Death by dissolution: Sediment saturation state as a mortality factor for juvenile bivalves

We show that death by dissolution is an important size-dependent mortality factor for juvenile bivalves. Utilizing a new experimental design, we were able to replicate saturation states in sediments after values frequently encountered by Mercenaria mercenaria in coastal deposits (Omega(aragonite) = 0.4 and 0.6). When 0.2-mm M. mercenaria were reared in sediments at Omega(aragonite) = 0.4 and 0.6, significant daily losses of living individuals occurred (14.0% and 14.4% d(-1), respectively), relative to supersaturated-control sediments (3.9% d(-1)). For 0.4-mm M. mercenaria, significant mortality occurred under the most undersaturated conditions (Omega(aragonite) = 0.4, mortality = 9.6% d(-1)), although mortality at Omega(aragonite) = 0.6 was not significant (mortality = 2.7% d(-1); control-saturated mortality = 0.2% d(-1)). For the largest size- class investigated, 0.6 mm, we show significant mortality for clams under the most undersaturated sediments (Omega(aragonite) = 0.4, 2.8% d(-1)). To test if buffered sediments would increase survivorship of juvenile bivalves during periods of recruitment, we manually manipulated sediment saturation state by adding crushed Mya arenaria shell to a mud flat in West Bath, Maine, U.S. A. Although we increased the average sediment saturation state within retrieved cores from Omega = 0.25 +/- 0.01 to only 0.53 +/- 0.06, numbers of live M. arenaria in buffered sediment increased almost three-fold in 2 weeks. Buffering muds against the metabolic acids that cause lowered saturation states may represent a potentially important management strategy to decrease dissolution mortality.