2018. At the mouth of the Tallo River, domestic runoff affects the dominance (D) of phytoplankton from the Makassar city river flow, and the reduction of nutrients from the sea cannot be predicted. Pangkep river estuary abundance of phytoplankton is more dominant than the genus Chaetoceros sp. The location is relatively strong research at the highest flow velocity at the estuary Pangkep is 10.45 cm/sec, and the lowest is located at the estuary Tallo is 5.87 cm/sec. The most abundant phytoplankton abundance in the west are found in sea level comes from Coscinodiscus sp class with the same abundance percentage composition of 71% and zooplankton groups are most often found originated from Temora sp class with composition percentage of 6.2%. The highest abundance of phytoplankton in the substrate Leptocylindricus sp is 73%, while the highest zooplankton abundance was 4.9%. The average value of the diversity index is 1.11; 0.082 and 0.521 while the value of diversity index, uniformity and dominance at sea subsurface 1.14; 0.088 and 0.55.

HUBUNGAN PHYTOPLANKTON DAN ZOOPLANKTON TERHADAP PRODUKTIVITAS KOLAM AGROWISATA UIR KECAMATAN SIAK HULU KABUPATEN KAMPAR PROVINSI RIAU

This study took plankton and water samples carried out in 5 (five) pond plots at several locations in the UIR Agro Tourism pond. Various types of fish are maintained in these ponds. A sampling of water is done once a week starting at 08.00 until 12.30 WIB. The method of sampling is carried out by determining seven points/places in each pool. Based on the results of the study found that there are 34 species of phytoplankton consisting of 3 classes, namely Chlorophyceae (15 species), Cyanophyceae (8 species) and Bacillariophyceae (11 species). The highest abundance of phytoplankton is in pond II, which is 3027 cells / l. and the lowest phytoplankton abundance is at a station I which is 953 cells / l. Zooplankton found 2 classes of zooplankton consisting of 4 species namely Crustacea class consisting of 3 species, and Sarcodina class 1 species. The highest zooplankton abundance in an IV, while the lowest abundance in an I. From multiple regression analysis of phytoplankton obtained Fcount 2.898 &lt;Ftable 2.90 and for zooplankton obtained Fcount 2,074 &lt;Ftable of 2.90, which means no influence some water quality parameters (temperature, brightness, pH, dissolved oxygen, phosphate and nitrate) to plankton abundance at a 95% confidence level. The relationship between plankton and water quality is not very real and not significant. The results of observations of water quality indicate that in general the results of physical-chemical water measurements indicate that the pond waters are still classified as good and can still support the life of organisms in it, especially plankton.

The influence of ontogeny and prey abundance on feeding ecology of age‐0 Lake Whitefish (Coregonus clupeaformis) in southeastern Lake Michigan

AbstractA shift towards oligotrophic conditions in Lake Michigan has led to concern that altered trophic pathways are leading to lower early life survival and recruitment for Lake Whitefish (Coregonus clupeaformis). This study evaluated ontogenetic shifts in age‐0 Lake Whitefish diets and evaluated how feeding ecology and the amount of food eaten varied with prey abundance and composition at a site in southeastern Lake Michigan during 2014–2017. Although prey densities varied among years, cyclopoid copepods were overall the most abundant prey available. In turn, cyclopoids were the predominant prey item in diets each year, particularly for the smallest larval Lake Whitefish. However, there was a tendency for the importance of cyclopoids to decline somewhat in each diet index as fish grew and other prey such as calanoid copepods, Bosminidae, Daphniidae and/or chironomids increased in importance. High zooplankton abundance, especially high cyclopoid abundance, available to the small size groups of Lake Whitefish (&lt;21 mm) in 2014 was associated with high food mass/fish, high number of zooplankton eaten/fish, and low incidence of empty stomachs compared with 2015–2017. As fish grew, the impact of food abundance on prey consumption diminished somewhat, indicating that the relationship between fish feeding ecology and the prey environment can change quickly with fish size during the early life period.

Ихтиопланктон и трофические взаимоотношения в планктонных сообществах прибрежной акватории Юго-Западного Крыма (Чёрное море) в летний сезон 2013 г.

В прибрежной акватории Юго-Западного Крыма летом 2013 г. изучены видовой состав и количественные показатели мезо-, макро- и ихтиопланктона, а также питание личинок рыб. В ихтиопланктоне обнаружены икра и личинки 33 видов рыб из 24 семейств, что вдвое превысило показатели 1990-х гг. В мае 2013 г. в прибрежной акватории Севастополя наблюдался результативный нерест хамсы, которому способствовали благоприятная температура воды в море (+21 °C) и хорошие кормовые условия. Наибольшее количество летненерестующих видов зарегистрировано в июне при температуре поверхностной воды +22,7 °C. Численность икры рыб в 2013 г. увеличилась по сравнению с таковой в 2000 г. в 3,4 раза, личинок ― в 2,3 раза, что связано с их большей выживаемостью при улучшившихся условиях питания в результате относительно высокой численности зоопланктона с преобладанием мелкоразмерной фракции и доминированием в ней ювенильных стадий копепод. Другими факторами, улучшившими состояние кормовой базы личинок, были низкая численность гребневика Mnemiopsis leidyi A. Agassiz, 1865 и его слабое воздействие

Kelimpahan Zooplankton sebagai Indikator Kesuburan Perairan di Rawa Banjiran Desa Sedang Kecamatan Suak Tapeh Kabupaten Banyuasin

The study of zooplankton abundance as an indicator of water fertility in the Banjiran swamp in the Sedang Village of Suak Tapeh Subdistrict, Banyuasin Regency was conducted in July to August 2017. The zooplankton sampling method was carried out at 3 (three) stations namely nebong kuning swamp station (station 1), poron swamp (station 2) and banan swamp (station 3) using purposive random sampling method. Data obtained in this study include data on zooplankton composition, zooplankton abundance index and zooplankton dominance index. While the data analysis was carried out descriptively. The results of zooplankton identification obtained during the study found 8 (eight) genera of zooplankton consisting of 3 (three) classes, namely Monogononta 1 genus, Mastigophora 5 genus and Ciliate 2 genus. The highest zooplankton abundance was found at station 1 kuning nebong swamp and banan swamp with an average value of 1.75 ind / L and 1,5 ind/L indicating the level of fertility of the floodwaters belongs to the mesotrophic category and the lowest at station 2 poron swamp with an average value of 0.92 ind / L indicating the level of fertility of the floodwaters in the Sedang village of Suak Tapeh Subdistrict, Banyuasin Regency belongs to the oligotrophic category.

Hydrobiological variables as a regulatory factor on the abundance of heterotrophic flagellates in an urban pond

The seasonal abundance of flagellates has been monitored over a period of 1 year from December 2013 to November 2014 (divided into 4 conjugative seasons namely winter, spring, summer, and autumn) in an experimental pond located in Rajshahi City Corporation area, Bangladesh. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships among heterotrophic flagellates (HF), bacteria and zooplankton in Bangladesh and the result obtained by this study will be beneficial for similar water ecosystem all over the world. Standard methods were used to determine the prescribed hydrological parameters and zooplankton cell density. Maximum HF abundance (14 346.00 cells/mL) was found in the spring and the minimum (5 215.00 cells/mL) occurred in the summer. Inverse to HF, significantly (P<0.05) higher zooplankton abundance was found during the winter (782.00±47.62 cells/mL) and the lowest value was found in the autumn (448.00±39.15 cells/mL). Whereas similar to the HF, total bacterial abundance was significantly higher during the spring ((2.25±1.05)×105 cells/mL) and lower in the summer ((0.79±0.06)×105 cells/mL). Multivariate analyses (ANOSIM and MDS) have shown significant seasonal differences for cell numbers where MDS ordination plot and cluster analysis based on similarity in the genera abundance of HF revealed overlapping condition between winter and spring. Canonical correspondence analysis (CCA) also showed a distinct separation among the genera based on the prevailing hydrological situation and indicated that temperature, pH, BOD5, and NO 3 − were the most important environmental variables in determining the observed variation in HF community structure. Among the biological factors, zooplankton showed negative but total bacteria were positively correlated with HF abundance.

Spatial Variation in Water Column Structure, Nutrients, Chlorophyll and Zooplankton in an Estuarine Transect of Southampton Water

Estuary systems are complicated and closely related to humans. The understanding of estuary systems is important to scientific study and human develop. An investigation was conducted on 3rd November 2009 by RV Callista along the Itchen estuary of Southampton Water with the aim of determining spatial variability in physical water column structure, nutrients, chlorophyll and zooplankton of Southampton Water, and recognizing the links between them. The salinity and temperature values are relatively lower at surface upper estuary than that of deep lower estuary. Water stratification is observed around upper and mid estuary. The nutrient Si exhibits conservative behaviour with a linear relationship with salinity gradient, while P shows non-linear with salinity, which may indicate an addition bahaviour. Chlorophyll distributes high concentration at surface upper estuary and relatively uniform and low concentration at downriver area which is mainly due to light and nutrients factors. Water turbidity affects chlorophyll distribution by reducing light availability in the water column, while chlorophyll can in turn influence water turbidity. The abundance dominant species of the estuary are Copepoda and Appendicularia. The mid estuary has the highest zooplankton abundance, while the lower estuary has the most zooplankton groups. Zooplankton distribution is relative to food distribution, temperature, light and salinity profiles.

Temperature and phytoplankton size class biomass drives the zooplankton food web dynamics in the Indian Ocean sector of the Southern Ocean

The abundance and vertical distribution of zooplankton community structure in the mesopelagic zone are important to better understand their role in the food web dynamics in the Southern Ocean ecosystem. During the austral summer of 2015, in the Indian sector of the Southern Ocean, the vertical profiles of zooplankton community structures between 0 and 1000 m were investigated using a Hydro-Bios, Multi Plankton Sampler (200-µm mesh, 0.25 m2 mouth area). A strong contrast in terms of population structure and biovolume was observed between the Subtropical Front and the Polar Front 2. High zooplankton abundance was recorded on each transect in the Polar Front. Zooplankton abundance was numerically dominated by calanoids and cyclopoids, constituting approximately 86% of the total zooplankton count. Abundance of copepods were the highest within the mixed layer depth. Under warm, stratified conditions, surface waters were dominated by picophytoplankton. These conditions result in the zooplankton being dominated by small crustaceans. This long, inefficient food web is of poor nutritional quality, supporting a smaller biomass of higher trophic levels. In contrast, under cold and well mixed conditions, surface waters were dominated by microphytoplankton. These conditions result in the zooplankton being dominated by crustaceans, such as large copepods. This short, nutritionally rich and efficient food web supports higher trophic levels.

Variability of pikeperch Sander lucioperca (L. 1758) cohorts in early life history

Year to year fluctuations in 0+ fish cohort strength are a common phenomenon. Many factors can affect cohort strength during the fish's early life period. In this study, development of a 0+ pikeperch Sander lucioperca cohort in the pelagic zone was studied by trawling for 50 days from first larvae hatching, in two consecutive years. In 2007, an abundant S. lucioperca cohort collapsed suddenly soon after hatching. After the incident, slow-growing S. lucioperca prevailed in the catch. In 2008, the catch gradually increased during the whole study period because of prolonged hatching. Environmental factors differed mainly in a slower temperature increase, higher water level and higher zooplankton abundance in 2008 compared to 2007. Our study revealed that a strong 0+ S. lucioperca cohort at the time of hatching might not result in a strong S. lucioperca cohort in general.