Meeting Abstract
Calcifying organisms in marine systems are experiencing environmental changes due to ocean acidification (OA), an increased oceanic uptake of atmospheric CO2. Previous studies have established that acidification often hinders calcification. However the potential of acidification to alter interactions between species is still poorly understood. The calcifying bryozoan, Membranipora membranacea, presents an informative model system to understand OA effects on species interactions. Membranipora rapidly forms defensive chitinous spines in the presence of the predatory nudibranch, Corambe steinbergae, which are effective in reducing predation. Spine formation is dependent on the growth of new calcified zooids. This project experimentally investigated effects of OA on bryozoan growth rates and nudibranch-induced spine formation in Membranipora. Bryozoan colonies were divided and cultured in ambient or low pH treatments, with or without nudibranch cue. OA impacts on growth, mortality and spine formation in Membranipora were assessed. The presence of nudibranchs reduced bryozoan growth rates in both ambient and low pH treatments. Contrary to hypothesized results, increased growth was observed in low pH treatments compared with ambient treatments. While there were general trends, there was also high variability among colony responses. Growth and mortality data were used to parameterize a size-structured partial differential equation model of bryozoan populations. The resulting model is an empirically-based representation of bryozoan growth, including predation and acidification effects, that scales up individual colony responses to population and community levels, and lends insight to how changes in inducible defenses under future oceanic conditions influence community dynamics.
