Rod Wilson, Ph.D.
University of Exeter, School of Biosciences
The Unexpected Contribution of Fish to the Marine Inorganic Carbon Cycle
Wednesday - March 25, 2009
Pacific Forum – 3:00 p.m.
The inorganic half of the marine carbon cycle includes biogenic reaction of seawater calcium and bicarbonate ions producing insoluble calcium carbonates (CaCO3) in the process of calcification. The majority of oceanic production of calcium carbonate is conventionally attributed primarily to marine plankton (coccolithophores and foraminifera in particular). However, marine teleost fish also produce precipitated carbonates within their intestines and excrete these at remarkably high rates. This is a by-product of drinking calcium-rich seawater, and active secretion of bicarbonate by the intestine. This plays important roles in a variety of physiological processes including osmotic and ionic regulation, acid-base balance and respiratory gas exchange. When CaCO3 excretion rates from individual fish are combined with estimates of global fish biomass it conservatively suggests they contribute 3-15% of total oceanic carbonate production, with more liberal assumptions providing values three times higher than this. Fish carbonates have a higher magnesium content and solubility than traditional sources, likely yielding faster dissolution with depth. This may explain up to a quarter of the increase in titratable alkalinity within 1000 m of the ocean surface, a controversial phenomenon that has puzzled oceanographers for decades. We also predict that fish carbonate production may rise in response to future increases in environmental CO2 (in contrast to other calcifying organisms), thus fish are likely to become an increasingly important component of the inorganic carbon cycle.