Zooplankton community response to eddy during dinoflagellate Noctiluca scintillans blooms off Pakistan,northern Arabian Sea

Eddies are major elements of ocean dynamics that affect ocean production.Understanding their effects on plankton distribution may help understand the dynamics of harmful phytoplankton blooms.Previous studies on the effects of eddies in the northern Arabian Sea have primarily focused on the zooplankton community,and few have observed zooplankton dynamics during winter blooms of Noctiluca scintillans.We investigated zooplankton community structure and the related environmental variability during a N.scintillans bloom that was affected by an eddy in February 2018.The sampling stations were deployed at eddy core and eddy edge distinguished in salinity,temperature,and velocity.Results show that N.scintillans bloomed at the eddy core with high-velocity currents induced by warm eddies that moved from eddy core to eddy edge.As a result,blooms significantly changed the zooplankton community structure.Non-bloom stations had higher zooplankton diversity than bloom stations.Zooplankton at non-bloom stations were dominated by either tunicates or copepods,such as Thalia democratica and Pleuromamma gracilis.In addition to the influence of N.scintillans blooms,the velocity of eddy currents was a crucial factor on the similarities in the zooplankton community composition between eddy edge and eddy core.Moreover,the lower abiotic factors in bloom area contribute to the structuring of the zooplankton community during N.scintillans blooms.

Physical-chemical and biological control of the zooplankton community in the Amundsen Sea, Antarctica

Zooplankton are critical components of the Southern Ocean ecosystems,acting as trophic links between phytoplankton and higher-level species.The composition,abundance,carbon biomass,and community structure of zooplankton were studied based on samples collected with a Norpac net(330-μm mesh,0.5-m^(2) net mouth)during the austral summers of 2017/2018.Three communities in a latitudinal gradient were identified based on both a zooplankton abundance dataset and a biomass dataset.Zooplankton were mainly dominated by small copepods(e.g.,Oithona similis and Ctenocalanus citer)in terms of abundance,while the total zooplankton biomass was dominated by krill(Euphausia superba and Thysanoessa macrura)and large copepods(e.g.,Calanoides acutus,Calanus propinquus,and Metridia gerlachei).Redundancy analysis demonstrated that environmental factors(e.g.,temperature,nitrate,dissolved oxygen,ammonium)accounted for more than 40%of the variance in zooplankton abundance/biomass.This indicates that physical processes significantly affect the zooplankton community.Meanwhile,a significant positive correlation was found between the abundance/biomass of zooplankton and that of dominant phytoplankton and ciliates,which suggests trophic links among various plankton functional groups.Our results reveal that both physical processes and biological factors shape the community structure of zooplankton in the Amundsen Sea.

Effects of sediment dredging on water quality and zooplankton community structure in a shallow of eutrophic lake

Effects of suction dredging on water quality and zooplankton community structure in a shallow of eutrophic lake, were evaluated. The results showed that a decreasing trend for levels of phosphorus, organic matter, total suspended solids, Chlorophyll a and Secchi transparency in the water column was found, while levels of water depth, electrical conductivity, total dissolved solids and NO3^--N concentration increased markedly post-dredging. The effects of dredging on dissolved oxygen, pH value and temperature were almost negligible. The zooplankton community structure responded rapidly to the environmental changes caused mainly by dredging. As a result, the abundance of rotifers decreased, while the density of zooplanktonic crustaceans increased markedly. The representative taxa were Brachionus angularis, B. budapestinensis, B. diversicornis, Synchaeta spp. and Neodiaptomus schmackeri. A distinct relationship between zooplankton taxa composition and their environment, unraveled by a redundancy analysis, indicating that the measured environment contributed to the variations in the zooplankton community structure to some extent. The first four synthetic environmental variables explained 51.7% of the taxonomic structure. Therefore, with the reduction of internal nutrient load and a shift in dominance by less eutrophic species, it inferred that dredging might be one of effective measures for environmental improvements of such lakes.

Impacts of algal blooms removal by chitosan-modified soils on zooplankton community in Taihu Lake,China

It is important to assess the effect on zooplankton when perform the environmental protection or restoration technology, especially removing algal blooms, because algae were the major primary producer in algal lakes. The influence on zooplankton community after half a year of algal blooms removed by chitosan-modified soils in Taihu Lake was assessed and the rationality of carrying out the process semiannually was evaluated in the present study. Morphological composition and genetic diversity of zooplankton community were investigated by microscope checkup and polymerase chain reaction-denatured gradient gel electrophoresis （PCR-DGGE）. A total of 44 zooplankton taxa （23 protozoa, 17 rotifers, 3 copepoda and 1 cladocera） were detected by microscope checkup, and a total of 91 bands （28 bands amplified by primers F1427-GC and R1616, 63 bands amplified by primers Fung-GC and NS1） were detected by PCR-DGGE. The results of cluster analysis or detrended correspondence analysis indicated that there was no considerable difference in morphological composition of zooplankton and DGGE profiles between experimental and control sites, and DGGE profiles could represent the biologic diversity. The study showed that zooplankton community could recover original condition after half year of algal blooms removed by chitosan-modified soils and it was acceptable to apply this process semiannually. In addition, the results revealed that PCR-DCJGE could be applied to investigate the impacts of the environmental protection or restoration engineering on zooplankton community diversity.

Striking taxonomic differences in summer zooplankton in the northern South China Sea: implication of an extreme cold anomaly

An extreme persistent cold anomaly was prevailing in the South China Sea in February 2008. In order to understand the effect of the cold anomaly on zooplankton community, the zooplankton composition, abundance and biomass were analyzed in the northern South China Sea in August 2007 and August 2008. A total of 467 zooplankton species representing 16 groups were identified, with 275 species in August 2007 and 351 in August2008. Copepods were the most dominant zooplankton group in the study area. Compared with 2007, a dramatic decline was observed in the abundance of four dominant copepod species： Subeucalanus subcrassus, Temora discaudata, Nannocalanus minor and Temora turbinata in 2008. Moreover, zooplankton abundance declined from 133.37 ind./m^3 in August 2007 to 75.49 ind./m^3 in August 2008. In contrast, the abundance of medusa, such as Diphyes chamissonis, and tunicate, such as Doliolum denticulatum and Dolioletta gegenbauri, increased during the same season. Cluster analysis showed that there was a difference in zooplankton community structure between the two years. These variations in zooplankton communities were indicative of an anomalous oceanographic condition along with the extreme cold event in 2008.