Experimental studies of rapid bioerosion of coral reefs in the Galápagos Islands

Abstract

Experimental carbonate blocks of coral skeleton,Porites lobata (PL), and cathedral limestone (LS) were deployed for 14.8 months at shallow (5–6 m) and deep (11–13m) depths on a severely bioeroded coral reef, Champion Island, Galápagos Islands, Ecuador. Sea urchins (Eucidaris thouarsii) were significantly more abundant at shallow versus deep sites.Porites lobata blocks lost an average of 25.4 kg m⁻²yr⁻¹ (23.71 m⁻²yr⁻¹ or 60.5% decrease yr⁻¹). Losses did not vary significantly at depths tested. Internal bioeroders excavated an average of 2.6 kg m⁻² yr⁻¹ (2.41 m⁻² yr⁻¹ or 0.6% decrease yr⁻¹), while external bioeroders removed an average of 22.8 kg m⁻² yr⁻¹). (21.31 m⁻² yr⁻¹). or 59.9% decrease yr⁻¹). few encrusting organisms were observed on the PL blocks. Cathedral limestone blocks lost an average of 4.1 kg m⁻² yr⁻¹). (1.81 m⁻² yr⁻¹). or 4.6% decrease yr-'), also with no relation to depth. Internal bioeroders excavated an average of 0.6 kg m⁻² yr⁻¹). (0.31 m⁻² yr⁻¹). or 0.7% decrease yr⁻¹). and external bioeroders removed an average of 3.5 kg m⁻² yr⁻¹). (1.51 m⁻² yr⁻¹). or 3.9% decrease yr⁻¹). from the LS blocks. Most (57.6%) encrustation occurred on the bottom of LS blocks, and there was more accretion on block bottoms in deep (61.4 mg cm⁻² yr⁻¹). versus shallow (35.0 mg cm⁻² yr⁻¹) sites. External bioerosion reduced the average height of the reef framework by 0.2 cm yr⁻¹). for hard substrata (represented by LS) and 2.3 cm yr⁻¹). for soft substrata (represented by PL). The results of this study suggest that coral reef frameworks in the Galápagos Islands are in serious jeopardy. If rates of coral recruitment do not increase, and if rates of bioerosion do not decline, coral reefs in the Galápagos Islands could be eliminated entirely.