Coral–macroalgal phase shifts or reef resilience: links with diversity and functional roles of herbivorous fishes on the Great Barrier Reef

Cheal, Alistair J.; MacNeil, M. Aaron; Cripps, Edward; Emslie, Michael J.; Jonker, Michelle; Schaffelke, Britta; Sweatman, Hugh

doi:10.1007/s00338-010-0661-y

Cited by 253 publications

(225 citation statements)

References 62 publications

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“…turf algae is increasing in many reefs due to pollution and human degradation, both stresses inducing a shift from coral to algae dominance (Hughes et al, 2007;Cheal et al, 2010). Therefore, turfs represent one of the most dominant benthic components on many coral reefs in the Caribbean (Vermeij et al, 2010), central Pacific (Haas et al, 2010;Barott et al, 2012), Red Sea (Haas et al, 2010), and Indonesia (Wangpraseurt et al, 2012), and their high contribution to total reef N 2 fixation has received increasing attention in the past years.…”

Section: N 2 Fixation In Coral Reef Ecosystems Description Of N 2 Fixmentioning

confidence: 99%

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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Coral reefs are highly productive ecosystems thriving in nutrient-poor waters. Their productivity depends largely on the availability of nitrogen, the proximate limiting nutrient for primary production. In reefs, the major nitrogen pathways include regeneration, nitrification, ammonification and dinitrogen (N 2 ) fixation. N 2 fixation is performed by prokaryotes called "diazotrophs" that abound in coral rubbles, sandy bottoms, microbial mats, or seagrass meadows. Corals, which are the main reef builders, have developed a partnership with dinoflagellates which transform dissolved inorganic nitrogen into amino acids and protein, and with diazotrophs to gain diazotrophically-derived nitrogen (DDN). Pioneering studies found active diazotrophic cyanobacteria in the corals' mucus and/or tissue, and later high throughput sequencing efforts have described diverse communities of non-cyanobacterial diazotrophs associated with scleractinian corals. Yet, the metabolic processes behind these associations and how they benefit corals are currently not well understood. While genomic studies describe the diversity of diazotrophs and isotopic tracer experiments quantify N 2 fixation rates, combined advanced methods are needed to elucidate the mechanisms behind the transfer of DDN to the coral holobiont and whether these mechanisms change according to the identity of the diazotrophs or coral species. Here we review our current knowledge on N 2 fixation in corals: the diversity and localization of diazotrophs in the coral holobiont, the environmental factors controlling N 2 fixation, the fate of DDN within the coral symbiosis as well as its potential role in coral resilience. We finally summarize the unknowns: are the diversity, abundance and localization of diazotrophs within the holobiont species-and/or site-specific? Do they have an impact on DDN production? What are the metabolic mechanisms implicated? Do they change spatially, temporally or according to environmental factors? We encourage scientists to undertake research efforts to tackle these questions in order to shed light on nitrogen cycling in reef ecosystems and to understand if coral-associated N 2 fixation can improve coral's resilience in the face of climate change.

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Section: N 2 Fixation In Coral Reef Ecosystems Description Of N 2 Fixmentioning

confidence: 99%

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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“…Reef fish abundance, species richness, and diversity are generally positively correlated with coral cover (Jones et al 2004;Wilson et al 2006). For reef fish communities, lowered coral cover could be accompanied by reduced functional redundancy or loss of function through low numbers (Cheal et al 2010(Cheal et al , 2013 Such changes in fish communities are generally linked to a reduced capacity for coral reef communities to recover after disturbances (reduced resilience; Nystrom 2006;Cheal et al 2013). The loss of coral cover, though, will not always correspond linearly with change in the structure of reef fish communities.…”

Section: Favia Symphyllia Goniastreamentioning

confidence: 99%

Contrasting rates of coral recovery and reassembly in coral communities on the Great Barrier Reef

2014

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Changes in the relative abundances of coral taxa during recovery from disturbance may cause shifts in essential ecological processes on coral reefs. Coral cover can return to pre-disturbance levels (coral recovery) without the assemblage returning to its previous composition (i.e., without reassembly). The processes underlying such changes are not well understood due to a scarcity of longterm studies with sufficient taxonomic resolution. We assessed the trajectories and time frames for coral recovery and reassembly of coral communities following disturbances, using modeled trajectories based on data from a broad spatial and temporal monitoring program. We studied coral communities at six reefs that suffered substantial coral loss and subsequently regained at least 50 % of their pre-disturbance coral cover. Five of the six communities regained their coral cover and the rates were remarkably consistent, taking 7-10 years. Four of the six communities reassembled to their pre-disturbance composition in 8-13 years. The coral communities at three of the reefs both regained coral cover and reassembled ten years. The trajectories of two communities suggested that they were unlikely to reassemble and the remaining community did not regain pre-disturbance coral cover. The communities that regained coral cover and reassembled had high relative abundance of tabulate Acropora spp. Coral communities of this composition appear likely to persist in a regime of pulse disturbances at intervals of ten years or more. Communities that failed to either regain coral cover or reassemble were in near-shore locations and had high relative abundance of Porites spp. and soft corals. Under current disturbance regimes, these communities are unlikely to re-establish their pre-disturbance community composition.

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“…Recruitment, growth and biomass of macroalgae are controlled in part by nutrient availability [81]. In addition, a high abundance of macroalgae suppresses coral resilience (e.g., [82][83][84]) by increased competition for space or by changing the microenvironment into which corals settle and grow (e.g., [57,85]). A high macroalgal cover is widely accepted as an indicator of reef degradation and the macroalgae data were accordingly used here as an indicator of the likelihood of increased coral-algal space competition [72].…”

Section: Coral Monitoring Programsmentioning

confidence: 99%

Estimating the Exposure of Coral Reefs and Seagrass Meadows to Land-Sourced Contaminants in River Flood Plumes of the Great Barrier Reef: Validating a Simple Satellite Risk Framework with Environmental Data

et al. 2016

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River runoff and associated flood plumes (hereafter river plumes) are a major source of land-sourced contaminants to the marine environment, and are a significant threat to coastal and marine ecosystems worldwide. Remote sensing monitoring products have been developed to map the spatial extent, composition and frequency of occurrence of river plumes in the Great Barrier Reef (GBR), Australia. There is, however, a need to incorporate these monitoring products into Risk Assessment Frameworks as management decision tools. A simple Satellite Risk Framework has been recently proposed to generate maps of potential risk to seagrass and coral reef ecosystems in the GBR focusing on the Austral tropical wet season. This framework was based on a "magnitudeˆlikelihood" risk management approach and GBR plume water types mapped from satellite imagery. The GBR plume water types (so called "Primary" for the inshore plume waters, "Secondary" for the midshelf-plume waters and "Tertiary" for the offshore plume waters) represent distinct concentrations and combinations of land-sourced and marine contaminants. The current study aimed to test and refine the methods of the Satellite Risk Framework. It compared predicted pollutant concentrations in plume water types (multi-annual average from 2005-2014) to published ecological thresholds, and combined this information with similarly long-term measures of seagrass and coral ecosystem health. The Satellite Risk Framework and newly-introduced multi-annual risk scores were successful in demonstrating where water conditions were, on average, correlated to adverse biological responses. Seagrass meadow abundance (multi-annual change in % cover) was negatively correlated to the multi-annual risk score at the site level (R 2 = 0.47, p < 0.05). Relationships between multi-annual risk scores and multi-annual changes in proportional macroalgae cover (as an index for coral reef health) were more complex (R 2 = 0.04, p > 0.05), though reefs incurring higher risk scores showed relatively higher proportional macroalgae cover. Multi-annual risk score thresholds associated with loss of seagrass cover were defined, with lower risk scores (ď0.2) associated with a gain or little loss in seagrass cover (gain/´12%), medium risk scores (0.2-0.4) associated with moderate loss (´12/´30%) and higher risk scores (>0.4) with the greatest loss in cover (>´30%). These thresholds were used to generate an intermediate river plume risk map specifically for seagrass meadows of the GBR. An intermediate river plume risk map for coral reefs was also developed by considering a multi-annual risk score threshold of 0.2-above which a higher proportion of macroalgae within the algal communities can be expected. These findings contribute to a long-term and adaptive approach to set relevant risk framework and thresholds for adverse biological responses in the GBR. The ecological thresholds and risk scores used in this study will be refined and validated through ongoing monitoring and assessment. As uncertainties are red...

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Coral–macroalgal phase shifts or reef resilience: links with diversity and functional roles of herbivorous fishes on the Great Barrier Reef

Cited by 253 publications

References 62 publications

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

Contrasting rates of coral recovery and reassembly in coral communities on the Great Barrier Reef

Estimating the Exposure of Coral Reefs and Seagrass Meadows to Land-Sourced Contaminants in River Flood Plumes of the Great Barrier Reef: Validating a Simple Satellite Risk Framework with Environmental Data

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