Coral Reef Environments Research Articles

Research Article: Study of coral reef benthic foraminiferal assemblages in Qeshm Island, Persian Gulf

Benthic foraminifera are important in sediment production of coral reef environments and are excellent indicators of water quality and reef health. There is a lack of precise information about the foraminifer’s fauna of the coral reefs in the Persian Gulf. In this study, sediment sampling was performed in June 2019 from two coral stations of Naz Island and Zeytoon Park. The surface sediment with three replicates for each location was collected using a mini corer and then were fixed in 70% ethanol. In this study, thirty species belong to 23 genera and 19 families of foraminifer's assemblages were identified based on morphological characters. Our results indicated that Foraminiferal assemblages were similar in both sampling localities. Quinqueloculina was the most abundant genera for both Naz Island and Zeytoon Park. Foraminifer's frequency of Zeytoon Park was higher than Naz Island. Symbiont-bearing foraminifera (e.g. Peneroplis) were observed just in Zeytoon Park. Higher frequency and the presence of symbiont-bearing foraminifera possibly indicate that Zeytoon Park has a more favorable condition for the coral reef growth in the future. Finally, we recommend that the structure of the foraminifer’s community could be used as an early warning system for water quality around coral reefs and in particular, would help resource managers make better decisions about protecting coral habitats.

Coral annual growth band impregnated microplastics (Porites sp.): a first investigation report

Microplastic pollution in marine environments has increased rapidly during the last decades. These microplastic particles are transported into the coral reef environment from terrestrial origin. Recent investigations suggest that microplastic ingestion can adversely affect marine invertebrates, especially in the coral reef ecosystem. The present attempt has been carried out to identify the coral growth band impregnated microplastics from polished coral slabs and acid leached insoluble residues through microscopic examination. The impregnated microplastics have been present in the following descending order: Nylon > Polyester > Polypropylene > Polyethylene. The irregular-shaped black and red microplastic particles have been dominantly observed. The annual growth band impregnated microplastics are most probably derived from tourist activities and chiefly controlled by oceanic currents and sediment re-suspension. The maximum distribution of microplastics has been observed in the coral annual growth bands of 1964 and 2005. Clinical Trials Registration The present work is not a clinically related project. Hence clinical registration is not obtained/not required for publishing the results.

A potential threat to the coral reef environments: Polybrominated diphenyl ethers and phthalate esters in the corals and their ambient environment (Persian Gulf, Iran)

Pollution of the surrounding habitat poses one of the biggest threats to the coral health and even survival. This study focuses on the occurrence, distribution, bioaccumulation and bioconcentration of polybrominated diphenyl ethers (PBDEs) and phthalate esters (PAEs) in corals, their zooxanthellae and mucus, as well as in their ambient environment in Larak coral reef (Persian Gulf) for the first time. The highest concentrations of the pollutants were recorded in mucus, followed by zooxanthellae, tissue and skeleton. Soft corals with higher lipid content contained more PBDEs and PAEs. Pollutants were both efficiently bioconcentrated from water and bioaccumulated from the ambient sediment, albeit bioconcentration played the most prominent role. Elevated PBDEs and especially PAEs concentrations were detected in the skeletons of the bleached corals if compared to the skeleton samples of the non-bleached individuals.

Automated two-dimensional localization of underwater acoustic transient impulses using vector sensor image processing (vector sensor localization).

Detecting acoustic transients by signal-to-noise ratio (SNR) becomes problematic in nonstationary ambient noise environments characteristic of coral reefs. An alternate approach presented here uses signal directionality to automatically detect and localize transient impulsive sounds collected on underwater vector sensors spaced tens of meters apart. The procedure, which does not require precise time synchronization, first constructs time-frequency representations of both the squared acoustic pressure (spectrogram) and dominant directionality of the active intensity (azigram) on each sensor. Within each azigram, sets of time-frequency cells associated with transient energy arriving from a consistent azimuthal sector are identified. Binary image processing techniques then link sets that share similar duration and bandwidth between different sensors, after which the algorithm triangulates the source location. Unlike most passive acoustic detectors, the threshold criterion for this algorithm is bandwidth instead of pressure magnitude. Data collected from shallow coral reef environments demonstrate the algorithm's ability to detect SCUBA bubble plumes and consistent spatial distributions of somniferous fish activity. Analytical estimates and direct evaluations both yield false transient localization rates from 3% to 6% in a coral reef environment. The SNR distribution of localized pulses off Hawaii has a median of 7.7 dB and interquartile range of 7.1 dB.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai\u2018i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

O‘ahu’s marine protected areas have limited success in protecting coral reef herbivores

Herbivorous fishes and urchins can contribute to reef resilience by removing algae that are competitive with corals, yet herbivorous fishes are frequently targeted by fishers. The deleterious effects of fishing on coral reef herbivore populations are thought to be decreased through the establishment of no-take marine protected areas (MPAs). We conducted surveys to compare the biomass, diversity, and size structure of herbivorous reef fish within three functional guilds (i.e., grazers, scrapers, and browsers) and herbivorous urchin populations inside and outside of four of O‘ahu’s current MPAs to determine if they were effectively protecting herbivorous fishes and assess any resulting effects on sea urchin competitors. We also characterized the benthos, including the identification of common taxa in algal turfs, to evaluate interactions between herbivory and benthic communities. Urchins and grazing fishes accounted for the majority of herbivore biomass across regions of O‘ahu, and the dominance of urchins suggests that they significantly contribute to herbivory. Coral cover was a significant predictor of urchin biomass, but urchins did not have a significant relationship with herbivorous fish biomass or MPA protection. MPA protection and depth had positive effects on herbivorous fish biomass when examined in aggregate. However, these results were largely influenced by a large MPA protection effect in the Hanauma Bay MPA, compared to weaker MPA effects in Kāne‘ohe Bay, Waikīkī, and Pūpūkea. Hanauma Bay had stark differences in the condition of reef habitats between the MPA and fished areas which may also confound the interpretation of a strongly significant protection effect. Depth and habitat complexity were significant predictors of both grazer biomass and aggregate herbivore community composition, suggesting that these bottom-up factors may have a greater impact on herbivorous fish biomass than protection. Turf communities were speciose and displayed similar trends to herbivore communities across regions, but within-region trends in the Hanauma Bay region suggest that turf species composition is not only dictated by top-down factors. Within-guild fish diversity was low across site and region, suggesting herbivory was dominated by a single or few species. The small size structure and densities of herbivorous fishes in MPAs across all regions limits their population-level functional and reproductive contributions. While MPAs serve as a popular fisheries management tool for coral reef environments, the limited benefits of MPAs for herbivorous fish and urchin populations around O‘ahu suggest a general need for improved fisheries management and enforcement, especially prior to the consideration of an expansion of the existing MPA network.

Impact of oyster culture on coral reef bacterioplankton community composition and function in Daya Bay, China

Subtropical coral reefs along the coast are facing multiple pressures. Mariculture is one of the main sources of such pressure. Oyster culture has become a worldwide phenomenon in coastal ecosystems. Due to the high filtration efficiency of oysters, their culture has helped to purify some coastal waters. However, high-density oyster culture has also had negative effects on coastal ecosystems, including the loss of natural habitat, changes in hydrology, cross infection of corals with pathogenic bacteria, and changes to the structure and function of bacterioplankton communities. In this study, the effect of oyster culture on coral reefs was characterized based on variability in the structure and function of bacterioplankton communities. Using 16S rRNA gene sequencing, a comprehensive bacterioplankton reference database was constructed for coral reef habitats associated with oyster culture and subjected to different disturbance gradients. Small shifts in the surrounding coral reef environment caused by oyster culture disturbance were detected by comparing the structure and function of bacterioplankton communities with biogeochemical parameters. The measured chemical dynamics explained 71.15% of the bacterioplankton community variability between habitats. Oyster culture increased the richness and diversity of bacterioplankton communities. Species composition similarity was highest between the oyster culture area and the nearest coral reef habitat. The spatial turnover in the bacterioplankton community was characterized by less uniform community assembly patterns. The bacterioplankton function of reefs relatively far from anthropogenic disturbance differed from that of those closer to such disturbances. Our results also show that the variability in structure and function of bacterioplankton communities between oyster culture areas and coral reef areas was mainly driven by salinity and ammonium. Oyster culture can impact bacterioplankton community composition and dynamics around coral reef habitats. The results provide an important context for developing frameworks for managing ecological interactions among oyster cultures and coral reef habitats of concern.

Stratigraphic development of a Late Oligocene Reef Complex under strong fluviatile influence in the Tertiary Piedmont Basin (Liguria, NWItaly)

The modern-day decline of coral reefs due to bleaching events has been recognized as one of the major consequences of man-driven climate change. However, also eutrophication has been highlighted as an equally great danger for coral reefs and as such for biodiversity hotspots. In the latest years this phenomenon has moved to the forefront in the scientific community. Fossil reefs play a key role in studying the emergence, development and faunal/floral diversity of reef environments under eutrophic conditions. Their importance as valuable data sources for studying long-term changes of coral reef environments and their resilience cannot be disputed, especially since they may record the complete life cycle of a reef complex. In this study, nine sections nearby the town of Dego (Savona Province, NW Italy) are presented and discussed with regards to their lithostratigraphic and paleontological contents. Due to the extensive amount of data, the original morphology of a fringing reef, consisting of core, flank and fore reef, under strong fluviatile influence could be reconstructed. This study emphasizes the importance of the coralline red algae association in such biocarbonatic build-ups as major constituent and as substrate stabilizers. The sections record the original colonization event of the local basement by the builder community, the emergence of the coral reef and finally the suffocation by the fluviatile sediments. The variation of the red algae association reflects a deepening trend and is possibly correlated to enhanced fluvial input, which tends to deteriorate ecological conditions and functions as a major trigger for initial reef suffocation.

Whole-Genome Transcriptome Analyses of Native Symbionts Reveal Host Coral Genomic Novelties for Establishing Coral-Algae Symbioses.

Reef-building corals and photosynthetic, endosymbiotic algae of the family Symbiodiniaceae establish mutualistic relationships that are fundamental to coral biology, enabling coral reefs to support a vast diversity of marine species. Although numerous types of Symbiodiniaceae occur in coral reef environments, Acropora corals select specific types in early life stages. In order to study molecular mechanisms of coral–algal symbioses occurring in nature, we performed whole-genome transcriptomic analyses of Acropora tenuis larvae inoculated with Symbiodinium microadriaticum strains isolated from an Acropora recruit. In order to identify genes specifically involved in symbioses with native symbionts in early life stages, we also investigated transcriptomic responses of Acropora larvae exposed to closely related, nonsymbiotic, and occasionally symbiotic Symbiodinium strains. We found that the number of differentially expressed genes was largest when larvae acquired native symbionts. Repertoires of differentially expressed genes indicated that corals reduced amino acid, sugar, and lipid metabolism, such that metabolic enzymes performing these functions were derived primarily from S. microadriaticum rather than from A. tenuis. Upregulated gene expression of transporters for those metabolites occurred only when coral larvae acquired their natural symbionts, suggesting active utilization of native symbionts by host corals. We also discovered that in Acropora, genes for sugar and amino acid transporters, prosaposin-like, and Notch ligand-like, were upregulated only in response to native symbionts, and included tandemly duplicated genes. Gene duplications in coral genomes may have been essential to establish genomic novelties for coral–algae symbiosis.

Estimating the fractional abundance of coral reef benthic compositions using linear spectral unmixing

The present work is focused on providing the application of linear spectral unmixing technique to Landsat-8 images of Operational Land Imager (OLI) bands in coral reef environment at Gulf of Mannar (GoM) islands along the coast of Tamilnadu, India. The spectral characteristics of benthic compositions namely sand, seagrass, branched corals and mass corals in the GoM are recorded in-situ using RAMSES-TriOS Hyperspectral radiometer and the signatures recorded from in-situ have been used as input for linear spectral unmixing technique. The results of linear spectral unmixing provide the fractional abundances of coral reef benthic communities in the Islands of GoM region. Such maps can be used to characterize the landscape structure and composition of reefs, which can in turn be linked to environmental and human impacts. This kind of approaches is cost-effective and acts as a valuable tool for the evaluation and periodical monitoring of coral reef community.

Modelling the optical properties of coral reefs and its implication for optical remote sensing

Effective monitoring of coral reefs remains a major goal in marine ecology and conservation as these communities representing the most productive ecosystems and hosting approximately one third of all known marine species have been seriously threatened by various anthropogenic activities and climate change events. Space-borne reflectance data are commonly used to monitor coral reefs and improve their management practices, yet an effective use of such data remains a challenge due to a high level of spatial heterogeneity of coral reef communities and surrounding water environments. Thus, it is crucial to understand the optical properties coral reef environments and their influence on the spectral remote sensing reflectance. This study presents an optical model based on field and laboratory data that relates the inherent optical properties (IOPs, such as absorption and backscattering) of the water constituents (phytoplankton, suspended sediments, colored dissolved organic matter, water itself) and coral components (symbiotic + coralline algae) to remote sensing reflectance via the bidirectional quantity (f/Q) of the upwelling light field. The absorption and backscattering coefficients are parameterized as a function of the individual contributions of coral component (symbiotic and coralline algae) and water constituents and the bidirectionality factor f/Q is derived as a function of solar-sensor zenith angles and IOPs. The wider applicability of these parameterizations is tested in diverse water types (with chlorophyll-a concentration 0.07–1239 mg m−3, suspended sediment concentration 0.1–104 g m−3, absorption coefficient of colored dissolved organic matter 0.02 to 8.8 m−1 at 412 nm). Modelled reflectance spectra were compared with in-situ data and Hydrolight radiative transfer simulations. For various coral reef species and water types, the modelled spectral reflectance and associated features across a spectral range of 400–750 nm showed good agreement with measured and simulated data within the error of 17%. The effect of strong attenuation of light by water which potentially affects and alters the spectral shapes and magnitudes of reflectance is further examined and discussed. This work will have significant implications for optical remote sensing of the coral reef ecosystems in diverse oceanic environments.

Automated two-dimensional localization of underwater acoustic transient impulses using vector sensor image processing

An algorithm is presented for automatically localizing transient impulsive sounds collected on several autonomous underwater vector sensors, spaced 15 to 23 m apart. The procedure, which does not require precise time synchronization, exploits transient signals of interest arriving from different azimuthal directions on each sensor. For each sensor the method first constructs time-frequency representations of both the squared acoustic pressure (spectrogram) and dominant directionality of the active intensity (azigram). Within each azigram sets of time-frequency cells associated with transient energy arriving from a consistent azimuthal sector are identified. Standard image processing techniques then link sets that share similar duration and bandwidth between different sensors, after which the algorithm triangulates the source location using the azimuths associated with the detection set. Data collected from shallow coral reef environments demonstrate the algorithm's ability to detect SCUBA bubble plumes and humpback whale song, and reveal consistent spatial distributions of somniferous fish activity. Analytical estimates and direct evaluations both yield false transient localization rates of 3%–6% in the coral reef environment. Many localized pulses have low signal-to-noise ratios, whose distribution has a median of 7.7 dB and an IQR of 7.1 dB. [Work sponsored by DARPA PALS.]

Microbiomes of fish, sediment and seagrass suggest connectivity of coral reef microbial populations.

The benthic environments of coral reefs are heavily shaped by physiochemical factors, but also the ecological interactions of the animals and plants in the reef ecosystem. Microbial populations may be shared within the ecosystem of sediments, seagrasses and reef fish. In this study, we hypothesize that coral reef and seagrass environments share members of the microbial community that are rare in some habitats and enriched in others, and that animals may integrate this connectivity. We investigated the potential connectivity between the microbiomes of sediments, seagrass blades and roots (Syringodium isoetifolium), and a seagrass-specialist parrotfish (C. spinidens) guts in reef areas of Fiji. We contrasted these with sediment samples from the Florida Keys, gut samples from surgeonfish (A. nigricauda, Acanthurinae sp. unknown, C. striatus), and ocean water microbiomes from the Atlantic, Pacific and Indian Oceans to test the robustness of our characterizations of microbiome environments. In general, water, sediment and fish gut samples were all distinct microbiomes. Sediment microbiomes were mostly similar between Fiji and Florida, but also showed some regional similarities. In Fiji, we show connectivity of a shared microbiome between seagrass, fish and sediments. Additionally, we identified an environmental reservoir of a surgeonfish symbiont, Epulopiscium. The connection of these ecosystem components suggests that the total microbiome of these environments may vary as their animal inhabitants shift in a changing ocean.

Measuring Temperature in Coral Reef Environments: Experience, Lessons, and Results from Palau

Sea surface temperature, determined remotely by satellite (SSST), measures only the thin “skin” of the ocean but is widely used to quantify the thermal regimes on coral reefs across the globe. In situ measurements of temperature complements global satellite sea surface temperature with more accurate measurements at specific locations/depths on reefs and more detailed data. In 1999, an in situ temperature-monitoring network was started in the Republic of Palau after the 1998 coral bleaching event. Over two decades the network has grown to 70+ stations and 150+ instruments covering a 700 km wide geographic swath of the western Pacific dominated by multiple oceanic currents. The specific instruments used, depths, sampling intervals, precision, and accuracy are considered with two goals: to provide comprehensive general coverage to inform global considerations of temperature patterns/changes and to document the thermal dynamics of many specific habitats found within a highly diverse tropical marine location. Short-term in situ temperature monitoring may not capture broad patterns, particularly with regard to El Niño/La Niña cycles that produce extreme differences. Sampling over two decades has documented large T signals often invisible to SSST from (1) internal waves on time scales of minutes to hours, (2) El Niño on time scales of weeks to years, and (3) decadal-scale trends of +0.2 °C per decade. Network data have been used to create a regression model with SSST and sea surface height (SSH) capable of predicting depth-varying thermal stress. The large temporal, horizontal, and vertical variability noted by the network has further implications for thermal stress on the reef. There is a dearth of definitive thermal information for most coral reef habitats, which undermines the ability to interpret biological events from the most basic physical perspective.

Relationship Between Species Composition of Butterflyfishes and Coral Cover (Study case: Taka Bonerate National Park)

The coral reef environment has a strong influence on associated organisms such as fishes, mollusks, and others. Wherein, the butterflyfishes are marine fishes which closely associated with the tropic group as dietary specialization i.e. obligate coral feeder, facultative, and generalist. The obligate may respond only to change in preferred corals and not indicate others. However, generalist show in different response in habitat deteriorates and may allow switching feeding to a less preferred one. Many questions remain about food specific at the species level which may potentially as bio-indicator for coral conditions. Here, we studied the species composition among coral coverage. We explore the environmental degradation in Taka Bonerate National Park impact on food resources and fishes especially for butterflyfishes community. This study focused on family Chaetodontidae with UVC method and UPT method for coral cover. This study was carried out at Taka Bonerate National Park, South Sulawesi between May and June 2019. There were 342 individuals observed and dominated by Chaetodon kleinii, Hemitaurichthys polylepis, Heniochus chrysostomus, C. lunulatus, C. melannotus, C punctatofasciatus, and Forcipiger flavissimus. However, we found a site with diversity index and coral cover has across conditions. Whilst, these benthic communities mostly dominated by Acropora, which may be preferenced by specific species. Butterflyfishes have several types of foraging tasks and may impact in utilizing the coral reef and other social habitats used. The species composition and abundance of butterflyfishes had relations not only by coral coverage but also benthic compositions. However, factors that regulate its specific species distribution and species compositions are still under study.

Pharmacological activities of coral reef associated actinomycetes, Saccharopolyspora sp. IMA1

Emergence of multidrug resistance among the aquatic pathogens enhances the demand for new antimicrobial compounds to replace currently using antibiotics in order to overcome resistance using microorganisms. The main scope of the present study was to isolate a potential antagonistic actinobacteria and appraise their antibacterial, antioxidant and anticancer properties for its therapeutic prospective . In the primary screening, the isolates were tested against aquatic bacterial pathogens ( viz. Vibrio harveyi, Vibrio parahemolyticus, Vibrio vulnificus ) by cross streak method. Saccharopolyspora jiangxiensis IMA1 showed maximum inhibition against aquatic bacterial pathogens. The extract of IMA1 showed maximum inhibition zone of 30 mm against aquatic pathogen, V. parahemolyticus. In addition, the IMA1 extract showed excellent antioxidant activity, significant degree of reducing power and ABTS radical scavenging properties. In vitro anticancer studies showed IC 50 values at 16.60 μg/ml in human breast cancer cell lines (MCF-7). The morphological changes were observed at 30 μg/ml. The pharmacologically active metabolites were identified by Gas chromatography–mass spectrometry analysis. It was concluded that the pharmacological activities are dose dependent. The present study shows the potential of IMA1 as promising strain in controlling aquatic bacterial pathogens as well as antioxidant and anticancer properties. • Saccharopolyspora sp. IMA1 was isolated from coral reef environment. • IMA1 metabolites inhibited V. harveyi, V. parahemolyticus, V. vulnificus . • IMA1 extract showed antioxidant and ABTS radical scavenging properties. • In vitro anticancer studies showed IC 50 values at 16.60 μg/ml in MCF-7 cell lines.

The Cone Shells (Gastropoda: Conidae) of the Abrolhos Platform, Brazil, with the Description of Three New Species

Three new species of cone shells, in the genera Coltroconus, Jaspidiconus, and Poremskiconus, have been discovered on the Abrolhos Platform off central Brazil. These new taxa, Coltroconus valianti n. sp., Jaspidiconus carlagrezziae n. sp., and Poremskiconus uhlei n. sp. are restricted to the coral reef environments of the central platform area and are the newest additions to a highly-endemic localized conid fauna comprising 17 known species

Mangrove and sand cay dynamics on Australian and Indonesian low wooded islands: A 45 year comparison of changes from remote sensing

Changes to coral reef landscapes are driven by regional processes that are unique to particular localities, yet much of our global knowledge about how landscape changes manifest in coral reef environments is generalised from work undertaken on the Great Barrier Reef. We compare observations of 45 years of change on sand cays and mangroves associated with low wooded islands in Australia and Indonesia. We draw on field observations from ground referencing campaigns, alongside remote sensing technology, including satellite images and unmanned aerial vehicle campaigns. Four low wooded island sites are compared: two in the Great Barrier Reef (GBR), Australia (Nymph Island and Two Isles) and two in the Spermonde Archipelago, Indonesia (Sabangko and Tanakeke Island). The Spermonde and GBR sites can be distinguished in relation to the process regimes that entrain, distribute and deposit sediments on the reef surface thereby providing a substrate for further mangrove colonisation, particularly the presence or absence of cyclones as a key determinant of sediment transport. The influence of human populations inhabiting these sites is also an important control on their geomorphology. In the Spermonde Archipelago, local communities have altered sand cays through the development of infrastructure and converted mangroves to shrimp farms, while sand cays and mangroves have remained largely unaltered by humans on the GBR. This comparative evaluation of changes to sand cays and mangrove forest across low wooded islands emphasises the importance of considering changes within the context of their local geographic setting, inclusive of natural environmental and anthropogenic drivers of change.

A baited remote underwater video system (BRUVS) assessment of elasmobranch diversity and abundance on the eastern Caicos Bank (Turks and Caicos Islands); an environment in transition

The present study was undertaken to assess the diversity and abundance of elasmobranch fishes in coral reef and sand flat environments on the eastern Caicos Bank, with a view to informing marine spatial planning as the island of South Caicos and its environs transition to a tourism-based economy. Using baited remote underwater video systems (BRUVS), the nurse shark Ginglymostoma cirratum, Caribbean reef shark Carcharhinus perezi, spotted eagle ray Aetobatus narinari, southern stingray Hypanus americanus, lemon shark Negaprion brevirostris, tiger shark Galeocerdo cuvier, blacknose shark Carcharhinus acronotus, and great hammerhead shark Sphyrna mokarran were observed to use these waters, with G. cirratum and C. perezi being particularly abundant. Species diversity and overall abundance was greater in the reef environment than on the sand flats, but G. cirratum was equally abundant in both environments. Furthermore, even reef-associated species such as C. perezi were occasionally encountered on the flats a considerable distance from the reef. This indicates that although marine conservation efforts in the Turks and Caicos Islands should continue to focus on coral reef areas, less dramatic environments such as sand flats should not be ignored.

Coral tentacle elasticity promotes an out-of-phase motion that improves mass transfer.

Corals rely almost exclusively on the ambient flow of water to support their respiration, photosynthesis, prey capture, heat exchange and reproduction. Coral tentacles extend to the flow, interact with it and oscillate under the influence of waves. Such oscillating motions of flexible appendages are considered adaptive for reducing the drag force on flexible animals in wave-swept environments, but their significance under slower flows is unclear. Using in situ and laboratory measurements of the motion of coral tentacles under wave-induced flow, we investigated the dynamics of the tentacle motion and its impact on mass transfer. We found that tentacle velocity preceded the water velocity by approximately one-quarter of a period. This out-of-phase behaviour enhanced mass transfer at the tentacle tip by up to 25% as compared with an in-phase motion. The enhancement was most pronounced under flows slower than 3.2 cm s-1, which are prevalent in many coral-reef environments. We found that the out-of-phase motion results from the tentacles' elasticity, which can presumably be modified by the animal. Our results suggest that the mechanical properties of coral tentacles may represent an adaptive advantage that improves mass transfer under the limiting conditions of slow ambient flows. Because the mechanism we describe operates by enhancing convective processes, it is expected to enhance other fitness-determining transport phenomena such as heat exchange and particle capture.