The Effects of Varying Temperatures and Food Availability on the Reproductive Output of the Acorn Barnacle: Chthamalus fissus

Climate change is predicted to intensify ocean warming and the reduction in phytoplankton abundance, potentially disrupting reproductive processes in filter-feeding intertidal invertebrates. This study investigated the combined effects of water temperature increases and food availability on the reproductive output on Chthamalus fissus, a dominant intertidal barnacle species found along the Southern California coastline. Using a controlled laboratory experiment, adult barnacles collected from the nearshore rocky intertidal habitat in La Jolla, California, were exposed to two temperature regimes (ambient water temperature ~ 18°C and elevated water temperature ~ 20-21°C) and two food concentration treatments (low and high phytoplankton and rotifer densities). Each week, temperature and salinity were monitored, tanks were cleaned, and the number of barnacle nauplii produced (barnacle reproductive output) was measured for each experimental treatment. Temperature had a significant effect on reproductive output (p=0.0046), with warm-water treatments producing more nauplii than cold-water treatments, regardless of food concentration. Food availability did not significantly affect reproductive output (p=0.3372), and no significant interaction between temperature and food was detected. These results suggest that elevated temperatures may enhance short-term reproduction in C. fissus, but the long-term effects under reduced food conditions remain uncertain. Given the ecological role of barnacles as habitat-forming species, shifts in their reproductive output under climate change could have cascading impacts on intertidal community structure.