Observations on the behaviour and coloration of some coral reef fish (family: Pomacentridae)

Observations were made on the behaviour of 16 pomacentrid coral reef fish living under natural conditions. On the basis of the habit recorded for the majority of individuals observed in each, the fish were divided into three groups (solitary, pairing and social). Correlations were established between coloration and behaviour. Six out of the 8 social species studied have patterns of black (or brown) and white (or yellow) dorso‐ventral stripes. All 6 of the solitary species have colours other than black, brown, grey‐green, and white.     

Brood-directed parental aggression and early brood loss in the coral reef fish, Acanthochromis polyacanthus (Pomacentridae)

Brood-directed parental aggression, in which parents attack and even kill their own young, is described for the coral reef fish Acanthochromis polyacanthus. This behaviour involves both parents, occurs on days 7–16 post-hatching, and is characteristic of all broods produced early in the spawning season. Such parental aggression appears to underlie widespread early brood loss in the species, i.e. disappearance of young before they reach an age at which they are viable in the absence of parental defence. Simultaneously, there is also a high frequency of sudden increases in the sizes of some tended broods. The data suggest that some brood-tending parents are forcibly expelling their broods from parental territories, and fostering them on to adults still tending broods. By expelling their young and re-spawning, pairs may realize a 7% increase in annual fecundity over pairs that do not expel their young, despite a low survival rate of expelled young.     

Fishing degrades size structure of coral reef fish communities

Fishing pressure on coral reef ecosystems has been frequently linked to reductions of large fishes and reef fish biomass. Associated impacts on overall community structure are, however, less clear. In size‐structured aquatic ecosystems, fishing impacts are commonly quantified using size spectra, which describe the distribution of individual body sizes within a community. We examined the size spectra and biomass of coral reef fish communities at 38 US‐affiliated Pacific islands that ranged in human presence from near pristine to human population centers. Size spectra ‘steepened’ steadily with increasing human population and proximity to market due to a reduction in the relative biomass of large fishes and an increase in the dominance of small fishes. Reef fish biomass was substantially lower on inhabited islands than uninhabited ones, even at inhabited islands with the lowest levels of human presence. We found that on populated islands size spectra exponents decreased (analogous to size spectra steepening) linearly with declining biomass, whereas on uninhabited islands there was no relationship. Size spectra were steeper in regions of low sea surface temperature but were insensitive to variation in other environmental and geomorphic covariates. In contrast, reef fish biomass was highly sensitive to oceanographic conditions, being influenced by both oceanic productivity and sea surface temperature. Our results suggest that community size structure may be a more robust indicator than fish biomass to increasing human presence and that size spectra are reliable indicators of exploitation impacts across regions of different fish community compositions, environmental drivers, and fisheries types. Size‐based approaches that link directly to functional properties of fish communities, and are relatively insensitive to abiotic variation across biogeographic regions, offer great potential for developing our understanding of fishing impacts in coral reef ecosystems.     

Disturbance and the structure of coral reef fish communities on the reef slope

Three levels of physical disturbance were applied to corals in permanent 10x10 m quadrats along a section of fringing reef at Lizard Island on the Great Barrier Reef to investigate the response of fish assemblages. Tabular and corymbose corals were overturned and left in situ, reducing total hard coral cover from ˜55% to ˜47%, ˜43%, and ˜34%. Despite pre-existing associations with benthic cover, all fish groups examined (pomacentrids, labrids, chaetodontids, and acanthurids) were resistent to benthic disturbances at the level and scale at which they were applied. Partial Mantel's tests, in combination with partial Canonical Correspondence Analysis enabled spatial and temporal variation to be factored out from experimental effects. Most of the variation in the fish community could be assigned to spatio-temporal variables, indicating that spatial structure over the reef landscape may moderate localised disturbance effects. This study indicates that coral reef fish assemblages may be more resistant to disturbance than many correlative studies would suggest, and highlights a need for further information on levels and scales of natural habitat disturbance in order to apply a structured approach to the experimental investigation of the importance of habitat in structuring coral-reef fish assemblages.     

The role of microhabitat preference and social organization in determining the spatial distribution of a coral reef fish

Both habitat preferences and social organization can influence the spatial distributions of individuals. We explored effects of individual behavior and social organization on distributions of arc-eye hawkfish (Paracirrhites arcatus) in lagoons of French Polynesia. Analysis of habitat selectivity data obtained during surveys revealed that the most highly preferred microhabitat of arc-eye hawkfish was large Pocillopora coral with an open branching morphology. However, such corals were rare and most hawkfish occupied smaller, less preferred Pocillopora. Indeed, total abundance of Pocillopora explained nearly two thirds of the lagoon-wide variation in abundance of hawkfish and the derived relationship between the numbers of hawkfish and Pocillopora predicted 86% of the spatial variation in hawkfish abundance during subsequent surveys. In contrast, large, open-branched Pocillopora explained little of the spatial variation in abundance of hawkfish. Individual behavior and social organization significantly impacted use of the most highly preferred Pocillopora. During a colonization experiment set up outside hawkfish home ranges, all colonizers resided on the most highly preferred corals. Following addition of the most highly preferred Pocillopora corals to areas occupied by hawkfish, only the largest, socially dominant individuals obtained access to added corals, spending significantly more time and increasing both aggressive acts and prey attacks from these substrates. These results illustrate the importance of understanding the modulating effects of social behavior on habitat use and explain why most hawkfish individuals do not occupy their most preferred microhabitat type.     

Multiple criteria analysis integrates economic, ecological and social objectives for coral reef managers

 Managing a coral reef in a small island state is a difficult task. Apart from having conflicting objectives and few data there is the added problem of how to evaluate the less tangible benefits of management. This study reports the successful use of multiple criteria analysis to help the managers of a coral reef to make “good” decisions. “Good” decisions are consistent with the community’s desires to, in this case, preserve social and ecological values while simultaneously maintaining the economic benefits of dive tourism and maintaining the park as a global model of successful management. Multiple criteria analysis provides a systematic framework for evaluating management options. This study presents one of the first times multiple criteria analysis has been used in coral reef management, let alone in a non-industrialised setting. The results suggest that the method may be more widely useful than previously thought. Accepted: 20 July 1999     

Impact of cyclones on hard coral and metapopulation structure,connectivity and genetic diversity of coral reef fish

Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km²); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.

     

The effect of territorial damselfish (family Pomacentridae) on the space use and behaviour of the coral reef fish, Halichoeres bivittatus (Bloch, 1791) (family Labridae)

Most demersal species of damselfish (family Pomacentridae) are territorial herbivores that aggressively chase other fishes away from their nests. This study investigates whether the aggressive territorial damselfish, Stegastes leucostictus, modifies behaviours and home range area use in a less aggressive, non-territorial species, the slippery dick wrasse, Halichoeres bivittatus (family Labridae). Damselfishes and wrasses are ubiquitous and abundant members of coral reef fish assemblages around the world; hence, this study has broader implications beyond the two Caribbean species chosen for this study. A manipulative field experiment consisted of transplanting one or three S. leucostictus into artificial shelters positioned within adult or adjacent to juvenile H. bivittatus home ranges. The introduction of damselfish had little effect on the size of home range areas of juvenile or adult wrasses, but had a significant effect on the location of their home ranges. The damselfish also affected adult microhabitat use but did not affect use by juveniles. In addition, there was an increase in damselfish-wrasse interactions that resulted in a significant reduction in the amount of time adult wrasses could spend foraging or in a foraging assemblage. It was concluded that aggressive interactions with territorial damselfish affect individual H. bivittatus space use and may consequently affect the spatial distribution of H. bivittatus populations.     

Disturbance,coral reef communities,and changing ecological paradigms

We examine changing ecological theory regarding the role of disturbance in natural communities and relate past and emerging paradigms to coral reefs. We explore the elements of this theory, including patterns (diversity, distribution, and abundance) and processes (competition, succession, and disturbance), using currently evolving notions concerning matters of scale (temporal and spatial), local versus regional species richness, and the equilibrium versus nonequilibrium controversy. We conclude that any attempt to categorize coral reef communities with respect to disturbance regimes will depend on the question being asked and the desired level of resolution: local assemblage versus regional species pool, successional versus geological time, and on the taxonomic and tropic affinities of species included in the study. As with many communities in nature, coral reefs will prove to be mosaics of species assemblages with equilibrial and nonequilibrial dynamics.     

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.     

Near‐term impacts of coral restoration on target species,coral reef community structure,and ecological processes

The global decline of corals has created an urgent need for effective, science‐based methods to augment coral populations and restore important ecosystem functions. To meet this challenge, the field of coral restoration has rapidly evolved over the past decade. However, despite widespread efforts to outplant corals and monitor survivorship, there is a shortage of information on the effects of coral restoration on reef communities or important ecosystem functions. To fill this knowledge gap, we examined the effects of restoration on three major criteria: diversity, community structure, and ecological processes. We conducted surveys of four restored sites in the Florida Keys ranging in restoration effort (500–2,300 corals outplanted) paired with surveys of nearby, unmanipulated control sites. Coral restoration successfully enhanced coral populations, increasing coral cover 4‐fold, but manifested in limited differences in coral and fish communities. Some restored sites had higher abundance of herbivorous fish, rates of herbivory, or more juvenile‐sized corals, but these effects were limited to individual reefs. Damselfish were consistently more abundant at restored compared to control sites. Despite augmenting target coral populations, 3 years of coral restoration has not facilitated many of the positive feedbacks that help reinforce coral success. In a time of increasingly frequent disturbances, it is urgent we hasten the speed at which reefs recover important ecological processes, such as herbivory and nutrient cycling, that make reefs more resistant and resilient if we are to achieve long‐term restoration success.     

Relationships between coral reef substrata and fish

 The objective of this work is to identify which substrata characteristics (such as coral morphology, coral diversity, coral species richness, percentage coverage by live coral or by algae) influence the structure and abundance of fish communities. The study was carried out at Reunion Island, Indian Ocean, where six sites were sampled in two zones (reef flat and outer reef slope). Quantitative data were collected by visual census techniques, along a linear transect of 50 m for the substratum, and a belt of 50×2 m for the fish communities. Correspondence analysis (CA) and an optimising cluster analysis, called dynamic clustering method (DCM) were used to describe and compare fish assemblages with the benthic composition. The relationships between benthic and fish communities were examined using the classes revealed by the partitioning of the substratum with DCM. This partitioning allowed us to derive four classes of substratum: the non-disturbed reef flat, the non-disturbed outer reef slope, the perturbed reef habitat and the reef pass. The analysis of the partitioning based on the coral variables suggests that there are significant relationships between benthic and fish assemblages. Accepted: 26 July 1996     

Structure of the parasite communities of a coral reef fish assemblage (Labridae): testing ecological and phylogenetic host factors

The role of ecological and phylogenetic processes is fundamental to understanding how parasite communities are structured. However, for coral reef fishes, such information is almost nonexistent. In this study, we analyzed the structure of the parasite communities based on composition, richness, abundance, and biovolume of ecto- and endoparasites of 14 wrasse species (Labridae) from Lizard Island, Great Barrier Reef, Australia. We determine whether the structure of the parasite communities from these fishes was related to ecological characteristics (body size, abundance, swimming ability, and diet) and/or the phylogenetic relatedness of the hosts. We examined 264 fishes from which almost 37,000 individual parasites and 98 parasite categories (types and species) were recorded. Gnathiid and cestode larvae were the most prevalent and abundant parasites in most fishes. Mean richness, abundance, and biovolume of ectoparasites per fish species were positively correlated with host body size only after controlling for the host phylogeny, whereas no such correlation was found for endoparasites with any host variable. Because most ectoparasites have direct transmission, one possible explanation for this pattern is that increased space (host body size) may increase the colonization and recruitment of ectoparasites. However, endoparasites generally have indirect transmission that can be affected by many other variables, such as number of prey infected and rate of parasite transmission.     

Spatio-temporal variability in fish recruitment to a coral reef (Moorea,French Polynesia)

Spatial and temporal patterns of recruitment of juvenile coral reef fishes were studied on the reefs of the high island of Moorea (Society Archipelago, French Polynesia) during the wet season (October 1988 to April 1989). Two size-classes of fishes (new-recruits and juveniles) were censused by visual counts within 24 quadrats along a transect across the lagoon. Correspondence analysis was used to calculate the hypothetical movements of the two size classes. Spatial variability was far more important than temporal variability; six main spatial communities were revealed, which could result from differences among habitats. Temporal variability in recuitment occurred only at nearshore stations; stations on the outer fringing reef and inner barrier reef displayed stable recruitment patterns.     

Simple ecological trade-offs give rise to emergent cross-ecosystem distributions of a coral reef fish

Ecosystems are intricately linked by the flow of organisms across their boundaries, and such connectivity can be essential to the structure and function of the linked ecosystems. For example, many coral reef fish populations are maintained by the movement of individuals from spatially segregated juvenile habitats (i.e., nurseries, such as mangroves and seagrass beds) to areas preferred by adults. It is presumed that nursery habitats provide for faster growth (higher food availability) and/or low predation risk for juveniles, but empirical data supporting this hypothesis is surprisingly lacking for coral reef fishes. Here, we investigate potential mechanisms (growth, predation risk, and reproductive investment) that give rise to the distribution patterns of a common Caribbean reef fish species, Haemulon flavolineatum (French grunt). Adults were primarily found on coral reefs, whereas juvenile fish only occurred in non-reef habitats. Contrary to our initial expectations, analysis of length-at-age revealed that growth rates were highest on coral reefs and not within nursery habitats. Survival rates in tethering trials were 0% for small juvenile fish transplanted to coral reefs and 24-47% in the nurseries. As fish grew, survival rates on coral reefs approached those in non-reef habitats (56 vs. 77-100%, respectively). As such, predation seems to be the primary factor driving across-ecosystem distributions of this fish, and thus the primary reason why mangrove and seagrass habitats function as nursery habitat. Identifying the mechanisms that lead to such distributions is critical to develop appropriate conservation initiatives, identify essential fish habitat, and predict impacts associated with environmental change.     

Island biogeography of Caribbean coral reef fish

Aim The goal of our study was to test fundamental predictions of biogeographical theories in tropical reef fish assemblages, in particular relationships between fish species richness and island area, isolation and oceanographic variables (temperature and productivity) in the insular Caribbean. These analyses complement an analogous and more voluminous body of work from the tropical Indo‐Pacific. The Caribbean is more limited in area with smaller inter‐island distances than the Indo‐Pacific, providing a unique context to consider fundamental processes likely to affect richness patterns of reef fish. Location Caribbean Sea. Methods We compiled a set of data describing reef‐associated fish assemblages from 24 island nations across the Caribbean Sea, representing a wide range of isolation and varying in land area from 53 to 110,860 km². Regression‐based analyses compared the univariate and combined effects of island‐specific physical predictors on fish species richness. Results We found that diversity of reef‐associated fishes increases strongly with increasing island area and with decreasing isolation. Richness also increases with increasing nearshore productivity. Analyses of various subsets of the entire data set reveal the robustness of the richness data and biogeographical patterns. Main conclusions Within the relatively small and densely packed Caribbean basin, fish species richness fits the classical species–area relationship. Richness also was related negatively to isolation, suggesting direct effects of dispersal limitation in community assembly. Because oceanic productivity was correlated with isolation, however, the related effects of system‐wide productivity on richness cannot be disentangled. These results highlight fundamental mechanisms that underlie spatial patterns of biodiversity among Caribbean coral reefs, and which are probably also are functioning in the more widespread and heterogeneous reefs of the Indo‐Pacific.     

Spatial structure of coral reef fish communities at Kudaka Island (Ryukyu Archipelago), Japan

The present study aimed to investigate the spatial structure of fish communities at juvenile and adult stages on coral reefs at Kudaka Island (Ryukyu Archipelago, Japan) and to relate spatial patterns in the structure of the fish communities to gradients in environmental variables. Diurnal visual censuses allowed us to record 2,602 juveniles belonging to 60 species and 1,543 adults belonging to 53 species from October to December 2005. The distribution of species highlighted that the juvenile community was organised into three distinct assemblages, rather than exhibiting gradual change in community structure along the cross-reef gradient. Correlations between spatial patterns of juvenile community and environmental variables revealed that the most significant factors explaining variation in community structure were coral rubble and coral slab. In contrast, the adult community was organised into one assemblage, and the most significant variation factors in community structure were depth, live coral in massive form, live coral in branched form, dead coral and sand. Overall, the present study showed that most juvenile and adult coral reef fish at Kudaka Island exhibited striking patterns in their distribution and depth and some biological factors (e.g., abundance of live coral, dead coral and coral rubble) might exert considerable influence on the distribution of fishes.     

Size, maturation and the social control of sex reversal in the coral reef fish Anthais squamipinnis

A major hypothesis to explain the causal initiation of protogynous sex reversal is that females change sex upon reaching a critical size. A study of the coral reef fish Anthias squamipinnis shows that the size hypothesis does not hold. Females from two neighbouring, but spatially discrete and probably genetically homogeneous populations on Aldabra Island changed sex at distinctly different sizes. Previous laboratory and field studies in which sex reversal has followed the removal of a male from social groups have been uncontrolled and thus permit the interpretation that sex reversal is caused by non-specific social disruption or by causes other than male removal. In this study, a male was removed from each of eleven single-male and five multi-male social groups in the laboratory ( N = 8 male removals) and in the field ( N = 19 male removals). In each group, the result was that one female changed sex. Laboratory controls made it unlikely that sex reversal was induced by non-specific disruption and field observations showed that sex reversals resulted from male removals and were not coincidental, ongoing events. Previous statements that sex change is controlled by the presence or absence of a male, by inhibition of a female's tendency to change sex, or by aggression or dominance are shown, by an analysis of the complexity of issues, to be premature. Gonadal histology on 130 specimens confirmed that this species is a monandric, protogynous hermaphrodite and provided details of gonadal transformation.     

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km²). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.