Effects of ocean acidification and shading on growth, exoskeleton calcification and behavior of hermit crabs

Abstract

Anthropogenic activities release high carbon dioxide concentrations in the atmosphere, which is absorbed by the oceans and cause Ocean Acidification (OA) due to a pH reduction. This process affects marine calcifying organisms due to changes in dissolution and deposition of calcium carbonate in their tissues. Hermit crabs are an example of these organisms and may present variations in growth rate, behavior and exoskeleton calcification. Furthermore, environmental shading is induced by coastal constructions (e.g. harbors and docks) and may also originate negative effects in growth and behavior of hermit crabs as well as reduce the adaptability of animals in relation to changes in pH. Hermit crabs are abundant in Araçá Bay, which is threatened by shading due to the project of Port of São Sebastião expansion. As these animals are appropriate models to evaluate acute and synergic effects of OA and shading, the present study aims to evaluate OA and shading effects on the growth rate, calcification rate and behavior of hermit crabs with juveniles of Pagurus criniticornis collected in Araçá Bay. The experiment will be maintained for six months with four treatments: pH=7.6 and photoperiod of 12:12h; pH=7.6 and photoperiod of 0:24h; pH=8.1 and photoperiod of 12:12h (control); and pH=8.1 and photoperiod of 0:24h. Hermit crabs' molts will be collected over the six months. Analysis of Variance (ANOVA) will be applied to compare the shield length of the first and the last molts of each individual and evaluate growth rate. To evaluate calcification rate, the density of the last molt of each individual will be measured by micro tomography and ANOVA will be applied to compare the density among the treatments. At the end of the experimental period, the same hermit crabs will be used in behavior tests with presence of predator odor (danger signal) and gastropod odor (new shell available signal). ANOVA will be used to compare the response behavior between the treatments. In this context, the present study aims to provide information about synergic effects of OA and shading in marine organisms, which will allow understanding the potential impacts of global climate changes in association with local human impacts. (AU)