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

• Published in: Coral reefs 1996, Vol.15 (2), p.101-107
• Main Authors: Reaka-Kudla, M L, Feingold, J S, Glynn, W
• Format: Article
• Language: English
• Subjects: Echinoidea; Eucidaris thouarsii; Marine; Porites lobata
• ISSN: 0722-4028; 1432-0975
• DOI: 10.1007/BF01771898

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 (11-13 m) depths on a severely bioeroded coral reef, Champion Island, Galapagos 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 super(-2) yr super(-1) (23.71 m super(-2) yr super(-1) or 60.5% decrease yr super(-1)). Losses did not vary significantly at depths tested. Internal bioeroders excavated an average of 2.6 kg m super(-2) yr super(-1) (2.41 m super(-2) yr super(-1) or 0.6% decrease yr super(-1)), while external bioeroders removed an average of 22.8 kg m super(-2) yr super(-1) (21.31 m super(-2) yr super(-1) or 59.9% decrease yr super(-1)); few encrusting organisms were observed on the PL blocks. Cathedral limestone blocks lost an average of 4.1 kg m super(-2) yr super(-1) (1.81 m super(-2) yr super(-1) or 4.6% decrease yr super(-1)), also with no relation to depth. Internal bioeroders excavated an average of 0.6 kg m super(-2) yr super(-1) (0.31 m super(-2) yr super(-1) or 0.7% decrease yr super(-1)), and external bioeroders removed an average of 3.5 kg m super(-2) yr super(-1) (1.51 m super(-2) yr super(-1) or 3.9% decrease yr super(-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 super(-2) yr super(-1)) versus shallow (35.0 mg cm super(-2) yr super(-1)) sites. External bioerosion reduced the average height of the reef framework by 0.2 cm yr super(-1) for hard substrata (represented by LS) and 2.3 cm yr super(-1) for soft substrata (represented by PL). The results of this study suggest that coral reef frameworks in the Galapagos 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 Galapagos Islands could be eliminated entirely.