Coral Reef Recovery on Guam (Micronesia) After Catastrophic Predation by Acanthaster Planci

Abstract

At Tanguisson Reef, Guam, in 1968-1969 a population explosion of the coral-eating sea star Acanthaster planci devastated the coral community. In the wake of this predation, coral species richness, density, and cover were drastically reduced, and the species composition was altered. In two of three reef zones examined, < 1% coral cover remained. At the time of disturbance, some considered the magnitude of this and similar Acanthaster disturbances unprecedented, and predicted long recovery times because reefs were viewed as mature, stable communities. This major disturbance offered an opportunity to study the processes and rate of community recovery. Using the data from previous studies in 1970, 1971, and 1974, and my data from 1980-1981, I present a long-term analysis of coral community development. I have focused on coral recruitment, survivorship, and species settlement patterns in relationship to the remnant surviving population. The preference of Acanthaster planci for certain prey (e.g., Montipora and Acropora) shifted the species composition to one in which nonpreferred prey predominated (e.g., Porites and Leptastrea). The predominance of nonpreferred prey was short-lived, and by 1980, preferred prey were the primary colonists of two zones. The three biological zones (reef front, submarine terrace, and seaward slope) had their own characteristic species assemblages soon after the disturbance. Nonrandom recruitment or survival of juvenile corals (diameter ≤ 4 cm) established these zones. Although the percentage of juvenile corals fell throughout the survey, their highest density was reached after adult colonies were established. In 1980, of the 34 species examined, 79% showed a significant coefficient of association between adult and juvenile conspecifics. This association caused clumped species dispersion patterns to develop within zones. As the result of recruitment, species diversity rose from 84 species in 1970 to 154 species in 1981. As surviving corals and new recruits developed, the distribution of coral growth forms became more diversified. There was a drastic increase in coral cover (e.g., submarine terrace zone, 0.9% in 1970 to 65% in 1981). This increase in cover corresponded to an increase in size and number of the coral colonies In 12 yr, species richness, cover, and composition reached or exceeded measurements of comparable reefs before the disturbance. The recovery occurred faster than predicted by a stable equilibrium model because long-term successional changes were not required. Recovery was accelerated because Acanthaster did not destroy the structural integrity of reef framework. This rapid recovery from a natural disturbance demonstrates that some coral communities have a greater resilience than was once believed.

Multiple stressors on coral reefs: A long ‐term perspective

“…Data on long-term changes in species composition following hurricanes or other disturbances on coral reefs are relatively rare, for the obvious reason that it takes too long to study easily, but it is clear that some species recruit and grow much faster than others (see e.g., Connell 1973;Hughes 1985;Colgan 1987;Loya 1990). In addition, some branching corals can recover quickly from minor damage though passive tumbling and reattachment of vegetative fragments (e.g., Shinn 1972).…”

“…In addition, some branching corals can recover quickly from minor damage though passive tumbling and reattachment of vegetative fragments (e.g., Shinn 1972). The number of species recovers much faster after a disturbance than cover, because many species can recruit almost immediately (and colonies are initially small) (e.g., Hughes 1985;Colgan 1987;Loya 1990). Larval recruitment does not appear to be restricted initially to a small subset of species, i.e., many species can establish themselves (albeit at very different rates) soon after space becomes available.…”

“…However, there is little evidence to support an equilibrium view of coral reefs and much to refute it (e.g., Connell 1978;Pearson 1981;Colgan 1987;Tanner et al 1994). Rates of mortality of reef-dwelling organisms are often very high, even in the absence of any major perturbations (e.g., Connell 1973;Stimson 1985;Bythell et al 1993).…”

Palau’s coral reefs show differential habitat recovery following the 1998-bleaching event

“…The dynamics and recovery processes of coral communities are complex because reefs are subjected to a variety of disturbances that vary in intensity, frequency and duration (Pearson 1981;Huston 1985;Done 1987;Hughes 1989;Karlson and Hurd 1993;Tomascik et al 1996). Recovery from major disturbances ranges anywhere from five to hundreds of years, depending on the type of disturbance, the initial conditions and the type of coral community that was impacted (Pearson 1981;Colgan 1987;Endean et al 1989;Done et al 1991;Dollar and Tribble 1993). For example, the recovery of a sheltered stand of 2 m Porites lutea and Diploastrea helipora coral colonies, through recruitment and regrowth, may take hundreds of years to reach former size-frequency structure (Done 1987), while the recovery of shallow Acropora hyacinthus and A. digitifera populations may reach similar size frequency distributions within 5 years after a disturbance (Tomascik et al 1996).…”

Growth and reproduction of an estuarine population of the colonial hydroidCordylophora caspia (Pallas) in the northern Baltic Sea

“…Rinkevich & Loya, 1985;Buss, 1990) and predation (e.g. Colgan, 1987) are suggested to be important factors affecting growth, reproductive output and mortality of clonal invertebrates. The intensity of competition and predation also may be connected to initiation of sexual reproduction in some colonial invertebrates (Harvell & Grosberg, 1988).…”