Coral Reefs 

About: Coral Reefs is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Coral reef & Reef. It has an ISSN identifier of 0722-4028. Over the lifetime, 3379 publications have been published receiving 157598 citations.

Coral bleaching: causes and consequences

Abstract: It has been over 10 years since the phenomenon of extensive coral bleaching was first described. In most cases bleaching has been attributed to elevated temperature, but other instances involving high solar irradiance, and sometimes disease, have also been documented. It is timely, in view of our concern about worldwide reef condition, to review knowledge of physical and biological factors involved in bleaching, the mechanisms of zooxanthellae and pigment loss, and the ecological consequences for coral communities. Here we evaluate recently acquired data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment. Cellular mechanisms of bleaching involve a variety of processes that include the degeneration of zooxanthellae in situ, release of zooxanthellae from mesenterial filaments and release of algae within host cells which become detached from the endoderm. Photo-protective defences (particularly carotenoid pigments) in zooxanthellae are likely to play an important role in limiting the bleaching response which is probably elicited by a combination of elevated temperature and irradiance in the field. The ability of corals to respond adaptively to recurrent bleaching episodes is not known, but preliminary evidence suggests that phenotypic responses of both corals and zooxanthellae may be significant.

Coral reef bleaching: ecological perspectives

Abstract: Coral reef bleaching, the whitening of diverse invertebrate taxa, results from the loss of symbiotic zooxanthellae and/or a reduction in photosynthetic pigment concentrations in zooxanthellae residing within the gastrodermal tissues of host animals. Of particular concern are the consequences of bleaching of large numbers of reef-building scleractinian corals and hydrocorals. Published records of coral reef bleaching events from 1870 to the present suggest that the frequency (60 major events from 1979 to 1990), scale (co-occurrence in many coral reef regions and often over the bathymetric depth range of corals) and severity (>95% mortality in some areas) of recent bleaching disturbances are unprecedented in the scientific literature. The causes of small scale, isolated bleaching events can often be explained by particular stressors (e.g., temperature, salinity, light, sedimentation, aerial exposure and pollutants), but attempts to explain large scale bleaching events in terms of possible global change (e.g., greenhouse warming, increased UV radiation flux, deteriorating ecosystem health, or some combination of the above) have not been convincing. Attempts to relate the severity and extent of large scale coral reef bleaching events to particular causes have been hampered by a lack of (a) standardized methods to assess bleaching and (b) continuous, long-term data bases of environmental conditions over the periods of interest. An effort must be made to understand the impact of bleaching on the remainder of the reef community and the long-term effects on competition, predation, symbioses, bioerosion and substrate condition, all factors that can influence coral recruitment and reef recovery. If projected rates of sea warming are realized by mid to late AD 2000, i.e. a 2°C increase in high latitude coral seas, the upper thermal tolerance limits of many reef-building corals could be exceeded. Present evidence suggests that many corals would be unable to adapt physiologically or genetically to such marked and rapid temperature increases.

Bleaching of corals on the Great Barrier Reef: differential susceptibilities among taxa

Abstract: Large-scale coral bleaching episodes are potentially major disturbances to coral reef systems, yet a definitive picture of variation in assemblage response and species susceptibilities is still being compiled. Here, we provide a detailed analysis of the bleaching response of 4160 coral colonies, representing 45 genera and 15 families, from two depths at four sites on reefs fringing inshore islands on the Great Barrier Reef. Six weeks after the onset of large-scale bleaching in 1998, between 11 and 83% of colonies along replicate transects were affected by bleaching, and mortality was 1 to 16%. There were significant differences in bleaching response between sites, depths and taxa. Cyphastrea, Turbinaria and Galaxea were relatively unaffected by bleaching, while most acroporids and pocilloporids were highly susceptible. The hydrocorals (Millepora spp.) were the most susceptible taxa, with 85% mortality. Spatial variation in assemblage response was linked to the taxonomic composition of reef sites and their bleaching history. We suggest, therefore, that much of the spatial variation in bleaching response was due to assemblage composition and thermal acclimation.

Competition between corals and algae on coral reefs : a review of evidence and mechanisms

Abstract: Despite widespread acceptance that competition between scleractinian corals and benthic algae is important to the structure of coral reef communities, there is little direct experimental evidence that corals and algae do compete, and very little data on the processes and causality of their interactions. Most available evidence is observational or correlative, with intrinsic risks of confounded causality. This paper reviews and categorises the available evidence, concluding that competition between corals and algae probably is widespread on coral reefs, but also that the interaction varies considerably. Widespread replacement of corals by algae may often indicate coral mortality due to external disturbances, rather than competitive overgrowth, but may lead to competitive inhibition of coral recruitment, with consequences for reef recovery. We list eight specific processes by which corals and algae may affect each other, and suggest life history properties that will influence which of these interactions are possible. We propose a matrix for algal effects on corals, which lists the subset of processes possible for each combination of coral life form and algal functional group. This table provides a preliminary framework for improved understanding and interpretation of coral-algal interactions.

Model of a coral reef ecosystem

Abstract: The ECOPATH model for French Frigate Shoals estimates the benthic plant production (net primary production in kg wet weight) required to support the atoll food chain. In this section we estimate the benthic net primary production and net community production of the atoll based on metabolism studies of reef flat, knolls, and lagoon communities at French Frigate Shoals Hawaii. Community metabolism was measured during winter and summer. The reef communities at French Frigate Shoals exhibited patterns and rates of organic carbon production and calcification similar to other reefs in the world. The estimate of net primary production is 6.1·106 kg wet weight km-2 year-1±50%, a value remarkably close to the estimate by the ECOPATH model of 4.3·106 kg wet weight km-2 year-1. Our estimate of net community production or the amount of carbon not consumed by the benthos was high; approximately 15% of the net primary production. Model results indicate that about 5% of net primary production is passed up the food chain to mobile predators. This suggests about 10% of net primary production (∼6% of gross primary production) may be permanently lost to the system via sediment burial or export offshore.