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 realistic ally undersaturated (experimental) and saturated (control) with respec t to biogenic carbonates in order to evaluate the impact of carbonate dissolution on the survival of carbonate-bearing meiobenthos. Experime ntal manipulation of saturation state clearly demonstrated that substa ntial calcite undersaturation, in a range typical of organic-rich surf ace sediment (Omega(calcite) = IMP/K'(sp) = similar to 0.4), not only resulted in dissolution of abandoned tests but also increased mortalit y of the live benthic foraminfera Elphidium clavatum (exclavatum) thre efold relative to controls. Dissolution of discarded foraminifera test s occurred on time scales of 14 d. In addition, although no statistica lly significant correlation of dissolution with survival was found for the aragonitic bivalves Nucula annulata and Tellina agilis, experimen ts did show a tendency for increased mortality in undersaturated sedim ents. Mortality induced by calcite and aragonite undersaturation has i mplications for existing theories on production recruitment of shell-b earing benthos in nearshore environments and the coupling of biogeoche mical processes with the benthic community. These results help explain the seasonal dynamics of foraminifera reported previously in the lite rature and show that both live and dead assemblages of some organisms are components of the annual cycle of CnCO(3) dissolution and precipit ation in nearshore, organic-rich sediments.