Peter F. Sale

Coral Reefs Under Rapid Climate Change and Ocean Acidification

Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided.

MAINTENANCE OF HIGH DIVERSITY IN CORAL REEF FISH COMMUNITIES

Data have been drawn together to demonstrate that reef fishes by and large are food and habitat generalists with a large amount of overlap in requirements among coexisting species. Suitable living space is the resource most likely to be in short supply for them, and their environment, although benign, is one in which the supply of living space is both spatially and temporally unpredictable. The argument is developed that reef fishes are adapted to this unpredictable supply of space in ways which make interspecific competition for space a lottery in which no species can consistently win. Thus, the high diversity of reef fish communities may be maintained because the unpredictable environment prevents development of an equilibrium community

Larval retention and connectivity among populations of corals and reef fishes: history, advances and challenges

The extent of larval dispersal on coral reefs has important implications for the persistence of coral reef metapopulations, their resilience and recovery from an increasing array of threats, and the success of protective measures. This article highlights a recent dramatic increase in research effort and a growing diversity of approaches to the study of larval retention within (self-recruitment) and dispersal among (connectivity) isolated coral reef populations. Historically, researchers were motivated by alternative hypotheses concerning the processes limiting populations and structuring coral reef assemblages, whereas the recent impetus has come largely from the need to incorporate dispersal information into the design of no-take marine protected area (MPA) networks. Although the majority of studies continue to rely on population genetic approaches to make inferences about dispersal, a wide range of techniques are now being employed, from small-scale larval tagging and paternity analyses, to large-scale biophysical circulation models. Multiple approaches are increasingly being applied to cross-validate and provide more realistic estimates of larval dispersal. The vast majority of empirical studies have focused on corals and fishes, where evidence for both extremely local scale patterns of self-recruitment and ecologically significant connectivity among reefs at scales of tens of kilometers (and in some cases hundreds of kilometers) is accumulating. Levels of larval retention and the spatial extent of connectivity in both corals and fishes appear to be largely independent of larval duration or reef size, but may be strongly influenced by geographic setting. It is argued that high levels of both self-recruitment and larval import can contribute to the resilience of reef populations and MPA networks, but these benefits will erode in degrading reef environments.

Coexistence of coral reef fishes - a lottery for living space*

SynopsisData are summarised from studies of two reef fish communities — pomacentrids territorial on rubble patches, and fishes resident in small isolated colonies of coral. In each case there is evidence that availability of living sites limits numbers of fishes, and that similar species of fish use the same kinds of spaces. Priority of arrival as recruits, rather than subtle differences in requirements or competitive abilities of adults, appears to determine which species holds each site. Faced with a limited and patchy supply of living space, most reef fishes are sedentary as adults, and produce frequent clutches of pelagic larvae over extended breeding seasons In this way they maximise their chances of getting offspring into suitable living sites as such sites appear. It is argued that by adopting this strategy, reef fishes are preadapted for forming inter-specific lotteries for living space if several species with similar requirements occur together. Such lotteries among similar species may be a feature common to many reef fish communities, and may explain the typically high within-site diversity found in them.

Patterns and processes in reef fish diversity

A central aim of ecology is to explain the heterogeneous distribution of biodiversity on earth. As expectations of diversity loss grow, this understanding is also critical for effective management and conservation. Although explanations for biodiversity patterns are still a matter for intense debate, they have often been considered to be scale-dependent. At large geographical scales, biogeographers have suggested that variation in species richness results from factors such as area, temperature, environmental stability, and geological processes, among many others. From the species pools generated by these large-scale processes, community ecologists have suggested that local-scale assembly of communities is achieved through processes such as competition, predation, recruitment, disturbances and immigration. Here we analyse hypotheses on speciation and dispersal for reef fish from the Indian and Pacific oceans and show how dispersal from a major centre of origination can simultaneously account for both large-scale gradients in species richness and the structure of local communities.

Are populations of coral reef fish open or closed

Dispersal plays a crucial role in several aspects of the biology, management and conservation of many species, including coral reef fish and other demersal marine organisms with pelagic larval stages. To know the origin of propagules that replenish benthic populations is a major challenge, yet, whereas earlier studies emphasized the broadly extensive dispersal of reef fish larvae, recent publications have emphasized the extent to which these larvae succeed in returning to their natal populations. Here, we critically analyse the evidence concerning the dispersal of coral reef fish, and conclude that: (1) at present, the extent to which reef fish populations are open or closed must be regarded as unknown; and (2) further improved research is likely to confirm that larval dispersal structures populations into more or less open populations depending on the particular attributes of species, physical oceanographical systems in which they occur and the scale at which the question is posed.

Length of larval life in twelve families of fishes at “One Tree Lagoon”, Great Barrier Reef, Australia

The length of larval life in some coral reef fishes was estimated from the number of growth increments in the otoliths of newly settled fishes. We examined 210 individuals comprising 38 species and 5 unidentified taxa, and belonging to 12 families. During 2 successive austral summers (1976–1977 and 1978–1979), specimens were collected from the lagoon at One Tree Reef, Great Barrier Reef, Australia. By assuming that growth increments in otoliths are laid down on a regular daily cycle commencing near the time of hatching, we calculated typical ages ranging from 3 to 6 wk with a minimum of just over 2 wk and a maximum of 12 wk. The otoliths also contain distinctive microstructural features which can serve as approximate temporal markers for the change from the postlarval to juvenile life stage.

Temporal Variability in the Community Structure of Fish on Coral Patch Reefs and the Relation of Community Structure to Reef Structure

Fish assembled on 20 lagoonal patch reefs were censused eight times over 33 mo. Reefs, which ranged in size from 2.71 m2 to 28.35 m2 surface area, supported an average of 128 fish of 21 species at any one time. These were drawn from a total pool of 143 species, and, because of successive recruitments and losses of individual fish, each reef supported many more species during the study than were present at any one census. Structure of the assemblages on each reef, in terms of species number, number of fish, and species composition, varied through time. Mean proportional similarity of assemblages on the same reef was 0.568, z 15% greater than that between assemblages on different reefs (0.422). Structural attributes of reefs, other than size, were of little value in predicting the structure of the fish assemblages formed. The results are compatible with an essentially nonequilibrial view of reef fish communities. This view holds that species recruit to reef sites at varying rates, and independently of each other, while individuals are lost from sites (through death or emigration) also in a way unstructured with respect to the species composition of the resident fauna.

Overlap in resource use, and interspecific competition

SummaryWhen several species co-exist, the amount by which they overlap in their use of resources is a measure of their similarity to one another. As such, resource overlap does not measure the amount of competition among them. When the resources are not limiting to population growth, patterns of resource use may overlap to any degree. However, when the species are frequently in competition for their resources, natural selection will favor the separation of their requirements, and the amount of resource overlap will be reduced.This paper presents a technique which permits comparison of the amount of resource overlap observed in a given case with that expected for a group of similar species co-existing in the absence of competitive interactions. From this comparison can be evaluated the likelihood of competitive processes being important in the situation under study.

Precision and accuracy of visual census technique for fish assemblages on coral patch reefs

SynopsisA visual census technique is described in which the results of three separate enumerations of fish at a site are combined to produce a ‘best estimate’ of the fish fauna present. Its precision and accuracy are examined, and compared to those of censuses obtained by modifications of the technique. Visual censuses can display high repeatability, but they seldom (if ever) completely sample the fish present at a site. Accuracy varies with technique used. In our tests, the preferred method yielded 82% of species and 75% of individuals known to be present and potentially censurable at the time the observations were made. Visual censuses are of comparable accuracy to ichthyocide collections of unenclosed sites, but the two methods sample different components of the total fish fauna. It is important when using visual censuses to remember that their accuracy is not 100%.