Comparative Analysis of Total and Size-Fractionated Chlorophyll a in the Yellow Sea and Western Pacific.

Measurements of different size-fractionated chlorophyll a concentrations (Chl a) of phytoplankton assemblages in situ are vital for advancing our understanding of the phytoplankton size structure and thus the marine biogeochemical cycle. In the present study, we thus made a comparative analysis of total and size-fractionated Chl a in the Yellow Sea (YS) and Western Pacific (WP). Our results suggest that the total Chl a was highly variable in the YS (averaging ~1.02 µg L-1) and was generally 3-4-fold more than that in the WP (averaging ~0.30 µg L-1). The pico-sized Chl a had a significant contribution to total Chl a in the WP (range 75-88%), while the average contributions of the nano-sized and pico-sized Chl a to total Chl a in the YS were 47 and 38%, respectively, suggesting that a majority of the total Chl a in the YS was associated with nano- and picophytoplankton. Moreover, we applied the generalized additive models (GAMs) to explore the relationships between the total Chl a and that contained in each of the three size classes. These GAMs relationships suggested a continuum from picophytoplankton dominated waters to large phytoplankton (cells> 2 µm) domination with increasing Chl a. Finally, we made a comparison of the total Chl a obtained with GF/F filters and that measured from size-fractionated filtration and revealed that their corresponding concentrations are in good agreement, indicating the size-fractionated filtration had no effect on total Chl a determination.

Marine litter on the seafloors of the Bohai Sea, Yellow Sea and northern East China Sea.

Seafloor litter was investigated in the Bohai Sea, Yellow Sea, and northern East China Sea (BYnECS) based on fisheries-independent bottom trawl surveys in 2019. The mean density of seafloor litter was 48.44 items∙km-2 (44.56 kg∙km-2) in the BYnECS, which was at an intermediate level compared with the values observed in other continental shelf areas worldwide. There were significant differences in the density of seafloor litter among different regions (P < 0.05), and the high-density litter accumulation areas in the northern Yellow Sea and Changjiang estuary and adjacent waters were close to the sediment accumulation areas. Plastics were predominant in the BYnECS and accounted for 72.80%/44.05% (number/weight) of the seafloor litter. Fishery-related litter was the main source of seafloor litter in the BYnECS. This study systematically reports the density, composition, sources and spatial distribution of seafloor litter in the BYnECS, thereby providing a scientific basis for the management of marine litter.

Is seafloor litter contributing to sea anemone blooms?

Increasing marine litter have become a global environmental disaster. The accumulation of seafloor litter (generally includes anthropogenic litter and natural debris) could change the habitat of benthic organisms and thereby affecting their population dynamics including spatial distribution. Metridium senile fimbriatum (i.e., M. senile), a fast-growing sea anemone, has become a dominant species of benthic community in the north Yellow Sea in recent years. In this study, we tested the hypothesis that the distribution of M. senile is positively correlated with that of seafloor litter, using data collected on seafloor litter and M. senile from three fisheries-independent bottom trawl surveys in the Yellow Sea in May, August and November 2019. Gradient Forest Model (GFM) was used to select appropriate response variables for characterizing the distribution of M. senile, and evaluate the influences of potential environmental factors on M. senile distribution. Surface area of anthropogenic litter (represented as 'Anthropogenic litter'), surface area of natural debris (represented as 'Natural debris') and latitude (Lat) were identified as the most significant variables influencing the distribution of M. senile. Furthermore, Generalized Additive Mixed Model (GAMM) was applied to model the abundance distribution of M. senile in terms of significant environmental variables, and evaluate its correlations with 'Anthropogenic litter' and 'Natural debris'. The best fitting GAMM showed that the abundance of M. senile has a significantly positive association with 'Anthropogenic litter' and 'Natural debris'. We therefore speculated that accumulation of seafloor litter might contribute to the bloom of M. senile, given that seafloor litter could serve as "vectors" for M. senile dispersal and provide with a preferable "natural habitat" for their settlement.