EFFECTS OF CLIMATE CHANGE ON THE STABLE CARBON ISOTOPE COMPOSITION OF ICHTHYOCARBONATE PRODUCED BY THE GULF TOADFISH

Marine bony fish are important contributors to the marine carbon cycle because they produce significant quantities of carbonate minerals (ichthyocarbonate) that are derived from high proportions of dietary carbon. The transformation of dietary carbon from the marine food web into ichthyocarbonate was proposed as a unique connection between the biological pump and the carbonate pump, which are central processes that drive Earth’s climate over sub-millennial timescales. While estimates suggest marine fish are one of the top carbonate producers in modern oceans, their contributions to the carbon cycle under future climate scenarios are poorly constrained. Published controlled experiments suggest that the production of ichthyocarbonate by the Gulf toadfish accelerated in response to increased pCO₂; however, the amount of dietary carbon incorporated into ichthyocarbonate has yet to be evaluated. Further, climate change encompasses both increased pCO₂ and elevated sea surface temperature, which may have synergistic impacts on marine fish and ichthyocarbonate production and composition. To examine the impacts of climate stressors on dietary carbon incorporation in ichthyocarbonate, Gulf toadfish (Opsanus beta) were exposed to increased temperature, increased pCO₂, and their combination (increased pCO₂ and temperature) in controlled laboratory experiments. Ichthyocarbonate was collected from the tanks daily, and from the intestines at the experiment conclusion to evaluate changes in the stable carbon isotope ratio (d¹³C value) of ichthyocarbonate in response to increased pCO₂ (1900 μatm by year 2300, as estimated by the Intergovernment Panel on Climate Change’s IS92a scenario) and temperature (~32˚C). Using a statistical source model based on d¹³C values to derive carbon source contributions, preliminary results indicate that higher temperature environments promote a greater incorporation of dietary carbon in ichthyocarbonate, with or without the addition of increased pCO₂. In addition, preliminary data suggests that ichthyocarbonate collected from the intestine contains more dietary carbon than excreted samples. Anticipated results will enhance understanding of climate change stressors on ichthyocarbonate composition, and further elaborate the role of marine fish in the carbon cycle.