Survival and behavioral responses of juvenile crabs of Cancer edwardsii to severe hyposalinity events triggered by increased runoff at an estuarine nursery ground

Abstract

Estuaries represent highly dynamic environments, especially with respect to salinity. Exploitation of these habitats by marine species can assist their ecological success, however they require specialized behavioral strategies as well as physiological abilities to cope with the fluctuations of physical stressors. The Valdivia River estuary, southern Chile, is a site of high larval recruitment and juvenile abundance of the commercial crab species Cancer edwardsii, particularly during the spring and summer months. This estuary experiences severe low salinity events (< 7.5) for periods exceeding 6 h, that are associated with rainfall events and the subsequent higher flow rates of the tributaries. To determine the strategies employed by juvenile crabs living in the inner portions of the estuary in the face of changes in salinity conditions, we evaluated their survival and behavioral responses when exposed to a salinity gradient. Early juveniles were incubated at salinities of 0, 7.5, 15–22.5, 32 and crab mortality was recorded after 1, 6 and 12 h of exposure. In addition, early juveniles were experimentally exposed to continuous and gradual changes in saline conditions to evaluate their behavior, which was recorded on video. The main results were (1) despite most Cancer species being considered weak osmoregulators, 30% of individuals of C. edwardsii were able to survive freshwater conditions for 12 h. (2) burying and not quiescence behavior was associated with a drop in salinity, (3) in severe hyposaline conditions, the crabs increased their survival burying in the substrate, probably using higher salinity (> 22) interstitial water. Our findings suggest that burying behavior plays a key role in allowing the crabs inhabit inner estuarine areas where sudden and unexpected severe hyposalinity events occur.