Macrobioerosion of the coral reef-building species and impact on carbonate budgets on the reefs of Huatulco, Mexico

Abstract

Background. Coral reefs exist thanks to the delicate balance between calcification and erosion processes. However, due to anthropogenic pressures, bioerosive processes have become the main forcing factors in reef growth patterns. Nevertheless, due to the morphology of the reefs located in the Mexican South Pacific (extensive plates of pociloporids), estimating internal macrobioerosion is a challenge, resulting in a critical gap in bioerosion processes, particularly those occurring inside corals. Objectives. To measure the internal macrobioerosion of the main coral species and to know its impact on carbonate production in reefs. Methods. We used a computed tomography (CT) based approach to measure the volume of CaCO3 removed by different groups of macrobioeroders. Results. We estimated percentages of internal macrobioerosion between 16.80 % and 26.67 % of the total volume of the colonies. We observed that sponges and mollusks are the guilds that most bioerode species of branching and massive morphology, respectively. We found macrobioerosion rates of 1.51 ± 0.11 kg CaCO3 m-2 yr-1 for branched species and 0.53 ± 0.03 kg CaCO3 m-2 yr-1 for massive species. The measured bioerosion processes accounted for 39.02 % and 43.86 % of CaCO3 production. Conclusions. Although CT scanning represents higher costs than other approaches (i.e., X-rays), it is the only approach capable of measuring the internal macrobioerosion that occurs within the entire coral skeleton. This approach will allow us to produce more accurate carbonate balances than those that do not consider internal macrobioerosion, improving our estimates of the state of health of the reefs.