Oceanography Seminar

Alyson Venti
Rosenstiel School of Marine and Atmospheric Sciences
University of Miami

"A spatial-temporal analysis of coral calcification rates in Bermuda"

By: A. Venti₁, A. Andersson₂, C. Langdon₁

Abstract: Coral metabolic rates have a direct impact on the surrounding water chemistry and can significantly alter the local environment at different temporal and ecological scales, though the importance of this impact in the context of global climate change and ocean acidification is unclear. To this end the present study, taking advantage of Bermuda’s unique threshold environment for tropical coral reefs, assesses coral calcification rates across temporal (winter and summer), physical (light and dark) and spatial (platform edge and near shore) gradients.

Seasonal calcification rates are measured by application of a calcein dye staining method to adult colonies of Dipliria strigosa and Porites astreoides in their natural habitat. The results show significant seasonal difference with seasonal gradients ranging from as summer maximum of 486 (±7) mmolCaCO3m-2d-1 and 548 (±6) mmolCaCO3m-2d-1 to a winter minimum of 247 (±9) mmolCaCO3m-2d-1 and 203 (±10) mmolCaCO3m-2d-1 for P. astreoides and D. strigosa respectively. Seasonal data also display a significant summertime spatial decline in rates of calcification across the Bermuda reef platform from the rim reef towards shore, though no spatial trend is observed in the winter. Hourly light and dark calcification rates are achieved by in situ incubations of coral nubbins from the same species and show net positive calcification during light treatments with a maximum rate of 101 (±73) mmolCaCO3m-2h-1 and 73 (±50) mmolCaCO3m-2d-1 averaged among replicate samples of P. astreoides and D. strigosa respectively, and depressed rates or net dissolution during dark treatments with dissolution rates up to -73 (±53) mmolCaCO3m-2d-1 to -51 (±48) mmolCaCO3m-2d-1 averaged among replicate samples of P. astreoides and D. strigosa respectively, despite seawater aragonite saturation state remaining above 2.3. Light calcification rates show no significant spatial trend across the Bermuda reef platform, while dark rates show a significant difference with depressed calcification rates or net dissolution near shore compared to the rim reef. Scaling calcification from hourly to daily rates and from individual corals to reef communities enables comparison between different methods of measuring calcification, provides new insight into the role corals play in net ecosystem calcification, and reveals the temporal and spatial dimensions at which calcification may be most sensitive to increasing pressures from ocean acidification.

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Free

Event Sponsor
Oceanography, Mānoa Campus

More Information
956-7633, Alyson Venti Bio (PDF)

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