Coral Reef Research Articles

Coral reef thermal microclimates mapped from the International Space Station

Abstract Satellite sea surface temperature (SST) is critical for describing marine environments. Traditional SST data, such as those provided by the Group for High Resolution Sea Surface Temperature (GHRSST) program, are valuable, but have a relatively coarse spatial resolution for mapping coral reef thermal environments. Hence, fine resolution SST from orbit would be of great utility to the coral reef research community and speed the pathway to an increased understanding of how, when, and where thermal stress afflicts individual reefs. Such data would support adaptive management, especially so for the design of marine protected areas. Flying aboard the International Space Station, the NASA ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) instrument may already fill this niche with a spatial resolution 204 times finer than GHRSST. To evaluate ECOSTRESS thermal data over reef environments, we deployed 21 temperature loggers over three years across two reef sites in the Red Sea. We compared temperature retrievals from both the coarse resolution GHRSST and the fine resolution, experimental, ECOSTRESS, to this in-situ logger dataset. While temperature data from both orbital platforms correlated strongly with the logger recordings, only ECOSTRESS, with its 70-m pixels, could construct thermal microclimate maps capturing the dynamic temperature fluctuations experienced by our studied reefs. We contend that ECOSTRESS represents a significant advancement in the capability to monitor heat stress on reefs from orbit.

Spaghetti worms from the reef: two new species of Loimia (Polychaeta: Terebellidae) from Bora-Bora and Moorea (Society Islands, French Polynesia) and a range extension of L. tuberculata Nogueira, Hutchings & Carrerette, 2015

Two new species of coral-reef inhabiting Loimia are described: L. poraporaensis sp. nov., from the lagoon at Bora-Bora, French Polynesia and Hawaii and L. aimehoensis sp. nov., from Moorea in French Polynesia. Loimia poraporaensis sp. nov. has large lateral lobes on segments 2 and 3, a smooth body and eye spots absent. Loimia aimehoensis sp. nov. has banded buccal tentacles, large lateral lobes on segments 2 and 3, with those on segment 3 extending dorsally and with a basal flange, a smooth body and eye spots absent. These species are morphologically and molecularly compared to other recently described species from Pacific coral reefs. This study also allowed us to expand the known distribution of Loimia tuberculata from the type locality at Lizard Island (northern Great Barrier Reef, Australia) Southern GBR, Western Australia, eastern Papua New Guinea and New Caledonia. We provide two maximum likelihood trees (COI and 16S genes) for all species of Loimia for which data are available, as well as an identification key and a table of the diagnostic characters for the species of Loimia of this Pacific region. We also discuss their habitat and association with living corals.

Invasion of the Atlantic Ocean and Caribbean Sea by a Large Benthic Foraminifer in the Little Ice Age

The larger benthic foraminifera is a group of marine protists harbouring symbiotic algae, that are geographically confined to shallow tropical and subtropical waters, often associated with coral reefs. The resulting controls on availability of habitat and rates of dispersion make these foraminifers, particularly the genus Amphistegina, useful proxies in the study of invasive marine biota, transported through hull fouling and ballast water contamination in modern commercial shipping. However, there is limited information on the importance of these dispersal mechanisms for foraminifers in the Pre-Industrial Era (pre-1850) for the Atlantic and Caribbean region. This paper examines possible constraints and vectors controlling the invasion of warm-water taxa from the Indo-Pacific region to the Atlantic and Caribbean region. Heterostegina depressa, first described from St. Helena, a remote island in the South Atlantic, provides a test case. The paper postulates that invasions through natural range expansion or ocean currents were unlikely along the possible available routes and hypothesises that anthropogenic vectors, particularly sailing ships, were the most likely means of transport. It concludes that the invasion of the Atlantic by H. depressa was accomplished within the Little Ice Age (1350–1850 C.E.), during the period between the start of Portuguese marine trade with east Africa in 1497 and the first description of H. depressa in 1826. This hypothesis is likely applicable to other foraminifers and other biota currently resident in the Atlantic and Caribbean region. The model presented provides well-defined parameters that can be tested using methods such as isotopic dating of foraminiferal assemblages in cores and genetic indices of similarity of geographic populations.

Organic ultraviolet filters in Hainan coral reefs: Distribution, accumulation, and ecological risks.

Organic ultraviolet filters (OUVFs) have been widely used as functional ingredients of sunscreen products and have entered into marine ecosystems, particularly in tropical areas where solar UV radiation is strong. These chemicals, with their potential toxicity and ecological risk, have raised widespread concern for the protection of the fragile marine ecosystem of coral reefs. In this study, fourteen OUVFs were analyzed among 24 coral species, together with their habitats including seawater and sediment from the coastal coral reef regions of Hainan Island, South China Sea. Surprisingly, all of fourteen OUVFs were detected in each sample, indicating the wide distribution of OUVFs among sites and samples. Among the fourteen OUVFs, benzophenone-3 (BP-3) and 4-methylbenzylidene camphor (4-MBC) were the most abundant, with concentrations ranging from 35.3 to 75.6 and 38.3 to 61.4ng/L in seawater, from 13.2 to 25.9 and 7.0 to 17.4ng/g dw in sediment, and from 4.5 to 21.3 and 4.4 to 19.7ng/g dw in corals, respectively. Analysis of OUVFs in 24 coral species pointed that OUVFs accumulation in corals is morphology dependent: the highest concentration of OUVFs was identified in Galaxea fascicularis with abundant of polyps and tentacles while the lowest levels of OUVFs were found in Porites mayeri (smooth or lobed surface). In corals, we found that these OUVFs accumulated, depending on the coral species and the types of OUVFs. The ecological risk assessment further indicated that BP-3, 4-MBC and BP-8 had posed risks to corals. In addition, significantly higher concentrations of OUVFs were observed in Sanya (a seaside tourist resort) than in the other sites, suggesting that tourist activity and use of sunscreen products are the key to high inputs of sunscreen agents into marine ecosystem. Overall, our study demonstrates a potential risk role for OUVFs in coral protection in tropical areas where coral bleaching events occur.

A New Subspecies of Scaphella junonia (Lamarck) from the East Coast of the United States

A new subspecies of the eastern Gulf of Mexico volute, Scaphella junonia (Lamarck, 1804), is described from the East Coast of the United States. The new subspecies, here named Scaphella junonia sheltoni Petuch & Berschauer, n. subsp., ranges from Cape Hatteras in North Carolina southward to Fort Pierce, St. Lucie County, Florida and is most common in the area around Cape Canaveral, Florida. Here it is frequently encountered during commercial scallop dredging operations. The new subspecies is absent from southeastern Florida, the Florida Keys, and the Dry Tortugas and is physically and genetically isolated from the western Florida nominate subspecies by the ecological barrier of the coral reef environments of the Florida Coral Reef Tract (Palm Beach to the Dry Tortugas).

How natural disasters affect the distribution of marine litter in protected island ecosystems (Seaflower Biosphere Reserve - Colombia).

Islands are particularly vulnerable to storms and hurricanes, which can cause severe environmental, economic, and social impacts, including the accumulation of waste in marine ecosystems. In November 2020, Hurricane Iota struck the islands of Providencia and Santa Catalina in the Seaflower Biosphere Reserve, Colombia. This study assesses the distribution, composition, and sources of marine litter after the hurricane, focusing on variations observed across coastal ecosystems such as beaches, mangroves, and coral reefs. A comparative analysis of data from 2019 and 2021 reveals significant differences in how the island's diverse ecosystems interact with marine litter, underscoring the impact of extreme events on these environments. While mangroves and back-beach vegetation act as retention zones, particularly for plastic waste, these ecosystems showed a marked reduction in litter density in 2021, likely due to direct removal efforts during recovery and hurricane-driven oceanographic processes that may have redistributed lighter litter. In contrast, sandy beaches experienced an increase in litter following the hurricane, highlighting their greater vulnerability to litter deposition transported by waves and wind during extreme weather events. These findings emphasize the complexity of managing marine litter after natural disasters and underscore the need for enhanced waste management strategies in vulnerable island ecosystems.

Evidence of oxidative stress in the soft coral Pinnigorgia flava (Nutting, 1910) exposed to secondary plastic nanofibers and related leachates

Awareness of plastic pollution in marine habitats, such as coral reefs, has grown in recent years. Several studies have shown that tiny particles resulting from plastic breakdown, especially microplastics, can potentially harm corals. However, to date, there is very little evidence regarding the impact that nanoplastics (< 1 μm) can have on the physiology and health of corals, particularly soft corals. In this study, we exposed the soft coral Pinnigorgia flava to two concentrations (0.1 and 1 mg/L) of secondary nanoplastics—specifically nanofibers obtained from the photodegradation of polypropylene nonwoven fabrics—and their related leachates, to evaluate the coral's cellular response through the analysis of antioxidant enzyme activities (SOD, CAT, GST, GR). Chemo-physical characterization of the nano-aggregates displayed an average size of 224.3 ± 8.1 nm, while GC-MS analyses of the leachates showed a variety of mono- and dicarboxylic acids. Although both nanoplastic treatments generated a cellular oxidative stress response, the physical interaction with secondary plastic fiber nano-aggregates affected cellular homeostasis more than the chemical interaction with the released compounds, triggering a stronger antioxidant response. The activity of all antioxidant enzymes increased with higher nanofiber concentrations, while this trend was not consistently observed for the leachates. Overall, SOD and CAT were the two most responsive antioxidant enzymes in cellular detoxification. Our study highlights the significant threat that plastic nanofibers and the polymers they release may pose to coral reefs.

The future of utilising semiochemical pest control methods to manage the destructive crown-of-thorns starfish outbreaks on coral reefs

The future of utilising semiochemical pest control methods to manage the destructive crown-of-thorns starfish outbreaks on coral reefs

Status of coral, giant clam and sea cucumber communities including CITES listed species on a remote Australian coral reef atoll and the potential impact of illegal fishing.

Following a recent dramatic increase in illegal fishing by Indonesian fishing vessels in Australian waters in 2022, we conducted an extensive survey of coral reef communities covering 33,000m2at Mermaid Reef Marine Park in the Rowley Shoals off north-western Australia in July 2022. Species richness of sea cucumbers was 13 species (three CITES listed) and 6 species of giant clams (all CITES listed). The most abundant sea cucumber species were the low or intermediate value, asexually reproducing species Holothuria atra and H. edulis. Seventy-one percent of all sea cucumbers were found in the deep lagoon habitat despite this habitat comprising only about one-third of total survey effort. Most of the higher value species, such as CITES listed Thelenota ananas, were more abundant in the deep lagoon habitat. The exceptions to this pattern were H. whitmaei (CITES listed) and Actinopyga mauritiana (high value) and Bohadschia marmorata (intermediate value) that were most abundant on the reef flat, reef slope and shallow lagoon habitats respectively. The burrowing giant clam Tridacna crocea was abundant in all habitat types, whereas T. squamosa and Hippopus hippopus were most abundant on the western outer slope, T. gigas on the reef flat and T. derasa in the deep lagoon. The results of previous and subsequent surveys in 2003, 2018 and 2023 were compared with our 2022 survey. High value species that mainly occur in shallow water (e.g., H. whitmaei) were more abundant in 2003 while T. ananas and Stichopus herrmanni were more abundant in the deep lagoon habitat in 2022 and less abundant in the shallow habitats than they were in 2003 while there was no change in the more abundant, low to intermediate value species (e.g., H. atra, H. edulis). There were no significant differences in sea cucumber densities between 2022 and 2018 or 2023, however the comparison was confounded by the small number of 2018 and 2023 survey sites which were spread over multiple habitat types. Survey results were consistent with the expectation that illegal fishing by free-diving occurs predominantly in shallow and intertidal habitats and that sea cucumbers in those habitats are more vulnerable to fishing than those in deep water habitats. We were unable to ascertain levels of catches from Mermaid Reef or the Rowley Shoals as a whole, however there were numerous reports of vessels being intercepted with catches of many tonnes of sea cucumbers. At Mermaid Reef, to remove one tonne of sea cucumbers, from reef flat and shallow lagoon habitats would require harvesting all sea cucumbers from 38ha (2037 individuals). This represents about 9% of the total area of reef flat and shallow lagoon at Mermaid Reef Marine Park and indicates how rapidly sea cucumber populations can be depleted through illegal fishing. Coral communities at Mermaid Reef were healthy, consistent with previous surveys over two decades with mean hard coral cover highest (40-50 %) on the exposed western outer reef slope and lowest on the reef flat (<10 %). Evidence of damage to coral communities from illegal fishing operations, bleaching or crown-of-thorns sea stars was negligible.

Micro- and Mesoplastic Consumption Tendency of Exaiptasia diaphana Sea Anemones

Microplastics are an increasingly common threat to the aquatic environment, and, due to their small size, it is easy for them to spread and enter the seas and oceans. Micro- and mesoplastic particles are often ingested by marine organisms, especially those that have the potential for successful settlement on artificial substrata, including plastic. In laboratory experiments, we tested the tendency of the sea anemone Exaiptasia diaphana to consume plastic fragments and fibers of various sizes and shapes; these organisms are widely distributed in coastal waters, tide pools, and coral reefs. The plastic fragments and fibers were placed either in natural food or covered with a special food in gel form, which allowed them to retain their original shape. Our studies have shown that plastic in the shape of fibers is less readily consumed than in the form of fragments. The E. diaphana anemones with oral discs of diameter 10–12 mm had difficulty consuming long fibers. A total of 67% of the studied animals were unable to consume fibers of 13 mm length, while those of 3 and 7 mm length were consumed by 100% of the sea anemones. We have also established that microplastics taken with food are harmful to these cnidarians: mechanical injury to the body column was caused by the ingested polypropylene microfragments, and we also observed significantly increased mortality. Injuries, combined with the possible toxicological effects of the polymers, may have been the cause of increased mortality of the Exaiptasia diaphana.

Probability Stability Evaluation of Coral Reef Limestone Reef Slopes Under Earthquake

With the rapid development of island construction and the frequent occurrence of natural disasters, the stability of coral reef slopes is attracting increasing attention. This study aims to assess the dynamic stability and instability risks of coral reef slopes under different earthquake intensities. Geological data were integrated, and the Newmark method and finite element analysis were employed for probabilistic stability assessment and permanent displacement evaluation, leading to the development of a validated model for slope stability assessment. The study explored the effects of varying earthquake intensities on slope stability. Results indicate that the stratified structure significantly influences stability. Reef limestone slopes exhibited higher stability, whereas multi-layered slopes, due to looseness, were less stable. Both slope types remained stable under static conditions. Earthquake intensity substantially impacted stability, with multi-layered slopes showing instability probabilities of 48% and 100% under peak ground accelerations (PGA) of 0.3 g and 0.4 g. Under extreme seismic conditions, the permanent displacement of multi-layered coral reef slopes significantly increased. This study aims to fill the gap in previous research by incorporating the random distribution of stratigraphic parameters, conducting probabilistic stability analysis based on the random distribution of geological parameters, and thereby providing references for island reef engineering construction.

Investigating the dynamic tensile behaviors of deep coral reef limestone under coupled static-dynamic loads

Investigating the dynamic tensile behaviors of deep coral reef limestone under coupled static-dynamic loads

Soundscape analysis reveals fine ecological differences among coral reef habitats

Soundscape analysis reveals fine ecological differences among coral reef habitats

The governance of marine and coral reef restoration, lessons and paths forward for novel interventions

The governance of marine and coral reef restoration, lessons and paths forward for novel interventions

Geomorphological signatures of known hurricanes and validation of theoretical emplacement formulations: Coastal boulder deposits on Cuban low-lying marine terraces

Coastal boulder deposits, observed worldwide, provide geomorphological evidence of extreme wave events such as storms, hurricanes and tsunamis. Theoretical formulations have been developed for determining hydrodynamic conditions responsible for boulder emplacement on the shore, which increasingly make use of boulder geometry and associated site geomorphology. Nevertheless, information on extreme events responsible for the emplacement of coastal boulders is rarely available, meaning there has been limited opportunity to test existing formulations in the light of real hydrodynamic and geomorphic data. In this study, we take advantage of the important record of coastal boulder deposits on Cuba Island to compare the hydrodynamic parameters (minimum flow velocity) deduced from the boulders' morphology and emplacement characteristics, with hydrodynamic conditions (maximum wave height and orbital velocity) that occurred during the tropical cyclones responsible for the boulders' actual emplacement. We selected four sites where three hurricanes have emplaced five boulders on low-lying coral reef terraces over the last 50 years. Using terrestrial Structure-from-Motion photogrammetry, we determined with precision the boulders' shape and volume, which in combination with density, mode of emplacement and distance from the shore, were used to calculate the minimum flow velocity responsible for dislocation of the coral reef terrace and inland transport. To serve as comparisons, available modelled data of wave height and period were used to estimate the maximum orbital velocity that possibly occurred during the weather event using linear wave theory. Our results show that for all boulders studied except one, there is a good agreement between the values of minimum flow and maximal orbital velocities, with minimum flow velocities for boulder emplacement consistently smaller than the maximum wave orbital velocity during the weather event. The difference observed for one boulder is attributed to specific site effects, highlighting in this case the limitation of using distant hydrometeorological data for characterizing wave processes responsible for coastal boulder deposits. Helped by detailed data collected on boulders with large differences in morphology including size, and mode of emplacement, this study confirms the pertinence of using formulations relating boulder morphology and site characteristics to the minimum flow velocity that detached and transported the boulder. It further emphasizes the importance of obtaining adequate boulder and geomorphic setting characterizations to link geomorphological proxies and extreme wave events.

Cellular Responses of Astrangia poculata (Ellis and Solander, 1786) and Its Symbiont to Experimental Heat Stress

Climate change has had devastating effects on tropical coral reefs; however, much less is known regarding how heat stress affects temperate coral. This research focuses on Astrangia poculata (Ellis and Solander, 1786) collected from Narragansett Bay, RI, during the summer and winter seasons and understanding the effect of experimental thermal extremes (i.e., 26 °C) on seasonally different populations. Photosynthetic efficiency (Fv/Fm), symbiont density (via an inverse relationship with pixel intensity), and oxidative stress via reactive oxygen species (ROS) concentrations were measured on symbiotic and aposymbiotic A. poculata. Higher Fv/Fm rates were observed in summer- vs. winter-collected corals (p ≤ 0.05). Lower symbiont density within symbiotic and aposymbiotic A. poculata were observed at elevated temperatures, and higher intensities as well as symbiotic coral were observed in winter compared to the summer collections (p ≤ 0.05). No differences in ROS were observed in host tissue cells, suggesting that ROS produced in the algal symbionts was not translocated into host tissues. Overall, higher ROS concentrations were observed in summer- vs. winter-collected corals (p ≤ 0.05) in both symbiotic states. ROS concentrations were higher in symbiotic compared to aposymbitoic colonies (p ≤ 0.05), albeit no differences were observed between temperature treatments, suggesting that antioxidants mitigate the deleterious effects of ROS on host tissues.

Genomes of the Caribbean reef-building corals Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea.

Coral populations worldwide are declining rapidly due to elevated ocean temperatures and other human impacts. The Caribbean harbors a high number of threatened, endangered, and critically endangered coral species compared to reefs of the larger Indo-Pacific. The reef corals of the Caribbean are also long diverged from their Pacific counterparts and may have evolved different survival strategies. Most genomic resources have been developed for Pacific coral species which may impede our ability to study the changes in genetic composition of Caribbean reef communities in response to global change. To help fill the gap in genomic resources, we used PacBio HiFi sequencing to generate the first genome assemblies for three Caribbean, reef-building corals, Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea. We also explore the genomic novelties that shape scleractinian genomes. Notably, we find abundant gene duplications of all classes (e.g., tandem and segmental), especially in S. siderea. This species has one of the largest genomes of any scleractinian coral (822Mb) which seems to be driven by repetitive content and gene family expansion and diversification. As the genome size of S. siderea was double the size expected of stony corals, we also evaluated the possibility of an ancient whole genome duplication using Ks tests and found no evidence of such an event in the species. By presenting these genome assemblies, we hope to develop a better understanding of coral evolution as a whole and to enable researchers to further investigate the population genetics and diversity of these three species.

Multidecadal Morphodynamic evolution of shorelines and coral reefs along the Arabian Sea Coast of Oman: Bar Al Hikman Peninsula

This study examines the morphodynamic evolution of the shoreline and coral reef coverage along the Arabian Sea coast of Oman over the past five decades (1972–2022). The Peninsula of Bar Al Hikman, the largest low-lying coastal area in Oman (550 km2; elevations < 10 m), hosts unique, monospecific coral reefs developing under a monsoon climate. Unlike other densely populated, low-lying coastal areas in the Middle East (e.g., the Gulf), the southern Arabian Plate has received limited attention, with few studies addressing its coastal evolution or future environmental risks. By combining sedimentological fieldwork with photo-interpretations of satellite images spanning 50 years, this study documents significant coastal geomorphological changes. The findings reveal a dramatic 60% reduction in the surface area of Bar Al Hikman’s main coral reefs. A significant consequence of this reef shrinkage is the rapid shoreline erosion on the leeward side of the disappearing reefs. Half of the southern shoreline of the peninsula is retreating northward at rates exceeding 1 m/year, with localized section (6%) eroding at extreme rates of over 10 m/year. At this pace, the ongoing reef decline is likely to exacerbate shoreline erosion, accelerate the landward migration of barrier bars and in turn close off lagoonal areas, and threaten intertidal ecosystems. Furthermore, with the ongoing global rise in sea level, a substantial portion of the peninsula is predicted to fall below the annual flood limit by 2050. This will result in the extensive landward migration of coastal sabkhas deeper into the peninsula's interior. Overall, this study provides a baseline for understanding the recent evolution of Oman’s Arabian Sea coastline and underscores the importance of developing policies and coastal management strategies to mitigate the effects of ongoing environmental and sea-level changes.

Concentration of Two Herbicides, Irgarol 1051 and Diuron, in Coastal Waters of Coral Reefs and Adjacent Waters in the Northwestern Part of Okinawa Island, Japan.

Irgarol 1051 and Diuron are used as boosters in copper-based anti-fouling paints, as well as in agriculture and home gardening. We monitored the coral reefs and adjacent waters of northern Okinawa Island three times, i.e., in August 2015, June 2016 and December 2016. The mean concentrations were 1.44 ng/L for Irgarol and 1.07 ng/L for Diuron. Although the range of these concentrations was lower than those previously recorded in southern Japan, Irgarol and Diuron were significantly higher in December 2016 than in June 2016. Several estimations of Predicted No Effect Concentrations (PNECs) have recently been published. In December 2016, compared to the lowest PNEC concentration of each substances, the concentrations of Irgarol and Diuron exceeded the PNEC at nine sites and three sites, respectively. These results suggest that the effects of low concentrations of Irgarol and Diuron, close to the PNEC, on hermatypic corals need to be investigated. The regulation of anti-fouling paints in Japan is self-regulated through industry cooperation. Irgarol and Diuron have not been registered as anti-fouling paints for fishing nets by the fishing cooperatives. The significant increase of these substances suggests that the activity of vessels with paints containing Irgarol has increased in December 2016. This study highlights the need for continuous monitoring of these herbicides in coral reefs and adjacent waters.

Tracking over 30 years of coral reef infrastructure degradation in Barbados

Coral reefs face escalating threats from global and local stressors, and these challenges are exacerbated in the Caribbean. This study focuses on coral reef structure in Barbados, where a previous study documented reef degradation in the 1990s. As 30 years have passed, we examined the rate of change of reef structure and quantified associated substrate presence along the western reefs of Barbados. Using satellite and geotagged imagery, we analyzed 19 reef structures over the interval 2013 to 2023 along the west coast of Barbados, comparing them to the previous study’s findings in 1950 and 1991. We ground-truthed five sites previously categorized as highly degraded reefs to confirm their structural integrity and substrate-type. Results confirmed ongoing reef structural loss, averaging ~ 137.68 m1 annually across all sites. We identified four primary substrate types: coral, algae-covered substrate, rubble, and sand, with algae-covered substrate predominating and projected to persist. Our results underscore the urgency of monitoring reef health and highlight the potential limitations of satellite assessment. This research enhances understanding of reef dynamics and offers a framework for identifying vulnerable areas, which are crucial for effective conservation efforts.