The hidden diversity of Saudi Arabian Red Sea octocorals revealed through a morpho-molecular assessment across bathymetric and latitudinal gradients.

Simple SummaryPlastic production has increased over the past decades, causing more plastic pollution to enter marine ecosystems. Because plastics persist in the environment for hundreds of years, they have become a threat to many living organisms. Animals may mistake plastic debris for food, which can cause illness or mortality. In this study, we analyzed the gastrointestinal tracts of ten sea turtles to assess the prevalence of plastic ingestion in the Saudi Arabian Red Sea. Plastics > 1 mm were collected and categorized into plastic type and color. This was the first report of plastic ingestion by turtles in the Red Sea. It is important to have baseline data on plastic ingestion because the human population surrounding the Red Sea is expected to increase within the coming decades. With more people residing in coastal areas, there may be an increased amount of plastic debris entering the ocean. This study found that 40% of the turtles had ingested plastics, meaning that plastic is currently a threat to turtles in the region, and conservation efforts should be implemented to remove plastics from the sea and to prevent plastic pollution from entering the environment.(1) Background: Plastic pollution is a major environmental concern confronting marine animals. Sea turtles are considered a bio-indicator of plastic pollution, but there is little information regarding plastic ingestion by turtles in the Red Sea. With large-scale development projects being built along the Saudi Arabian coast, it is important to have a baseline for plastic ingestion before construction is complete. (2) Methods: Ten deceased sea turtles (four hawksbill and six green turtles) were collected along the Saudi Arabian coastline. Necropsies were conducted, and the entire gastrointestinal tracts were extracted and the contents were passed through a 1 mm mesh sieve. (3) Results: We found that 40% of the turtles in this study had ingested plastics. Thread-like plastics were the most common plastic category, and multi-colored was the most prevalent color category. (4) Conclusions: Monitoring of the plastic ingestion by marine megafauna should be conducted as a long-term assessment of the developments’ impacts. Additionally, conservation efforts should be focused on removing plastics (namely ghost nests and fishing lines) from the reefs and reducing the amount of plastic entering the sea.

This work provides a comprehensive description of the Scleractinian family Merulinidae (Verrill, 1865) of the Red Sea at species level based on skeletal structure for helping in evaluating and estimation of actual species diversity, as well as predicting their response to environmental changes. The present study is a first attempt to describe and illustrate the coral species of the family Merulinidae in the Farasan Islands (Saudi Arabian Coast). Moreover, coral reef terraces are investigated around El Quseir‐Marsa Alam area on the Egyptian Red Sea Coast. Overall, 42 scleractinian coral species from the family Merulinidae (Verrill, 1865) have been identified. They belong to 14 genera: Dipsastraea, Favites, Echinopora, Goniastrea, Coelastrea, Paragoniastrea, Paramontastraea, Astrea, Cyphastrea, Erythrastrea, Merulina, Platygyra, Leptoria, and Hydnophora. About 37 species are recorded for the first time from the Farasan Islands and 26 species from El Quseir‐Marsa Alam area, among them three species are recognized as new records. Two species are added to coral communities of the Red Sea (Goniastrea favulus and Paragoniastrea deformis), and six species were added to the fossil record of the Red Sea. The terminology, systematic classification, and the criteria of identification for all studied coral taxa are generally updated according to recent results. The known age and all recorded stratigraphic range of these species are illustrated and discussed. From the results, most of the corals are still living in the present Red Sea except for three species: Favites micropentagonus, Goniastrea favulus, and Paragoniastrea deformis. All species are extended down to the Pleistocene and a few to the Pliocene and Miocene.

During a survey of the coastal biodiversity of the Saudi Arabian Red Sea, four species of callianassid ghost shrimps were collected:Gilvossius bouvieri(Nobili, 1904),Neocallichirus mucronatus(Strahl, 1862a),Podocallichirus madagassus(Lenz & Richters, 1880), andCallianidea typaH. Milne Edwards, 1837. Of these,N. mucronatusis recorded from the Red Sea for the first time. With this new record, 29 species of the group are now known in the Red Sea fauna. The distribution of the species within the Red Sea is discussed in detail.

BackgroundDespite being frequently landed in fish markets along the Saudi Arabian Red Sea coast, information regarding fundamental biology of the Scalloped hammerhead shark (Sphyrna lewini) in this region is scarce. Satellite telemetry studies can generate important data on life history, describe critical habitats, and ultimately redefine management strategies for sharks. To better understand the horizontal and vertical habitat use of S. lewini in the Red Sea and to aid with potential future development of zoning and management plans for key habitats, we deployed a pop-up satellite archival transmitting tag to track a single female specimen (240 cm total length) for a tracking period of 182 days.ResultsThe tag was physically recovered after a deployment period of 6 months, thus providing the complete archived dataset of more than one million depth and temperature records. Based on a reconstructed, most probable track, the shark travelled a circular distance of approximately 1000 km from the central Saudi Arabian Red Sea southeastward into Sudanese waters, returning to the tagging location toward the end of the tracking period. Mesopelagic excursions to depths between 650 and 971 m occurred on 174 of the 182 days of the tracking period. Intervals between such excursions were characterized by constant oscillatory diving in the upper 100 m of the water column.ConclusionsThis study provides evidence that mesopelagic habitats might be more commonly used by S. lewini than previously suggested. We identified deep diving behavior throughout the 24-h cycle over the entire 6-month tracking period. In addition to expected nightly vertical habitat use, the shark exhibited frequent mesopelagic excursions during daytime. Deep diving throughout the diel cycle has not been reported before and, while dive functionality remains unconfirmed, our study suggests that mesopelagic excursions may represent foraging events within and below deep scattering layers. Additional research aimed at resolving potential ecological, physiological and behavioral mechanisms underpinning vertical movement patterns of S. lewini will help to determine if the single individual reported here is representative of S. lewini populations in the Red Sea.

BackgroundThere is relatively little published information about sea turtle nesting distribution and seasonality in the Saudi Arabian Red Sea. Upcoming large-scale developments occurring along the Saudi Arabian Red Sea coast could negatively affect many sea turtle nesting beaches with potential impacts on the survival of local populations.MethodsIn 2019, two coastal beaches and three near-shore islands were surveyed for turtle nesting in the central Red Sea. We recorded all emergences, examined beach morphology, and collected sand samples to determine grain size, moisture content and colour.ResultsSea turtle nesting was found at all surveyed sites, though emergence counts were often low. The limited occurrence of nesting at several previously undocumented sites suggests that nesting activity may be widespread, but sparsely distributed, in the central Red Sea region. In addition, nesting at novel sites appeared to favour the seaward side of islands, a pattern that was not observed in previously documented areas. The substrate of most surveyed sites was composed of calcium carbonate with Ras Baridi as the only exception; it was composed of dark quartz-rich sediment. This study highlights several important sea turtle rookeries while also demonstrating that low levels of nesting occur throughout the region, although inter-annual nesting patterns still need to be determined. Future developments should be steered away from key nesting areas and the seaward bias in marginal rookeries should be taken into account where possible.

AimThe aim of the study was to assess the diversity of algal symbionts of the family Symbiodiniaceae associated with the coral genus Porites in the Red Sea, and to test for host‐specificity and environmental variables driving biogeographical patterns of algal symbiont distribution.LocationSaudi Arabian Red Sea.TaxonEndosymbiotic dinoflagellates of the family Symbiodiniaceae in association with the reef‐building coral genus Porites.MethodsEighty Porites coral specimens were collected along the Saudi Arabian Red Sea coast. Species boundaries were assessed morphologically and genetically (putative Control Region – mtCR; ITS region – ITS). Community composition of symbiotic dinoflagellates of the family Symbiodiniaceae was also assessed. Using the ITS2 marker with the SymPortal framework, Symbiodiniaceae data at the genus, majority ITS2 sequence and ITS2 type profile were used to assess symbiont diversity and distribution patterns. These were analysed in relation to coral host diversity, geographic location and environmental variables.ResultsAmong the 80 Porites samples, 10 morphologies were identified. These corals were clustered into five lineages (clades I–V) by each of the markers independently. Clades I, II and III each comprised of a single Porites morphology, while clades IV and V contained up to five distinct morphologies. The diversity of Symbiodiniaceae associated with Porites was high and latitudinal differentiation was observed. In particular, a shift from a Cladocopium‐dominated to a Durusdinium‐dominated community was found along the north–south gradient. Symbiont diversity showed the patterns of geographic‐specific association at Symbiodiniaceae genus, majority ITS2 sequence and ITS2 type profile level. Specific associations with host genotypes (but not morphological species) were also recovered when considering Symbiodiniaceae majority ITS2 sequence and ITS2 type profiles.Main conclusionsThis study provides the first large‐scale molecular characterization of Symbiodiniaceae communities associated with Porites corals from the Saudi Arabian Red Sea. The use of intragenomic diversity data enabled the resolution of host‐symbiont specificity and biogeographical patterns of distribution, previously unachievable with the ITS2 marker alone. Finally, correlation among symbiont diversity and Red Sea environmental gradients was documented.

Harmful algal blooms (HABs) and the high biomass associated with them have afflicted marine desalination plants along coastal regions around the world. Few studies of HABs have been conducted in the Red Sea, where desalination plants along the Saudi Arabian Red Sea coast provide drinking water for millions of people. This study was conducted along the Saudi Arabian Red Sea coast from 2014 to 2015 to assess the potential for using Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing of chlorophyll a (Chl a) or fluorescence line height (FLH) to identify risks for biofouling at these desalination plants. Ship-based surveys of phytoplankton were conducted along the Saudi Arabian coastline offshore of desalination plants at Jeddah, Al Shoaibah and Al Qunfudhuh to assess the density of phytoplankton populations and identify any potential HAB species. Ship-based surveys showed low to moderate concentrations of phytoplankton, averaging from 1800–10,000 cells L−1 at Jeddah, 2000–11,000 cells L−1 at Al Shoaibah and 1000–20,500 cells L−1 at Al Qunfudhuh. Sixteen different species of potentially toxigenic HABs were identified through these surveys. There was a good relationship between ship-based total phytoplankton counts and monthly averaged coastal MODIS Chl a (R2 = 0.49, root mean square error (RMSE) = 0.27 mg m−3) or FLH (R2 = 0.47, RMSE = 0.04 mW m−2 µm−1 sr−1) values. Monthly average near shore Chl a concentrations obtained using MODIS satellite imagery were much higher in the Red Sea coastal areas at Al Qunfudhuh (maximum of about 1.3 mg m−3) than at Jeddah or Al Shoaibah (maximum of about 0.4 and 0.5 mg m−3, respectively). Chlorophyll a concentrations were generally highest from the months of December to March, producing higher risks of biofouling desalination plants than in other months. Concentrations decreased significantly, on average, from April to September. Long-term (2005–2016) monthly averaged MODIS Chl a values were used to delineate four statistically distinct zones of differing HAB biomass across the entire Red Sea. Sinusoidal functions representing monthly variability were fit to satellite Chl a values in each zone (RMSE values from 0.691 to 0.07 mg m−3, from Zone 1 to 4). December to January mean values and annual amplitudes for Chl a in these four sinusoidal functions decreased from Zones 1–4. In general, the greatest risk of HABs to desalination occurs during winter months in Zone 1 (Southern Red Sea), while HAB risks to desalination plants in winter months are low to moderate in Zone 2 (South Central Red Sea), and negligible in Zones 3 (North Central) and 4 (Northern).

Large scale patterns of ecologically relevant traits may help identify drivers of their variability and conditions beneficial or adverse to the expression of these traits. Antimicrofouling defenses in scleractinian corals regulate the establishment of the associated biofilm as well as the risks of infection. The Saudi Arabian Red Sea coast features a pronounced thermal and nutritional gradient including regions and seasons with potentially stressful conditions to corals. Assessing the patterns of antimicrofouling defenses across the Red Sea may hint at the susceptibility of corals to global change. We investigated microfouling pressure as well as the relative strength of 2 alternative antimicrofouling defenses (chemical antisettlement activity, mucus release) along the pronounced environmental gradient along the Saudi Arabian Red Sea coast in 2 successive years. Microfouling pressure was exceptionally low along most of the coast but sharply increased at the southernmost sites. Mucus release correlated with temperature. Chemical defense tended to anti-correlate with mucus release. As a result, the combined action of mucus release and chemical antimicrofouling defense seemed to warrant sufficient defense against microbes along the entire coast. In the future, however, we expect enhanced energetic strain on corals when warming and/or eutrophication lead to higher bacterial fouling pressure and a shift towards putatively more costly defense by mucus release.

IntroductionThe Red Sea is a narrow rift basin characterized by latitudinal environmental gradients which shape the diversity and distribution of reef-dwelling organisms. Studies on Symbiodiniaceae associated with select hard coral taxa present species- specific assemblages and concordant variation patterns from the North to southeast Red Sea coast at depths shallower than 30 m. At mesophotic depths, however, algal diversity studies are rare. Here, we characterize for the first-time host-associated algal communities of a mesophotic specialist coral species, Leptoseris cf. striatus, along the Saudi Arabian Red Sea coast.MethodsWe sampled 56 coral colonies spanning the eastern Red Sea coastline from the Northern Red Sea to the Farasan Banks in the South, and across two sampling periods, Fall 2020 and Spring 2022. We used Next Generation Sequencing of the ITS2 marker region in conjunction with SymPortal to denote algal assemblages.Results and discussionOur results show a relatively stable coral species-specific interaction with algae from the genus Cladocopium along the examined latitudinal gradient, with the appearance, in a smaller proportion, of presumed thermally tolerant algal taxa in the genera Symbiodinium and Durusdinium during the warmer season (Fall 2020). Contrary to shallow water corals, our results do not show a change in Symbiodiniaceae community composition from North to South in this mesophotic specialist species. However, our study highlights for the first time that symbiont communities are subject to change over time at mesophotic depth, which could represent an important phenomenon to address in future studies.

The coral genus Madracis has a global distribution from shallow waters to over 1200 m depth. In the Red Sea, the azooxanthellate endemic species Madracis interjecta is known to occur from depths of 120 to 350 m. This species is often observed in mesophotic ecosystems and has been reported to form sediment-binding bioherms, yet the conditions required for these formations are not understood. Here, we extracted quantitative data from video footage to identify the distribution of M. interjecta for the first time along the Saudi Arabian Red Sea coast. We present a habitat suitability model to identify potential habitats in the northern Red Sea and Gulf of Aqaba for this species. Combining presence data with geomorphometric variables and environmental data, we identified both depth and seafloor ruggedness as main drivers of this species distribution. Through multivariate statistics, we found that bioherms were found in deeper and cooler waters than individual M. interjecta colonies. Due to the narrow continental shelf and steep slopes of the northern Red Sea and Gulf of Aqaba, the effects of coastal development are threatening shallow, mesophotic and deep ecosystems. This work provides both a baseline survey and predicted distributions of an important habitat-forming scleractinian coral, which can inform conservation planning in the region.

Background The Red Sea Research Center is part of a relatively new university on the Saudi Arabian Red Sea coast, the King Abdullah University of Science and Technology (KAUST). KAUST officially opened in 2009 but began global collaborative research projects in 2007. Among the early discoveries arising from these collaborative projects was the identification of a whale shark aggregation site in the Red Sea. KAUST researchers have been studying this aggregation site since 2008. Approach KAUST researchers have employed various methods and technologies to track whale sharks, including acoustic tagging, satellite tagging technologies, genetics, and some technologies integrating the use of autonomous vehicles. Our whale shark studies include determining the population demographics of the sharks visiting our sites, the site fidelity of the sharks, and any potential connections with populations outside of the Red Sea. In 2012, KAUST began a collaborative effort with colleagues in the Marine Megafauna Foundation to study a whale shark aggregation at Mafia Island, Tanzania. Results The results from our movement studies highlight the pros and cons of various methodologies, and overall emphasize the importance of using multiple methods simultaneously to maximize the clarity of results. In Saudi Arabia, the whale sharks are very near to 50% male and 50% female, unusual compared to most aggregations. Satellite tracking suggests that the Saudi sharks migrate away from the site in the “off-season” and some are confirmed to have left the Red Sea. However, the majority of the sharks remain within the southern half of the Red Sea. Acoustic tracking of whale sharks at Mafia Island, in Tanzania, shows unexpected cryptic residency with many sharks being detected year-round despite a clear seasonal pattern in the sightings of whale sharks in boat-based surveys. These and brief summaries of our findings from other methods will be discussed. Conclusions The results from the Saudi aggregation are strikingly different from results of an aggregation we have been studying at Mafia Island, Tanzania. Future studies of plankton dynamics and fine-scale analysis of whale shark behavior may reveal fundamental differences in the sites that explain these differences in residency. Many emerging technologies hold great promise for improving our ability to learn more about the world's largest fish.

Microplastic in the gastrointestinal tract of fishes along the Saudi Arabian Red Sea coast

Fish market surveys indicate unsustainable elasmobranch fisheries in the Saudi Arabian Red Sea

The yellow-edged lyretail grouper, Variola louti, is ecologically and commercially important in the Red Sea. As a carnivorous species, V. louti plays a vital role in maintaining coral reef ecosystem health. Annually, an estimated 260 tonnes of V. louti are landed along the Saudi Arabian Red Sea coast, contributing approximately 6.5 million USD to the national economy. Given its significance, effective fishery management is crucial for sustainability. This study assessed the growth, maturity, and mortality of V. louti using fishery-dependent samples collected from the eastern Red Sea (February 2022–December 2024). Fork length (FL, n = 7,087) ranged from 10.5 to 64.3 cm, while total weight (W, n = 2,629) varied from 53 to 2,910 g. The FL–W relationship for both sexes combined was W = 0.0117×FL3.1. Von Bertalanffy growth parameters, based on sagittal otolith readings, were FL∞ = 62.28 cm, K = 0.12 year−1, and t0 = −2.26 years. Median FL at first maturity was 24.98 cm, with no significant sex differences. Mean natural mortality (M), derived from three different methods, was 0.243 year−1. Total mortality (Z), estimated using a linearized exponential decay model, was 0.38 year−1. Based on these Z and M estimates, fishing mortality (F) was calculated as 0.137 year−1. Yield-per-recruit and spawning potential ratio analyses indicate that the current F estimate places the stock near the target reference point. The current exploitation rate (E = 0.36) remains well below the limit reference point of 0.5. The V. louti fishery encompasses a broad FL range and multiple age groups, with immature individuals comprising less than 12% of total landings. However, according to the minimum landing size of 33 cm FL set by Saudi Arabian fisheries regulations, 47% of the total catch consisted of mature fish aged 2–3 years but below this threshold (25 cm ≤ FL < 33 cm), while only 41% met the legal-size requirement (FL > 33 cm). The high proportion of legally undersized individuals in landings underscores the need for ongoing monitoring and additional management measures, such as catch quotas, seasonal restrictions, and fishing effort reduction, to ensure long-term stock sustainability.

Use of benthic polychaetes to assess anthropogenic impacts in the southern Saudi Arabian Red Sea Coast SALEH A. AL FARRAJ This paper studied the polychaete community structures and their response to anthropogenic impacts in the southern Saudi Arabian Red Sea Coast. Samples were collected from four stations, i.e. Jazan Port, Fisherman’s Port, Corniche North Park and Al Qunfudah, along the southern Saudi Arabian Red Sea Coast for benthic polychaetes and environmental variables during July 2012. A total of 75 polychaete taxa were identifi ed from the study area. Spatial trends showed Jazan Port and Fisherman’s Port to have low species abundance, richness and diversity compared to the reference site (Al Qunfudah). Species richness, abundance and diversity were intermediate at Corniche North Park The reference station had the highest species richness, species diversity and evenness with the following dominant polychaete species: Owenia fusiformis, Pista macrolobata, Euclymene africana, Maldane sarsi and Syllis gracilis. Capitella capitata, Cirratulus cirratus and Heteromastides bifi dus were most abundant at Fisherman’s Port and Jazan Port. The study revealed that polychaetes of the southern Saudi Arabian Red Sea Coast are sensitive to various types of pollution. The data obtained serve as a baseline against which data obtained on subsequent monitoring can be compared. It is recommended that relevant authorities should carry out a continual assessment on the levels of pollutants in the studied area.Grant Funding Source: king saud university