EXPERIMENTAL STUDIES OF RAPID BIOEROSION OF CORAL-REEFS IN THE GALAPAGOS-ISLANDS

Experimental carbonate blocks of coral skeleton, Porites lobata (PL), and cathedral limestone (LS) were deployed for 14.8 months at shallow (5-6m) and deep (11-13 m) depths on a severely bioeroded coral reef, C hampion Island, Galapagos Islands, Ecuador. Sea urchins (Eucidaris tho uarsii) were significantly more abundant at shallow versus deep sites. Porites lobata blocks lost an average of 25.4 kg m(-2) yr(-1) (23.7 l m(-2) yr(-1) or 60.5% decrease yr(-1)). Losses did not vary significan tly at depths tested. Internal bioeroders excavated an average of 2.6 kg m(-2) yr(-1) (2.4 lm(-2) yr(-1) or 0.6% decrease yr(-1)), while ext ernal bioeroders removed an average of 22.8 kg m(-2) yr(-1) (21.3 lm(- 2) yr(-1) or 59.9% decrease yr(-1)); few encrusting organisms were obs erved on the PL blocks. Cathedral limestone blocks lost an average of 4.1 kg m(-2) yr(-1) (1.8 lm(-2) yr(-1) or 4.6% decrease yr(-1)), also with no relation to depth. Internal bioeroders excavated an average of 0.6 kg m(-2) yr(-1) (0.3 lm(-2) yr(-1) or 0.7% decrease yr(-1)), and external bioeroders removed an average of 3.5 kg m(-2) yr(-1) (1.5 lm( -2) yr(-1) or 3.9% decrease yr(-1)) from the LS blocks. Most (57.6%) e ncrustation occurred on the bottom of LS blocks, and there was more ac cretion on block bottoms in deep (61.4 mg cm(-2) yr(-1)) versus shallo w (35.0 mg cm(-2) yr(-1)) sites. External bioerosion reduced the avera ge height of the reef framework by 0.2 cm yr(-1) for hard substrata (r epresented by LS) and 2.3 cm yr(-1) for soft substrata (represented by FL). The results of this study suggest that coral reef frameworks in the Galapagos Islands are in serious jeopardy. If rates of coral recru itment do not increase, and if rates of bioerosion do not decline, cor al reefs in the Galapagos Islands could be eliminated entirely.