Coral recruitment, calcification & bioerosion

Investigating the rates of coral recruitment, calcification, and bioerosion and the factors that influence them on a relatively pristine reef system.

Coral recruitment, calcification and bioerosion are important processes on coral reefs that influence the amount of live coral cover, a reef’s physical complexity, and ultimately the community that lives on the reef and its health. We are investigating these processes in detail on the reefs of Palmyra Atoll. To measure recruitment, we are using clay tiles, each about 10 cm by 10 cm, which were hand-made in San Francisco in part from recycled toilets. The tiles provide a uniform surface for coral and algal recruits (or babies) to settle on. To measure calcification, we measure the amount of calcium carbonate produced by algae which settled on the tiles. To estimate calcification rates of adult corals, we collect small pieces of an abundant coral species, measure the density of their skeletons, and then use images of the reef (taken by the Benthic Community Patterns team) to determine how much the corals have grown. This makes it possible for us to find out how much weight the corals added to their skeleton during that year. Finally, to measure bioerosion (living organisms eroding coral skeletons, clam shells and reef rock), small pieces of coral skeleton (from the species Fungia paumotensis) are glued to a PVC tray and installed on the reef next to the settlement tiles so that we can measure the weight and volume loss of the coral over time. This equipment has been installed at 10 sites around Palmyra that are also used by other RTI research groups to facilitate cross-project data integration.

This research will help to explain variation in benthic community composition, contributing to our understanding of the factors that cause changes between benthic types – e.g., between coral and algae – and therefore coral reef resilience. By working closely with the other research groups within RTI, we will be able determine the factors that are responsible for differences in recruitment, calcification and bioerosion rates across a range of different sites and different environmental conditions. For example, we are working closely with the Herbivory and Coral Recruitment team to understand how recruitment patterns are influenced by biological factors, such as herbivory and fish grazing, and with the Physical Oceanography team to understand how recruitment patterns are influenced by physical factors, such as wave forcing and current flow. This new knowledge will help us to better understand what drives benthic recruitment and reef accretion, as well as how these processes influence other components of coral reef ecosystems. This will be useful for coral reef managers worldwide, providing a better understanding of key processes on reefs and how man-made modifications to local environments can impact upon coral reef health.

This research is led by Professor Jonathan Gardner and Dr. James Bell from Victoria University of Wellington in New Zealand, whose team includes Ms. Franziska Elmer. In addition, the team collaborates with Dr. Dan Brumbaugh from the Center for Biodiversity & Conservation at the American Museum of Natural History.