Influence of sediment acidification on the burrowing behaviour, post-settlement dispersal, and recruitment of juvenile soft-shell clams (Mya arenaria l.)

Abstract

Ocean acidification (OA) is expected to elicit biological impacts in the near future by impacting the behaviour and physiology of marine animals, potentially leading to decreased fitness and survival. While acidification in the water column has received much attention, sediment acidification has received relatively little, although conditions in sediment porewater can already reach conditions far beyond those of near-future OA projections. This dissertation assesses some impacts of porewater acidification on the burrowing behaviour, post-settlement dispersal, and recruitment of juvenile soft-shell clams (Mya arenaria), and attempts to elucidate the biological mechanism for observed burrowing responses. In addition, this thesis attempts to assess the potential impact of sediment acidification on burrowing behaviour in the context of another ocean climate driver – ocean warming. In laboratory and field experiments, burrowing was depressed and post-settlement dispersal was increased by sediment acidification (low sediment pH) comparable to conditions often experienced by clams in the Bay of Fundy. In the lab, increasing temperature appeared to partially alleviate the effect of sediment acidification on burrowing, and GABAA-like neurotransmitter interference under low pH conditions was found to be the mechanism for hindered burrowing responses. In a field study, air temperature and sediment pH were good predictors of juvenile clam abundance, explaining 68% of the variability in clam abundance, although other factors such as rainfall appeared important. Coupled with previous studies, this thesis suggests that bivalve burrowing and recruitment will likely be impacted by near-future OA in areas where sediments will become more acidic as overlying seawater pH drops.