Coral growth and reef growth: a brief review

The growth potential of modern zooxanthellate corals from the major reef provinces is reviewed with respect to Holocene reef growth. Both coral growth and reef growth is enhanced globally at the beginning of the Holocene and is maintained regionally in the Caribbean Sea up to the present in contrast to reefs of the Indo-Pacific Ocean. This regional difference is mainly caused by the siphoning effect of the tropical Atlantic, which is characterised still by a rising sea level in contrast to global ocean. Hence, Indo-Pacific reefs exhibit a well-cemented reef crest and reef roof barren of living corals. The evaluation of reef growth rates throughout the Phanerozoic shows reduced growth rates of more than one order of magnitude in comparison to their modern counterparts. This is a result of compaction and diagenesis but also strongly biased by uncertainties in absolute dating. Point counting of individual framebuilders with known growth rate may result in more comparative figures for growth rates of fossil reefs with respect to modern ones.     

Reef fish and habitat relationships in a Caribbean seascape: the importance of reef context

Marine protected area (MPA) effectiveness is contingent on understanding key ecological patterns and processes at appropriate spatial scales and may depend upon maintaining critical linkages among essential habitat patches to conserve reef-fish communities. Hypotheses were tested to investigate the importance of habitat linkages in the US Virgin Islands. As expected, reef context (the spatial pattern of surrounding habitat patches) was a strong predictor of reef fish assemblage structure. Specific relationships were functionally consistent with the ecology of the fishes of interest. For example, reefs with large amounts of seagrass nearby harbored the greatest numerical abundance of fishes, particularly mobile invertebrate feeders and the exploited fish families of Haemulidae (grunts) and Lutjanidae (snappers). Species richness for the entire fish community and within these fish groups was also strongly associated with reef context. Furthermore, reef fish mobility influenced how fishes related to reef context. Fish-habitat relationships were detected as far as 1 km from study reefs, suggesting that fish movements result in habitat encounter rates that may influence their patterns of distribution. Consequently, functional habitat connectivity of habitat patches appears important in structuring reef-fish assemblages, and suggests that landscape-scale metrics may provide insights useful to managers in the design of MPAs.     

Escaping the heat: range shifts of reef coral taxa in coastal Western Australia

One of the most critical challenges facing ecologists today is to understand the changing geographic distribution of species in response to current and predicted global warming. Coastal Western Australia is a natural laboratory in which to assess the effect of climate change on reef coral communities over a temporal scale unavailable to studies conducted solely on modern communities. Reef corals composing Late Pleistocene reef assemblages exposed at five distinct localities along the west Australian coast were censused and the results compared with coral occurrence data published for the modern reefs offshore of each locality. The resulting comparative data set comprises modern and Late Pleistocene reef coral communities occurring over approximately 12° of latitude. For the modern reefs this gradient includes the zone of overlap between the Dampierian and Flindersian Provinces. Modern reef coral communities show a pronounced gradient in coral composition over the latitudinal range encompassed by the study, while the gradient in community composition is not as strong for Pleistocene communities. Tropical‐adapted taxa contracted their ranges north since Late Pleistocene time, emplacing two biogeographic provinces in a region in which a single province had existed previously. Beta diversity values for adjacent communities also reflect this change. Modern reefs show a distinct peak in beta diversity in the middle of the region; the peak is not matched by Pleistocene reefs. Beta diversity is correlated with distance only for comparisons between modern reefs in the north and the fossil assemblages, further supporting change in distribution of the biogeographic provinces in the study area. Coral taxa present in modern communities clearly expanded and contracted their geographic ranges in response to climate change. Those taxa that distinguish Pleistocene from modern reefs are predicted to migrate south in response to future climate change, and potentially persist in ‘temperature refugia’ as tropical reef communities farther north decline.     

Non‐reef habitats in a tropical seascape affect density and biomass of fishes on coral reefs

Nonreef habitats such as mangroves, seagrass, and macroalgal beds are important for foraging, spawning, and as nursery habitat for some coral reef fishes. The spatial configuration of nonreef habitats adjacent to coral reefs can therefore have a substantial influence on the distribution and composition of reef fish. We investigate how different habitats in a tropical seascape in the Philippines influence the presence, density, and biomass of coral reef fishes to understand the relative importance of different habitats across various spatial scales. A detailed seascape map generated from satellite imagery was combined with field surveys of fish and benthic habitat on coral reefs. We then compared the relative importance of local reef (within coral reef) and adjacent habitat (habitats in the surrounding seascape) variables for coral reef fishes. Overall, adjacent habitat variables were as important as local reef variables in explaining reef fish density and biomass, despite being fewer in number in final models. For adult and juvenile wrasses (Labridae), and juveniles of some parrotfish taxa (Chlorurus), adjacent habitat was more important in explaining fish density and biomass. Notably, wrasses were positively influenced by the amount of sand and macroalgae in the adjacent seascape. Adjacent habitat metrics with the highest relative importance were sand (positive), macroalgae (positive), and mangrove habitats (negative), and fish responses to these metrics were consistent across fish groups evaluated. The 500‐m spatial scale was selected most often in models for seascape variables. Local coral reef variables with the greatest importance were percent cover of live coral (positive), sand (negative), and macroalgae (mixed). Incorporating spatial metrics that describe the surrounding seascape will capture more holistic patterns of fish–habitat relationships on reefs. This is important in regions where protection of reef fish habitat is an integral part of fisheries management but where protection of nonreef habitats is often overlooked.     

Reef fish assemblages in north-western Sri Lanka: distribution patterns and influences of fishing practises

The distribution and abundance of reef fishes in relation to habitat structure were studied within Bar Reef Marine Sanctuary (BRMS) and on an adjacent reef, disturbed by destructive fishing techniques, in north-western Sri Lanka, by visually censusing 135 species groups using fifty metre belt-transects. Two types of continental shelf patch-reefs are found in the study area: coral reefs and sandstone reefs, which are divided into distinct habitats, four for the coral reef (shallow reef flat, shallow patch reef, deep reef flat and Porites domes) and two for the sandstone reef (structured sandstone-reef and flat sandstone-reef). Fish assemblages varied in structure between reef types and among habitats within reef types. Functional aspects of habitat structure and composition, such as available food and shelter, seemed to be important factors influencing distribution patterns. The strongest separation in the organisation of fish assemblages in BRMS was between reef types: 19% of all species were confined to the coral-reef patches while 22% were restricted to the sandstone reef patches and 59% were represented on both reef types. In terms of distribution among habitats, 21% of all species were restricted to one habitat while only 1.5% were present in all. The highest density of fish was in the coral reef habitats while highest species diversity was found in the most structurally complex habitat: the structured sandstone-reef. This habitat also had the highest proportion of species with restricted distribution. Planktivores were the most abundant trophic group in BRMS, and the species composition of the group varied among habitats. The comparison of the disturbed reef with BRMS suggested that habitat alteration caused by destructive fishing methods has strongly influenced the fish community. Within the fished area the structure of the fish assemblages was more heterogeneous, fish abundance was lower by an order of magnitude and species numbers were lower than in BRMS.     

Scale-dependent spatial variability of coral assemblages along the Florida Reef Tract

 Coral reef communities of the western Atlantic have changed over the past two to three decades, but the magnitude and causes of this change remain controversial. Part of the problem is that small-scale patterns observed on individual reefs have been erroneously extrapolated to landscape and geographic scales. Understanding how reef coral assemblages vary through space is an essential prerequisite to devising sampling strategies to track the dynamics of coral reefs through time. In this paper we quantify variation in the cover of hard corals in spur-and-groove habitats (13–19 m depth) at spatial scales spanning five orders of magnitude along the Florida Reef Tract. A videographic sampling program was conducted to estimate variances in coral cover at the following hierarchical levels and corresponding spatial scales: (1) among transects within sites (0.01- to 0.1-km scale), (2) among sites within reefs (0.5- to 2-km scale), (3) among reefs within sectors of the reef tract (10- to 20-km scale), and (4) among sectors of the reef tract (50- to 100-km scale). Coral cover displayed low variability among transects within sites and among sites within reefs. This means that transects from a site adequately represented the variability of the spur-and-groove habitat of the reef as a whole. Variability among reefs within sectors was highly significant, compared with marginally significant variability among sectors. Estimates from an individual reef, therefore, did not adequately characterize nearby reefs, nor did those estimates sufficiently represent variability at the scale of the sector. The structure and composition of coral reef communities is probably determined by the interaction of multiple forcing functions operating on a variety of scales. Hierarchical analyses of coral assemblages from other geographic locations have detected high variability at scales different from those in the present study. A multiscale analysis should, therefore, precede any management decisions regarding large reef systems such as the Florida Reef Tract. Accepted: 19 July 1999     

ECOLOGY AND MORPHOLOGY OF RECENT CORAL REEFS

1. The classical ‘coral reef problem’ concerned the geological relationships of reefs as major topographical features; modern coral studies consider reefs both as complex biological systems of high productivity and as geological structures forming a framework for and being modified by coral growth. 2. Deep borings in reefs have conclusively confirmed the general arguments of Darwin, that oceanic reefs developed by progressive subsidence of their foundations. Darwin failed to take account of Pleistocene changes in sea level and their effect on the present surface features of reefs. Daly's alternative ‘glacial control theory’ was based on false assumptions concerning marine erosion rates during glacial periods, but if sea level during the Holocene was higher than at present, as Daly also supposed, the effects on reef features would be profound. 3. Reefs are complex biological systems in tropical seas, dominated by scleractinian corals. Coral faunas are larger and more diverse in the Indo-Pacific than in the Atlantic. Hermatypic corals are restricted to shallow water by the light requirements of their symbiotic algae, but temperature is a major control of worldwide distributions. Temperature, salinity and sediment tolerances of corals are wider than formerly supposed, and corals can survive brief emersion except when it coincides with heavy rainfall. Water turbulence is an important ecological control, but difficult to measure. 4. The trophic status of corals is still unclear, but in spite of their anatomical and physiological specialization as carnivores it is likely that they derive some nutrient substances from zooxanthellae. Suggestions that filamentous algae in coral heads play a major part in the economy of the corals have not been supported by later work, but biomass pyramids constructed on the basis by Odum and Odum remain the only ones available. Most reefs are apparently autotrophic, with 1500–3500 g. Carbon being fixed per m.² per year. 5. Few animals eat corals, which may account for their success. Important predators are fish and the echinoderm Acanthaster. Quantitative estimates of biogenic erosion of organic skeletons on reefs are high. Fish affect not only corals but other invertebrates, algae and marine phanerogams. 6. Corals may be killed by ‘dark water’, intense rain or river floodwaters, earth movements, human interference and especially hurricanes. Reef recovery after hurricanes may take 10–20 years. 7. In addition to fringing, barrier and atoll reefs, intermediate types are recognised. The main types may consist of linear reefs or faros. Smaller lagoon reefs include pinnacles, patches and platforms, and submerged knolls. Complex cellular or mesh reef patterns are also found. 8. Reefs are conspicuously zoned, both laterally in response to changing exposure to waves to form windward and leeward reefs, and transversely, as a result of steep environmental gradients across reef flats from sea to lagoon. Topographic and ecological zones may be characterized by particular coral species, but these vary widely from reef to reef. A major distinction can be made between reefs with and without algal ridges, which are common on open-ocean trade-wind reefs, in the Indo-Pacific, but are absent on Caribbean reefs and on Indo-Pacific reefs in more sheltered waters. gorgonians are common on Caribbean reefs, alcyonaceans in the Indo-Pacific. 9. Much of the difficulty in comparing reefs stems from the lack of uniformity in surveying methods. Problems of describing the complex three-dimensional patterns of organisms on reefs have yet to be solved, and hence little progress has been made in explanation of these patterns. Explanation in terms of simple environmental controls is inadequate. 10. Understanding the distribution of corals is made more difficult both by taxo-nomic problems and by the plasticity of growth form in different situations. 11. Growth of corals and reefs may be estimated by measuring the growth of individual colonies, measuring rates of calcium carbonate deposition in the skeleton, measuring topographic change on the reef and deducing net rates of reef growth from geological evidence. Massive corals may increase in diameter by 1 cm./year, branches of branching corals may increase in length by 10 cm./year. Study of deposition rates shows variation within colonies, between species, in light and dark, and seasonally. Rates of reef growth extrapolated from colony measurements reach 2–5 cm./year, and contrast with figures as low as 0–02 cm/year averaged over 70 million years from borehole data. Both colony growth rates and geological data suggest worldwide variations in rates of reef growth. 12. In spite of clear evidence of long-continued subsidence, present surface features of reefs, often only thinly veneered by modern corals, have been much affected by recent sea level fluctuations. Many slightly raised reefs at 2–10 m. above sea level date at 90–160 thousand years B.P.; there is evidence for a sea level at about the present level at 30–35 thousand years B.P.; and controversy continues over whether sea level has stood higher than the present at any time since the last sea level rise began about 20,000 years ago. Evidence from many reefs suggests a slightly higher sea level in the last 4000 years, but on other reefs such evidence is lacking. 13. Several reef features (submerged terraces, groove-spur systems, algal ridge, reef flat, reef blocks and reef islands) have been interpreted either as relict features dating from a higher sea level in the last 5000 years, or contemporary features developed in response to present processes. In some cases the evidence is equivocal; in others it is clear that diverse features are being grouped together under the same name. If such features are referable to a higher sea level, this may have been of last Interglacial or even Interstadial age rather than Holocene. 14. A reef consists of a rigid framework defining several major depositional environments within and around it. Sediments are of biological, mainly skeletal origin, except in unusual environments such as the Bahama Banks. The characteristics of sediments derived from organisms depend partly on the breakdown patterns of particular skeletons, partly on transportation and sorting processes. Fine sediments may be either detrital, or physicochemical precipitates. 15. Organisms affect sediments after deposition, by disturbance, transportation and probably comminution. Fish and holothurians have been studied in detail. 16. While new theories of coral reefs are proposed from time to time, the need is less for new theories than for standardised procedures to ensure comparability of reef studies and the identification of variations in reefs both on local and regional scales. While reefs as biological systems adjust relatively rapidly to changes, reefs as geological systems adjust much more slowly. Because of the magnitude and recency of Pleistocene fluctuations in sea level, many biological features of reefs are out of phase with inherited geological features, and this had led to much controversy.     

Quantifying movement patterns for shark conservation at remote coral atolls in the Indian Ocean

Grey reef sharks (Carcharhinus amblyrhynchos) are apex predators found on many Indo-Pacific coral reefs, but little is known about their movement patterns and habitat requirements. We used acoustic telemetry to determine movements and habitat use of these sharks at the isolated Rowley Shoals atolls, 250 km off the coast of north-western Australia. We equipped 12 male and 14 female sharks ranging from 0.79 to 1.69 m in total length with transmitters that were detected by an array of 11 strategically placed receivers on two atoll reefs. Over 26,000 detections were recorded over the 325 days of receiver deployment. No sharks were observed to move between reefs. Receivers on the outer slopes of reefs provided nearly all (99%) of the detections. We found no differences in general attendance parameters due to size, sex or reef, except for maximum period of detection where larger sharks were detected over a longer period than smaller sharks. Male and female sharks were often detected at separate receivers at the outer slope habitat of one reef, suggesting sexual segregation, but this pattern did not occur at the second reef where males and females were detected at similar frequencies. We identified two patterns of daily behaviour: (1) sharks were present at the reef both day and night or (2) sharks spent more time in attendance during day than at night. Fast Fourier transforms identified 24-h cycles of attendance at the reef and a secondary peak of attendance at 12 h for most sharks, although no individuals shared the same attendance patterns. Our study provides baseline data that can be used to optimise the minimum area and habitat requirements for conservation of these apex predators.     

The relationship between habitat structure and fish faunas on New Zealand reefs

Reef fish abundances were sampled at 11 shallow reef localities extending over 1000 km of coastline in northern New Zealand. Sampling was restricted to the 4–10-m depth stratum and included six coastal and five island localities. These were either coralline reef flats dominated by echinoids, or algal reefs with high densities of laminarian and fucoid algae. Reefs dominated by macroscopic algae supported large numbers of small fishes, mainly labrids, and few large benthic-feeding fishes. Echinoid-dominated reefs supported a different fish fauna with more large benthic-feeding species. Additional sampling of echinoiddominated reefs and algal stands in deeper water provided confirmation of these findings. A second sampling programme was carried out at a series of eight sites within a single locality covering 5 km of coastline. These spanned a moderate exposure gradient and ranged from algal dominated reefs to typical coralline reef flats with high densities of grazing invertebrates. The relationship between habitat structure and reef fish species composition and size frequency was similar to that of the large-scale sampling programme. Thirdly, observations on reef fish foraging and feeding patterns within a single reef site suggested that larger benthic-feeding reef fishes were less likely to feed within macroscopic algal stands. Experimental reductions of grazing invertebrates designed to produce brown algal stands on echinoid-dominated reef flats supported these observations. Larger individuals capable of removing echinoids and grazing gastropods did not frequent or feed in laminarian and fucoid algal stands. This pattern is discernible at several spatial scales. Our conclusion is that the type of shallow reef habitat, echinoid- as opposed to algal-dominated, will have an important rôle in determining the associated reef fish fauna.     

Diet and Habitat use by Bluefish, Pomatomus Saltatrix, in a Chesapeake Bay Estuary

Bluefish, Pomatomus saltatrix, are recreationally valuable finfish along the Atlantic seaboard and in the Chesapeake Bay. Diet and habitat use patterns for bluefish life history intervals in Chesapeake Bay estuaries are poorly described although it is widely acknowledged that this apex piscivorous species relies on estuarine habitat for feeding and nursery grounds after oceanic spawning and inshore migration of larvae. Bluefish diet, distribution, and abundance patterns were examined in relation to oyster reef, oyster bar, and sand bottom habitat in the Piankatank River, Virginia. Bluefish from all sites were predominantly piscivorous and were more abundant at reef sites than non-reef sites. Bluefish caught in association with the oyster reef consumed a wider diversity of prey items than fish from other sites; diet diversity may contribute to bluefish success during periods when small pelagic food fish abundance is reduced. Bluefish estuarine habitat use is positively correlated with the presence of oyster shell habitat and the complex trophic communities centering on oyster reefs.     

Habitat selection by recruits establishes local patterns of adult distribution in two species of damselfishes: Stegastes dorsopunicans and S. planifrons

Local patterns of adult distribution in organisms that disperse young as pelagic larvae can be determined at the time of recruitment through habitat selection or, shortly thereafter, through post-recruitment processes such as differential juvenile survivorship and interspecific competition. This study addresses the importance of habitat selection by recruits in establishing the local pattern of adult distribution in two sympatric Caribbean damselfish species, Stegastes dorsopunicans and S. planifrons. Both species inhabit shallow reefs but show little overlap in their distribution; S. dorsopunicans predominates in the reef crest and S. planifrons occurs primarily on the reef slope. Furthermore, S. dorsopunicans is associated with rocky substrate, while S. planifrons occupies live coral. The substrate cover follows a similar pattern with coral being much less common on the reef crest than on the reef slope. Monitoring recruitment every other day in reciprocal removal experiments and artificial reefs indicates that the observed pattern of local adult distribution is a product of habitat selection for both species. The presence or absence of conspecifics did not influence recruitment patterns for either species. Stegastes dorsopunicans recruited primarily to shallow, rocky areas, appearing to cue on both substratum type and depth. Stegastes planifrons recruited exclusively to coral substratum independent of depth. These results indicate that local adult patterns of distribution can be explained by habitat selection at recruitment, and that substrate type and depth may be important cues. Received: 27 May 1997 / Accepted: 4 January 1998     

Fishes associated with artificial reefs: attributing changes to attraction or production using novel approaches

Two widely‐recognized hypotheses propose that increases in fish abundance at artificial reefs are caused by (a) the attraction and redistribution of existing individuals, with no net increase in overall abundance and (b) the addition of new individuals by production, leading to a net increase in overall abundance. Inappropriate experimental designs have prevented many studies from discriminating between the two processes. Eight of 11 experiments comparing fish abundances on artificial reefs with those on adjacent soft bottom habitats were compromised by a lack of replication or spatial interspersion in the design itself. Only three studies featured proper controls and replicated designs with the interspersion of reef and control sites. Goodness of fit tests of abundance data for 67 species from these studies indicated that more fishes occur on reefs than on controls, particularly for species that typically occur over hard substrata. Conversely, seagrass specialists favour controls over reefs. Changes in the appearance of fish abundance trajectories driven by manipulation of sampling intervals highlight the need for adequate temporal sampling to encompass key life history events, particularly juvenile settlement. To ultimately determine whether attraction and production is responsible for increased abundances on reefs, requires two experimental features: 1) control sites, both interspersed among artificial reefs and at reef and non‐reef locations outside the test area and 2) incorporation of fish age and length data over time. Techniques such as otolith microchemistry, telemetry and stable isotope analysis can be used to help resolve feeding and movement mechanisms driving attraction and production.     

Spatial separation without territoriality in shark communities

Spatial separation within predator communities can arise via territoriality but also from competitive interactions among and within species. However, linking competitive interactions to predator distribution patterns is difficult and theoretical models predict different habitat selection patterns dependent on habitat quality and how competition manifests itself. While models generally consider competitors to be either equal in ability, or for one phenotype to have a fixed advantage over the other, few studies consider that an animal may only have a competitive advantage in specific habitats. We used  10 years of telemetry data, habitat surveys and behavioral experiments, to show spatial partitioning between and within two species of reef shark (grey reef Carcharhinus amblyrhinchos and blacktip reef sharks C. melanopterus) at an unfished Pacific atoll. Within a species, sharks remained within small ‘sub‐habitats’ with very few movements of individuals between sub‐habitats, which previous models have suggested could be caused by intra‐specific competition. Blacktip reef sharks were more broadly distributed across habitat types but a greater proportion used lagoon and backreef habitats, while grey reef sharks preferred forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef sharks are absent, were distributed more broadly between habitat types than when both species were present. A series of individual‐based models predict that habitat separation would only arise if there are competitive interactions between species that are habitat‐specific, with grey reefs having a competitive advantage on the forereefs and blacktips in the lagoons and backreef. We provide compelling evidence that competition helps drive distribution patterns and spatial separation of a marine predator community, and highlight that competitive advantages may not be constant but rather dependent on habitats.     

Phanerozoic reef evolution: Basic questions and data base

An up-dated data base is a matter of importance and urgency in order for encouraging a process-oriented approach to the study of reef evolution. The evolution of reefs is a major section of a Priority Program of the Deutsche Forschungsgemeinschaft devoted to ‘Global and regional controls of biogenic sedimentation’. Biological, paleontological and geological approaches in the study of ancient and modern reefs are needed for providing a better understanding of the following basic questions:

Management implications of fish trap effectiveness in adjacent coral reef and gorgonian habitats

A combination of visual census and trap sampling in St. John, USVI indicated that traps performed better in gorgonian habitat than in adjacent coral reef habitat. Although most families were seen more commonly in coral habitat, they were caught more often in gorgonian areas. Traps probably fished more effectively in gorgonian habitats, especially for migrating species, because traps provided shelter in the relatively topographically uniform environment of gorgonian dominated habitats. Recently, trap fishermen on St. John have been moving effort away from traditionally fished nearshore coral reefs and into a variety of more homogeneous habitats such as gorgonian habitat. Consequently, exploitation rates of the already over-harvested reef fish resources may be increasing. Reef fish managers and marine reserve designers should consider limiting trap fishing in gorgonian habitats to slow the decline of reef fisheries.     

Environmental and geometric constraints on Indo-Pacific coral reef biodiversity

The Indo-Australian Archipelago supports the world's richest coral reef biodiversity hotspot. Traditional hypotheses that account for such exceptional biodiversity have highlighted the importance of environmental variables such as habitat area and energy input. Recently, however, an additional explanation has been proposed based on geometric constraints in the placement of geographical ranges within a bounded domain, which cause a mid-domain peak in species richness; the mid-domain effect (MDE). Here, for the first time, we examine the relative importance of area, energy and MDE jointly on species richness patterns. Model selection indicates that the best model incorporates MDE and reef area, but no energy effect; moreover, this best-fit model captures all major features of reef fish and coral species richness patterns. Habitat area is the major environmental factor influencing species richness. The prevention of further fragmentation and loss of habitat area is of critical importance for the conservation of coral reef biodiversity.     

The structure of a nearshore fish community of Western Australia: diel patterns and the habitat role of limestone reefs

Synopsis Extensive limestone reefs are a characteristic feature of much of the coastline of Western Australia, and potentially represent a major habitat feature influencing the structure of the coastal fish community. The structure and temporal dynamics of the fish fauna and its relationships to nearshore patch reefs and surrounding habitat near Dongara, Western Australia, were examined using (1) diel gill-netting and (2) quantitative rotenone sampling of enclosed areas of substratum. Long-term and day-to-day variability of the fauna was low. Dominant species of gill-net collections were either associated with reefs or occurred in similar abundances at both reefs and surrounding sand/seagrass flats. The overall abundance, number of species and biomass of netted fishes was higher around reefs. Rotenone collections of the more sedentary species showed a similar pattern, but suggested, however, that a simple reef versus surrounding sand and seagrass habitat comparison is complicated by the canopy-forming seagrass Amphibolis that occurs on reef tops. Time of day had an important effect on overall fish abundance and number of species, with peaks occurring at crepuscular periods. This reflected dusk and dawn activity peaks of a dominant species rather than overlapping activities of many diurnal and nocturnal species. Diel switches between reef-edge habitat and surrounding sand/seagrass flats were uncommon despite expectations (based on literature examples) that patch reefs would function primarily as sheltering habitats and surrounding non-reef areas act as foraging habitat. High catches at reef-edge sites suggest that the majority of fishes forage on or near limestone patch reefs. Fish densities of around 0.8 individuals per m^-2 of bottom on these Western Australian reefs are relatively high in comparison to visual census estimates obtained for temperate reef systems in South Australia and New Zealand, but similar to those obtained using comparable netting methods in temperate Australian seagrass systems.     

Patterns of generic extinction in the fossil record

Analysis of the stratigraphic records of 19,897 fossil genera indicates that most classes and orders show largely congruent rises and falls in extinction intensity throughout the Phanerozoic. Even an ecologically homogeneous sample of reef genera shows the same basic extinction profile. The most likely explanation for the congruence is that extinction is physically rather than biologically driven and that it is dominated by the effects of geographically widespread environmental perturbations influencing most habitats. Significant departures from the congruence are uncommon but important because they indicate physiological or habitat selectivity. The similarity of the extinction records of reef organisms and the marine biota as a whole confirms that reefs and other faunas are responding to the same history of environmental stress.     

Relationships between habitat structure and fish communities on coral

The influence of habitat structure on reef-fish communities at Bar Reef Marine Sanctuary, Sri Lanka, was investigated. The relationship between habitat characteristics and the distribution and abundance of 135 species of fishes was examined on two reef types: coral and sandstone reefs. Results suggested that the reef-fish communities were strongly influenced by various aspects of reef structure. However, relationships between habitat variables and fish communities structure, varied between the two reef types. Fish species diversity was correlated with a number of habitat variables on the sandstone reefs, although structural complexity seemed to play the dominant role. There were no correlations between habitat structure and fish diversity on the coral reefs. Total abundance was not related to any one habitat parameter on either reef type. However, abundances of some species, families and trophic groups were correlated with habitat features. These specific correlations were commonly related to food or shelter availability. For example, coral feeders were correlated with live coral cover, and pomacentrid species, which used branching corals for protection, showed a significant relationship with the density of Acropora colonies. This shows that a summary statistic such as total abundance may hide important information. Effects of habitat structure on the distribution patterns of the fish communities was further investigated using multi-dimensional scaling ordination (MDS) and the RELATE-procedure. With the MDS ordinations for both habitat and fish-community composition it was possible to show that the multivariate pattern between the two ecological components was clearly correlated.