UC San Diego

Echinoderms are important members of diverse marine ecosystems worldwide, necessitating that many species possess the physiological plasticity to adapt to highly variable environments. Yet, echinoderms generally exhibit strong sensitivity to changes in seawater pCO2/pH associated with ocean acidification (OA) and increases in seawater temperature associated with ocean warming (OW), often emerging in physiological changes that can alter their ecological interactions. The Western spiny brittle star, Ophiothrix spiculata, is one of the most abundant echinoderm species in the highly variable Southern California Bight, where they rely on limb autotomy and mobility to evade their many fish and invertebrate predators. The goal of this study was to determine the effects of climate change stressors on the anti-predator behaviors of O. spiculata, with the hypothesis that OA and OW would have measurable, contrasting effects on brittle star mobility. Brittle stars were exposed one of four treatments (N=12 each): control (pH 8.0/12°C), OA (pH 7.7/12°C), OW (pH 8.0/15°C), and OW+OA (pH 7.7/15°C). Following 29 days of exposure, kinematics of the righting, escape, and arm retraction responses were analyzed, along with arm flexibility. We found that brittle stars exposed to the combined OW+OA treatment had a shorter lag time for initiation of the escape response, but none of the other kinematics nor arm flexibility were affected by OA and OW. Under the combined OW+OA conditions used in this study, brittle stars appear to be more reactive, but otherwise the performance of their various anti-predator behaviors remain unaltered by experimental pH and temperature. Overall, O. spiculata exhibits little sensitivity to OA and OW conditions in regard to these specific ecologically important behaviors.