Limited Genetic Connectivity Among Sargassum horneri (Phaeophyceae) Populations in the Chinese Marginal Seas Despite Their high Dispersal Capacity.

Sargassum horneri is a habitat-forming species in the Northwest Pacific and an important contributor to seaweed rafts. In this study, 131 benthic samples and 156 floating samples were collected in the Yellow Sea and East China Sea (ECS) to test the effects of seaweed rafts on population structure and connectivity. Our results revealed high levels of genetic diversity in both benthic and floating samples based on concatenated mitochondrial markers (rpl5-rps3, rnl-atp9, and cob-cox2). Phylogenetic analyses consistently supported the existence of two lineages (lineages I and II), with divergence dating to c. 0.692 Mya (95% HPD: 0.255-1.841 Mya), indicating that long-term isolation may have occurred during the mid-Pleistocene (0.126-0.781 Mya). Extended Bayesian skyline plots demonstrated a constant population size over time in lineage I and slight demographic expansion in lineage II. Both lineages were found in each marginal sea (including both benthic and floating samples), but PCoA, FST , and AMOVA analyses consistently revealed deep genetic variation between regions. Highly structured phylogeographic pattern supports limited genetic connectivity between regions. IMA analyses demonstrated that asymmetric gene flow between benthic populations in the North Yellow Sea (NYS) and ECS was extremely low (ECS→NYS, 2Nm = 0.6), implying that high dispersal capacity cannot be assumed to lead to widespread population connectivity, even without dispersal barriers. In addition, there were only a few shared haplotypes between benthic and floating samples, suggesting the existence of hidden donors for the floating masses in the Chinese marginal seas.

[Effects of environmental factors on catch distribution of stow net Pseudosciaena polyactis and Lophius litulon in southern Yellow Sea in spring].

Stow net fishery is one of the important fishing methods in southern Yellow Sea. Based on the 2006-2009 data from the stow net fishery resources survey in the southern Yellow Sea in spring, and by using the generalized linear model (GLM) and generalized additive model (GAM), this paper quantitatively analyzed the relationships between the catch distribution of Pseudosciaena polyactis and Lophius litulon and the environmental factors such as year, position, water depth, and sea surface temperature (SST). Compared with GLM model, GAM model could better explain the relationships between the spatiotemporal distribution of the catch per unit effort (CPUE) of P. polyactis and P. litulon and the environmental factors. There was a significant negative correlation between the CPUE of the two fish species. The P. polyactis' CPUE showed a decreasing trend from north to south along the latitude direction, being smaller especially around the Yangtze River estuary, and the L. litulon' s CPUE was also smaller near the Yangtze River estuary. The CPUE of the two species showed a significant correlation with the SST. The calculated optimal scale of the SST for L. polyactis and P. litulon was 9-11 degrees C and 9-14 degrees C, respectively.