Gross calcium carbonate production in Eastern Tropical Pacific coral reefs (Gorgona Island, Colombia)

Abstract

The production and accumulation of carbonate reef framework is the positive component of reef development. The main organisms participating in this process are corals and crustose coralline algae (CCA) because their combined calcareous skeletons construct and help to consolidate reef frameworks. We assessed the contribution (i.e. gross production) of corals and CCA to the calcium carbonate (CaCO3) budget of the 2 largest and most developed reefs of Gorgona Island (Pacific coast of Colombia). On each zone (back reef [BR], reef flat [RP], reef front [RF], and reef slope [RS]) of these reefs, we measured substrate rugosity, coral (Pocillopora spp.) and CCA cover, colony density for corals, skeletal density for CCA, and growth rates for the estimation of CaCO3 production rates. Pocillopora spp. corals contributed 93.1% of the total carbonate production, while CCA supplied the remaining 6.9%. CaCO3 production was higher at Playa Blanca reef, although CaCO3 production in the RF of La Azufrada (12.31 kg m-2 yr-1) was higher in comparison to the RF at Playa Blanca (8.45 kg m-2 yr-1). Otherwise, CaCO3 production was higher in all other reef zones (BR, RP, RS) of Playa Blanca, although only significantly higher in the BR (2.25 kg m-2 yr-1 at Playa Blanca against 0.29 kg m-2 yr-1 at La Azufrada). The RF contributed the most CaCO3, mainly due to its high live coral cover and rapid coral growth. Although the contribution of CCA is low, they are key for reef stability. CaCO3 production rates reported here (2.86 and 3.80 kg m-2 yr-1 in La Azufrada and Playa Blanca, respectively) are within the limits reported for Eastern Tropical Pacific reefs, and raise hope for the continued existence of coral reefs in an era of increasing threats to this ecosystem.