Linear extension rates and gross carbonate production of Acropora cervicornis at Coral Gardens, Belize.

Tuesday, 16 December 2014
Erin Peeling, Pennsylvania State University Main Campus, University Park, PA, United States, Lisa Greer, Washington and Lee University, Geology, Lexington, VA, United States, Halard Lescinsky, Otterbein University, Biology & Earth Sciences, Westerville, OH, United States, Robert Humston, Washington and Lee University, Biology, Lexington, VA, United States, Karl R Wirth, Macalester College, Saint Paul, MN, United States, Iliana B Baums, Pennsylvania State University Main Campus, Biology, University Park, PA, United States and Allen Curran, Smith College, Geology, Northampton, MA, United States
Branching Acropora coral species have fast growth and carbonate production rates, and thus have functioned as important reef-building species throughout the Pleistocene and Holocene. Recently, net carbonate production (kg CaCO3 m-2 year-1) has been recognized as an important measure of reef health, especially when monitoring endangered species, such as Acropora cervicornis. This study examines carbonate production in a thriving population of A. cervicornis at the Coral Gardens reef in Belize. Photographic surveys were conducted along five transects of A. cervicornis-dominated reefs from 2011-2014. Matching photographs from 2013 and 2014 were scaled to 1 m2 and compared to calculate 84 individual A. cervicornis linear extension rates across the reef. Linear extension rates averaged 12.4 cm/yr and were as high as 17 cm/yr in some areas of the reef. Carbonate production was calculated two ways. The first followed the standard procedure of multiplying percent live coral cover, by the linear extension rate and skeletal density. The second used the number of live coral tips per square meter in place of percent live coral multiplied by the average cross-sectional area of the branches. The standard method yielded a carbonate production rate of 113 kg CaCO3 m-2 year-1 for the reef, and the tip method yielded a rate of 6 kg m-2 year-1. We suggest that the tip method is a more accurate measure of production, because A. cervicornis grows primarily from the live tips, with only limited radial growth and resheeting over dead skeleton. While this method omits the contributions of radial growth and resheeting, and is therefore somewhat of an underestimate, our future work will quantify these aspects of growth in a more complete carbonate budget. Still, our estimate suggests a carbonate production rate per unit area of A. cervicornis that is on par with other Caribbean coral species, rather than two orders of magnitude higher as reported by Perry et al (2013). Although gross coral production at Coral Gardens is high by Caribbean standards, further assessment is required to understand the complete carbonate budget and how well live coral growth may balance bio-erosion or future predicted high CO2 acidification at this site.