Reef Flats Research Articles

Additional floristic study of planktonic and seaweed-associated diatoms in Chuuk, Micronesia

AbstractThe present study enhances knowledge of the biodiversity of diatoms in Chuuk, Micronesia following our 2018 study on the seaweed-associated diatoms. We collected planktonic samples of diatoms from five sites of reef flats using a 20 μm mesh net, and two samples of seaweeds with epiphytes by hand from an islet on the barrier reef. In addition, the seaweed-associated diatoms from our 2018 study were analysed using scanning electron microscopy. A total of 109 diatom taxa are documented in the present study. Of these, 70 species were from net samples, and 39 species from the seaweed-associated diatoms. Thirty-one species are newly recorded from Micronesian waters. Most taxa are benthic or tychoplanktonic; euplanktonic diatoms were rare. The occurrence of benthic diatoms from the water column might be related to the Chuuk environmental conditions which include shallow water, strong light intensity and high grazing pressure, to which benthic diatoms seem to be able to better adapt than planktonic diatoms.

Destructive outbreaks of the corallivorous starfish Acanthaster cf. solarisspare coral assemblages in the shallowest reef flat areas in New Caledonia

Abstract Outbreaks of the corallivorous starfish Acanthaster cf. solaris (COTS) are not fully understood, especially in the shallowest areas behind the reef crests where limited COTS impacts are often reported. Here, we investigated the outbreak occurrence and compared post-outbreak habitat impacts in reef flats vs. upper fore reefs at 13 sites in New Caledonia. In this Pacific territory so far considered marginally affected by COTS, we documented wide occurrences of aggregations, combining massive population increases (maximum 605 COTS per swim, abundances >100 COTS recorded in 46% of the sites) with limited spatiotemporal boundaries. Abundance levels met the highest values in the literature, but were restricted to relatively small, isolated mid-shelf reefs. Typical residence time was short (< two years), with at least one site where COTS seemingly disappeared within seven months. The spread of COTS population and subsequent impacts appeared self-contained, and never affected the reef flats (0.5–1.5 m). The transition to severely affected fore reefs was abrupt, with live coral cover divided by nine and morphological diversity halved within a very few meters (3–5 m). We suggest that these differential impacts likely result from harsh environmental conditions making shallow, coral-rich areas less suitable for COTS, thereby pushing predation pressure further downwards.

The upper thermal limit of epaulette sharks (Hemiscyllium ocellatum) is conserved across three life history stages, sex and body size

Owing to climate change, most notably the increasing frequency of marine heatwaves and long-term ocean warming, better elucidating the upper thermal limits of marine fishes is important for predicting the future of species and populations. The critical thermal maximum (CTmax), or the highest temperature a species can tolerate, is a physiological metric that is used to establish upper thermal limits. Among marine organisms, this metric is commonly assessed in bony fishes but less so in other taxonomic groups, such as elasmobranchs (subclass of sharks, rays and skates), where only thermal acclimation effects on CTmax have been assessed. Herein, we tested whether three life history stages, sex and body size affected CTmax in a tropical elasmobranch, the epaulette shark (Hemiscyllium ocellatum), collected from the reef flats surrounding Heron Island, Australia. Overall, we found no difference in CTmax between life history stages, sexes or across a range of body sizes. Findings from this research suggest that the energetically costly processes (i.e. growth, maturation and reproduction) associated with the life history stages occupying these tropical reef flats do not change overall acute thermal tolerance. However, it is important to note that neither embryos developing in ovo, neonates, nor females actively encapsulating egg cases were observed in or collected from the reef flats. Overall, our findings provide the first evidence in an elasmobranch that upper thermal tolerance is not impacted by life history stage or size. This information will help to improve our understanding of how anthropogenic climate change may (or may not) disproportionally affect particular life stages and, as such, where additional conservation and management actions may be required.

Quantifying functional consequences of habitat degradation on a Caribbean coral reef

Abstract. Coral reefs are declining worldwide. The abundance of corals has decreased alongside a rise of filter feeders, turf, and algae in response to intensifying human pressures. This shift in prevalence of functional groups alters the biogeochemical processes in tropical water ecosystems, thereby influencing reef functioning. An urgent challenge is to understand the functional consequences of these shifts to develop suitable management strategies that aim at preserving the biological functions of reefs. Here, we quantify biogeochemical processes supporting key reef functions (i.e. net community calcification (NCC) and production (NCP) and nutrient recycling) in situ for five different benthic assemblages currently dominating shallow degraded Caribbean reef habitats. To this end, a transparent custom-made enclosure was placed over communities dominated by either one of five functional groups – coral, turf and macroalgae, bioeroding sponges, cyanobacterial mats, or sand – to determine chemical fluxes between these communities and the overlying water, during both day and night. To account for the simultaneous influence that distinct biogeochemical processes have on measured variables, the rates were then derived by solving a model consisting of differential equations describing the contribution of each process to the measured chemical fluxes. Inferred rates were low compared to those known for reef flats worldwide. Reduced accretion potential was recorded, with negative or very modest net community calcification rates for all communities. Net production during the day was also low, suggesting limited accumulation of biomass through photosynthesis and remineralisation of organic matter at night was relatively high in comparison, resulting in net heterotrophy over the survey period for most communities. Estimated recycling processes (i.e. nitrification and denitrification) were high but did not fully counterbalance nutrient release from aerobic mineralisation, rendering all substrates sources of nitrogen. Results suggest similar directions and magnitudes of key biogeochemical processes of distinct communities on this shallow Curaçaoan reef. We infer that the amount and type of organic matter released by abundant algal turfs and cyanobacterial mats on this reef likely enhances heterotroph activity and stimulates the proliferation of less diverse copiotrophic microbial populations, rendering the studied reef net heterotrophic and drawing the biogeochemical “behaviour” of distinct communities closer to each other.

Scraping and grazing herbivorous/detritivorous fish display opposite feeding behaviours under different protection regulations

ABSTRACT Herbivorous and detritivorous fish display complex feeding behaviour, and research into how feeding behaviour changes with environmental and social variables is lacking. Such knowledge is imperative to infer how herbivory/detritivory will differ, in light of shifting resources and communities and specifically whether reefs can recover from disturbance. Fish abundance, feeding rate, body size, diet and schooling feeding of three major functional groups (scrapers, grazers and browsers) were examined across reef types under different fishing regulations. Scrapers and grazers (parrotfishes and surgeonfishes) were more abundant and displayed the highest feeding rates on reef flats. Scrapers mainly resided inside the restricted zone, while more grazers were found in the general use zone, where macroalgal abundance was highest. Browsers (rabbitfishes) were seldom observed and patchily gathered on the reef flat and reef slope in both zones. Thus, fishing protection did not appear to benefit grazers and browsers, whereas more scrapers gathered on shallow reef flats in the protection zone. Scraper and grazer feeding rates increased from an individual to a pair and increased with body size, these factors led to variations in feeding behaviours across reef types and protection regulations. Protection appears to benefit scrapers and variations in feeding rates were largely related to school size. Lastly, grazer density was associated more with macroalgal coverage than protection status. The opposite feeding behaviours of scrapers and grazers indicates not only protection status, but fishing restrictions and size limit regulations are needed to maintain coral reef fisheries and functional diversity on coral reefs in Taiwan.

Antagonistic effects of seawalls and urban sedimentation on epilithic algal matrix (EAM)-feeding fishes

Marine urbanisation often results in the proliferation of artificial coastal defences and heavy sedimentation, adversely impacting coral reef systems in tropical coastal cities. Knowledge of how motile organisms, such as reef fish, respond to novel human-made habitats and high sedimentation is limited. Here, we examine the role of sloping granite seawalls in supporting reef fishes that utilise the epilithic algal matrix (EAM) as a food resource. We surveyed fish assemblages and feeding activities on seawalls and reef flats, and conducted a field experiment to examine the effects of sediment on EAM feeding rates. Seawalls and reef flats supported distinct fish assemblage composition with significantly greater feeding activity on seawalls. However, reduced feeding activity on EAM with elevated sediment loads suggests that urban sedimentation may limit the utility of this novel feeding ground for nearshore communities. These findings illustrate the complexities and interactive effects of anthropogenic changes driven by coastal urbanisation.

Environmental Atrocities in the South China Sea: The Science Behind Conservation Recourse

Extensive damage to reefs and exploitation of threatened species of the South China Sea raise questions regarding national obligations under international treaties. An historic test of these obligations under the United Nations Convention on the Law of the Sea (UNCLOS) was presented by the Philippine government before the Permanent Court of Arbitration at the International Court of Justice at the Peace Palace in Den Hague in November 2015. High resolution satellite imagery and on-site photographs, videos, and eye witness accounts provide ample evidence of unparalleled direct environmental damage to highly productive and biodiverse coral reefs of the South China Sea. Experts witness testimony indicated that this damage is a result of extensive island building on reef flats and sedimentation from dredging activities. Scientific evidence also indicates that this damage to coral reefs is likely to influence reef productivity throughout the region, including in adjacent Exclusive Economic Zones. Additional evidence of unrestrained exploitation targeting giant clams, corals, and reef fishes was presented that are indicative of irresponsible fishing practices and pose additional threats to endangered species. The decision of the Tribunal of the Permanent Court of Arbitration was handed down in July 2016 that upheld the claims of the Philippines government and has far-reaching policy implications for environmental actions in international waters. An evaluation of the ruling of the tribunal shows that nearly all points presented under UNCLOS were merited, with the possible exception of claims of connectivity of reefs of the South China Seas with adjacent Exclusive Economic Zones. Further research is needed to provide evidence for this claim.

Sea Cucumbers (Holothuroidea) of Northeastern and Western Mindanao, Philippines: The Potential Role of Marine Protected Areas in Maintaining Diversity and Abundance

Marine protected areas (MPAs) are considered strategic tools in conserving biodiversity and maintaining stocks of valuable resources. We assessed sea cucumbers in five provinces in northeastern and western Mindanao to describe the state of diversity and abundance and evaluate the role of MPAs in sustaining stocks of exploited species. We identified 36 species of sea cucumbers from fishery-independent surveys on shallow reef flats and deeper reef slopes, of which 33 species (92%) belong to order Aspidochirotida and three species belong to Order Apodida. The majority are shallow-water holothurians occurring on reef flats and seagrass beds, while a few species are found along reef slopes or in fresh catches by fishers sold to local traders or processors in some sites. Nine species are considered high-value to the global trepang trade but occur at low densities, while the rest are abundant or common species with low commercial value. Species richness (S=17-30 spp.) varies across sites, but species composition similarity is relatively high (Sørensen’s SQ = 0.62-0.78). Mean population densities and variances of high-value species are significantly higher inside enforced MPAs than in non-MPA sites(t-test, p <0.05; F-test, p<0.005) across five survey sites. The abundance of high-value H. scabra in Tubajon and H. fuscogilva in Capayas Island demonstrates the critical role of MPAs in conserving biodiversity, maintaining population levels, and ensuring natural recruitment of sea cucumber resources. Urgent management measures such as formulating a national management plan, regulating harvests, and establishing no-take MPAs are recommended.

Influence of Land Reclamation on Fresh Groundwater Lenses in Oceanic Islands: Laboratory and Numerical Validation

AbstractFresh groundwater lenses in tropic oceanic islands are important freshwater resources for local inhabitants and ecosystems. These reef‐carbonate islands typically have a dual‐aquifer structure, with poorly consolidated Holocene sediments deposited unconformably on Pleistocene limestone reef deposits. Land reclamation has been carried out on the reef flats or shallow water areas in coral islands, a very common practice in the Indian Ocean and the South China Sea. However, there is a lack of comprehensive understanding of how the groundwater system will respond to land reclamation. In this study, the impact of land reclamation on the fresh groundwater lens in an island is investigated using multiple methods: sand‐tank experiments, sharp‐interface analytical solutions, and numerical modeling. This study demonstrates that land reclamation can increase the freshwater storage of the lens and shift the water divide toward the reclamation area. Furthermore, a lower permeability fill material especially with a greater scale or thickness leads to higher freshwater storage. However, the expansion of the lens will be truncated due to the high‐permeability of the lower layer. These observations and findings from the laboratory experiments and two‐dimensional numerical simulations are further ground‐truthed by the three‐dimensional modeling of Yongxing Island in the South China Sea. The findings of this study provide a comprehensive understanding of the impact of land reclamation on island groundwater system and the theoretical supports for Small Island Developing States to use the reclamation not only for urban development but also for extra aquifer to enhance the water resource sustainability under the climate change.

Coral Reef Geometry and Hydrodynamics in Beach Erosion Control in North Quintana Roo, Mexico

Coral reefs are increasingly recognized for their shoreline protection services. The hydrodynamic performance of this ecosystem is comparable to artificial low-crested structures often used in coastal protection, whose objective is to emulate the former. Coral reefs also provide other important environmental services (e.g., food production, habitat provision, maintenance of biodiversity and social and cultural services) and leave almost no ecological footprint when conservation and restoration actions are conducted to maintain their coastal protection service. However, studies have focused on their flood protection service, but few have evaluated the morphological effects of coral reefs through their ability to avoid or mitigate coastal erosion. In this paper, we investigate the relation between shoreline change, reefs’ geometry and hydrodynamic parameters to elucidate the physics related to how the Mesoamerican Reef in Mexico protects sandy coastlines from erosion. Using numerical wave propagation and historical shoreline change calculated from satellite imagery, a direct correlation was found between shoreline movement, the depths and widths of reef flats, changes in the wave energy flux, and the radiation stresses of breaking waves. The findings indicate that the most remarkable efficacy in preventing beach erosion is due to reefs with shallow crests, wide reef flats, a dissipative lagoon seabed, located at ∼300 m from the coastline. The results provide essential insights for reef restoration projects focused on erosion mitigation and designing artificial reefs in microtidal sandy beaches. Results are limited to wave-dominated coasts.

Global decline in capacity of coral reefs to provide ecosystem services

Global decline in capacity of coral reefs to provide ecosystem services

Reduction in Cover of Two Introduced Invasive Macroalgae by Herbivores on Coral Reefs of Kāne‘ohe Bay, Hawai‘i1

Two introduced invasive red macroalgae, Eucheuma denticulatum (Burman) Collins & Hervey and Gracilaria salicornia C. Ag., progressively declined in abundance in Kāne‘ohe Bay, Hawai‘i, following ∼30 years of increase since their introduction in the mid-1970s. The declines were not the result of biological control or mechanical control efforts, but instead were the result of grazing by native herbivores, probably fishes, as demonstrated by field experiments conducted in 2014 with algal thalli exposed to, and protected from grazing. Two long-term time-series of the abundance of herbivorous fishes at Kāne‘ohe Bay patch and fringing reef sites indicated that the abundance of herbivorous fishes increased from 2007 through 2014 over the period when these macroalgae declined in cover. Analyses of data of algal cover from surveys of Kāne‘ohe Bay reefs carried out between 1996 and 2018 indicate that the declines in E. denticulatum and G. salicornia began in approximately 2008, several years before control programs commenced on some of the reefs in the bay. In addition to intense herbivory, high summer water temperatures in 2014 and 2015 may have contributed to the decline in E. denticulatum. Naturally occurring declines in the abundance of alien invasive marine algal species have rarely been reported in the literature. These reductions in macroalgal abundance are the second instance of decline in invasive macroalgae in Kāne‘ohe Bay since 2006, and have reduced competition between macroalgae and corals on reef flats and reef slopes across the bay.

How to tie dangerous surgical knots: easily. Can we avoid this?

ObjectiveSecure knots are essential in all areas of surgical, medical and veterinary practice. Our hypothesis was that technique of formation of each layer of a surgical knot was important to...

Preliminary assessment of Tripneustes gratilla populations in Seagrass Beds of the Spermonde Archipelago, South Sulawesi, Indonesia

Many sea urchins, including the collector urchin Tripneustes gratilla, are well known for their role as herbivores, contributing to the control of fast growing macroalgae that can potentially overgrow and dominate seagrass beds and reef flats. Tripneustes gratilla is a short-spined sea urchin that can be easily found and collected by hand from the seagrass meadows which are their main habitat, especially during low tide. The exploitation of this species in Indonesia began to expand several years ago when the demand for T. gratilla gonads started to rise, for both commercial purposes and household consumption. This study aimed to determine the population and distribution of T. gratilla in seagrass ecosystems with different conditions across the Spermonde Archipelago, South Sulawesi, Indonesia. The results indicate that T. gratilla population abundance and size distribution are affected by several factors: seagrass condition, water quality, and the intensity of sea urchin collection. The results also emphasize the urgent need for developing and implementing effective management to ensure the sustainability of this important sea urchin species.

Nursery and grow-out culture of the abalone Haliotis asinina on a reef flat: A comparison of growth and survival using different culture containers

The study was conducted to compare four different culture containers [cage, recycled oil container, tray (control), and tube] in the nursery and grow-out culture of the abalone Haliotis asinina on a reef flat. For nursery culture, early juvenile abalone with mean shell length (SL) of 1.30 ± 0.006 cm and mean body weight (BW) of 0.45 ± 0.007 g were stocked in the containers at 100 ind m−2 and reared until they attained the 3 cm SL size required for grow-out culture in three of the four culture containers. For grow-out culture, juvenile abalone harvested from nursery culture with mean SL of 3.23 ± 0.018 cm and mean BW of 7.33 ± 0.131 g were stocked in the containers at 50 ind m−2 and reared until they were harvestable at 5 cm SL cocktail size in three of the four culture containers. The 3 cm SL grow-out size was attained at 90 days of culture (DOC) in recycled containers, trays, and tubes, while the 5 cm SL cocktail size at 180 DOC in the same containers. Abalone reared in tubes had the highest mean SL after 90 DOC in nursery culture (3.21 cm), while those in trays after 180 DOC in grow-out culture (5.30 cm). However, at the end of the nursery and grow-out culture, there were no significant differences in mean SL among the abalone reared in these three culture containers. In both culture phases, abalone reared in cages had the lowest mean SL, 2.88 and 4.44 cm, respectively. Survival was highest in trays (98.64%) during nursery culture and in tubes (96.57%) during grow-out culture. With comparable results in recycled containers, trays, and tubes for both growth and survival at the nursery and grow-out phases, tubes are recommended for use when culture is to be done on reef flats. Tubes are the most stable and durable among the four culture containers tested. They can withstand strong winds and waves and may be reused for several culture runs.

SeeCucumbers: Using Deep Learning and Drone Imagery to Detect Sea Cucumbers on Coral Reef Flats

Sea cucumbers (Holothuroidea or holothurians) are a valuable fishery and are also crucial nutrient recyclers, bioturbation agents, and hosts for many biotic associates. Their ecological impacts could be substantial given their high abundance in some reef locations and thus monitoring their populations and spatial distribution is of research interest. Traditional in situ surveys are laborious and only cover small areas but drones offer an opportunity to scale observations more broadly, especially if the holothurians can be automatically detected in drone imagery using deep learning algorithms. We adapted the object detection algorithm YOLOv3 to detect holothurians from drone imagery at Hideaway Bay, Queensland, Australia. We successfully detected 11,462 of 12,956 individuals over 2.7ha with an average density of 0.5 individual/m2. We tested a range of hyperparameters to determine the optimal detector performance and achieved 0.855 mAP, 0.82 precision, 0.83 recall, and 0.82 F1 score. We found as few as ten labelled drone images was sufficient to train an acceptable detection model (0.799 mAP). Our results illustrate the potential of using small, affordable drones with direct implementation of open-source object detection models to survey holothurians and other shallow water sessile species.

Trace element and stable isotope variations in larger benthic foraminifer Baculogypsina sphaerulata: A potential proxy of seawater temperature

Larger benthic foraminifera (LBF) contribute significantly to the modern reef carbonates. They were also the major producers of carbonate in the shallow marine environments of the Paleogene. It is thus imperative to investigate their potential as a paleotemperature proxy. It is common to calculate past seawater temperatures using trace elements and stable isotope proxies on foraminiferal calcite. The various LBF genera comprise tests with different MgCO3% and exhibit vital effects, making it important to carry out genus-specific temperature calibration studies. For the present study, live specimens of Baculogypsina sphaerulata were collected over seven months from reef flats of Akajima (Okinawa, Japan). The whole-shells of B. sphaerulata from each of the seven sampling months were analyzed using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) and IRMS (Isotope Ratio Mass Spectrometer) techniques. The relationship between Mg/Ca and δ18O with seawater temperature is established, and thus its potentiality for temperature calibration is discussed. The following proxy-temperature calibrations are proposed in this study: (i) Mg/Ca (mmol/mol) = 0.0267e0.3389T and (ii) T (oC) = 19.0–2.94 (δ18Of−δ18Ow).

SIPUT PROSOBRANCHIA (GASTROPODA, MOLUSKA) PADA RATAAN TERUMBU KARANG DI TELUK MANADO

Molluscs are marine organisms that do not have a backbone, these organisms are associated with coral reefs. This research was conducted with the aim of describing the density and diversity of Prosobranchia snails’ species on coral reef flats. By applying the belt transect method, the results show that the density of the four Mokupa stations has a relatively high density between Tongkeina, Malalayang and Bulo. While for species diversity, Mokupa and Bulo had the highest value than Tongkeina and Malalayang. According to the results of the belt transect method, is the concluded that stations close to people’s homes have the lowest density and species diversity values, this factor is influenced by anthropogenic activities or human activities. Therefore, it is recommended that there be monitoring of snails on coral reefs, especially reef flattening in order to provide information about Prosobranchia snails.Keywords: Prosobranchia, Density, diversity, belt transects, Reef Flats

KEANEKARAGAMAN DAN KEPADATAN ECHINOIDEA DAN ASTEROIDEA DI RATAAN TERUMBU KARANG PERAIRAN TONGKAINA DAN BAHOWO KOTA MANADO (

The waters of Tongkaina, which are part of northern Manado's waters, are known to have mangrove, seagrass, and seaweed ecosystems. Therefore efforts are needed to manage the population and diversity of echinoderms in these waters. Echinoderms' ecology has an essential role in maintaining the marine ecosystem's balance, which plays a role in recycling nutrients. This study aimed to determine diversity, species density, species relative density, species frequency, species relative frequency, dominance, and the index of importance of Echinoidea and Asteroidea's species in the waters of the Tongkaina Village and their density. The method used in this research is the quadratic line transect method. First of all, the survey was conducted to the sampling site's location in the coral reef flats of Tongkaina Village's waters, including Tongkaina beach and Bahowo beach, before operating the sampling. Then the observation stations were determined, namely Tongkaina waters (near Batu Meja) and Bahowo waters. The quadratic line transect method is used in this research. Species of class Echinoidea and Asteroidea in the quadrat were recorded among the total of individuals, and the species is documented. This study's results indicate that six species were found, including the survey, and five species were found based on the line transect method with 182 individuals. Including Asteroidea 85 Individuals and Echinoidea 99 Individuals. Value of Diversity at station 1 has a value of H '= 1.170 with a dominance of C = 0.364, while at Station 2 has a value of H' = 1.232 and dominance value of C = 0.316. the highest density in Station 1 is Diadema savigny 1.967 ind/m2 relative 50.86%, and Linckia laevigata with the highest frequency Fi = 0.533. The highest important value index is Diadema savigny, with a value of 81.09%, while at station 2, the Protoreaster nodosus has the highest value of important value index with a value of 87.51%. These species also have the highest density of 0.933 ind/m2 and a relative number of 41.79%.Keywords: Tongkaina, Echinoderm, Line Transect Quadrat Method, Asteroidea, Echinoidea, Coral Reef Flat

Composition and structure of tropical intertidal hard coral communities on natural and man-made habitats

Living scleractinian corals form a narrow but often conspicuous band of marine life along tropical intertidal shores worldwide but they have generally been considered as outliers of mainstream coral communities and are thus poorly characterized. This study examined coral communities at three intertidal habitats, i.e., reef flats, sloping seawalls, and vertical seawalls, in Singapore, looking at species diversity, abundances, growth forms, and colony sizes. A total of 35 coral species were recorded, of which the majority (51%) were typically of massive growth form. Reef flats had the highest number of species (30), followed by sloping seawalls (21). Species on vertical seawalls (11) were a subset of the two other habitats. Colonies were dominantly massive (72%) and sparsely distributed with average colony densities between 0.05 and 0.4 colonies/m2. Species Porites lobata-lutea complex was widespread and most abundant, comprising 21–30% of colonies in each habitat. Six other species common across all habitats were Dipsastraea speciosa, Favites abdita, Goniastrea retiformis, Platygyra verweyi, Platygyra pini, and Platygyra sinensis. Of these, only colony sizes of G. retiformis (mean ± SE, reef flats 30 ± 4 cm, sloping seawalls 9.5 ± 1.7 cm, vertical seawalls 11.7 ± 1.4 cm) and Porites lobata-lutea complex (41.8 ± 8.3 cm, 26.8 ± 6.3 cm, 12.3 ± 1.6 cm) showed significant differences (p < 0.05) amongst habitats. Relative abundances on the reef flats correlated moderately with those on the sloping seawalls (Pearson’s ρ = 0.6) and vertical seawalls (Pearson’s ρ = 0.7), respectively. Multivariate analyses showed that habitat origin (natural vs man-made) and surface rugosity (heterogeneous vs. homogeneous) were factors that significantly (p < 0.05) differentiated intertidal coral communities. Nevertheless, sloping seawall communities bore higher resemblance to those on natural reef flats than to man-made vertical seawalls in species and growth form richness and also coral densities. These findings highlight interesting opportunities for incorporating coral-friendly designs into existing man-made sloping coastal structures to encourage the growth of coral communities in the intertidal zone.