Meeting Abstract
Ocean acidification (OA), resulting from increased oceanic CO2 concentrations, causes a suite of chemical changes that present significant environmental stress for calcifying organisms. OA effects may potentially be synergistically amplified or reduced by species interactions as they propagate up to population and community levels, altering effects predicted by studies of calcifier responses in isolation. The colonial calcifying bryozoan, Membranipora membranacea, and the predatory nudibranch, Corambe steinbergae, present a unique model system to explore effects of OA on predator-prey interactions at multiple levels. Membranipora colonies exhibit a quantifiable inducible defense, protective spines on newly calcified zooids, on chemically detecting Corambe. OA effects on prey growth and defenses were quantified across a wide range of pH (7.0 to 7.9) with or without waterborne predator cue. Following exposure, predation rates were assessed by quantifying zooids consumed by Corambe over a 24-hour period. Consistent with previous studies, bryozoan colonies exhibited maximum growth at moderately low pH. Spine formation continued at pH values as low as 7.0. While predator responses were variable, preliminary results suggest that predation rates on undefended colonies may be unaffected by pH. However, in defended colonies, spines formed in low pH may confer less advantage than those formed in ambient conditions. A population dynamics model, used to compare spatial distributions of Membranipora under various combinations of predation pressure and acidification, suggests interactions between these stressors experienced earlier in the season may be more influential in determining demographic patterns as space competition is intense.
