Coral and fish distribution patterns in Mafia Island Marine Park, Tanzania: fish–habitat interactions

We examined coral reef communities at 11 sites within Mafia Island Marine Park using a point count method for substrate and visually censused belt transects for fish populations. Multivariate ordinations showed that the benthic habitat differed among reefs. The patterns were mainly attributed to variations in depth, hydrodynamics and benthic composition. In total, the substratum was dominated by dead coral (49%) and algae (25%), with a live coral cover of only 14%. Three hundred and ninety-four fish species belonging to 56 families were recorded. According to MDS-ordinations and RELATE procedures, fish assemblage composition varied among sites in concordance with the habitats provided. Sites with highest proportion of dead coral exhibited highest degree of dispersion in the multivariate ordinations of fish assemblages. Stepwise multiple regression was used to determine the proportion of variance among sites which could be explained by depth, exposure, rugosity, substrate diversity, branching substrate, live coral cover, dead coral cover and different types of algae. The results showed that habitat variables explained up to 92% of the variation in species numbers and in total, and taxon-specific, abundance. Live coral cover was the foremost predictor of both numerical and species abundance, as well as of corallivores, invertivores, planktivores and of the families Pomacentridae, Chaetodontidae and Pomacanthidae. Our results suggest that habitat characteristics play a dominant role in determining fish assemblage composition on coral reefs.     

Relative Importance of Coral Cover,Habitat Complexity and Diversity in Determining the Structure of Reef Fish Communities

The structure of coral reef habitat has a pronounced influence on the diversity, composition and abundance of reef-associated fishes. However, the particular features of the habitat that are most critical are not always known. Coral habitats can vary in many characteristics, notably live coral cover, topographic complexity and coral diversity, but the relative effects of these habitat characteristics are often not distinguished. Here, we investigate the strength of the relationships between these habitat features and local fish diversity, abundance and community structure in the lagoon of Lizard Island, Great Barrier Reef. In a spatial comparison using sixty-six 2m² quadrats, fish species richness, total abundance and community structure were examined in relation to a wide range of habitat variables, including topographic complexity, habitat diversity, coral diversity, coral species richness, hard coral cover, branching coral cover and the cover of corymbose corals. Fish species richness and total abundance were strongly associated with coral species richness and cover, but only weakly associated with topographic complexity. Regression tree analysis showed that coral species richness accounted for most of the variation in fish species richness (63.6%), while hard coral cover explained more variation in total fish abundance (17.4%), than any other variable. In contrast, topographic complexity accounted for little spatial variation in reef fish assemblages. In degrading coral reef environments, the potential effects of loss of coral cover and topographic complexity are often emphasized, but these findings suggest that reduced coral biodiversity may ultimately have an equal, or greater, impact on reef-associated fish communities.     

Evaluation of the impact of recreational dive activity on the community structure of some coral reefs at Los Roques Archipelago National Park, Venezula

In order to evaluate if snorkeling had significant effects on coral community structure, three different coral reefs (Madrizquí, Pelona de Rabusquí and Crasquí) located at Archipelago Los Roques National Park, Venezuela, were surveyed. For each site, the coral community structure of two different areas, one subjected to intense snorkeling use (FB) and other not frequently used (PFB), were compared. Community structure was determined with 1 m2-quadrants and 20 m-long transects. These communities were described in terms of species richness, diversity (Shannon-Wiener) and evenness indexes, live and dead coral cover and cover of other organisms (sponges, octocorals and algae). Comparisons within sites were performed with a Kruskall-Wallis test. A total of 24 species of scleractinian corals were found. Live coral cover ranged from 29.9% +/- 26.43 (Crasquí) to 34.55% +/- 6.43 (Madrizquí), while dead coral cover ranged from 32.51% +/- 2.86 (Madrizquí) to 60.78% +/- 21.3 (Pelona de Rabusquí). The PFB areas showed higher live coral cover compared to FB areas; however, significant differences were only found in Crasquí and Pelona de Rabusquí (p < 0.05). Species richness, diversity and evenness were variable and no trends were observed between FB and PFB areas. The frequency of both damaged and diseased colonies were low (< 1%), most damages observed were natural (parrotfish predation). Damages caused by divers such as fin impacts, were not found at the reefs studied. These results suggest that, currently, diving pressure is not as high to cause massive loses of live coral cover in these reefs. However, the lack of strict controls for these activities might produce long-term changes in the structure of these coral communities.     

海南鹿回头岸礁造礁石珊瑚群落结构动态Ⅱ.物种多样性

根据石珊瑚物种的总数、石珊瑚覆盖的百分率、物种多样性和均匀度,对鹿回头岸礁造礁石珊瑚群落结构类型所处在演替阶段的时间状态和生境的空间状态进行分析。在中等和深水区物种多样性的时间变异,随演替的发展而有所下降;浅水区不随演替而变化。在不同生境区珊瑚生长的聚群上,与时间的发展无关;每个演替时期,物种多样性的类型与生境的变化有关。     

Maintenance of fish diversity on disturbed coral reefs

Habitat perturbations play a major role in shaping community structure; however, the elements of disturbance-related habitat change that affect diversity are not always apparent. This study examined the effects of habitat disturbances on species richness of coral reef fish assemblages using annual surveys of habitat and 210 fish species from 10 reefs on the Great Barrier Reef (GBR). Over a period of 11 years, major disturbances, including localised outbreaks of crown-of-thorns sea star (Acanthaster planci), severe storms or coral bleaching, resulted in coral decline of 46–96% in all the 10 reefs. Despite declines in coral cover, structural complexity of the reef framework was retained on five and species richness of coral reef fishes maintained on nine of the disturbed reefs. Extensive loss of coral resulted in localised declines of highly specialised coral-dependent species, but this loss of diversity was more than compensated for by increases in the number of species that feed on the epilithic algal matrix (EAM). A unimodal relationship between areal coral cover and species richness indicated species richness was greatest at approximately 20% coral cover declining by 3–4 species (6–8% of average richness) at higher and lower coral cover. Results revealed that declines in coral cover on reefs may have limited short-term impact on the diversity of coral reef fishes, though there may be fundamental changes in the community structure of fishes.     

Coral reef distribution, status and geomorphology–biodiversity relationship in Kuna Yala (San Blas) archipelago, Caribbean Panama

Most of the knowledge of the reef geomorphology and benthic communities of Kuna Yala coral reefs (Caribbean Panama) comes from the western side of the archipelago, a few tens of kilometers around Punta San Blas (Porvenir). To bridge the gap between Porvenir and the Colombia–Panama border, we investigated with Landsat images the extent and geomorphological diversity of the entire Kuna Yala to provide geomorphologic maps of the archipelago in 12 classes. In addition to remote sensing data, in situ survey conducted in May–June 2001 provided a Kuna Yala-wide first synoptic vision of reef status, in terms of benthic diversity (number of species of coral, octocorals, and sponges) and reef health (coral versus algal cover). For a total reef system estimated to cover 638 km² along 480 km of coastline, 195 km² include coral dominated areas and only 35 km² can be considered covered by corals. A total of 69 scleractinian coral, 38 octocoral, and 82 sponge species were recorded on the outer slopes of reef formations, with a slightly higher diversity in the area presenting the most abundant and diverse reef formations (western Kuna Yala). Attempts to relate benthic diversity and geomorphological diversity provided only weak relationships regardless of the taxa, and suggest that habitat heterogeneity within geomorphological areas explain better the patterns of coral diversity. This study confirms the potential of combined remote sensing and in situ surveys for regional scale assessment, and we suggest that similar approaches should be generalized for reef mapping and assessment for other reef sites.     

Reef community structure at Falcón, Venezuela, before and after a mass mortality

Morrocoy National Park used to be considered the most important continental coral reef of Venezuela. However, in January of 1996, there was a massive mortality of the benthic organisms for unknown reasons. The coral reef community was monitored since 1995, the year before the event, and yearly after that, until June 1999, by sampling linear transects and quadrats. A total of 26 hard corals were recorded in the study site (Playa Mero) in 1995 (36.56% cover), which already had some deterioration because 90.86% of the living coral cover was represented basically by four species, M. annularis with 51.36%, Colpophyllia natans with 18.22%, Agaricia agaricites with 11.58% and Porites porites with 9.70%. Three months after the event, living coral cover was only 4.84% and algae, particularly Dyctiota spp. covered most of the surface (81.89%). Benthic organisms suffered massive mortality over the whole depth gradient and in most park reefs. Even after three years the reef community shows highly perturbed conditions, with 85% of the total cover represented by the categories: dead coral, dead coral overgrowth by algae and sand. From the initial coral richness of the area (26 species) only nine species were observed although in very low cover (<1%), except for M. annularis and M. franksi, which presented lightly higher percentages.     

Species-specific habitat distribution of coral reef fish assemblages in relation to habitat characteristics in an Okinawan coral reef

We determined the species-specific habitat associations of coral reef fishes and environmental characteristics in an Okinawan coral reef in Japan. We focused on three families (Pomacentridae, Gobiidae and Labridae) and attempted to determine differences in habitat utilization. We selected six sites along the coast of Amitori Bay, from the entrance to the innermost part, in order to cover a wide range of habitat characteristics (exposed habitat, semi-exposed habitat and sheltered habitat). The species diversity of coral assemblages was greater at the exposed and semi-exposed habitats, whereas branching coral mostly covered the sheltered habitat. The environmental factors that determine the species-specific spatial association in fishes differed among families. Both biological characteristics (coral morphology and coral species diversity) and physical characteristics (water depth and wave exposure) affected the spatial association of pomacentrids and gobiids. In contrast, physical characteristics such as substrate complexity and water depth affected the species-specific spatial association of labrid species. Further study is needed to determine the ecological factors that regulate the species-specific habitat preference in Okinawan coral reefs.     

Non-colonial coral macro-borers as indicators of coral reef status in the South Pacific of Costa Rica

Coral reef status was surveyed in three south Pacific coral reefs of Costa Rica, one in Ca?o Island and two in Golfo Dulce, and the density, richness and distribution of non-colonial macro borers (> 1 mm) was determined in dead and live coral fragments from these reefs. Based upon traditional indicators of degradation such as high particulate suspended matter and low live coral cover, the reefs at Ca?o Island are in better condition than those at Golfo Dulce. Reef degradation in Golfo Dulce is mainly due to high loads of terrestrial sediments as a consequence of watersheds deforestation. In this study, 36 coral boring species are reported for the eastern Pacific. At the family level, there is high endemism (10%) and greater affinity with the Indo-Pacific (34%), as compared with the eastern Atlantic and Mediterranean (29%) and western Atlantic and Caribbean (27%). The dominant non-colonial macro boring families at the study reefs are mytilid bivalves, eunicid polychaetes and aspidosiphonid sipunculans, with the bivalves considered the main internal bioeroders due to their greater body size and abundances. The level of mortality of the coral colonies and the general level of reef degradation influenced the composition of non-colonial macro-borers. Diversity and total macro-borer density, especially aspidosiphonid density, is higher in corals with greates dead than live cover. In the healthiest coral colonies (less than 50% of partial mortality), mytilids domination, macro-borer diversity and total density, is higher in Golfo Dulce, where reefs are more degraded. In the most affected coral colonies (more than 50% dead), macro-borers total density, especially aspidosiphonids density, is higher, of the healthiest reef of this study, Platanillo. Bivalve relative abundance increases and sipunculan relative abundance decreases with increasing site degradation. In conclusion bioeroder variables can also be used as reef health indicators.     

Growth of reef fishes in response to live coral cover

Although the global decline in coral reef health is likely to have profound effects on reef associated fishes, these effects are poorly understood. While declining coral cover can reduce the abundance of reef fishes through direct effects on recruitment and/or mortality, recent evidence suggests that individuals may survive in disturbed habitats, but may experience sublethal reductions in their condition. This study examined the response of 2 coral associated damselfishes (Pomacentridae), Chrysiptera parasema and Dascyllus melanurus, to varying levels of live coral cover. Growth, persistence, and the condition of individuals were quantified on replicate coral colonies in 3 coral treatments: 100% live coral (control), 50% live coral (partial) and 0% live coral (dead). The growth rates of both species were directly related to the percentage live coral cover, with individuals associated with dead corals exhibiting the slowest growth, and highest growth on control corals. Such differences in individual growth between treatments were apparent after 29 d. There was no significant difference in the numbers of fishes persisting or the physiological condition of individuals between different treatments on this time-scale. Slower growth in disturbed habitats will delay the onset of maturity, reduce lifetime fecundity and increase individual's vulnerability to gape-limited predation. Hence, immediate effects on recruitment and survival may underestimate the longer-term impacts of declining coral on the structure and diversity of coral-associated reef fish communities.     

Spatial scales of bacterial diversity in cold-water coral reef ecosystems

Background

Cold-water coral reef ecosystems are recognized as biodiversity hotspots in the deep sea, but insights into their associated bacterial communities are still limited. Deciphering principle patterns of bacterial community variation over multiple spatial scales may however prove critical for a better understanding of factors contributing to cold-water coral reef stability and functioning.

Methodology/Principal Findings

Bacterial community structure, as determined by Automated Ribosomal Intergenic Spacer Analysis (ARISA), was investigated with respect to (i) microbial habitat type and (ii) coral species and color, as well as the three spatial components (iii) geomorphologic reef zoning, (iv) reef boundary, and (v) reef location. Communities revealed fundamental differences between coral-generated (branch surface, mucus) and ambient microbial habitats (seawater, sediments). This habitat specificity appeared pivotal for determining bacterial community shifts over all other study levels investigated. Coral-derived surfaces showed species-specific patterns, differing significantly between Lophelia pertusa and Madrepora oculata, but not between L. pertusa color types. Within the reef center, no community distinction corresponded to geomorphologic reef zoning for both coral-generated and ambient microbial habitats. Beyond the reef center, however, bacterial communities varied considerably from local to regional scales, with marked shifts toward the reef periphery as well as between different in- and offshore reef sites, suggesting significant biogeographic imprinting but weak microbe-host specificity.

Conclusions/Significance

This study presents the first multi-scale survey of bacterial diversity in cold-water coral reefs, spanning a total of five observational levels including three spatial scales. It demonstrates that bacterial communities in cold-water coral reefs are structured by multiple factors acting at different spatial scales, which has fundamental implications for the monitoring of microbial diversity and function in those ecosystems.     

A comparison of proxy performance in coral biodiversity monitoring

The productivity and health of coral reef habitat is diminishing worldwide; however, the effect that habitat declines have on coral reef biodiversity is not known. Logistical and financial constraints mean that surveys of hard coral communities rarely collect data at the species level; hence it is important to know if there are proxy metrics that can reliably predict biodiversity. Here, the performances of six proxy metrics are compared using regression analyses on survey data from a location in the northern Great Barrier Reef. Results suggest generic richness is a strong explanatory variable for spatial patterns in species richness (explaining 82 % of the variation when measured on a belt transect). The most commonly used metric of reef health, percentage live coral cover, is not positively or linearly related to hard coral species richness. This result raises doubt as to whether management actions based on such reefscape information will be effective for the conservation of coral biodiversity.     

Habitat Selectivity and Reliance on Live Corals for Indo-Pacific Hawkfishes (Family: Cirrhitidae)

Hawkfishes (family: Cirrhitidae) are small conspicuous reef predators that commonly perch on, or shelter within, the branches of coral colonies. This study examined habitat associations of hawkfishes, and explicitly tested whether hawkfishes associate with specific types of live coral. Live coral use and habitat selectivity of hawkfishes was explored at six locations from Chagos in the central Indian Ocean extending east to Fiji in the Pacific Ocean. A total of 529 hawkfishes from seven species were recorded across all locations with 63% of individuals observed perching on, or sheltering within, live coral colonies. Five species (all except Cirrhitus pinnulatus and Cirrhitichthys oxycephalus) associated with live coral habitats. Cirrhitichthys falco selected for species of Pocillopora while Paracirrhites arcatus and P. forsteri selected for both Pocillopora and Acropora, revealing that these habitats are used disproportionately more than expected based on the local cover of these coral genera. Habitat selection was consistent across geographic locations, and species of Pocillopora were the most frequently used and most consistently selected even though this coral genus never comprised more than 6% of the total coral cover at any of the locations. Across locations, Paracirrhites arcatus and P. forsteri were the most abundant species and variation in their abundance corresponded with local patterns of live coral cover and abundance of Pocilloporid corals, respectively. These findings demonstrate the link between small predatory fishes and live coral habitats adding to the growing body of literature highlighting that live corals (especially erect branching corals) are critically important for sustaining high abundance and diversity of fishes on coral reefs.     

Habitat utilization by coral reef fish: implications for specialists vs. generalists in a changing environment

1. The impact of environmental disturbance and habitat loss on associated species is expected to be dependent on a species' level of specialization. We examined habitat use and specialization of coral reef fish from the diverse and ecologically important family Pomacentridae, and determined which species are susceptible to declines in coral cover due to disturbance induced by crown-of-thorns seastar (COTS, Acanthaster planci L.). 2. A high proportion of pomacentrid species live in association with live coral as adults (40%) or juveniles (53%). Adults of many species had strong affiliations with branching corals, while juveniles favoured plating growth forms, reflecting the sizes of refuge provided by coral types. 3. Juveniles of species that associated with coral had narrower niche breadths than adult conspecifics, due to associations with specific coral types. The especially high coral association and narrower niche breadth of juveniles suggest that the presence of live coral is crucial for many species during early life history, and that disturbance-induced coral loss may have serious flow-on effects on adult abundance. 4. Microhabitat availability was a poor predictor of fish species abundance. Significant correlations between coverage of coral types and abundance of five adults and two juvenile species were detected; however, these relationships explained <35% and <10% of the variation in abundance of adult and juvenile species, respectively. 5. Niche breadth explained 74% of the variation in species' mean response to coral decline and it is clear that disturbance has a greater impact on resource specialists, suggesting that increasing frequency and intensity of coral loss will cause reef fish communities to become dominated by habitat generalists at the expense of coral-dwelling specialists.     

Habitat associations of juvenile fish at Ningaloo Reef, Western Australia: the importance of coral and algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority.     

Influence of habitat degradation on fish replenishment

Temperature-induced coral bleaching is a major threat to the biodiversity of coral reef ecosystems. While reductions in species diversity and abundance of fish communities have been documented following coral bleaching, the mechanisms that underlie these changes are poorly understood. The present study examined the impacts of coral bleaching on the early life-history processes of coral reef fishes. Daily monitoring of fish settlement patterns found that ten times as many fish settled to healthy coral than sub-lethally bleached coral. Species diversity of settling fishes was least on bleached coral and greatest on dead coral, with healthy coral having intermediate levels of diversity. Laboratory experiments using light-trap caught juveniles showed that different damselfish species chose among healthy, bleached and dead coral habitats using different combinations of visual and olfactory cues. The live coral specialist, Pomacentrus moluccensis, preferred live coral and avoided bleached and dead coral, using mostly visual cues to inform their habitat choice. The habitat generalist, Pomacentrus amboinensis, also preferred live coral and avoided bleached and dead coral but selected these habitats using both visual and olfactory cues. Trials with another habitat generalist, Dischistodus sp., suggested that vision played a significant role. A 20 days field experiment that manipulated densities of P. moluccensis on healthy and bleached coral heads found an influence of fish density on juvenile weight and growth, but no significant influence of habitat quality. These results suggests that coral bleaching will affect settlement patterns and species distributions by influencing the visual and olfactory cues that reef fish larvae use to make settlement choices. Furthermore, increased fish density within the remaining healthy coral habitats could play an important role in influencing population dynamics.