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.     

Opening of an MPA to fishing: Natural variations in the structure of a coral reef fish assemblage obscure changes due to fishing

Marine Protected Areas (MPAs) are known to enhance diversity, density and biomass of coral reef fishes and to modify the size and trophic structures of these fish assemblages. Opening to fishing has the opposite effects, but on a much shorter time scale. The present study compares the evolution of the fish assemblages of two adjacent reef zones, both initially MPAs, one of them being afterwards opened to fishing. The study was conducted on Aboré Reef, a New Caledonian barrier reef (SW Pacific) which constituted a 148 km² marine protected area, of which 69 km² are within the lagoon. Two surveys of a coral reef fish assemblage, using underwater visual censuses, were performed, the first one was conducted in July 1993 following 5 years of protection from fishing, the second one was conducted in July 1995; part of the reef having been opened to fishing activity in September 1993. This study examined the effects of two factors on these fish communities: time (1993 vs. 1995) and zone (reefs protected from fishing vs. unprotected reefs); the interaction of these two factors indicating an effect of either protection or opening to fishing. Diversity (species/transect), density and biomass were tested for all species together (377 species), then according to diet, size and commercial use. There was a significant decrease over time of most values in both fished and unfished areas, the decrease being greater in the zone opened to fishing. The magnitude of decrease over time was within the range of known time variations from other studies in New Caledonia and other Pacific locations. However, this decrease was so large that it prevented the detection of effects linked to protection. Only some minor effects could be detected for 16 species with no specific pattern according to diet, size or use. The density and biomass of species of low commercial value were also affected by opening to fishing. Relative changes in diversity could be better detected than relative changes in density or biomass. This study demonstrates that on a short-term basis (2 years), natural variations can be of larger magnitude than changes that may be induced by management options, especially when fishing pressure is not very high.     

Inventory of the Maldives’ coral reefs using morphometrics generated from Landsat ETM+ imagery

In this study, we present exact measures of the number, area, and basic morphometric statistics for every single reef of the Maldivian archipelago, as derived from the interpretation of remotely sensed data collected by the Landsat-7 ETM+ earth-observing satellite sensor. We classified and mapped seven morphological attributes of reefs (six marine habitats and reef-top islands) to 30-m depth at 30×30 m spatial resolution (pixel size) for the entire archipelago. The total archipelagic area (all coral reef and lagoon habitats) of the 16 atolls, five oceanic faros, and four oceanic platform reefs which comprise the Maldives is 21,372.72±1,068.64 km² (approx. 20% of the Maldives Territorial Sea). A total of 2,041±10 distinct coral reef structures larger than 0.01 km² occur in the Maldives, covering an area of 4,493.85 km² (including enclosed reef lagoons and islands) to 30-m depth. Smaller areas of coral reef substratum cover another 19.29 km², bringing the total area of Maldivian coral reefs to 4,513.14±225.65 km². Shallow coral platforms thus occupy 21.1% of the total area of the archipelago (0.0052% of the EEZ area of the Maldives). Of these reefs, 538 are rim and oceanic reefs, covering 3,701.93 km² (82.5% of the total reef area), and 1,503 are patch reefs within the atoll lagoons, covering 791.92 km² (17.5% of the total reef area). Islands occupy only 5.1% of the total reef area. Mapping the Maldives coral reefs at high spatial resolution is only possible with remote sensing and spatial analysis technologies. These greatly reduce the large uncertainty around current estimates of reef area. Our accurate measure of total reef area is only 50.6% of the current best estimate, a result having significant implications for predictions of the Maldives reef productivity and response to global climate change. Here we present current best practice and compare the methods and measures with previous approaches.     

Diversity, biomass and distribution pattern of Sargassum beds in the South West lagoon of New Caledonia (South Pacific)

Sargassum (Phaeophyceae, Fucales) is a genus of worldwide distribution recently recognised to proliferate in several regions of the South Pacific. In New Caledonia, species of this genus naturally structure one of the major lagoon habitats but their extent, composition and biomass remain largely unknown. To fill these gaps in our knowledge over large areas, we applied a combination of remote sensing and in situ methods applied to the Neo Caledonian South West Lagoon. Space borne high resolution Landsat (30-m resolution) and Quickbird (2.4-m resolution) images of the Neo Caledonian South West lagoon were used to estimate the spatial extent of the different beds of interest. Species composition was determined for 11 Sargassum beds and seasonal variations were investigated for four representative beds over an 18 month period using quadrats and transects. Relationships between surface cover and biomass were estimated from seasonal field data sets. Finally, four methods requiring variable levels of sampling effort were designed to estimate the total biomass at the scale of each bed, considering (or not) the specific composition, and spatial and temporal variations. Seven Sargassaceae species were identified. Mean surface cover (24.4–51.6%) and total biomass [3.4–1,461.9 t dry matter (DM)] varied widely between beds. Overall, biomass temporal variations were not significantly different, but species-level variations seemed to be bed-specific. The extent of the 11 beds was 9 km²; their total biomass was estimated and compared using each of the four methods, and the most precise method provided an estimate of 2,900 t DM. This study demonstrates a way of characterising Sargassum beds, efficiently and on a large scale, using a combination of remotely sensed and in situ data. These methods should be useful for possible future biomonitoring of Sargassum beds in New Caledonia, and in other areas worldwide.     

Cyclone effects on coral reef habitats in New Caledonia (South Pacific)

The impacts of the unusually strong Cyclone Erica (March 2003) on coral reef habitats at a site located on the northwest coast of New Caledonia (South Pacific) were assessed using a 6-year data set (2002–2007). We examined the interannual variations of key variables describing reef habitats (live hard and soft corals, dead corals in place, coral debris, algae and relative proportion of mechanically vulnerable and resistant live hard corals). The cyclone-induced disturbances of habitats differed according to three reef types: patch reefs, barrier reefs far from passes (more than 3 km from the nearest pass) and barrier reefs near passes (less than 3 km from the nearest pass). Short-term mechanical damage was detected on the three-dimensional structure of reef habitats with a notable shift from a community dominated by mechanically vulnerable corals to one dominated by resistant corals on barrier reefs far from passes. The history of habitats and their pre-disturbance characteristics, in link with local hydrodynamics, was found to influence their short-term susceptibility to extreme events such as cyclones. However, the most significant effects appeared in the midterm (within 2 years after the cyclone) as the cover of live hard corals significantly decreased by approximately 45% between 2002 and 2004 on all reef types. The short- and midterm disturbances of coral reef habitats are discussed with regard to published temporal variations in reef fish assemblages, underlining the delayed effects of this cyclonic event on fish as well as benthic habitats. Coral reef habitats and live corals had shown significant patterns of recovery 4 years after the cyclone, followed by similar recovery in fish community, suggesting good resilience in a face of this major natural disturbance in an area under moderate anthropogenic pressure.     

Review of coral reef ecosystem remote sensing

Coral reef communities face unprecedented pressures at local, regional and global scales as a consequence of climate change and anthropogenic disturbance. Remote sensing, from satellites or aircraft, is possibly the only means to measure the effects of such stresses at appropriately large spatial scales. In the past 30 years, remote sensing of coral reefs has made rapid progress. However, the current technology is still not mature enough to monitor complicated coral reef ecosystems. Compared with foreign research in this field, our work lags far behind. There are still deficiencies in many aspects, such as basic data collection, theoretical research and platform construction. In our nation, it is even unclear how coral reefs disperse and where they may be unhealthy. In this paper, general characteristics of coral reef ecosystems and spectral features of different reef benthos have been summarized, based initially on a review of relevant literature in recent years. Based on the spectral separability of different reef types or benthos, remote sensing can be used to monitor two aspects of coral reefs: (1) Measurement of the ecological properties of reefs. (2) Health assessment of the coral reef ecosystem. In the first part, optical remote sensing methods are widely used to map reef geomorphology and habitats or biotopes. The investigation of geomorphologic zonation has proven to be one of the most successful applications, as different geomorphologic zones are associated with characteristic benthic community structures and occur at spatial scales of tens to hundreds of meters, they are amenable to remote detection by moderate to high resolution sensors. With more and more attention on the ecological problems of coral reefs, a number of studies have used high resolution sensors to map reef communities. The number of classes distinguishable depends on many factors, including the platforms, resolution (spectral, spatial and temporal resolution) and environmental conditions (water depth, water clarity, surface roughness, etc.). Compared with deep water color remote sensing, or terrestrial remote sensing, three techniques for the measurement of reef ecological properties are examined in this paper: (1) Coral reef classification system using remote sensing. (2) Techniques of sea surface correction and water column correction. (3) Techniques of coral reef information extraction from images. In terms of the complexity of coral reef ecosystems, the current techniques still need further improvement or optimization. In the health assessment of coral reef ecosystems, there are two ways to carry out the monitoring using remote sensing: (1) Monitoring the pigment or symbiotic zooxanthellae contents in corals. (2) Measuring the environmental properties of reefs. The first way is theoretically feasible, but difficult to achieve in practice. Currently, most reef health assessments are carried out by measuring environmental parameters, including sea surface temperature, solar radiation, ultraviolet radiation, water color, wind speed and direction, rainfall, ocean acidification, sea level, etc., of which sea surface temperature has been routinely measured by NOAA to monitor coral bleaching. In addition to the contents above, this article puts forward five main prospects for development in the future: (1) Establishment of a coral reef classification system using remote sensing. (2) Satellite launch for monitoring coral reefs. (3) Theoretical and methodological development. (4) Establishment of a spectral database for different reef benthos. (5) Integrated application of multi-source remote sensing data. It is hoped that the information provided here will be a reference for subsequent similar studies.     

Does Herbivorous Fish Protection Really Improve Coral Reef Resilience? A Case Study from New Caledonia (South Pacific)

Parts of coral reefs from New Caledonia (South Pacific) were registered at the UNESCO World Heritage list in 2008. Management strategies aiming at preserving the exceptional ecological value of these reefs in the context of climate change are currently being considered. This study evaluates the appropriateness of an exclusive fishing ban of herbivorous fish as a strategy to enhance coral reef resilience to hurricanes and bleaching in the UNESCO-registered areas of New Caledonia. A two-phase approach was developed: 1) coral, macroalgal, and herbivorous fish communities were examined in four biotopes from 14 reefs submitted to different fishing pressures in New Caledonia, and 2) results from these analyses were challenged in the context of a global synthesis of the relationship between herbivorous fish protection, coral recovery and relative macroalgal development after hurricanes and bleaching. Analyses of New Caledonia data indicated that 1) current fishing pressure only slightly affected herbivorous fish communities in the country, and 2) coral and macroalgal covers remained unrelated, and macroalgal cover was not related to the biomass, density or diversity of macroalgae feeders, whatever the biotope or level of fishing pressure considered. At a global scale, we found no relationship between reef protection status, coral recovery and relative macroalgal development after major climatic events. These results suggest that an exclusive protection of herbivorous fish in New Caledonia is unlikely to improve coral reef resilience to large-scale climatic disturbances, especially in the lightly fished UNESCO-registered areas. More efforts towards the survey and regulation of major chronic stress factors such as mining are rather recommended. In the most heavily fished areas of the country, carnivorous fish and large targeted herbivores may however be monitored as part of a precautionary approach.     

Extent of Mangrove Nursery Habitats Determines the Geographic Distribution of a Coral Reef Fish in a South-Pacific Archipelago

Understanding the drivers of species'' geographic distribution has fundamental implications for the management of biodiversity. For coral reef fishes, mangroves have long been recognized as important nursery habitats sustaining biodiversity in the Western Atlantic but there is still debate about their role in the Indo-Pacific. Here, we combined LA-ICP-MS otolith microchemistry, underwater visual censuses (UVC) and mangrove cartography to estimate the importance of mangroves for the Indo-Pacific coral reef fish Lutjanus fulviflamma in the archipelago of New Caledonia. Otolith elemental compositions allowed high discrimination of mangroves and reefs with 83.8% and 98.7% correct classification, respectively. Reefs were characterized by higher concentrations of Rb and Sr and mangroves by higher concentrations of Ba, Cr, Mn and Sn. All adult L. fulviflamma collected on reefs presented a mangrove signature during their juvenile stage with 85% inhabiting mangrove for their entire juvenile life (about 1 year). The analysis of 2942 UVC revealed that the species was absent from isolated islands of the New Caledonian archipelago where mangroves were absent. Furthermore, strong positive correlations existed between the abundance of L. fulviflamma and the area of mangrove (r = 0.84 for occurrence, 0.93 for density and 0.89 for biomass). These results indicate that mangrove forest is an obligatory juvenile habitat for L. fulviflamma in New Caledonia and emphasize the potential importance of mangroves for Indo-Pacific coral reef fishes.     

Mapping and imaging deep-sea coral reefs off Norway, 1982–2000

The survey and mapping group (SMG) of Statoil is responsible for all seafloor mapping for pipelines and field development in Statoil. During numerous reconnaissance and pipeline route surveys over large portions of our contintental shelf, in the North, Norwegian and Barents Seas, we have only detected deep-water coral reefs in a few specific areas. The first reef we found was in 1982, using a combined side scan sonar and sub-bottom profiler system off Fugløy, northern-Norway. Thereafter, numerous reefs were mapped with similar systems off mid-Norway, during the period 1985–1990 for the reconnaissance and final route mapping of the Haltenpipe project. During 1997, we also mapped some previously known reefs in the Trondheimsfjord area while surveying a route for the Tjeldbergodden - Skogn pipeline project. Between 1997 and 2000, we have mapped more reefs along pipeline routes on the outer mid-Norway continental shelf. These reefs are of a smaller size (less than 5 m high) than those mentioned above (5–31 m high). Although side scan sonar and sub-bottom profilers provide a less ambiguous detection of reefs, we have found that modern multi-beam echosounder data can provide adequate remotely sensed data for deep-water coral reef mapping. The interpretation of the reefs is based on visual documentation by ROV (remotely operated vehicle) or by sampling with gravity corers and grabs (ground-truthing). Based on a limited amount of such ground-truthing, it has been possible to extrapolate and use the specific morphological characteristics of the reefs to map their density and distribution. For the Haltenpipe project, we mapped an offshore route corridor of about 200 km length at a width of 3 km with multi-beam echosounder. On the basis of ground-truthing 14 of the suspected coral reefs, we have found the total number of reefs to be 57 within the 600 km² mapped area. All these reefs are higher than 5 m (the highest is 31 m) and of diameters at their base of more than 50 m. Although they occur in local clusters with up to 10 reefs per km², the mean density of reefs along the entire (200 km long) transect is only 0.09 suspected reefs per km². However, there is a large regional density variation, with the highest regional density being 1.2 reefs per km² in an area of subcropping Palaeocene sedimentary rocks. A brief discussion of why the corals have constructed their reefs in the deep, cool, and generally `hostile' waters of the Norwegian continental shelf and fjords concludes with them probably subsisting on a reliable and steady nutrient source, independent of season and variations in the Atlantic Drift (`Gulf stream'). This positive environmental component is called `hydraulically active substrata'. It is thus speculated that micro-organisms, bacteria etc., utilizing the hydraulically activated chemical porewater gradients, cause a local enrichment on which the cnidarian organisms ultimately depend.     

Last interglacial reef limestones, northeastern St. Croix, US Virgin Islands—evidence of tectonic tilting and subsidence since MIS 5.5

Most last interglacial (MIS 5.5) coral reef deposits in the Caribbean are emergent. However, in St. Croix, these are found mainly at depth, underneath Holocene material and confirmed by TIMS U–Th dated corals from eight cores through Holocene reefs. The only emergent MIS 5.5 marine deposit peaks at +1.5 m MSL at the northwestern end of the island. The Late Pleistocene surface decreases at least 9.25 m (based on reef crest elevations) in elevation over 15 km along a 0.62 m/km eastward (alongshore) slope. Neither differential erosion nor a naturally sloping deposit is likely, thus the directional elevation decrease requires the influence of tectonic processes. Platform tilting or differential subsidence increasing in rate to the east probably operated both during and since the last interglacial and created progressively greater accommodation space for increasingly thicker overlying Holocene reefs in an eastward direction. Rates of subsidence since MIS 5.5 increase from west to east, from 0.02 mm/year to 0.1 mm/year, assuming a MIS 5.5 +6-m sea level and +4 m initial reef elevation. St. Croix’s association with extensional shelf faulting from the northern part of the Virgin Islands Basin, the Anegada Fault to the east and the Puerto Rico Trench to the north may be significant in terms of identifying mechanisms for, or past events resulting in, directional tilting. Identification of differential elevations of MIS 5.5 reefs adds substantially to the information on Late Quaternary tectonism of the area.     

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.

     

Predicting spatially explicit coral reef fish abundance, richness and Shannon–Weaver index from habitat characteristics

The assessment of biodiversity in coral reefs requires the application of geographic information systems (GIS), remote sensing and analytical tools in order to make cost-effective spatially explicit predictions of biodiversity over large geographic areas. Here we present a spatially explicit prediction for coral reef fish diversity index, as well as habitat classification according to reef fish diversity index values in Chinchorro Bank Biosphere Reserve, one of the most important plain/atoll type reef systems in the Caribbean. We have used extensive ecological data on depth, fish and habitat characteristics to perform such prediction. Fish species assemblages and different biotic variables of benthic organisms were characterized using visual censuses and video-transects, respectively at 119 sampling stations. The information was integrated in a GIS, along with satellite imagery (LANSDAT 7 ETM+) and a digital bathymetric model. From the recorded data and a hierarchical classification procedure, we obtained nine different classes of habitats. We used a generalized regression analysis and spatial prediction methodology to create predictive maps (GIS layers) of the different reef benthic components, and a second modeling run produced predictive maps of coral reef fish diversity index. Predictive accuracy of the diversity index map presented a good correlation coefficient (r = 0.87), with maximum diversity index values en reefscapes composed of aggregation of coral colonies with seagrass beds. The implementation of our application was successful for the prediction of fish diversity hot spots and surrogate habitats.     

Bathymetric zonation of modern microborers in dead coral substrates from New Caledonia—Implications for paleodepth reconstructions in Holocene corals

Microboring endoliths were studied in dead modern corals collected at various depths and in growth position on La Surprise atoll in New Caledonia. Eight taxa of microborers were regularly observed: three cyanobacteria (Hyella caespitosa, Mastigocoleus testarum, and Plectonema terebrans), two chlorophytes (Ostreobium quekettii and Phaeophila dendroides) and three fungal forms (Dodgella priscus, and two unidentified fungi). The relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval (from 0 down to 40 m water depth). This allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard-substrates of corals. In this model, the occurrence of the cyanobacteria Hyella and Mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively. The chlorophyta O. quekettii, associated with the cyanobacterium P. terebrans and fungi, is dominant from 10 to 40 m depth, which is the lower limit of our sampling. The distribution ranges of individual taxa observed in the dead coral substrates from New Caledonia are much narrower than those reported in the literature for other substrates.The bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in Holocene corals collected by drilling on two reef sites of New Caledonia : La Surprise islet, in the vicinity of the sampling sites of the modern corals, and the barrier reef of Bayes, on the NE coast of Grande Terre. The paleodepth interpretations performed at various levels along the cores allow identification of several shallowing-upward sequences during the last 7000 years of reef growth in New Caledonia. Differences in the thickness of these sequences between La Surprise and Bayes sites were interpreted as differences in the space available for accommodation between the two sites, in turn related to the differential subsidence that affected New Caledonia during Holocene times. The use of the microendolith trace assemblages in paleodepth reconstructions of Holocene reefs from New Caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages.     

The role of topography in promoting fractal patchiness in a carbonate shelf landscape

Satellite remote sensing has shown numerous aspects of coral reef seascapes to be fractal. That is, they display characteristics of scale-invariance and complexity. To date, an understanding of why reefscapes adopt this curious scaling has been lacking. This property was investigated using high-resolution terrain models built using bathymetric LiDAR soundings of the shallow Puerto Rico insular shelf. A computer-simulation model constructed using simple random processes was adequate to describe many of the intricacies of actual coral reef terrain. This model, based on fractional Brownian motion (fBm), produced surfaces that were visually and statistically indistinguishable from natural seabeds, at spatial scales of 0.001–25 km². The conformity between model and nature allowed us to ascertain the importance of topography as a driver for the fractal patchiness that has been shown to occur in plan-view maps of reefscapes (e.g. Purkis et al. J Sediment Res 75:861–876, 2005, J Geol 115:493–508, 2007). For the considered Puerto Rican shelf, the necessary Brownian-like seabed topography likely arose through karst erosion overprinted by several episodes of reef development. Communicated by Geology Editor Dr. Bernhard Riegl     

Settlement behaviour of larvae of the Stripey Snapper, <Emphasis Type="Italic">Lutjanus carponotatus</Emphasis> (Teleostei: Lutjanidae)

Larval behaviour is important to dispersal and settlement, but is seldom quantified. Behavioural capabilities of larval Lutjanus carponotatus in both offshore pelagic and reef environments at Lizard Island, Great Barrier Reef were observed in situ to determine if they were sufficient to influence dispersal. Offshore, larvae swam with higher directional precision and faster on the windward side of the island (28 cm.s⁻¹) than on the leeward side (16 cm s⁻¹). Most larvae swam directionally. Mean swimming directions were southerly in the windward area and northerly in the leeward area. Larvae avoided the surface and remained mostly between 3–15 m. Larvae released near reefs were 2–3 times faster swimming away from reefs (19 cm s⁻¹) than swimming toward or over them (6–8 cm s⁻¹). Speed swimming away was similar to that offshore. Of 41 larvae released near reefs, 73% reached the reef, 59% settled, and 13% of those reaching the reef were eaten. Larvae settled onto hard and soft coral (58%), topographic reef features (29%) and sand and rubble (13%). Settlement depth averaged 5.5 m (2–8 m). Before settling larvae spent up to 800 s over the reef (mean 231 s) and swam up to 53 m (mean 14 m). About half of the larvae interacted with reef residents including predatory attacks and aggressive approaches by residents and aggressive approaches by settling larvae. Settlement behaviour of L. carponotatus was more similar to a serranid than to pomacentrids. Settlement-stage larvae of L. carponotatus are behaviourally capable, and have a complex settlement behaviour.     

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.     

Competition for shelter in a high-diversity system: structure use by large reef fishes

Competition among large reef fishes for shelter beneath tabular structures provides a rare opportunity to study competition in a species-rich environment. The system permits a detailed study of localised competition with major implications for coral reefs with respect to human impacts including climate change. Using underwater video cameras, this study examined competition among 30 species of large reef fishes (from nine families) for access to shelter provided by 26 tabular structures, which may be the highest reported diversity of vertebrates competing for a single resource. Mean concentrations of fishes under tabular structures were also among the highest biomass recorded on reefs (4.71 kg m⁻²). A generated dominance hierarchy for the occupation of shelter appeared to be primarily driven by the size of fishes. In contrast to previous studies, fishes higher in the hierarchy tended to exhibit the lowest levels of aggression. However, size difference between fishes was found to be strongly negatively correlated with the proportion of aggressive interactions (R ² = 0.971, P < 0.0001). The strong competition for the shade provided by these corals highlights concerns about future shifts in the structure of large reef fish communities as corals are lost. This is particularly concerning given the critical functional roles played by certain species of large reef fishes that utilise tabular structure for shelter and which occupy the lower ranks of the dominance hierarchy.

     

江苏海门蛎岈山牡蛎礁生态现状评价

基于2013—2014年间的生态调查结果,评价了江苏海门蛎岈山牡蛎礁的生态现状。无人机航拍结果显示,江苏海门蛎岈山分布有750个潮间带区牡蛎礁斑块,总面积约为201519.37 m2;与2003年相比,海门蛎岈山牡蛎礁面积约下降了38.8%。活体牡蛎的平均盖度约为66%,2013年5和9月熊本牡蛎Crassostrea sikamea的平均密度分别为(2199±363)个/m2和(2894±330)个/m2。2013年5月海门蛎岈山熊本牡蛎种群的平均肥满度(CI)和性腺指数(GI)分别为(9.76±0.95)%和(1013±82)mg/g,均显著低于浙江象山港养殖的熊本牡蛎种群(P0.05)。海门蛎岈山熊本牡蛎的单倍体多样性和核苷酸多样性指数分别为0.119和0.00028,均高于长江口野生种群和浙江象山港养殖种群。海门蛎岈山熊本牡蛎种群受到尼氏单孢子虫(Haplosporidium nelson)的轻度浸染,其感染率(17.2%)低于浙江象山港养殖群体(47.3%)。泥沙沉积和人类捕捞是江苏海门蛎岈山牡蛎礁面临的主要胁迫因子,今后牡蛎礁恢复的重点是增加附着底物的数量。     

Non-native regal demoiselle,Neopomacentrus cyanomos,presence, abundance,and habitat factors in the North-Central Gulf of Mexico

Remotely operated vehicle (ROV) surveys were conducted at reef sites in the northern Gulf of Mexico (nGOM) during 2018–2019. Artificial (AR?=?63) and natural (NR?=?139) reefs were located in a 2?×?10⁵ km² area south of Mobile, AL to Destin, FL at depths of 13–75 m. We observed a total of 5371 damselfishes (Family: Pomacentridae) belonging to eight taxa. The non-native regal demoiselle (regal), Neopomacentrus cyanomos, was present at 30.2% of ARs but only 1.4% of NRs with densities ranging from 0.19 to 18.11 fish per 100 m². Regals were most dense at shallow ARs, comprising 53% of the damselfish community, and least dense at deeper reefs comprising?<?1% of observed damselfishes. Results from generalized linear mixed models (GLMMs) indicated the interaction among reef type, complexity, relief, and depth had a significant effect on regal density but that reef type (36%) and the interaction between reef type and depth (25%) explained the greatest proportions of variance in the data (partial η²) while the interaction among all four main effects explained only a small amount (2%). Our data indicate regals prefer shallow artificial structures with low complexity but can occupy deeper reefs, including NRs, despite less-favorable conditions. Our data document the persistence of regals in the nGOM and identify habitat factors that are significantly related to their presence and density in the region. However, the dynamics controlling their distribution are still uncertain and potential negative impacts on native reef fish communities remain unclear.