AbstractsBiology & Animal Science

As a result of human activities, the level of CO2 in the Earth’s atmosphere has increased by nearly 40% since the industrial revolution. The rate of green house gas emission is accelerating, with current trends exceeding those predicted by “worst case” global climate change scenarios. The chemistry of the ocean is fundamentally changing as a result of increasing atmospheric CO2, which dissolves in seawater, making it more acidic, a process referred to as ocean acidification (OA). A rapidly expanding body of science is now being generated to understand the impact of this global environmental change. To date, most studies evaluating OA effects have centered on simplified laboratory analyses that expose single populations to short-term treatments in order to quantify responses of individuals. These designs offer a limited assessment of the degree to which phenotypic plasticity and local adaptation might influence the response of populations to OA. To address these questions, I carried out studies on members of Phylum Bryozoa, a species-rich clade of calcified colonial marine invertebrates distributed throughout the global ocean. Bryozoans were selected as a model system for this work because the clade exhibits a broad array of growth and calcification strategies, and because of the relative paucity of data regarding their expected response to future acidification. In addition, bryozoans can be subdivided into genetically identical replicate clones, which can then be assigned to separate treatments, allowing variation across treatments to be uniquely partitioned into the variance components of statistical models. In order to culture bryozoans for comparative experiments, I designed and constructed a new flow-through OA system at the Bodega Marine Laboratory, capable of finely manipulating both the temperature and carbonate chemistry of seawater, allowing for controlled laboratory experiments of long duration. In Chapter 1, I performed a comparative 9-month laboratory experiment examining the effects of ocean acidification on the native Californian bryozoan Celleporella cornuta. C. cornuta was sampled from two regions of coastline that experience different oceanographic conditions associated with variation in the intensity of coastal upwelling. Under different CO2 treatments, the biology of this bryozoan was observed to be remarkably plastic. Colonies raised under high CO2 grew more quickly, invested less in reproduction, and produced skeletons that were lighter compared to genetically identical clones raised under current atmospheric values. Bryozoans held in high CO2 conditions reduced their investment in skeletal carbonate, changed the Mg/Ca ratio of skeletal walls and increased the expression of organic coverings that may serve a protective function. Differences between populations in growth, reproductive investment, and the frequency of organic covering production were consistent with adaptive responses to…