Impacts of Climate Change on Intertidal Communities: Effects of Elevated Temperature and Predator Exposure on Chthamalus fissus

Elizabeth Bushnell, University of San Diego, EOSC, San Diego, CA, United States and Nathalie Reyns, University of San Diego, Environmental and Ocean Sciences, San Diego, CA, United States
There is increasing concern that climate change might negatively impact foundation species such as barnacles that create important habitats in the rocky intertidal. In southern California, as sea surface temperature has increased, the predatory snail, Mexacanthina lugubris lugubris has expanded its range northward into the San Diego region where it preys on the barnacle Chthamalus fissus. In addition to higher predatory pressure, barnacles might also be experiencing thermal stress due to increased warming. We evaluated the impacts of temperature and M. lugubris snails on growth and mortality of the barnacle C. fissus. Newly-settled barnacle metamorphs were collected in the field on plates, and were reared under lab conditions using two experimental protocols. First, to examine the effects of temperature, replicate barnacles were reared at 14°C, 22°C and 28°C for eight weeks. Barnacles were counted daily to track mortality and photographed weekly to measure growth. Barnacles reared at 22°C were significantly larger at 8 weeks than those at 14°C but had lower survivorship; barnacles reared at 28°C did not survive beyond 6 weeks. Secondly, we examined the effects of snail predation on barnacle morphology by rearing replicate barnacles in direct and indirect contact with snails for 8 weeks. The operculum length and width were measured near the end of the experiment to determine if barnacle morphology changed in response to snail exposure. Although, no significant differences in morphology were found between barnacle metamorphs or adults reared in contact or in the absence of snails, mortality was significantly higher in metamorphs and adults when barnacles were exposed to snails at 8 weeks post settlement. Results from our temperature experiments indicate that C. fissus would not tolerate the projected 4°C warming by 2100 due to climate change. Additionally, with increasing snail densities in southern California, we predict higher barnacle mortality. Thus, increased sea surface temperature can have ecological consequences on rocky intertidal communities.