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The Ulva prolifera green tides in the Yellow Sea, China, which have been occurring since 2007, are a serious environmental problem attracting worldwide attention. Despite extensive research, the outbreak mechanisms have not been fully understood. Comprehensive analysis of anthropogenic and natural biotic and abiotic factors reveals that human activities, regional physicochemical conditions and algal physiological characteristics as well as ocean warming and biological interactions (with microorganism or other macroalgae) are closely related to the occurrence of green tides. Dynamics of these factors and their interactions could explain why green tides suddenly occurred in 2007 and decreased abruptly in 2017. Moreover, the consequence of green tides is serious. The decay of macroalgal biomass could result in hypoxia and acidification, possibly induce red tide and even have a long-lasting impact on coastal carbon cycles and the ecosystem. Accordingly, corresponding countermeasures have been proposed in our study for future reference in ecosystem management strategies and sustainable development policy.

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 in China. The massive green algae bloom in the coastal region of Qingdao China between May and July 2008 brought the world attention because the algae bloom covered an area of approximately 13,000-30,000 km 2 including the sailing venue for the 29th Olympic Games (Fig. 1). To avoid any anoxia and harmful algal blooms due to potential decomposition of organic matters during the post algal bloom period, a heroic effort was made to remove the green algae by more than 16,000 people using more than 1,000 transportation vehicles and 1,600 fishing and transportation vessels. Approximate 1 million fresh weight (FW) tons of algae were removed from beaches and nearby coastal waters while an estimate of another 2 million FW tons settled into deep waters.

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Cadmium, and its compounds, has been placed on the blacklists of most international pollution conventions by virtue of its toxicity, potential for bioaccumulation and persistence (Taylor, 1983).The ability of many marine molluscs, and in particular gastropods, to accumulate Cd to a high degree in apparently unregulated fashion has led to their frequent use in monitoring programmes. Thus Cd levels in the winkle,Littorina littorea(L.) closely reflect gradients in environmental contamination (Bryanet al. 1983), demonstrating the excellent ‘indicator’ properties of this group.

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