Interactive effects of temperature, food, and skeletal mineralogy mediate responses to ocean acidification in a globally distributed bryozoan

Daniel S. Swezey (1), Jessica R. Bean (2), Aaron T. Ninokawa (1), Tessa M. Hill (1), Brian P. Gaylord (1), Eric D. Sanford (1)

1 Bodega Marine Laboratory, University of California at Davis, Bodega Bay, California 94923, USA
2 Museum of Paleontology, University of California, Berkeley, California 94720, USA

Background

Skeletal mineralogy varies substantially among marine invertebrate taxa, complicating predictions regarding the consequences of ocean acidification (OA). Organisms with skeletons made of high-magnesium (Mg) calcite could be especially vulnerable to OA given the elevated solubility of this form of calcification. Mg content is known to vary in response to temperature, CaCO3 saturation state, nutrients, and other factors. However, it is unknown how multiple concurrent changes in these oceanographic conditions might interact to affect calcification and growth.

Methods

In a 6-month laboratory experiment, we cultured genetically identical replicate clones of the globally cosmopolitan bryozoan Membranipora tuberculata, sampled from the northern California coast. Clones were raised under a factorial design, with varying food, temperature and dissolved CO2 levels, such that genetic replicates of a given colony were simultaneously exposed to different conditions. Colonies were photographed through time to assess changes in growth under experimental conditions, and the skeletal Mg content of colonies was analysed at the conclusion of the experiment using an electron microprobe.

Findings

Decreased food and warm temperatures (16°C, 21°C) simultaneously increased Mg concentrations in skeletal calcite, and this skeletal material was markedly more susceptible to dissolution compared to calcification added under cool temperatures (11°C) and high food availability. High CO2 and cool temperatures also induced breakdowns in zooid function, while elevated food availability increased growth.

Conclusions

These results suggest that oceanographic factors interact synergistically to affect dissolution potential. Moreover, organisms that poorly regulate the Mg content of calcification may be particularly sensitive to OA and future work should examine whether this is a widespread phenomenon in other taxa.