Influence of carbonate dissolution on survival of shell-bearing meiobenthos in nearshore sediments

Sediment plugs containing natural populations of benthic foraminifera and juvenile bivalves were introduced into seawater chambers realistically undersaturated (experimental) and saturated (control) with respect to biogenic carbonates in order to evaluate the impact of carbonate dissolution on the survival of carbonate-bearing meiobenthos. Experimental manipulation of saturation state clearly demonstrated that substantial calcite undersaturation, in a range typical of organic-rich surface sediment (Ω(calcite) = IMP/K'(sp) = ~0.4), not only resulted in dissolution of abandoned tests but also increased mortality of the live benthic foraminfera Elphidium clavatum (exclavatum) threefold relative to controls. Dissolution of discarded foraminifera tests occurred on time scales of 14 d. In addition, although no statistically significant correlation of dissolution with survival was found for the aragonitic bivalves Nucula annulata and Tellina agilis, experiments did show a tendency for increased mortality in undersaturated sediments. Mortality induced by calcite and aragonite undersaturation has implications for existing theories on production recruitment of shell-bearing benthos in nearshore environments and the coupling of biogeochemical processes with the benthic community. These results help explain the seasonal dynamics of foraminifera reported previously in the literature and show that both live and dead assemblages of some organisms are components of the annual cycle of CaCO₃ dissolution and precipitation in nearshore, organic-rich sediments.