Journal of Conference Abstracts

Disease and the Changing Face of Caribbean Coral Reefs

Richard B. Aronson (raronson@jaguar1.usouthal.edu)¹, William F. Precht (BPrecht@lawco.com)² & Ian G. Macintyre (Macintyre.Ian@nmnh.si.edu)³

¹ Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island, Alabama 36528, USA

² Law Engineering & Environmental Services, Inc., 5845 NW 158th Street, Miami Lakes, Florida 33014, USA

³ Department of Paleobiology, National Museum of Natural History, Washington, DC 20560-0121, USA

In recent decades, the cover of fleshy macroalgae has increased and coral cover has declined on Caribbean reefs. Macroalgal dominance is generally explained in terms of reduced herbivory or increased nutrient input. These hypotheses do not account for the increase in macroalgal cover even on relatively isolated reefs, where herbivory has not declined and nutrient concentrations have not increased recently. Coral mortality appears to be the most important prerequisite to macroalgal dominance, but macroalgal growth is enhanced by changes in herbivory and nutrient input. Populations of Acropora cervicornis (staghorn coral) and A. palmata (elkhorn coral), two of the most important framework-building species of Caribbean reefs, have died at many or most localities, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past twenty years, but white-band disease, a bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region (Aronson and Precht in press).

As in the Recent, hurricanes affected local populations of A. cervicornis and A. palmata during the Pleistocene and Holocene. On a regional scale, rapid increases in relative sea level during the Pleistocene deglaciations and early in the Holocene Transgression drowned some Acropora populations outright, resulting in deepening-upward sequences. Other populations were poisoned as inimical, lagoonal waters flowed onto fore reef habitats (Neumann and Macintyre 1985). Nevertheless, in many cases Acropora populations caught up to and kept pace with early Holocene rises in sea level, even in lagoonal settings (Macintyre 1988; Aronson et al. in press). The question is whether there was a regional Acropora kill at any time in the late Holocene that was comparable to the one observed over the past decades. The late Holocene was a time of relatively static sea level, so if any Caribbean-wide mortality events occurred they cannot be attributed to drowning or poisoning.

Coring studies in Belize suggest that the Recent, disease-induced mortality of A. cervicornis is without precedent in the late Holocene. A. cervicornis was the primary ecological and geological constituent of reefs in the central shelf lagoon of the Belizean barrier reef. After constructing reef framework for thousands of years, A. cervicornis has suddenly been drastically reduced in the area (Aronson and Precht 1997). Limited information from other parts of the Caribbean supports the pattern of continuous Holocene accumulation and sudden, Recent decimation of Acropora spp. (Hubbard et al. 1994).

The prospects are poor for rapid recovery of A. cervicornis populations, because the reproductive strategy of this species emphasizes asexual fragmentation at the expense of dispersive sexual reproduction. A. palmata also relies on fragmentation, but this species has a higher rate of sexual recruitment than its congener. The outbreak of white-band disease is coincident with increased human activity, and the possibility of a causal connection should be investigated.

Aronson RB & Precht WF, Paleobiology, 23, 326-346, (1997).

Aronson RB & Precht WF, Evolutionary Paleoecology; Columbia Univ. Press, (In press).

Aronson RB, Precht WF & Macintyre IG, Coral Reefs, 17, (In press).

Hubbard DK, Gladfelter EH & Bythell JC, Global Aspects of Coral Reefs; Univ. of Miami, 201-207, (1994).

Macintyre IG, AAPG Bull, 72, 1360-1369, (1988).

Neumann AC & IMacintyre, Proc. 5th Intl. Coral Reef Congr. , Tahiti, 3, 105-110, (1985).

184