Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

The biogeography of tropical reef fishes: endemism and provinciality through time

The largest marine biodiversity hotspot straddles the Indian and Pacific Oceans, driven by taxa associated with tropical coral reefs. Centred on the Indo‐Australian Archipelago (IAA), this biodiversity hotspot forms the ‘bullseye’ of a steep gradient in species richness from this centre to the periphery of the vast Indo‐Pacific region. Complex patterns of endemism, wide‐ranging species and assemblage differences have obscured our understanding of the genesis of this biodiversity pattern and its maintenance across two‐thirds of the world's oceans. But time‐calibrated molecular phylogenies coupled with ancestral biogeographic estimates have provided a valuable framework in which to examine the origins of coral reef fish biodiversity across the tropics. Herein, we examine phylogenetic and biogeographic data for coral reef fishes to highlight temporal patterns of marine endemism and tropical provinciality. The ages and distribution of endemic lineages have often been used to identify areas of species creation and demise in the marine tropics and discriminate among multiple hypotheses regarding the origins of biodiversity in the IAA. Despite a general under‐sampling of endemic fishes in phylogenetic studies, the majority of locations today contain a mixture of potential paleo‐ and neo‐endemic fishes, pointing to multiple historical processes involved in the origin and maintenance of the IAA biodiversity hotspot. Increased precision and sampling of geographic ranges for reef fishes has permitted the division of discrete realms, regions and provinces across the tropics. Yet, such metrics are only beginning to integrate phylogenetic relatedness and ancestral biogeography. Here, we integrate phylogenetic diversity with ancestral biogeographic estimation of lineages to show how assemblage structure and tropical provinciality has changed through time.     

Population genetic analyses of Hypoplectrus coral reef fishes provide evidence that local processes are operating during the early stages of marine adaptive radiations

Large-scale, spatially explicit models of adaptive radiation suggest that the spatial genetic structure within a species sampled early in the evolutionary history of an adaptive radiation might be higher than the genetic differentiation between different species formed during the same radiation over all locations. Here we test this hypothesis with a spatial population genetic analysis of Hypoplectrus coral reef fishes (Serranidae), one of the few potential cases of a recent adaptive radiation documented in the marine realm. Microsatellite analyses of Hypoplectrus puella (barred hamlet) and Hypoplectrus nigricans (black hamlet) from Belize, Panama and Barbados validate the population genetic predictions at the regional scale for H. nigricans despite the potential for high levels of gene flow between populations resulting from the 3-week planktonic larval phase of Hypoplectrus . The results are different for H. puella , which is characterized by significantly lower levels of spatial genetic structure than H. nigricans . An extensive field survey of Hypoplectrus population densities complemented by individual-based simulations shows that the higher abundance and more continuous distribution of H. puella could account for the reduced spatial genetic structure within this species. The genetic and demographic data are also consistent with the hypothesis that H. puella might represent the ancestral form of the Hypoplectrus radiation, and that H. nigricans might have evolved repeatedly from H. puella through ecological speciation. Altogether, spatial genetic analysis within and between Hypoplectrus species indicate that local processes can operate at a regional scale within recent marine adaptive radiations.     

Temporal consistency of ontogenetic shifts in habitat use by coral reef fishes in the northernmost coral ecosystem in the world (Kudaka Island, Japan)

The prevalence of major habitat shifts in tropical fishes between juvenile and adult stages (ontogenetic shifts) in one of the northernmost coral reefs in the world (Kudaka Island, Japan) is given. The comparative analysis of spatial distribution of juveniles v . adults highlighted four ontogenetic patterns: no change in habitat use between juveniles and adults (five species), a decrease in the number of habitats used by adults compared to juveniles (three species), an increase in the number of habitats used during the adult stage (four species) and use of nursery areas by juveniles followed by extensive movements to different adult habitats (three species). The comparative analysis of fish distribution over time ( i.e. during three consecutive settlement months) showed that 84% of species had temporal consistency in ontogenetic patterns of habitat use.     

Nocturnal relocation of adult and juvenile coral reef fishes in response to reef noise

Juvenile and adult reef fishes often undergo migration, ontogenic habitat shifts, and nocturnal foraging movements. The orientation cues used for these behaviours are largely unknown. In this study, the use of sound as an orientation cue guiding the nocturnal movements of adult and juvenile reef fishes at Lizard Island, Great Barrier Reef was examined. The first experiment compared the movements of fishes to small patch reefs where reef noise was broadcast, with those to silent reefs. No significant responses were found in the 79 adults that were collected, but the 166 juveniles collected showed an increased diversity each morning on the reefs with broadcast noise, and significantly greater numbers of juveniles from three taxa (Apogonidae, Gobiidae and Pinguipedidae) were collected from reefs with broadcast noise. The second experiment compared the movement of adult and juvenile fishes to reefs broadcasting high (>570 Hz), or low (<570 Hz) frequency reef noise, or to silent reefs. Of the 122 adults collected, the highest diversity was seen at the low frequency reefs; and adults from two families (Gobiidae and Blenniidae) preferred these reefs. A similar trend was observed in the 372 juveniles collected, with higher diversity at the reefs with low frequency noises. This preference was seen in the juvenile apogonids; however, juvenile gobiids were attracted to both high and low sound treatments equally, and juvenile stage Acanthuridae preferred the high frequency noises. This evidence that juvenile and adult reef fishes orientate with respect to the soundscape raises important issues for management, conservation and the protection of sound cues used in natural behaviour.     

Connectivity and the development of population genetic structure in Indo‐West Pacific coral reef communities

Aim To identify connectivity patterns among coral reefs of the Indo‐West Pacific. Projecting connectivity forward in time provides a framework for studying long‐term source–sink dynamics in the region, and makes it possible to evaluate the manner in which migration shapes population genetic structure at regional scales. This information is essential for addressing critical gaps in knowledge for conservation planning efforts in one of the most biologically diverse regions on earth. Location Coral reefs of the Indo‐West Pacific, ranging from 15° S to 30° N and 95° E to 140° E. Methods Individual‐based biophysical dispersal models were used in conjunction with matrix projection to identify the expected patterns of exchange between coral reefs over time. Results Present‐day oceanographic conditions lead to the transport of larvae from the South China Sea into the Coral Triangle region via the Sulu Sea, and from northern Papua New Guinea and the Solomon Islands via Halmahera. The directionality of the system leads to the expected accumulation of organisms from outlying areas into the Coral Triangle region over time, particularly in the vicinity of the Maluku Islands and eastern Sulawesi. Coral reefs in Papua New Guinea, the Sulu Archipelago and areas within the Philippines are expected to be areas of high diversity as well. Main conclusions Biophysical dispersal models, used in conjunction with matrix projection, provide an effective means of simulating connectivity structure across the Indo‐West Pacific and thereby evaluating the directionality of genetic diversity. Migration appears to have a significant influence on population genetic structure in the region. Based on present‐day ocean currents, coral reefs in the South China Sea, northern Papua New Guinea and the Solomon Islands are contributing to high levels of diversity in the Coral Triangle.     

Comparative demography of commercially important species of coral grouper,Plectropomus leopardus and P. laevis,from Australia's great barrier reef and Coral Sea marine parks

Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus: Plectropomus), is important for establishing effective management and conservation strategies. Herein we compare the demography of Plectropomus leopardus and P. laevis between Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length-at-age data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions. Plectropomus laevis populations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages of P. laevis were also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no-take marine reserves (NTMRs). Plectropomus leopardus, individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length-at-age comparisons of P. laevis and P. leopardus suggest that the environmental differences between the CSMP and the GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species, P. laevis.     

Diversity, endemism and evolution in the Coral Triangle

In a recent paper by D. R. Bellwood and C. P. Meyer ('Searching for heat in a marine biodiversity hotspot', Journal of Biogeography , 2009, 36 , 569–576), the authors had two evident objectives: (1) to disprove the theory that the geographical origins of reef organisms could be determined by locating concentrations of endemic species, and (2) to emphasize that the high diversity of the Coral Triangle was due to an accumulation of species from outside that area. With regard to the first point, no such theory had previously been proposed to my knowledge. Second, the accumulation theory was promoted without consideration of the facts supporting the centre of origin hypothesis, except to dismiss it by saying that it had its origin in pre-continental drift ideas. This short response outlines the properties and evidence for the operation of centres of origin in this region.     

Host preference and specialization in Gnathia sp., a common parasitic isopod of coral reef fishes

A gnathiid species (Crustacea: Isopoda; one of the most common ectoparasites of coral reef fishes) from the Great Barrier Reef, Australia, was allowed to choose among fishes from three different families to feed on (using two species of fishes per family). Gnathiids showed a strong preference for labrids, rarely feeding on pomacentrids or apogonids. In a separate experiment, gnathiid host preference did not vary among three labrid fish species. Gnathiids that fed on labrids had higher survival than those that fed on apogonids. Male gnathiids that fed on labrids also moulted to the adult stage more quickly. This suggests that host specialization and local adaptation might be occurring between these ectoparasites and their host fishes at the host fish family level.     

Diurnal temporal patterns of the diversity and the abundance of reef fishes in a branching coral patch in New Caledonia

Small‐scale spatial and temporal variability in animal abundance is an intrinsic characteristic of marine ecosystems but remains largely unknown for most animals, including coral reef fishes. In this study, we used a remote autonomous unbaited video system and recorded reef fish assemblages during daylight hours, 10 times a day for 34 consecutive days in a branching coral patch of the lagoon of New Caledonia. In total, 50 031 fish observations belonging to 114 taxa, 66 genera and 31 families were recorded in 256 recorded videos. Carnivores and herbivore‐detritus feeders dominated the trophic structure. We found significant variations in the composition of fish assemblages between times of day. Taxa richness and fish abundance were greater in the early morning and in the late afternoon than during the day. Fourteen taxa displayed well‐defined temporal patterns in abundance with one taxon influenced by time of day, six influenced by tidal state and seven influenced by both time of day and tidal state. None of these 14 taxa were piscivores, 10 were herbivore‐detritus feeders, three were carnivores and one was plankton feeder. Our results suggest a diel migration from feeding grounds to shelter areas and highlight the importance of taking into account small‐scale temporal variability in animal diversity and abundance when studying connectivity between habitats and monitoring communities.     

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.     

New insights into global patterns of ocean temperature anomalies: implications for coral reef health and management

Aim Coral reefs are widely considered to be particularly vulnerable to changes in ocean temperatures, yet we understand little about the broad‐scale spatio‐temporal patterns that may cause coral mortality from bleaching and disease. Our study aimed to characterize these ocean temperature patterns at biologically relevant scales. Location Global, with a focus on coral reefs. Methods We created a 4‐km resolution, 21‐year global ocean temperature anomaly (deviations from long‐term means) database to quantify the spatial and temporal characteristics of temperature anomalies related to both coral bleaching and disease. Then we tested how patterns varied in several key metrics of disturbance severity, including anomaly frequency, magnitude, duration and size. Results Our analyses found both global variation in temperature anomalies and fine‐grained spatial variability in the frequency, duration and magnitude of temperature anomalies. However, we discovered that even during major climatic events with strong spatial signatures, like the El Niño–Southern Oscillation, areas that had high numbers of anomalies varied between years. In addition, we found that 48% of bleaching‐related anomalies and 44% of disease‐related anomalies were less than 50 km², much smaller than the resolution of most models used to forecast climate changes. Main conclusions The fine‐scale variability in temperature anomalies has several key implications for understanding spatial patterns in coral bleaching‐ and disease‐related anomalies as well as for designing protected areas to conserve coral reefs in a changing climate. Spatial heterogeneity in temperature anomalies suggests that certain reefs could be targeted for protection because they exhibit differences in thermal stress. However, temporal variability in anomalies could complicate efforts to protect reefs, because high anomalies in one year are not necessarily predictive of future patterns of stress. Together, our results suggest that temperature anomalies related to coral bleaching and disease are likely to be highly heterogeneous and could produce more localized impacts of climate change.