Can heterotrophic uptake of dissolved organic carbon and zooplankton mitigate carbon budget deficits in annually bleached corals?
- 569 Downloads
Annual coral bleaching events due to increasing sea surface temperatures are predicted to occur globally by the mid-century and as early as 2025 in the Caribbean, and severely impact coral reefs. We hypothesize that heterotrophic carbon (C) in the form of zooplankton and dissolved organic carbon (DOC) is a significant source of C to bleached corals. Thus, the ability to utilize multiple pools of fixed carbon and/or increase the amount of fixed carbon acquired from one or more pools of fixed carbon (defined here as heterotrophic plasticity) could underlie coral acclimatization and persistence under future ocean-warming scenarios. Here, three species of Caribbean coral—Porites divaricata, P. astreoides, and Orbicella faveolata—were experimentally bleached for 2.5 weeks in two successive years and allowed to recover in the field. Zooplankton feeding was assessed after single and repeat bleaching, while DOC fluxes and the contribution of DOC to the total C budget were determined after single bleaching, 11 months on the reef, and repeat bleaching. Zooplankton was a large C source for P. astreoides, but only following single bleaching. DOC was a source of C for single-bleached corals and accounted for 11–36 % of daily metabolic demand (CHARDOC), but represented a net loss of C in repeat-bleached corals. In repeat-bleached corals, DOC loss exacerbated the negative C budgets in all three species. Thus, the capacity for heterotrophic plasticity in corals is compromised under annual bleaching, and heterotrophic uptake of DOC and zooplankton does not mitigate C budget deficits in annually bleached corals. Overall, these findings suggest that some Caribbean corals may be more susceptible to repeat bleaching than to single bleaching due to a lack of heterotrophic plasticity, and coral persistence under increasing bleaching frequency may ultimately depend on other factors such as energy reserves and symbiont shuffling.
KeywordsCoral Zooplankton DOC Bleached Annual Heterotrophy
We thank Roberto Iglesias-Prieto, Ania Banaszak, Susana Enriquez, Robin Smith, and the staff of the Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico for their generous time and logistical support. We also thank Yohei Matsui, Teresa Huey, Dana Borg, and Amy Barrett for field and laboratory assistance. This research was funded by the National Science Foundation division of Biological Oceanography grants OCE-0825490 to AG and OCE-0825413 to MW. We also thank the Ford Foundation. Data archived at http://www.bco-dmo.org/project/516103. All work undertaken in this study complied with the current laws of Mexico and the USA.
- Bythell JC (1988) A total nitrogen and carbon budget for the elkhorn coral Acropora palmata (Lamarck). Proc 6th Int Coral Reef Symp 2:535–540Google Scholar
- D’Croz L, Mate JL, Oke JE (2001) Responses to elevated seawater temperature and UV radiation in the coral Porites lobata from upwelling and non-upwelling environments on the Pacific coast of Panama. Bull Mar Sci 69:203–214Google Scholar
- Niggl W, Glas M, Laforsch C, Mayr C, Wild C (2009) First evidence of coral bleaching stimulating organic matter release by reef corals. Proc 11th Int Coral Reef Symp, pp 905–911Google Scholar
- Tanaka Y, Miyajima T, Koike I, Hayashibara T, Ogawa H (2008) Production of dissolved and particulate organic matter by the reef-building corals Porites cylindrica and Acropora pulchra. Bull Mar Sci 82:237–245Google Scholar
- Wilkinson C (2008) Status of coral reefs of the world 2008. Global Coral Reef Monitoring Network and Reef and Rainforest Research Centre, Townsville Google Scholar