The coral algal phase shift results in reduced biodiversity and ecosystem maturity. It is widely recognized that persistence times of these shifts have increased in. Pdf coral reef fishing and coralalgal phase shifts. Hyperspectral and physiological analyses of coralalgal.
Influence of coral and algal exudates on microbially. Local and global stressors have affected coral reef ecosystems worldwide. It is widely recognized that persistence times of these shifts have increased in the past few decades. A phase shift occurs on a coral reef when the cover of a substrate by scleractinian corals is reduced in favor of macroalgal dominance, and resilience of the former condition is retarded because of ecological processes andor environmental conditions. Coral reef degradation, whether driven by overfishing, eutrophication, declining water quality, or other anthropogenic factors, is associated with a phase shift towards a benthic habitat dominated by fleshy algae hughes 1994, mccook 1999, fabricius 2005. However, there are relatively few published studies exploring the variability in this interaction. Other components of the benthic community included turf algae 36. The coral algal phase shift phenomenon in coral reefs is generally believed to be the result of gradual increases in stress due to loss of herbivory andor increases in nutrient levels, but is usually triggered by a major perturbation such as a hurricane, crownofthorns infestation, outbreak of coral disease, or bleaching event. This phase shift done, 1992 could be a result of chronic pressures which favour. Pdf coral reef fisheries support tens of millions of people, mostly in developing countries. Herbivores help keep the substrate free from algae so that coral recruits can settle.
Anthropogenic stress has been shown to reduce coral coverage in ecosystems all over the world. This transition is referred to often as a phase shift. However, most of the knowledge concerning microbialization has not considered physical disturbances e. On coral reefs, it has been posited that the shift to an algal dominated state could be irreversible even after the disturbance is resolved because a feedback may exist if the algae are.
We assume that any free space on the reef is immediately covered with turf. A coralalgal phase shift in mesoamerica not driven by. Alternative stable states and phase shifts in coral reefs under. This study assessed the progression of a coral algal phase shift at a fringing reef around bonaire, dutch caribbean, by comparing current coral and algal benthic cover to historical data, from 1997 to 2008, at a site nearby. The year in ecology and conservation biology, 2009 coral reefs threats and conservation in an era of global change bernhard riegl,a andy bruckner,b steve l.
Switches from coral to algal dominance states and microbialization are the major processes underlying the global decline of coral reefs. The longterm shift from coral dominated reefs to algae dominated reefs is known as a coral algal phase shift. Our finding of a persistent phase shift from macroalgal to coral. In jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. Coral algal phase shifts in which coral cover declines to low levels and is replaced by algae 1,2,3 challenge the management of coral reefs worldwide 4,5, including in mesoamerica. Pdf coral reefs around the globe are subject to environmental and anthropogenic stressors that are causing. Here, we experimentally examine the resilience of coral dominated assemblages on the great barrier reef and the processes underlying a phase shift to macroalgal dominance figure 1a. Degradation of coral reefs typically involves a shift in community structure from a coral dominated reef to an algal dominated reef, a process known as coral algal phase shift 57. Recovery of diadema antillarum reduces macroalgal cover.
Coral algal phase shifts in which coral cover declines to low levels and is replaced by algae have often been documented on coral reefs worldwide. There are a wide variety of factors that can work in concert to lead to a coral algal phase shift. Many coral reefs around the world have degraded to a degree that their present intrinsic value and utility are greatly reduced. Experimental support for alternative attractors on coral reefs pnas. I conclude that nutrient overloads can contribute to reef degradation, but that they are unlikely to lead to phase shifts simply by enhancing algal growth rates and hence allowing overgrowth of corals. Paper progression of the coralalgal phase shift in the. This is particularly the case for coral reefs 11, 16, 17, 22, 24, where an important but unresolved issue is whether coral and macroalgae can be multiple attractors under the same environmental conditions or whether a persistent phase shift to macroalgae simply reflects a longterm change in the value of an underlying driver e. This study assessed the progression of a coral algal phase shift at the yellow sub study site on bonaire, dutch caribbean, by comparing current coral and algal benthic cover to historical data at a nearby study site. Spatial and temporal limits of coralmacroalgal competition.
Pdf a coralalgal phase shift in mesoamerica not driven. The most notorious phase shift in the mhi was first described in the 1960s and early 1970s in kaneohe bay, o. The coral algal phase shift phenomenon in coral reefs is generally believed to be the result of gradual increases in stress due to loss of herbivory andor increases in nutrient levels, but is usually triggered by a major perturbation such as a hurricane, crownofthorns infestation, outbreak of coral. Pdf progression of the coralalgal phase shift in the caribbean. We define resilience as the ability of reefs to absorb recurrent disturbances e. Catastrophes, phase shifts, and largescale degradation of a caribbean coral reef terence p. This paper expands the range of documented coral algal interactions by comparing the. Coralalgal phase shifts alter fish communities and reduce. Macroalgae, nutrients and phase shifts on coral reefs. Coralalgal phase shifts alter fish communities and reduce fisheries. A coral algal phase shift in mesoamerica not driven by changes in herbivorous fish abundance article pdf available in plos one 124. Pdf progression of the coralalgal phase shift in the.
In some instances, the alternative ecosystem state is undesirable from an. These shifts in benthic community structure have dramatic implications for the overall trophic structure of tropical reefs. Coral algal competition a major concern in assessments of global coral reef status is the shift from coral to algal dominance on reefs jameson et al. This has motivated coral reef management responses that include restriction and regulation of fishing. The term coral algal phase shift refers to the phenomenon of coral reefs shifting to unusually low levels of coral cover, associated with persistent states of high cover of.
Assessing evidence of phase shifts from coral to macroalgal. The vulnerabilities are free to increase to a maximum of 2. A phase shift occurs on a coral reef when the cover of a substrate by scleractinian corals is reduced in favor of macroalgal dominance, and resilience of the. A phase shift from macroalgal to coral dominance in the. Catastrophes, phase shifts, and largescale degradation of. Variant of model with direct negative effects by macroalgae on coral. The discussion emphasizes the role of various biological factors, such as sexual and asexual recruitment, competition, and predation, on coral populations and communities. Information about the openaccess article a coral algal phase shift in mesoamerica not driven by changes in herbivorous fish abundance. In contrast to other models of coralalgae phase shifts, reefs in our. This deprives corals of essential sunlight which can cause declines in coral condition and cover, and reduces the space available for coral settlement. Community phase or state shifts are characterized by a persistent change in the composition of dominant species and are known to occur in a variety of ecosystems, including savannas, lakes, and temperate subtidal reefs dublin et al. Many coral reefs throughout the western atlantic region have undergone dramatic changes in community structure over the past two decades. However, cage studies indicate that reduction in herbivory can lead to the proliferation of algae even in the absence of eutrophication.
Frontiers metagenomics of coral reefs under phase shift. A combination of factors can lead to phase shifts, including widespread coral mortality, declines in herbivory e. Coral resilience at malaukaa fringing reef, kaneohe bay. Despite being a welldocumented phenomenon, the underlying dynamics and mechanistic processes leading to algal dominance are still unclear. Following the 1979 sewage diversion, coral cover in the bay more than doubled in just four years 21 as nutrient levels decreased 19.
In jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose. High cover of dead coral, low cover of macroalgae, and a lack of correlation between the two are contrary to expectations of an algal phase shift 16. Macroalgae size refuge from herbivory promotes alternative stable. Shifts from coral dominance to algal dominance that suggest. This study assessed the progression of a coralalgal phase shift at a fringing reef around bonaire. Assessing evidence of phase shifts from coral to macroalgal dominance. A coralalgal phase shift in mesoamerica not driven by changes in. Similarly, sponges not only have the ability to colonize free sub.
Similar phase shifts in response to shipwrecks where coral and ccadominated communities change to communities dominated by opportunist benthic organisms have been documented on other coral reefs the term phase shift refers to the observation described by done 1992, where environmental conditions favor algal overgrowth of previously coral. The best known examples of these changes are found in the caribbean, where reefs that were formerly dominated by scleractinian corals and diminutive algal turfs have become overgrown by macroalgae. Based on this threshold, only 25 of the 1851 reefs coral to algal phase shift fig. In the caribbean, a combination of release from topdown control due to loss of the sea urchin diadema antillarum to disease, coupled with.
Hughes many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. Similar phase shifts in response to shipwrecks where coral and ccadominated communities change to communities dominated by opportunist benthic organisms have been documented on other coral reefs the term phase shift refers to the. Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. Phase shifts may be caused by many factors, encompassing both episodic pressures of short duration and chronic pressures of long duration. The coralalgal phase shift results in reduced biodiversity and ecosystem maturity. Though we can sometimes identify proximal causes outbreaks of coral predators and eroders. Relative increases in the biomass of smallbodied fish species mean higher productivity on reefs overall, but much reduced landings of traditionally targeted species. Coral algal phase shifts in which coral cover declines to low levels and is replaced by algae 1,2,3 challenge the management of coral reefs worldwide 4,5, including in mesoamerica 6. Degradation of coral reefs often involves a phase shift from abundant coral to abundant macroalgae. Phase shifts may be caused by many factors, encompassing both episodic pressures of short duration and chronic pressures of long duration 2. Coral reefs around the globe are subject to environmental and anthropogenic stressors that are causing habitat degradation and a decline in reef resilience. Phase shift severity is a continuum, so categorical delineations of relative severity are subjective and may be not be ecologically relevant.
Between 1996 and 2006, phase shift severity decreased in the. Turf algaemediated coral damage in coastal reefs of. The coralalgal phase shift results in reduced biodiversity and ecosystem. Phase shifts, herbivory, and the resilience of coral reefs. Reductions in herbivory caused by overfishing may enhance the likelihood of organic pollution causing a coralalgal phase shift following major disturbances.
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