This study explores macrobenthic communities' spatial and temporal dynamics and their responses to eutrophication gradients and subsequent ecological recovery in the semi-enclosed bays of Bohai Bay, China. Over the past decades, intensive anthropogenic activities have resulted in significant nutrient enrichment and ecological degradation in these coastal areas. To understand the recovery process following pollution control measures, seasonal sampling of macrobenthic communities was conducted across estuarine, nearshore, and offshore zones during both wet and dry seasons. A total of 166 species were identified, including polychaetes, crustaceans, mollusks, and other taxa. Results showed that pollution-sensitive species such as Iphinoe tenera and Protankyra bidentata gradually increased in abundance in areas where nutrient levels had decreased due to improved water quality. Conversely, in regions still heavily affected by nutrient loading, pollution-tolerant species such as Capitella capitata dominated the benthic community, reflecting the ongoing environmental stress.
Functional diversity indices, including functional richness (FRic), functional evenness (FEve), and functional dispersion (FDis), were used to assess the ecological functioning of the macrobenthic communities. In highly eutrophic areas, species diversity and functional richness declined significantly, with smaller-bodied and opportunistic species, often burrowing or feeding on detritus, becoming more prevalent. This shift reduced ecological functions within the benthic habitat, such as bioturbation and nutrient cycling. Seasonal variations also played a role in community structure, with environmental factors such as salinity, total phosphorus, and sediment characteristics influencing species distribution and functional diversity across different regions.
Despite notable improvements in water quality due to pollution abatement efforts, full recovery of the benthic habitats remains hindered by habitat instability, particularly in nearshore and estuarine areas where nutrient inputs from riverine sources continue to exert pressure. The study underscores the need for continuous monitoring and adaptive management strategies to mitigate ongoing anthropogenic pressures and foster sustainable recovery of benthic ecosystems in coastal bays.

Bohai Bay, macrobenthic community, eutrophication, functional diversity, pollution-tolerant species