MEPS 641:101-110 (2020)  -  DOI: https://doi.org/10.3354/meps13298

ABSTRACT: The form, condition, and survival of coral reefs depends on the balance between construction and destruction. Natural processes such as bioerosion can cause this balance to lean towards destruction, threatening these ecosystems. Polychaetes and sipunculids are members of the boring community; however, knowledge of their identity and role in the bioerosive process and their capacity to remove calcium carbonate (CaCO₃) in the coral reefs of the Eastern Tropical Pacific (ETP) is scarce. To tackle this problem, 5 experimental units of Pocillopora spp. branches were deployed in 4 reef zones (back-reef, reef-flat, reef-front, reef-slope) at 2 reefs (La Azufrada, Playa Blanca) for 2 time periods (P1: 6 mo, P2: 9 mo; n = 80) in Gorgona National Natural Park, Colombia. All worms (polychaetes and sipunculids) were identified and net removal and bioerosion rate were determined. In total, 137 worms were found: 64.2% in La Azufrada and 35.8% in Playa Blanca. There were no significant effects of reef, reef-zone, or duration of exposure (6 vs. 9 mo) for either net removal of CaCO₃ or bioerosion rate. Irrespective of reef or exposure duration, average net removal was 0.022 and 0.027 g during P1 and P2, and 0.032 and 0.018 g at La Azufrada and Playa Blanca, respectively. Average bioerosion rate, also irrespective of reef or exposure duration, was 2.553 and 2.011 g kg^-1 yr^-1 for P1 and P2, and 2.839 and 1.807 g kg^-1 yr^-1 at La Azufrada and Playa Blanca, respectively. The trend between periods was opposite for net removal and bioerosion rate, which indicates a decelerating impact of worms on the coral substrate as time passes. We suggest that, regardless of the small size of the boring worms, their role in CaCO₃ removal is very important. The information provided here—species involved and amounts removed—is key in understanding the bioerosion process in ETP coral reefs.

KEY WORDS: Bioerosion · CaCO₃ removal · Colombian Pacific · Gorgona Island