Porewater acidification alters the burrowing behavior and post-settlement dispersal of juvenile soft-shell clams (Mya arenaria)

Abstract

Although ocean acidification will impact marine organisms in the future, few studies have addressed the effects of sedimentary porewater acidification on benthic invertebrates. This study suggests that burrowing behavior and post-settlement dispersal of juvenile bivalves are altered by porewater acidification under present day conditions. We tested the efficacy of a novel method of stabilizing porewater pH using sediment underlain with food grade gelatin in both the lab and field, and then employed this method to test if porewater acidification could alter post-settlement clam dispersal under natural conditions. In the field, clams were exposed to a gradient of porewater acidification in manipulated (CO2 added) sediments for 24h to determine if acidification could alter dispersal patterns of juvenile clams under natural flow conditions; juvenile clam dispersal in the presence of different buffer types was also tested. In addition, juvenile clams were placed on unmanipulated, field-collected sediment cores in the lab which varied naturally with respect to acidification to test burrowing behavior in response to natural porewater pH. Gelatin stabilized porewater pH for 24–48h and its presence did not influence clam burrowing behavior. In the field, a significant negative relationship between the percent of clams dispersed and acidification was observed, while stabilizing porewater pH significantly decreased clam dispersal. In the lab, there was a significant positive relationship between the percent of clams burrowed and porewater acidification. This study suggests that porewater acidification has the capacity to alter the burrowing behavior and dispersal patterns of juvenile bivalves under natural conditions.