Changes in abundance of coral-reef bottom components related to mass mortality of the sea urchin Diadema antillarum

Abstract

We studied the effect of a reduction in grazing pressure, following mass mortallties of the abundant sea urchin Diadema antillarum, on coral-reef bottom components at Curaqao (Netherlands Antilles). We surveyed cover of fleshy and fllamentous algae, scleractinlan corals, crustose coralline algae, loose sediment and a miscellaneous category in permanent quadrats at depths of 27, 15 and 3 m during 1 yr. At all depths, cover of fleshy and filamentous algae increased significantly, reaching a new equhbrium. Corals, crustose corallines and/or loose sediment generally decreased in cover, but not all changes were significant. At the species level, we found the coral Agar~cia agaricites, at 15 m, to be relatively vulnerable among corals. The macroalgae Lobophora variegata and Dictyota spp. increased significantly in cover at 27 and 15 m, respectively. We expect, in view of the observed continuously low rates of recrutment of D. antillarum, and in vlew of the new equilibrium in algal cover, no rapid return to the origlnal situation, unless other herbivorous organisms will take over the role of D. anWlarum.

Does Slow and Variable Recovery of Diadema antillarum on Caribbean Fore-Reefs Reflect Density-Dependent Habitat Selection?

“…Disease hit the population on October 6th 1983 and spread to affect the entire island during the following weeks, causing population decreases between 98 and 100% (Bak et al, 1984). The loss of D. antillarum in Curacao, like elsewhere, preceded a significant increase in fleshy and filamentous algae on shallow reefs (Vansteveninck and Bak, 1986) and a significant decrease in bio-erosion and structural complexity (Bak et al, 1984).…”

Deep water vegetations of Lobophora variegata (Phaeophycae) in the coral reef of Curagao: population dynamics in relation to mass mortality of the sea urchin Diadema antillarum

“…This increase was most prominent between October 1983 and Apnl 1984 and pardelled the same trend in mean blade size. But, as fluctuations in mean growth rate were not significant, and as trends at B1 (with high pre-mortality Diadema antilldrum densities) were not parallelled by similar trends at HB (with low premortality D. antdlarum densities), we attribute this increase to an effect of D. antillarum mass mortality (Bak et al 1984, de Ruyter van Steveninck & Bak 1986) rather than to seasonal effects.…”

“…Higher disappearance rates between May 1984 and January 1985, probably as a consequence of increased grazing by herbivorous fishes (Ogden et al 1973, Hay & Taylor 1985, limited further expansion of the L. variegata vegetation and a new equilibrium was reached between L. variegata cover and grazing. It is interesting that de Ruyter van Steveninck & Bak (1986) observed the same shift in the abundance of algal turfs: 7 mo after Diaderna antiUarum mass mortality cover of turf a!gae at 27 m depth, at ! c c a k : : 51, h& reached a new equilibrium level, ca 20% higher than that in October 1983.…”

“…Evidently, this does not mean that L. variegata cannot extend its distribution by colonizing newly available substratum. According to Carpenter (1981) Bak (1986) and in Jamaica by Morrison (1984b) andLddel &Ohlhorst (1986).…”

“…Cover, blade size, growth rate, longevity and presence of sporangia were recorded. The results are interpreted in relation to the disappearance of the D. antiUarum population, which suffered mass mortality in the course of this investigation (B& et al 1984, de Ruyter van Steveninck & Bak 1986). AU through 1984 and 1985 D. anwarurn remained virtually absent from the coral reef of Curaqao (Table 1).…”