Individual, population, and ecosystem effects of hypoxia on a dominant benthic bivalve in Chesapeake Bay

Hypoxia is an environmental stressor that affects abundance, biomass, diversity and ecosystem function of benthic assemblages worldwide, yet its collective impact at individual, population, and ecosystem levels has rarely been investigated. We examined the effects of hypoxia on the biomass-dominant clam, Macoma balthica, in the York and Rappahannock Rivers (Chesapeake Bay, USA). We (i) surveyed the M. balthica populations in both rivers in 2003 and 2004, (ii) determined the effects of low DO on M. balthica fecundity in a laboratory experiment, and (iii) employed a predator-exclusion field experiment to establish the effects of hypoxia and prey density on predation upon M. balthica. The resultant data were used to parameterize a matrix model, which was analyzed to define potential effects of hypoxia at the population level. In both rivers, hypoxia decreased individual clam growth and caused local extinction of populations. Hypoxia reduced egg production of M. balthica by 40% and inc...