Calcium Carbonate Dissolution Above the Lysocline: Implications of Copepod Grazing on Coccolithophores

Meredith M White1,2, Jesica Davis Waller3, Laura Lubelczyk4, David Drapeau4, Bruce Bowler4, Amy Wyeth4, David Fields4 and William M Balch4, (1)Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States, (2)Bowdoin College, Earth and Oceanographic Science, Brunswick, ME, United States, (3)University of Maine, School of Marine Sciences, Walpole, ME, United States, (4)Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States
Copepod-coccolithophore predator-prey interactions are of great importance because they facilitate the export of particulate inorganic and organic carbon (PIC and POC) from the surface ocean. Coccolith dissolution in acidic copepod guts has been proposed as a possible explanation for the paradox of PIC dissolution above the lysocline, but warrants further investigation. Using a new application of the 14C-microdiffusion technique, we investigated the dissolution of coccoliths in copepod guts. We considered both an estuarine predator-prey model (Acartia tonsa and Pleurochrysis carterae) and an open ocean predator-prey model (Calanus finmarchicus and Emiliania huxleyi). Additionally, we considered the impacts of pCO2 on this process to advance our understanding of the effects of ocean acidification on trophic interactions. In the estuarine predator-prey model, fecal pellets produced immediately after previously-starved copepods grazed on P. carterae had PIC/POC ratios 27-40 % lower than that of the algae, indicating PIC dissolution within the copepod gut, with no impact of pCO2 on this dissolution. Subsequent fecal pellets showed increasing PIC/POC, suggesting that calcite dissolution decreases as the gut fills. The open ocean predator-prey model showed equivocal results, indicating high variability among individual grazing behavior, and therefore no consistent impact of copepod grazing on coccolith dissolution above the lysocline in the open ocean. We will further discuss the effects of fecal pellet PIC/POC ratios on sinking rate.