Do bioturbators modify ocean acidification effects on marine meiobenthos? An experimental study on Abra alba

Allison Durand

The uptake of anthropogenic CO2 by the oceans has caused a decline in ocean pH of 0.1 and a further decrease of 0.2 and 0.3 units has been predicted for the current century. To investigate whether the presence of the biodiffuser Abra alba may alter ocean acidification effects on meiobenthos communities, a 6-week laboratory experiment was carried out. Sediment cores using subtidal sediment with bivalves present or absent were exposed to seawater at either pH 8.1 (ambient) or 7.8 (reduced).

The present study shows that neither pH nor the presence of A. alba seems to affect significantly meiofauna densities from Abra alba communities. Observed trends suggest that meiofauna vertical distribution might be structured by the presence of this bivalve. In the absence of Abra, acidification could have shifted vertical nematode distribution, probably related to migration and mortality. The presence of Abra seems to increase or decrease meiofauna density due to a possible change in the feeding behavior of Abra alba from suspension- and deposit-feeding to a higher deposit-feeding under reduced pH conditions. This thesis suggests that ocean acidification may, therefore, exert cascading effects on the meiofauna, altering A. alba communities and its ecosystem functioning.