Bioerosión por ramoneo en los arrecifes coralinos del Pacífico colombiano: el caso de Diadema mexicanum (Echinoidea: Diadematidae)

Abstract

Echinoids are an important component of benthic communities; they can directly modify the distribution and relative abundance of algae and corals as well as be an agent in the process of bioerosion. Despite research on echinoids in the Colombian Pacific, the bioerosion rate due to grazing by Diadema mexicanum on the coral reefs of Gorgona Island remains unknown. Therefore,considering the relative high abundance of this echinoid and its potential negative effects on coral reefs, the main objective of this study was to determine the rate of bioerosion. To accomplish this, 1-m2 quadrats were randomly established in each of three reef zones (at lowtide, Backreef: ±1 m depth, Reef plain: ±0.5 m and Reef front: ±3.0 m) of La Azufrada fringing reef (Gorgona Island National Natural Park). Sea urchins were counted and measured (test diameter) inside the quadrats, and 30 urchins per zone (90 in total) were collected toestimate the bioerosion rate. The average sea urchin density and size (±SD) were 8.28±11.65 ind/m2 and 19.62±5.02 mm, respectively. The average bioerosion rate for the reef was 0.083 kg CaCO3/m2/yr, and it was significantly affected by echinoid size (p<0.001) and reefzone (p=0.0002). Additionally, a direct relationship was observed between intestinal calcium carbonate (CaCO3) and depth (p=0.043) and size (p<0.001). Finally, although large sea urchins may have important effects, it is unlikely that the bioerosion caused by D. mexicanumpresents a threat to La Azufrada fringing reef due to its low relative abundance; this is reflected by the relatively low bioerosion rate relative to other reefs in the Tropical Eastern Pacific.