Metabarcoding analysis of trophic sources and linkages in the plankton community of the Kuroshio and neighboring waters

Trophic sources and pathways supporting early life stages are crucial for survival of forage fishes recruiting around the oligotrophic and unproductive Kuroshio. However, information is limited for the Kuroshio planktonic food web and its trophodynamics because of its high biodiversity. Here, we explore trophic sources and linkages in the Kuroshio plankton community using metabarcoding analysis of gut-content DNA for 22 mesozooplankton groups. The major prey was dinoflagellates and calanoids for omnivorous groups, and calanoids and gelatinous organisms for carnivorous groups. Larvaceans and hydrozoans were the most frequently appeared prey for both omnivores and carnivores, whereas they were minor constituents of the available prey in water samples. Although calanoids overlapped as major prey items for both omnivores and carnivores because they were the most available, contributions from phytoplankton and gelatinous prey differed among taxonomic groups. Further analysis of the metabarcoding data showed that in addition to omnivorous copepods like calanoids, gelatinous groups like larvaceans and hydrozoans were important hubs in the planktonic food web with their multiple trophic linkages to many components. These findings suggest that gelatinous organisms are important as supplementary prey and provide evidence of niche segregation on trophic sources among mesozooplankton groups in the Kuroshio.

Spatial distribution and structure of plankton in Paminggir Swamp of the Hulu Sungai Utara Regency, South Kalimantan Indonesia

Plankton is a biota community that is able to adapt and serve as natural food for fish. This study aims to analyze the structure of the plankton community and its spatial distribution so that this research can be used as information for swamp aquaculture. This research was conducted in July and August 2019. Sampling was done at ten stations by considering the duration of inundation. The method used was quantitative exploration and inverse distance weighting (IDW). The results showed that the swamp waters of Paminggir and Danau Panggang had the highest abundance of phytoplankton (850 cells/liter), the lowest in Ambahai (150 cells/liter) in July and Bararawa (180 cells/liter) in August 2019. Zooplankton (10 cells/liter) has been identified in Jenamas with the lowest abundance, and the highest (70 cells/liter) in Babirik in August 2019. Bacillariophyceae was dominate with relative abundance of 53% species and the most zooplankton comes from Protozoa by 50%. The range of index values of diversity, evenness and dominance of phytoplankton were 1.79 to 0.21 while zooplankton were 0.46 to 0.72. Phytoplankton with appropriate abundances are spatially distributed in the western part of the swamp along the Ambahai and Babirik while the spatial distribution of the abundance of zooplankton properties clustered in the middle and southern of the swamp. Water quality parameters of the nitrate ranged 0.13 – 0.25 mg/l and phosphate ranged 0.12 – 0.52 mg/l.

Hydrodynamics Regulate Longitudinal Plankton Community Structure in an Alpine Cascade Reservoir System

Previous studies report significant changes on biotic communities caused by cascade reservoir construction. However, factors regulating the spatial–temporal plankton patterns in alpine cascade reservoir systems have not been fully explored. The current study explored effects of environmental factors on the longitudinal plankton patterns, through a 5-year-long study on the environmental factors and communities of phytoplankton and zooplankton in an alpine cascade reservoir system located upstream of Yellow River region. The findings showed that phytoplankton and zooplankton species numbers in the studied cascade reservoir system were mainly regulated by the hydrological regime, whereas nutrient conditions did not significantly affect the number of species. Abundance and biovolume of phytoplankton in cascade reservoirs were modulated by the hydrological regime and nutrient conditions. The drainage rate, N:P ratio, and sediment content in cascade reservoirs were negatively correlated with abundance and biovolume of phytoplankton. Abundance and biovolume of zooplankton were not significantly correlated with the hydrological regime but showed a strong positive correlation with nutrient conditions in cascade reservoirs. Shannon–Wiener index (H’) and the Pielou index (J) of phytoplankton were mainly regulated by the hydrological regime factors, such as drainage rate and sediment content in cascade reservoirs. However, temperature and nutrient conditions were the main factors that regulated the Shannon–Wiener index (H’) and the Pielou index (J) of zooplankton. Species number, abundance, and biovolume of phytoplankton showed a significant positive correlation with those of zooplankton. Hydrodynamics and nutrient conditions contributed differently in regulating community structure of phytoplankton or zooplankton. These findings provide an understanding of factors that modulate longitudinal plankton community patterns in cascade reservoir systems.