Broad-scale effects of hypoxia on benthic community structure in Chesapeake Bay, USA

Benthic communities provide secondary production for higher trophic levels, and changes in benthic community structure can be a harbinger for associated food web alterations. Benthic communities can be affected by variations in water quality, with low dissolved oxygen reducing benthic abundance and biomass. We quantified the effects of dissolved oxygen and other environmental factors upon changes in density, biomass, and diversity of the macrobenthic community from long-term data (1996–2004) from the Chesapeake Bay Program's benthic monitoring. Benthic density, biomass, and diversity were significantly and negatively correlated with water depth and positively correlated with the dissolved oxygen level. In an assessment of multiple models using Akaike's Information Criteria, oxygen was the single best predictor of summer benthic infaunal density by depth. Biomass was best predicted by depth, salinity, and dissolved oxygen together. Moreover, oxygen was among the important factors determining Shannon (H′) diversity. Benthic diversity in Chesapeake Bay over 2001–2004 was historically low compared to that over the years 1996–2000 and was directly correlated with the severity of hypoxia. Hypoxia leads to mass mortality of benthos, which reduces the overall availability of secondary production to higher trophic levels and can affect overall productivity in Chesapeake Bay. Regions with low dissolved oxygen should be managed to minimize deleterious anthropogenic effects on benthos that may affect higher trophic levels.