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Abstract As mariculture expands offshore in response to the increasing demand for seafood, a new set of ecological concerns arises. We report on presented phosphate and silicate deficiencies in spring in the Zhangzi Island area, northern Yellow Sea, used for farming scallops. Silicon limitation was observed at up to 77.3% of stations, with an average silicate concentration as low as 1.7 μM in March 2014. Average phosphate concentration decreased from 0.12 to 0.05 μM from March to May. Stoichiometric ratios and absolute concentrations indicate that 78%–90% of stations showed phosphate limitation. Correspondingly, the phytoplankton community shifted from predominately diatoms to dinoflagellates. The higher frequency of nutrient limitation in farmed areas, compared with unseeded areas and northern Yellow Sea in general, imply intensified bottom-up controls on scallop production. The "bottle-neck" effect of limited food availability in spring suggests that carrying capacity was originally overestimated, when calculated from annual primary production. Highlights • New ecological concerns accompany expanding offshore mariculture. • Severe silicate and phosphate limitations occur near Zhangzi Island scallop farms. • The natural dominance of diatoms shifts to dinoflagellates as a result. • Bottom-up controls on scallop production intensify. • Carrying capacity based on annual primary production is overestimated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Planktonic ciliate can act as bioindicator for water mass in the Southern Ocean. • Tintinnids showed distinctive regional and vertical distribution characteristics. • Variations in tintinnid survival habitat can be regarded as indicators for future climate change. • Environmental variables play a vital role in determining ciliate community structure. Although the pelagic ciliate (microzooplankton) play important role in carbon flux of marine ecosystems, their ecological function, habitat suitability classification and response to global warming were poorly documented in the Southern Ocean (SO). During summer of 2020/2021, ciliate (including aloricate ciliates and tintinnids) communities in waters from surface to 1000 m were investigated in the SO. Rapid attenuation of ciliate abundance and biomass occurred at 100 m depth in most stations. According to distinctive hydrographic features, five water masses were identified in the SO with unique ciliate community structure. Aloricate ciliate small size-fraction (10–20 μm) was dominant in water masses deeper than 200 m. Tintinnids showed distinctive regional and vertical distribution characteristics, and their habitat suitability characterized by the Bio-index exhibiting different optimum survival zones. Variations in tintinnid habitat can be regarded as indicators for future SO climate change. Correlation between environment factors and biota revealed that depth, Chl a and dissolved oxygen were main factors determining ciliate composition. Combining tendency of phytoplankton and meso-/macro-zooplankton to rapid global warming, ciliates may become smaller and more prominent in the future SO marine pelagic ecosystem. Our study has laid a foundation for recognizing the ciliate community and reinforcing the ideas about tintinnid indication for the change of future SO marine ecosystem. [ABSTRACT FROM AUTHOR]

Abstract: Calanus sinicus, a dominant calanoid copepod in the Yellow Sea, is an important link in the food web between phytoplankton and higher trophic levels. Its populations typically start to develop in later winter with a maximum of individuals in early summer. To study the correlation between changes in the abundance of this species and changes in food resources and the physical environment, RNA and DNA concentrations and egg production rates (EPR) were measured, and RNA:DNA ratios were calculated as indices of growth and nutritional conditions of copepods collected in the Yellow Sea from February to July. We observed pronounced seasonal and spatial variations of RNA concentrations and resulting RNA:DNA ratios. There was a positive correlation between the EPR and RNA:DNA ratios. The copepods collected in March and April, when phytoplankton were more abundant, had high RNA:DNA ratios, and contained more RNA than copepods collected during the other months. There was no significant correlation between the growth indices (RNA:DNA ratios and EPR) and chlorophyll-a concentrations (Chl a) or temperature at large temporal and spatial scales. We tracked the development of two phytoplankton blooms in April, which were dominated in turn by diatoms and dinoflagellates. We observed high concentrations of RNA and a high RNA:DNA ratio at both bloom sites during the respective blooms. During the diatom bloom, the RNA:DNA ratios in copepods increased at the onset of the bloom and decreased thereafter. In addition, we observed a positive correlation (P<0.001) between RNA-based indices and Chl a. Our results suggest that food availability plays a more important role than temperature in controlling the growth of C. sinicus in the field. Thus, the spring phytoplankton blooms in the Yellow Sea are important regulators of copepod abundance. [Copyright &y& Elsevier]