Impacts of ocean acidification on Antarctic pteropods
In this part of our research program, we are collaborating with Dr. Victoria Fabry (Cal State San Marcos) to develop genomic resources for the pteropod Limacina helicina. The primary goal of this project is to collect samples of pteropod tissues in order to obtain DNA sequence from coding genes in the pteropod genome. Using these samples, we will then use 454 sequencing (www.454.com) to generate DNA sequence for L. helicina. This DNA sequence will then be available to facilitate gene expression profiling in pteropods.
Our target study organism is Limacina helicina, a shelled (thecosomatous) mollusk that is planktonic and routinely found in the plankton. The choice here is driven by the intersection of its ecological importance and the very high likelihood that shell formation and physiology will be detrimentally impacted by ocean acidification. Notably, thecosomatous pteropods are important food sources for a variety of Antarctic organisms (Foster & Montgomery 1993, Pakhomov et al. 1996) and can reach incredibly high densities with some regions of the Southern Ocean reporting thousands of individuals per cubic meter (Pane et al. 2004). Limacina helicina is abundant throughout the Southern Ocean, sometimes displacing krill as the dominant zooplankton (Cabal et al. 2002). In McMurdo Sound (where krill are absent), L. helicina may constitute more than 20% of the zooplankton biomass and reach concentrations exceeding 300 ind m-3 along the ice edge (Hopkins 1987, Foster 1989). In light of such central importance to the Antarctic foodweb, pteropods have been targeted as a critical study species with information regarding the impact of OA on this species being classified as urgent (Kleypas et al. 2006). This urgency is due to the fact that, since pteropod mollusc shells are made of aragonite, a form of CaCO3 that is very soluble, these organisms will be highly impacted by elevated CO2 and the resulting under-saturation of carbonate ion in seawater. Additionally, within the next 50 to 100 years, surface waters of the Southern Ocean will be the among the first surface ocean waters to become undersaturated with respect to aragonite due to ocean acidification (Orr et al. 2005). Taken together, these observations underscore the need to understand the response of pteropods such as L. helicina as a critical step in predicting the impact of ocean acidification on the Antarctic marine ecosystem.