The effects of climate change induced ocean acidification on the physiology of adult sea urchin Evechinus chloroticus

Chair: Vonda Cummings

Emily J. Frost (1), Mary A. Sewell (1)
1 School of Biological Sciences, University of Auckland, New Zealand

Background
Ocean acidification can affect organisms by driving them outside a window of optimal fitness, altering the energetic costs of important physiological processes. The maintenance of acid-base homeostasis is central to the ability for organisms to tolerate changes in seawater pCO2 and is typified by the efficiency of ion and acid/base regulation. Acid/base regulation can, however, require large amounts of energy. Often, this increase in energy can only be attained when ATP is shifted from other physiological processes, reducing the energy available to processes such as somatic and gonadal growth.

Methods
Adult Evechinus chloroticus were exposed to pCO2 treated seawater (380 µatm, 1000 µatm and 1800 µatm) for three-months, during which, we assessed the changes in the scope for growth, aerobic metabolism, coelomic fluid pH, concentration of coelomic Na+, K+, Ca2+ and Mg2+ through Atomic Absorption Spectrophotometry, coelomic total CO2, the expression of key ion-regulating and reproductive enzymes, and changes in reproductive capacity through gonadosomatic index and histology.

Findings
Significant changes in coelomic fluid pH, Na +, K+ and total CO2 were observed, such that, those animals from both pCO2 treatments had a significant increase in the concentration of total CO2, which mirrored increases in coelomic [Na+] and [K+].These animals also exhibited a reduction in aerobic metabolism, weight gain and test growth. Moreover, animals maintained in 1800 µatm seawater were unable to fully compensate for the reduction in coelomic fluid pH. This paralleled the observed 73% reduction in gonadosomatic index.

Conclusions
Acid/base disturbance was observed in the coelomic fluid of adult E.chloroticus, resulting in significant changes in coelomic fluid biochemistry, this was especially evident in the adults maintained at seawater pCO2 of 1800µatm. In addition to the reduction in aerobic metabolism, the results suggests that there is a re-partitioning of available energy away from somatic and gonadal growth.