Annelid biodiversity studies in the Red Sea are limited and integrative taxonomy is needed to accurately improve reference libraries in the region. As part of the bioblitz effort in Saudi Arabia to assess the invertebrate biodiversity in the northern Red Sea and Gulf of Aqaba, Perinereis specimens from intertidal marine and lagoon-like rocky environments were selected for an independent assessment, given the known taxonomic ambiguities in this genus. This study used an integrative approach, combining molecular with morphological and geographic data. Our results demonstrate that specimens found mainly in the Gulf of Aqaba are not only morphologically different from other five similar Perinereis Group I species reported in the region, but phylogenetic analysis using available COI sequences from GenBank revealed different molecular operational taxonomic units, suggesting an undescribed species, P.kaustianasp. nov. The new species is genetically close and shares a similar paragnath pattern to the Indo-Pacific distributed P.helleri, in particular in Area III and Areas VII-VIII. Therefore, we suggest it may belong to the same species complex. However, P.kaustianasp. nov. differs from the latter mainly in the shorter length of the postero-dorsal tentacular cirri, median parapodia with much longer dorsal Tentacular cirri, posteriormost parapodia with much wider and greatly expanded dorsal ligules. Additionally, two new records are reported for the Saudi Neom area belonging to P.damietta and P.suezensis, previously described only for the Egyptian coast (Suez Canal) and are distributed sympatrically with the new species, but apparently not sympatric with each other.

Semi-enclosed seas are often associated with elevated local threats and distinct biogeographic patterns among marine fishes, but our understanding of how fish assemblage dynamics vary in relation to relatively small semi-enclosed seas (e.g., the Gulf of Aqaba) remains limited. Baited remote underwater video surveys (n = 111) were conducted across ~300 km of coral reef habitats in the Gulf of Aqaba and the northern Red Sea. A total of 55 predatory fish species were detected, with less than half of all species (n = 23) observed in both basins. Relative abundance patterns between the Gulf of Aqaba and the northern Red Sea were variable among taxa, but nearly twice as many predatory fish were observed per unit of effort in the northern Red Sea. In general, assemblages in both basins were dominated by three taxa (Epinephelinae, Carangidae, and Lethrinidae). Large-bodied and threatened species were recorded at very low abundances. Multivariate analysis revealed distinct assemblage structuring of coral reef predators between the Gulf of Aqaba and the northern Red Sea. Most of the species driving these differences were recorded in both basins, but occurred at varying levels of abundance. Environmental factors were largely unsuccessful in explaining variation in assemblage structuring. These findings indicate that biological assemblages in the Gulf of Aqaba are more distinct than previously reported and that reef fish assemblage structuring can occur even within a relatively small semi-enclosed sea. Despite inter-basin assemblage structuring, the overall low abundance of vulnerable fish species is suggestive of overexploitation in both the Gulf of Aqaba and the northern Red Sea of Saudi Arabia. As the region surveyed is currently undergoing large-scale coastal development, the results presented herein aim to guide spatial management and recovery plans for these coral reef systems in relation to this development.

Halophila stipulacea is a tropical seagrass species, native to the Red Sea, Persian Gulf, and Indian Ocean, while invasive to the Mediterranean and Caribbean Seas. The benthic fauna assemblages associated with H. stipulacea in its native habitats and the potential effects of anthropogenic stressors on these assemblages remain unknown. We compared meadow characteristics, associated fauna assemblages and trophic niche structures of H. stipulacea from an impacted and a pristine site in the northern Red Sea. Seagrass cover and biomass were higher in the impacted site, however, the associated fauna community was more abundant and diverse in the pristine site. Both meadows showed comparable trophic niches based on stable isotope analysis. This study provides first insights into the macrozoobenthos associated with H. stipulacea in its native habitat and highlights the importance of better understanding the relationship between seagrasses and their associated biota and the potential effects of urbanization on this relationship.

The purpose of this study was to assess the health of stony coral Porites sp. based on the presence of bacterial pathogens, specifically Vibrio coralliilyticus, in the Gulf of Aqaba, and to assess the impact of anthropogenic activities on Porites sp. Porites sp. specimens were collected from the Marine Science Station (MSS) and a public beach (Yamanyeh) in Jordan. Mucus, water and sediment samples were collected throughout the year. The Vibrio-like population was higher in diseased samples than in healthy samples and was slightly higher in Yamanyeh than in MSS in all the samples. In samples from both sites, there was a seasonal variation in the Vibrio-like population, with a decline in population as the temperature reduced. All samples contained virulent isolates clustered with V. coralliilyticus strains. Inoculation of healthy Porites sp. fragments with virulent isolates and V. coralliilyticus strain caused bleaching of the coral after 48 h. Therefore, V. coralliilyticus represents a pathogenic agent which may contribute to bleaching in Porites sp. in the Gulf of Aqaba and may not be affected considerably by anthropogenic activities. This is the first report of a bacterial pathogen of corals in Jordan; future studies should identify other coral pathogens in this region.

Rising ocean temperatures are pushing reef-building corals beyond their temperature optima (Topt ), resulting in reduced physiological performances and increased risk of bleaching. Identifying refugia with thermally resistant corals and understanding their thermal adaptation strategy is therefore urgent to guide conservation actions. The Gulf of Aqaba (GoA, northern Red Sea) is considered a climate refuge, hosting corals that may originate from populations selected for thermal resistance in the warmer waters of the Gulf of Tadjoura (GoT, entrance to the Red Sea and 2000 km south of the GoA). To better understand the thermal adaptation strategy of GoA corals, we compared the temperature optima (Topt ) of six common reef-building coral species from the GoA and the GoT by measuring oxygen production and consumption rates as well as photophysiological performance (i.e. chlorophyll fluorescence) in response to a short heat stress. Most species displayed similar Topt between the two locations, highlighting an exceptional continuity in their respective physiological performances across such a large latitudinal range, supporting the GoA refuge theory. Stylophora pistillata showed a significantly lower Topt in the GoA, which may suggest an ongoing population-level selection (i.e. adaptation) to the cooler waters of the GoA and subsequent loss of thermal resistance. Interestingly, all Topt were significantly above the local maximum monthly mean seawater temperatures in the GoA (27.1°C) and close or below in the GoT (30.9°C), indicating that GoA corals, unlike those in the GoT, may survive ocean warming in the next few decades. Finally, Acropora muricata and Porites lobata displayed higher photophysiological performance than most species, which may translate to dominance in local reef communities under future thermal scenarios. Overall, this study is the first to compare the Topt of common reef-building coral species over such a latitudinal range and provides insights into their thermal adaptation in the Red Sea.

The dinoflagellates of the genus Gambierdiscus are found in almost all oceans and seas between the coordinates 35° N and 35° S. Gambierdiscus and Fukuyoa are producers of ciguatoxins (CTXs), which are known to cause foodborne disease associated with contaminated seafood. The occurrence and effects of CTXs are well described in the Pacific and the Caribbean. However, historically, their properties and presence have been poorly documented in the Indian Ocean (including the Bay of Bengal, Andaman Sea, and the Gulf). A higher occurrence of these microorganisms will proportionately increase the likelihood of CTXs entering the food chain, posing a severe threat to human seafood consumers. Therefore, comprehensive research strategies are critically important for developing effective monitoring and risk assessments of this emerging threat in the Indian Ocean. This review presents the available literature on ciguatera occurrence in the region and its adjacent marginal waters: aiming to identify the data gaps and vectors.

The water pollution index (PIj), degree of contamination (Cd), heavy metal pollution index (HPI), and statistical analyses were used to assess seawater pollution and identify the possible sources of heavy metals from the Red Sea-Gulf of Aqaba coastline, northwest Saudi Arabia. Concentrations of Cr, Sb, Co, Ni, Cu, Zn, Cd, As, Fe, Mn, Hg, and Pb were analyzed and interpreted in 33 surface seawaters samples. The mean heavy metals of seawater were in the following order: Zn (5.51 μg/l) > Ni (2.45) > As (2.43) > Cu (2.34) > Mn (2.20) > Fe (1.81) > Pb (1.31) > Sb (0.64) > Co (0.31) > Cr (0.26) > Cd (0.05) > Hg (0.008). The spatial distribution of heavy metals showed high levels in some individual samples, especially nearby the residential cities, may be due to anthropogenic sources. PIj and Cd indicated light and low pollution for the seawater samples, respectively, while HPI indicated low pollution for 10 samples and medium pollution for the rest ones. The lack of significant correlations between metal pairs (except Cu and As) indicated different sources of pollution. Pollution indices, principal component analysis, and Pearson\'s correlation coefficient reveal that the quality of seawater in the Red Sea-Gulf of Aqaba coastline is mainly controlled by geogenic processes with minor anthropogenic input.

The Gulf of Aqaba (hereafter \'the Gulf\') is a narrow, semi-enclosed, warm, high saline, and oligotrophic water body. This baseline study provides the first quantitative data on deep-sea (207-1281 m depth) benthos of the Gulf. Fifty-five benthic species (predominantly polychaetes) with a density of 160-670 ind. m-2, species richness of 11-25, and Shannon-Wiener diversity (H\') of 3.14-4.17 bits. ind.-1 were recorded from nine stations. The density and H\' of benthos of the Gulf are comparable with those of the Red Sea, while both are lower than those reported from the Arabian Sea and the Mediterranean Sea. The good-high ecological status of benthic communities indicates the absence of major stress in the deep-sea habitats of the Gulf. As large-scale urbanization is proposed in the Saudi coastal areas of the Gulf, this study is expected to provide a baseline dataset for future environmental impact assessments.

To investigate the distribution, source, contamination, and ecological risk status of heavy metals in the Red Sea-Gulf of Aqaba coast, Saudi Arabia, 33 surface sediment samples were collected for Fe, Zn, Sb, Co, Cu, Hg, Pb, Mn, Cr, Ni, Cd, As, and TOC analysis using ICP-MS. Three single and three multi-element contamination indices were used to assess the sediment quality. Evaluation of the three single pollution indices suggested some contamination or anthropogenic inputs with Cu, Cd, Hg, and, to a great extent, As. The potential ecological risk indicated low ecological risk at all sites for Pb, Zn, Ni, Cu, Co, Cr, and Sb; and considerable risk for Cd, Hg, and As. Moreover, the average values of Hg and As were higher than those recorded in the sediment quality guidelines. The multivariate statistical tools revealed that Fe, Mn, Cd, Cu, Co, Zn, and Cr were mostly of terrestrial origin, derived from weathering of the nearby Pre-Cambrian basement rocks, Tertiary, and Quaternary sedimentary rocks; while As, Sb, Hg, Ni, and Pb were mostly attributed to anthropogenic activities from traffic emissions, industrial activities, and the dredging of marine sediments. The results of this work will guide the future projects of environmentally sustainable development in northwest Saudi Arabia.

To evaluate the effect of the industrial activities on the sediment quality, we investigated long-term records of physical and chemical properties of bottom-surface sediments from a complex industrial site along the Jordanian coast of the Gulf of Aqaba. Sediment samples were collected from 10 m depth once a year from six different stations (S1-S6) and analyzed for grain size, loss on ignition (LOI), organic carbon (OC), hydrogen sulfide (H2S), total nitrogen (TN), total phosphorus (TP), and heavy metal contents. Temporal variations show a constant/decreasing trend for H2S, OC, and LOI, whereas an increasing trend for TN and TP was observed. Heavy metal concentrations reveal almost constant trends over time for Cd, Cu, and Zn and a decreasing trend for Cr and Pb. Statistical analysis indicates that the differences between the different sampling stations were insignificant for almost all variables. However, some differences were observed, as the highest values were recorded in S3 and the lowest values in S1. The textural proprieties show no significant variation among sites. As a result, the sediment quality at the industrial site is comparable with that in other sites along the northern Gulf of Aqaba. Sediments at the industrial site appear to have attained steady-state equilibrium where basic environmental parameters are insignificantly modified from the baseline values of the area. The decreasing trend observed over time indicates a significant improvement in the environmental quality attributed to the stringent implementation of environmental regulation in Aqaba (e.g., zero discharge policy).