A laboratory-based, experimental system for the study of ocean acidification effects on marine invertebrate larvae

Nann A. Fangue, Michael J. O'Donnell, Mary A. Sewell, Paul G. Matson, Anna C. MacPherson, and Gretchen E. Hofmann

Limnol. Oceanogr. Methods 8:441-452 (2010) | DOI: 10.4319/lom.2010.8.441

ABSTRACT: Ocean acidification, a reduction in ocean pH due to the uptake of anthropogenic carbon dioxide (CO2) by surface waters, has recently emerged as a research theme in marine biology due to an expected deleterious effect of altered seawater chemistry on calcification. Owing to the importance of larval survival and dispersal for the maintenance of adult populations, early life history stages of calcifying marine invertebrates have been a central focus of this research. Here, we present an experimental system that unites the culturing needs of larval invertebrates with methods for careful control, monitoring, and manipulation of seawater carbonate chemistry necessary to conduct laboratory-based studies of ocean acidification. Using a series of mass flow controllers, the system produces three unique pCO2 levels, which are bubbled into gas-mixing reservoirs for equilibration with filtered seawater. This seawater is then delivered to larval culturing vessels providing the larvae with a continual supply of clean seawater consistent with optimal culturing methodologies. In this flow-through system, pCO2 levels are determined at 3 points: the inflowing seawater, the gas-mixing reservoirs, and the larval culture vessels. The delivered gas pCO2 values are adjusted to achieve the desired stable-state relationship for each experimental pCO2 treatment. We evaluated the performance of this system in terms of 1) the stability of the parameters of the inorganic carbonate system in all experimental vessels and 2) our ability to successfully rear larvae using these methodologies. Our results indicate the suitability of this design for successful manipulation of pCO2 for ocean acidification experiments on larvae.