Antarctic Pteropods (Limacina helicina antarctica) as a Sentinel Organism for the Impact of ocean acidification

Chair: Vonda Cummings

Gretchen E Hofmann (1)*, Kevin M. Johnson (1), Umihiko Hoshijima (1), Juilet M. Wong (1)

1 Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara CA 93106 USA

Background
The pteropod Limacina helicina antarctica is a dominant member of the zooplankton assemblage in the Antarctic marine ecosystem, and is an important member of a relatively simple food web in nearshore waters. Limacina is a shelled pteropod, and the formation of the shell is jeopardized by dissolution in response to ocean acidification. Pteropods in general have been proposed as indicator organisms for the stress induced by future ocean acidification. Our goal was to develop a transcriptomic resource for this species that would support mechanistic studies to examine the physiological response of Limacina to acidification stress. We hoped to explore how gene expression analysis might be part of a larger effort to use pteropods as sentinel organisms in response to ocean acidification.

Methods
RNA sequencing (RNA-Seq) was performed on individuals exposed to a range of pH environments and elevated temperature. De novo assembly of the transcriptome was performed using Trinity. For gene expression analysis, pteropods were exposed to variable pCO2 conditions in a flow-through CO2 system set-up at McMurdo Station, Antarctica.

Findings
Annotation of the assembled L. antarctica transcriptome resulted in the identification of 81,229 sequences and with genes in numerous functional pathways. Using the de novo transcriptome, after 1 week of exposure to one of three pH treatments (8.2, 7.9 and 7.7), we identified over 2,000 differentially expressed genes. Genes for numerous cellular pathways were represented, including pathways involved in ion pumping, metabolism, and calcification. [These pH values represented pCO2 levels of 257, 531 and 938 μatm CO2 , respectively.]

Conclusions
The study identified numerous genes of interest that would support employing a molecular ecology approach in studying the response of L. antarctica to environmental stress. We propose that this resource is also applicable to pteropods collected in all sectors of the Southern Ocean, the Arctic and temperate regions.