Mussels (Bivalve: Mytilidae) have adapted to various habitats, from fresh water to the deep sea. To understand their adaptive characteristics in different habitats, particularly in the bathymodiolin mussels in deep‐sea chemosynthetic ecosystems, we conducted a comparative transcriptomic analysis between deep‐sea bathymodiolin mussels and their shallow‐water relatives. A number of gene families related to stress responses were shared across all mussels, without specific or significantly expanded families in deep‐sea species, indicating that all mussels are capable of adapting to diverse harsh environments, but that different members of the same gene family may be preferentially utilized by different species. One of the most extraordinary trait of bathymodiolin mussels is their endosymbiosis. Lineage‐specific and positively selected TLRs and highly expressed C1QDC proteins were identified in the gills of the bathymodiolins, suggesting their possible functions in symbiont recognition. However, pattern recognition receptors of the bathymodiolins were globally reduced, facilitating the invasion and maintenance of the symbionts obtained by either endocytosis or phagocytosis. Additionally, various transporters were positively selected or more highly expressed in the deep‐sea mussels, indicating a means by which necessary materials could be provided for the symbionts. Key genes supporting lysosomal activity were also positively selected or more highly expressed in the deep‐sea mussels, suggesting that nutrition fixed by the symbionts can be absorbed in a “farming” way wherein the symbionts are digested by lysosomes. Regulation of key physiological processes including lysosome activity, apoptosis and immune reactions is needed to maintain a stable host–symbiont relationship, but the mechanisms are still unclear.

The massive green algae (Enteromorpha prolifera) bloom in a coastal area of Qingdao between May and July 2008 prior to the sailing competition of the 29th Olympic Games has raised great concerns in local and regional communities and governmental agencies on environmental deterioration, causes and mitigation of such massive algal blooms. Results from field and laboratory studies during the bloom and post-bloom periods revealed that the bloom was originated from an offshore area 150 km south of Qingdao, and caused by complex coupled land-ocean and natural-human processes associated with increases in nutrient and organic matter loadings to the coastal ocean due to rapid expansions of agriculture, aquaculture and urbanization, behavior of algae, seasonal wind and coastal currents, and transport of nutrients and biota. This environmental disaster has brought us emerging challenges on how to integrate monitoring, analysis and prediction of complex coupled natural and human processes, environmental regulations, and management in land-ocean uses for the sustainable socioeconomic development.

Ecological and physiological features of the planktonic copepod Calanus sinicus in the southern Yellow Sea in summer were studied to reveal its life history strategy. From the coastal shallow waters to the central part of the southern Yellow Sea, a shift of the stage composition occurs from being dominated by the egg-nauplius stage to being dominated by the fifth copepodite (CV) stage. Most CVs reside in the Yellow Sea Cold Water Mass (YSCWM), where both temperature and food abundance are low. CVs in the YSCWM have longer body lengths, heavier body weights and higher carbon contents than those outside the YSCWM. Onboard incubations show that the development of CVs in the YSCWM is suspended. Energy conservation, development suspension and lack of diel vertical migration (DVM) behavior suggest a diapause status for the CVs in the YSCWM, although vertical distribution patterns indicate the CV individuals are not fully synchronous in physiology and development. This adaptive oversummering strategy would help C. sinicus to live through the warm and food-limited summer in the central part of the southern Yellow Sea; both low temperature and low food supply are necessary for CV to maintain the resting state in the YSCWM. Calanus sinicus exhibits different life history strategies in different regions of the southern Yellow Sea in summer.