Algal blooms on coral reefs have been associated with negative ecological impacts on reefs smith et al. However, there are relatively few published studies exploring the variability in this interaction. We observed sites under different coral turf algae dominance stages, coupled with extremely low fish. On south pacific coral reefs, the macroalga turbinaria 26 ornata has expanded its range and habitat but, unlike algae that often dominate after 27 phase shifts, t. These clues may facilitate broad area assessments of shallow reef areas via aircraft, space shuttles, or satellites. A coralalgal phase shift in mesoamerica not driven by changes in. The longterm shift from coral dominated reefs to algae dominated reefs is known as a coral algal phase shift. 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. This phase shift done, 1992 could be a result of chronic pressures which favour. Within a short period of time may to september, coral coverage shrank to 17. Whether the shift takes place abruptly or over a long period, there is usually the implication that the phase shift will persist e. Algal blooms are becoming increasingly widespread on a worldwide scale with the phenomenon involving both geographical expansion and increased biomass. The emergent role of smallbodied herbivores in pre.
It is widely recognized that persistence times of these shifts have increased in the past few decades. However, pinpointing the actual factors potentially responsible can be. Permanent phase shifts or reversible declines in coral. The overgrowth of coral by the macroalga dictyosphaeria. Microbial bioenergetics of coralalgal interactions peerj. 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. Reversing this coralalgal phase shift has proven hugely challenging, but a. Frontiers metagenomics of coral reefs under phase shift. Understanding the causes and consequences of phase shifts from coral to algal dominance on tropical reefs has been a central theme in reef. In the degradation of coral life forms, massive corals were more highly damaged 7. However, most of the knowledge concerning microbialization has not considered physical disturbances e.
Various reasons have been proposed to explain this phenomenon including increased human disturbance, pollution, or changes in coral reef biota that serve a major ecological function such as depletion of grazers. Shifts from coral dominance to algal dominance that suggest. Pdf coralalgal phase shifts alter fish communities and. 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. 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. Transient grazing and the dynamics of an unanticipated coral. Crustose coralline algae cca, in contrast, are gen erally. Such surprising outcomes may pinpoint important yet overlooked mechanisms that drive ecosystems into undesirable states. There is an urgent need for studies aimed at quantifying and simulating cause and effect aspects of the phase shift, including humanenvironment coupling.
Phase shift from a coral to a corallimorphdominated reef. These paired shocks undermined the resilience of the ecosystem, leaving many reefs incapable of full recovery when damaged. Effects of ocean acidification on the potency of macroalgal. Coralalgal phase shifts alter fish communities and reduce. Coral algal phase shift the reduction in the abundance of herbivorous indicator species leads to a reduction of grazing mcmanus and polsenberg 2004. Coral reef fishing and coralalgal phase shifts citeseerx. 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. Coralalgal phase shifts alter fish communities and. Our results demonstrate a shift in community metabolism towards heterotrophic dominance at the coral algal interaction interface.
Phase shifts in coral reef communities and their ecological significance. B after 32 months, the cage mesh was removed, exposing intact macroalgal stands approx 5 to 8 kg algae m2 to resident herbivores. In recent years coral reefs have suffered many impacts, from local anthropogenic influences such as pollution, fishing, and coastal development, to. 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. High resilience masks underlying sensitivity to algal. Paper progression of the coralalgal phase shift in the. Phase shifts may be caused by many factors, encompassing both episodic pressures of short duration and chronic pressures of long duration 2.
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. The fish population on jamaican reefs has also been steadily declining over the years as a result of poor fishing practices and this has had a direct impact on the resilience of these reefs. Pdf progression of the coralalgal phase shift in the. Algal dominance and impacts of tourism on coral reefs in. Jun 20, 2018 extreme disturbances often lead to community reorganisations, yet sometimes ecosystems unexpectedly fail to recover. As these ecosystems undergo transition, there is an increased incidence of coral macroalgal interactions. Based on this threshold, only 25 of the 1851 reefs coral to algal phase shift fig. Coral cover has been sustained despite low urchin densities 0. We investigated the impact of algal overrunning and tourism on coral reefs over the last eight years. Ocean acidification oa due to elevated co2 is hypothesised to. In this case, the composition of the reefassociated fish assemblage will change and. Experimental support for alternative attractors on coral reefs.
Pdf sleeping functional group drives coralreef recovery. Phase shifts in coral reef communities and their ecological. Baseline survey results indicated a vast competition and phase shift of corals to algal state. Virtually all macroalgal blooms appear to be initiated by nutrient enrichment. Coral reef fisheries support tens of millions of people, mostly in developing. Transient grazing and the dynamics of an unanticipated. 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.
The emergent role of smallbodied herbivores in preempting. However, cage studies indicate that reduction in herbivory can lead to the proliferation of algae even in the absence of eutrophication. Using longterm field observations, experimental manipulations and mechanistic modelling, we document the drivers of an unexpected phase shift from coral to. Jun 21, 2014 the coral algal phase shift results in reduced biodiversity and ecosystem maturity. Coral algal phase shifts in which coral cover declines to low levels and is replaced by algae have often been documented on coral reefs. Subjects marine biology keywords coral reef ecology, phase shift, coastal influence, coral algae contacts introduction phase shifts from scleractinian corals to other invertebrates such as sponges maliao. 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.
Sensitivity of coral recruitment to subtle shifts in early. A coralalgal phase shift in mesoamerica not driven by. Current biology 16 2006 elsevier ltd all rights reserved doi. Coral reefs in casurina beach are largely used by native fishermen for artisanal fishing, sea cucumber collection and for tourism. Reductions in herbivory caused by overfishing may enhance the likelihood of organic pollution causing a coral algal phase shift following major disturbances. Many coral reefs have phase shifted from coral to macroalgal dominance. This study assessed the progression of a coral algal phase shift at a fringing reef around bonaire, dutch. Coralalgal interactions dutch caribbean biodiversity. Local and global stressors have affected coral reef ecosystems worldwide. Coral reefs, although generally located in oligotrophic environments, are one of the most biodiverse ecosystems on the planet, due largely to their high productivity and efficient nutrient recycling mechanisms done et al. Modeling alternative stable states in caribbean coral reefs. Inhibition of coral recruitment by macroalgae and cyanobacteria.
Experimental support for alternative attractors on coral reefs russell j. The most notorious phase shift in the mhi was first described in the 1960s and early 1970s in kaneohe bay, o. Turf algaemediated coral damage in coastal reefs of belize. The observed shift of average marine climate zones south by 200 km since 1950 lough, 2008 could potentially result in the gbr extending south, causing an algal to coral phase shift as coral settlement follows the changing environmental gradient. Influence of coral and algal exudates on microbially. Switches from coral to algal dominance states and microbialization are the major processes underlying the global decline of coral reefs. As a result, investigations into the drivers of coralalgal phase shifts have. Coral algal phase shifts after natural disturbances have long been documented throughout coral reef history. Human impacts are causing ecosystem phase shifts from coral to algal dominated reef systems on a global scale. A combination of factors can lead to phase shifts, including widespread coral mortality, declines in herbivory e. High resilience masks underlying sensitivity to algal phase. Returning caribbean coral reefs to their former glory.
This leads to an increase in catabolic reactions, which use biologically available oxygen. Metagenomics of coral reefs under phase shift and high hydrodynamics. Mounting evidence indicates that the outcome of these interaction events is, in part, governed by microbially mediated dynamics. 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. Topdown control of algae is dependent on herbivore grazing, thus when overexploitation of grazers or diseaserelated mortality of grazers occurs, algae can proliferate. High resilience masks underlying sensitivity to algal phase shifts of pacific coral reefs.
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. In contrast, alternative stable states exist when there is a discontinuous phase shift such that multiple stable states can coexist. This paper expands the range of documented coral algal interactions by comparing the. Trend in coralalgal phase shift in the mandapam group of. Discovery bay caricomp data 1994 to 2007 showed an increase in coral cover from less than 5% reported in the mid 1980s to 11. This publication is available as a download from the iucn global marine programme website at the. Despite being a welldocumented phenomenon, the underlying dynamics and mechanistic processes leading to algal dominance are still unclear. Aug 20, 2008 coral reefs can undergo relatively rapid changes in the dominant biota, a phenomenon referred to as phase shift. Global assessment of the status of coral reef herbivorous fishes. Reefs located in lower wave exposure regimes, impacted or unimpacted by the typhoons, did not undergo any macroalgal phase shift roff et al.
Phase shift introduction macroalgae are major competitors with corals and other benthic organisms on tropical reefs, especially where. Instead seaweeds macroalgae created a community phase shift as they increasingly replaced corals figure 1b. However, explicit demonstration of the processes involved and. The influence of these stressors on the coastal ecosystems has resulted in a phase shift from coral to algal dominated reefs. Current biology 16 2006 elsevier ltd all rights reserved. Reversing this coral algal phase shift has proven hugely challenging, but a new study by spadaro and butler. Phase shift introduction macroalgae are major competitors with corals and other benthic organisms on tropical reefs, especially where rates of herbivory are low and nutrient enrichment is high fong and paul 2011. Reductions in herbivory caused by overfishing may enhance the likelihood of organic pollution causing a coral algal phase shift. 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. Feb 01, 2004 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. Coral reef degradation often involves a phase shift from coral to macroalgaldominated reefs. Macroalgae, nutrients and phase shifts on coral reefs. One well documented such phase shift has been from coral to algal 25 domination on tropical reefs. This, in combination with an increment of the nutrients levels, leads to a phenomenon called coral algal phase shift, which involves the.
Assessing evidence of phase shifts from coral to macroalgal. We documented the species responsible for this transition from macroalgal domination to epilithic algae and coral by using remote underwater dv cameras. Influence of coral and algal exudates on microbially mediated. The dynamics of coralalgal interactions in space and. Rapid reversal of an experimentally induced phase shift on a coral reef a experimental cages each 25 m2 simulate overfishing and trigger a phase shift from corals and epilithic algae to macroalgae. Coralalgal interactions dutch caribbean biodiversity database. Degradation of coral reefs often involves a phase shift from abundant coral to dominance. Apr 26, 2017 coralalgal 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.
It is widely recognized that persistence times of these shifts have increased in. Phase shift severity is a continuum, so categorical delineations of relative severity are subjective and may be not be ecologically relevant. Coralalgal phase shifts alter fish communities and reduce fisheries. The fish population on jamaican reefs has also been steadily declining over the years as a result of poor fishing practices and this has had a. Tropical herbivores provide resilience to a climate. Instead seaweeds macroalgae created a community phase shift as they. This includes shifts to fleshy algal dominance as overfishing and nutrient. Browsing herbivores are thought to provide critical resilience to coral reefs by consuming canopy forming seaweeds and facilitating phase shift reversals of degraded reefs back to coral dominant states bellwood et al. A phase shift towards an algaedominated system may accompany coral loss. Surprisingly, reversal of the phase shift through the direct removal of macroalgae was not a result of grazing by parrot. Baseline survey results indicated a vast competition and phase shift of corals to algal. Although the potential for algal phase shifts are well documented done, 1992. Frontiers metagenomics of coral reefs under phase shift and. Adamb adepartment of ecology, evolution and marine biology, university of california, santa barbara, ca 931069620.
1344 1487 410 1078 108 1645 1116 616 608 1562 1206 362 229 572 218 1097 225 1423 1180 788 1128 80