Effects of ocean acidification on bioerosion of burrowing bivalves in Moorea, French Polynesia.

Anthropogenic pCO₂ causing ocean acidification (OA) is predicted to decrease ocean surface pH by 0.14–0.35 units by 2100. Coral reef ecosystems will be particularly vulnerable to this unprecedented rate of decline in ocean pH. Most studies have focused on how OA will affect rates of calcification of coral reef organisms. However, bioerosion also could be sensitive to rapid change in ocean carbonate chemistry. I tested the effects of ocean acidification on the boring capacity of Lithophaga laevigata living within living massive Porites. L. laevigata, a boring bivalve, is abundant within massive Porites on the back reef of Moorea, French Polynesia. Data were collected for Lithophaga abundance in massive Porites across the backreef ranging in abundance from 3 to 95 ind/m². Size analysis of Lithophaga showed a correlation of the borehole opening and the size of the bivalve with allows quantification of growth and changes in the volume of the burrow over time. I conducted a month-long mesocosm experiment where coral cores with and without Lithophaga, were incubated in ambient (400 μatm) and elevated (800 μatm) pCO₂ treatments held at a constant temperature. I compared the bioerosion rate of Lithophaga in coral cores (based on changes in buoyant weight), and tested the hypothesis that OA increases the ability of bivalves to bioerode in elevated pCO₂ conditions. A better understanding of this abundant and active bioeroder under simulated future environmental conditions can provide insight to the poorly understood effects of OA on bioerosion.