Effects of ocean warming and acidification on the early benthic ontogeny of an ecologically and economically important echinoderm

The sea urchin Loxechinus albus is a benthic shallow water coastal herbivore and an exploited natural resource. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) for small juveniles of this species. Individuals were exposed for 7 mo to contrasting pCO(2) (similar to 400 and 1200 mu atm) and temperature (similar to 16 and 19 degrees C) levels. We compared grazing rates during the first 2 mo of rearing. After an additional period (2 to 7 mo), we compared body size change (in terms of diameter, and wet and buoyant weight), self-righting, dislodgement resistance, foraging speeds, test dissolution rate, oxygen consumption and strength of structural integrity. Regardless of the temperature, urchins reared under present-day pCO2 grazed preferentially on algae also reared under present-day pCO2 conditions. However, urchins reared under elevated pCO2 at both temperatures exhibited no grazing preference. Other traits such as growth rate in terms of diameter, vertical foraging speed and tenacity were not affected significantly by pCO2, temperature and the interaction between them. However, growth rate in terms of wet weight, metabolism and dissolution rate of empty urchin tests was significantly affected by temperature and pCO2 but not by the interaction between them. At 16 degrees C, self-righting was faster for individuals reared at elevated pCO2 but no differences were found at 19 degrees C. We conclude that OA and OW may disrupt some early benthic ontogenetic traits of this species and thus have negative ecological and economic consequences. However, most traits will be not threated by the 2 investigated stressors.