Microphytoplankton community structure in the Gulf of Aqaba and northern Red Sea

Geological Evolution of the Red Sea: Historical Background, Review, and Synthesis

The externae of parasitic sacculind, Sacculina leptodiae (Sacculindae: Rhizocephala: Cirripedia) on the xanthid crab, Leptodius exaratus (Xanthidae: Brachyura) were recorded during this study. A total of 691 individuals (400 males and 291 females) of this crab were collected from the intertidal coasts of the Egyptian Red Sea, Gulf of Suez and Gulf of Aqaba, of them 38 (23 males and 15 females) were infected with this parasite. The overall infection rate recorded 5.50% for all populations and was slightly higher in males (5.75%) than in females (5.15%). It showed seasonal, spatial and sex variations, recorded the highest rate (7.91%) at Gulf of Suez, declined sharply to 3.85 % at Gulf of Aqaba, and 2.43 % at all populations of the Red Sea, recorded the minimum rate of 0.57% at the southern populations. Autumn has the highest rate (10.34 %) at Hurghada (northern Red Sea), followed by summer with 9.34 % and 7.69 % at the Gulf of Suez and Ras Mohammed (Northern Red Sea), respectively, declined to 2.94 % in summer at Gulf of Aqaba, but increased again to 5.56% during spring. A total of 41 externae were recorded on the infected individuals, comprised 35 individuals with single externa (92.11 %), and only three with double externe (7.89 %). The highest number of externae was 13 (31.70 %) occurred on the 6th abdominal segment, followed by 11 (26.82 %) on the 5th segments, declined to 1-5 on the other segments except the first. The size of externae varied from 1.0 to 10.4 mm in breadth, averaged 5.19± 2.76 mm in males and 5.63± 3.17 mm in females. The rootlets of internae of the parasite invaded ovaries, testes, hepatopancreas, and all spaces within the crab body cavities. The disappearance or destruction of testes in infected males accompanied by remarkable broadness and segmentation of abdomens fringed with dense and length setae lead to “Parasitic castration”, compared with a hyperfiminzation in infected females due to the destruction of undeveloped ovaries and increasing abdominal setae dense and length.

Zooplankton and zooneuston observations were made at seven stations (four from the Gulf of Aqaba and three from the northern Red Sea), during September and October 2016. The main objective of this study was to assess the variability of nycthemeral fauna in relation to the sampling methods using two different types of nets namely, WP2 net and Neuston net along the two study sites, i.e., the Gulf of Aqaba and the northern Red Sea. Zooplankton was sampled vertically using a standard WP2 net from a depth of 200 m to the surface, whereas zooneuston was made using a standard Neuston net from a depth of 0–10 cm of the water surface. Total zooplankton density was maximum during night time ((617.83 ± 201.84) ind./m3) at the Gulf of Aqaba and total zooneuston was maximum during night at the northern Red Sea ((60.94±29.48) ind./m3), respectively. The most abundant taxa were Copepoda, Gastropoda, Bivalva, Chaetognatha, Tunicata and Ostracoda. The abundance was almost 50% higher at night time at both the Gulf of Aqaba and the northern Red Sea. Overall, 30 taxa covering 10 phyla and 27 taxa covering 8 phyla were recorded in the Gulf of Aqaba and the northern Red Sea.

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.

Quantitative studies of coral communities in the central and northern Red Sea were designed for comparison of the community structure in both areas. The central Red Sea provides reef-building Scleractinia and reef-inhabiting Alcyonaria with optimal temperature conditions, whereas the north tip of the Gulf of Aqaba (29°30′ N) represents the northernmost outpost of coral reefs in the Indian Ocean. It is generally assumed that coral diversity decreases towards the margins of the global reef-belt. In the Red Sea, generic diversity of hermatypic Scleractinia slightly decreases from the central to the northern part (51 : 48 genera); but cnidarian species abundance (species number per 25 m2 area) was found to increase from 62 to 98 species and the Shannon-Wiener diversity index increased from 2.58 to 3.67 with regard to colony number. The mean colony size was 189 cm2 at Sanganeb-Atoll, but only 52 cm2 at Aqaba. The mean numbers of colonies were inversely related: 662 per 25 m2 at Sanganeb-Atoll and 2028 at Aqaba. Uninhabited parts of the studied areas amounted to 47 % at Sanganeb-Atoll and to 56 % at Aqaba. The community structure of the studied areas indicates that occasional perturbations prevent the progress of the community towards a low-diversity equilibrium state. Since severe hydrodynamic damage is extremely rare in 10 m depth, major disturbances may occur by sedimentation, by the interference of grazers (e. g.Diadema setosum) and due to overgrowth by space-competitors (mainly soft corals). These events are to be regarded as throwbacks in the process of monopolization of the area by well adapted species. Recovery from such perturbations (i.e. recolonization of dead areas) obviously takes place at different velocities in the northern and central Red Sea, for the mean water temperature at Aqaba is 5 °C lower than in the central Red Sea. Hence the process of taking over a given space by a few species proceeds further in the central Red Sea than at its northern end. The increase in diversity per area towards high latitudes is comparable to that with depth. It is concluded from the great number of species at Aqaba that these reefs mark the northernmost outpost of the Indian Ocean only geographically but not ecophysiologically; they would occur at even higher latitudes, if the Gulf of Aqaba extended farther north.

Seasonal flux patterns of planktonic foraminifera in a deep, oligotrophic, marginal sea: Sediment trap time series from the Gulf of Aqaba, northern Red Sea

The distribution pattern, taxonomic composition and community structure of mesozooplankton was studied along a transect with 10 positions between the Gulf of Aqaba and the northern Red Sea. Five positions were resampled two or three times during a cruise of RV 'Meteor' in February/March 1999. In spite of char differences in the density stratification between the Gulf of Aqaba and the northern Red Sea, the mesozooplankton composition was very similar: Copepods were by far the most abundant taxon, contributing 76-95% to the total community. The remainder was composed largely of ostracods, chaetognaths, appendicularians and molluscs. The mesozooplankton of the deeply mixed stations was homogeneously distributed, at all other stations the hulk of the mesozooplankton (>70%) was concentrated in the mixed surface layer with peaks of calanoids, cyclopoids and appendicularians in the vicinity of the chlorophyll a (Chl a) maximum layer. Ostracods and poecilostomatoids dominated the layers below. Standing stocks within the total water column (550-1200 m) varied between 93 and 431 x 10 3 individuals m 2 for copepods and 5-76 × 10 3 individuals m -2 for other mesozooplankton with highest numbers in the northern Gulf of Aqaba, where vertical mixing was deep (400-500 m) and Chl a and mesozooplankton distributions homogeneous throughout the water column. Towards the south, the mixed depth decreased from 300 m in the central Gulf of Aqaba to 50 m in the Red Sea. Cluster analysis separated three distinct groups of stations, compounding the observed differences between the northern Gulf of Aqaba (Position I) and the other positions. The analysis also revealed temporal differences between the February and March sections of the cruise, indicating the winter-spring transition. The stations sampled in March are characterised by a higher total abundance and by a higher percentage of appendicularians and ostracods than the stations sampled in February.

The Red Sea and Gulf of Aden constitute parts of the Afro-Arabian rift system that are in the most advanced stages of continental break-up. These basins have therefore received extensive scrutiny in the geoscientific literature, but several aspects of their evolution remain enigmatic. Many of their most important features lie beneath several kilometers of water, in places covered by several kilometers of evaporite deposits, and along international political boundaries. All these factors greatly complicate the acquisition and interpretation of both subsurface wellbore and geophysical datasets. Much of our understanding of the evolution of the Red Sea has therefore relied on the integration of outcrop geology and land-based analytical studies with these more difficult to obtain marine observations. While stratigraphic, radiometric and structural data indicate that extension and rifting initiated in the southern Red Sea during the Late Oligocene (~28–25 Ma), the start of rifting in the northern Red Sea is more difficult to constrain due to paucity of rift-related volcanism and reliable biostratigraphy of the oldest syn-kinematic sedimentary strata. A regional NW-SE trending alkali basalt dike swarm, with associated extensive basalt flows in the vicinity of Cairo, appears to mark the onset of crustal-scale extension and continental rifting. These dikes and scarce local flows, erupted at the Oligocene-Miocene transition (~23 Ma) and coeval with similar trending dikes along the Yemen and Saudi Arabian Red Sea margin, are interbedded with the oldest part of the paleontologically dated siliciclastic syn-rift stratigraphic section (Aquitanian Nukhul Fm.), and are associated with the oldest recognized extensional faulting in the Red Sea. Bedrock thermochronometric results from the Gulf of Suez and both margins of the Red Sea also point to a latest Oligocene onset of major normal faulting and rift flank exhumation and large-magnitude early Miocene extension along the entire length of the Red Sea rift. This early phase of rifting along the Egyptian Red Sea margin and in the Gulf of Suez resulted in the formation of a complex, discontinuous fault pattern with very high rates of fault block rotation. The rift was segmented into distinct sub-basins with alternating regional dip domains separated by well-defined accommodation zones. Sedimentary facies were laterally and vertically complex and dominated by marginal to shallow marine siliciclastics of the Abu Zenima, Nukhul and Nakheil Formations. Neotethyan faunas appeared throughout all of the sub-basins at this time. During the Early Burdigalian (~20 Ma) tectonically-driven subsidence accelerated and was accompanied by a concordant increase in the denudation and uplift of the rift shoulders. The intra-rift fault networks coalesced into through-going structures and fault movement became progressively more focused along the rift axis. This reconfiguration of the rift structure resulted in more laterally continuous depositional facies and the preponderance of moderate-to-deep marine deposits of the Rudeis, Kareem and Ranga Formations. The early part of the Middle Miocene (~14 Ma) was marked by dramatic changes in rift kinematics and sedimentary depositional environments in the Red Sea and Gulf of Suez. The onset of the left-lateral Gulf of Aqaba transform fault system, isolating the Gulf of Suez from the active northern Red Sea rift, resulted in a switch from orthogonal to oblique rifting and to hyperextension in the northern Red Sea. The open marine seaway was replaced by an extensive evaporitic basin along the entire length of the rift from the central Gulf of Suez to Yemen/Eritrea. In Egypt these evaporites are ascribed to the Belayim, South Gharib, Zeit and Abu Dabbab Formations. Evaporite deposition continued to dominate in the Red Sea until the end of the Miocene (~5 Ma) when a subaerial unconformity developed across most of the basin. With the onset of seafloor spreading in the southern Red Sea, Indian Ocean marine waters re-entered through the Bab el Mandab in the earliest Pliocene and re-established open marine conditions. During the Pleistocene, glacial-isostatic driven sea-level changes resulted in the formation of numerous coral terraces and wave-cut benches around the margins of the Red Sea, Gulf of Suez and Gulf of Aqaba. Their present elevations suggest that the Egyptian Red Sea margin has been relatively vertically stable since the Late Pleistocene. While there is general agreement that full seafloor spreading, producing well-defined magnetic stripes, has been occurring in the southern Red Sea since ~5 Ma, there is ongoing debate whether and when lithospheric break-up has occurred in the northern Red Sea. Industry wellbore and seismic data demonstrate that continental crust extends at least several tens of kilometers offshore from the present-day coastline, and that the northern Red Sea is a non-volcanic rifted margin. On the basis of integrated geophysical, petrological, geochemical and geological datasets, we contend that true, laterally integrated sea-floor spreading is not yet manifest in the northern Red Sea.

[1] We investigate the coupling between the dynamics in the Gulf of Aqaba (Gulf of Eilat, northern Red Sea) and the exchange flow through the Straits of Tiran in response to seasonally varying surface fluxes and northern Red Sea hydrographic conditions. Because the gulf is a relatively small basin, winter mixing between the surface and intermediate layers occurs over most places in the gulf including in the vicinity of the straits, and leads to a maximal exchange flow in the strait. During the spring, warming in the Red Sea forces an influx of warm Red Sea water into the gulf, the surface layer is refilled, and consequently the exchange flow in the straits changes from a maximal to a submaximal flow regime. As a result, the dense wintertime water formation in the gulf and the exchange flow through the strait are strongly coupled on seasonal time scales. In addition, the hydrographic conditions in the northern Red Sea undergo strong seasonality. These characteristics prevent the direct application of current theories for strait‐marginal sea systems, which commonly assume steady conditions in the “open ocean” side of the strait and/or an annual mean surface flux over the marginal sea. We explain why the exchange of volume and heat between the Gulf of Aqaba (Gulf of Eilat) and the northern Red Sea is larger during spring‐summer despite the net surface buoyancy input into the gulf and why it diminishes during fall‐winter despite the large buoyancy loss to the atmosphere. The applicability of the results to other systems is discussed.

The Red Sea, Gulf of Suez, and Gulf of Aqaba comprise the active plate boundaries that separate Africa-Nubia, Arabia and Sinai. This tripartite configuration has been in existence since the Middle Miocene, or about the past 12–14 Ma. We describe the ongoing and geologically recent tectonics of these regions. The Red Sea rift lies east of a broad region of E-W maximum horizontal stress (SHmax) that covers much of central Africa-Nubia. On its Arabian side, SHmax is oriented N-S to NE-SW. These far field stresses owe their origins to the spreading centres of the Atlantic Ocean and collision between Arabia and Eurasia along the Bitlis-Zagros suture. At the continental scale, the Red Sea is therefore subjected to compression perpendicular to or at a high-angle to its margins. The realm of shallow crustal stresses conducive to extensional faulting in a Red Sea orientation (rift-normal Shmin) is presently restricted to the Red Sea marine basin itself, and perhaps narrow belts along its shoulders. In the Gulf of Suez there is enough data to show that each of its sub-basins is presently undergoing extension, but in conjunction with differently oriented, sub-regional shallow crustal stress fields. These appear to be spatially related to the original Early Miocene syn-rift basin geometries. NNE-SSW extension in the southern Gulf of Suez is probably generated by sinistral slip on the similarly oriented Gulf of Aqaba transform margin. Large M > 6 earthquakes are generally restricted to the central basin of the Gulf of Aqaba, the southern Gulf of Suez, and the greater Afar region. The geodynamic details responsible for the focusing of these large events are specific to each locale but all are in general associated with the junctions of major plate boundaries. Catalogues of earthquake activity and GPS datasets show that the Sinai micro-plate is still moving away from Africa with a component of left-lateral slip. This results in components of extension perpendicular to both the Gulf of Suez and the Gulf of Aqaba. The kinematics of the southern Red Sea are similarly complex. Not all opening has jumped to the west side of the Danakil horst and significant tectonic activity still occurs along the southernmost Red Sea axis in the vicinity of the Zubair Archipelago. This is the only volcanically active segment of the Red Sea basin that is above sea level. Dike intrusions are ~N-S and not aligned parallel to the rift axis and may indicate that the underlying magmatism is swinging to the west to link with the Afar triple junction. All of the margins of the Red Sea, Gulf of Suez and Gulf of Aqaba underwent tectonically-driven rift shoulder uplift and denudation in the past, particularly during the main phases of continental rifting. However, during the past 125 kyr uplift has been focused along the footwalls of a few, active extensional faults. These include the Hammam Faraun-Tanka fault in the central Gulf of Suez, the Gebel el Zeit-Shadwan Island fault in the southern Gulf of Suez, the Sinai and Arabia coastal boundaries of the Gulf of Aqaba, and faults at Tiran Island at the junction of the Gulf of Aqaba and northern Red Sea. Smaller-scale extensional faulting is also occurring along the Saudi Arabian margin of the northern Red Sea, in the Dahlak and Farasan Archipelagos, and on the volcanically active islands of the Zubair Archipelago in the southernmost Red Sea. On the Farasan and Dahlak islands this is largely related to the movement of underlying salt bodies, similar to effects documented along the coastal plain of Yemen. Though not active at the present time, a broad belt of small-offset, very linear extensional faults dissected the western margin of the central Gulf of Suez during the Plio-Pleistocene. Similar age and style deformation has not been identified in the Suez sub-basins to the north or south. The most significant large-scale neotectonic features of the Red Sea rift system are its southern oceanic spreading centre and the northern linkage to the left-lateral Gulf of Aqaba—Levant transform fault. However, many segments of the rift margins and in particular the Gulf of Suez remain tectonically active. These areas provide stress field and horizontal and vertical displacement data that are relatively inexpensive to acquire and complementary to analyses of the offshore main plate boundaries themselves.

Genetic population structure of the lionfish Pterois miles (Scorpaenidae, Pteroinae) in the Gulf of Aqaba and northern Red Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 342:265-275 (2007) - doi:10.3354/meps342265 Microhabitat specialisation and ecological consequences for coral gobies of the genus Gobiodon in the Gulf of Aqaba, northern Red Sea Markus Dirnwöber1, Jürgen Herler2,* 1Department of Marine Biology, and 2Department of Theoretical Biology, Morphology Section, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria *Corresponding author. Email: juergen.herler@univie.ac.at ABSTRACT: The microhabitat selection and distribution of 6 coral-associated species of Gobiodon were examined in the Gulf of Aqaba, northern Red Sea, including 3 recently discovered species. A total of 1626 fishes were counted visually using 10 × 1 m belt transects in 1731 colonies of 13 species of Acropora. Niche segregation was observed at the level of coral species. Gobiodon sp. 2 was the most specialised, occupying only A. hyacinthus; Gobiodon sp. 1 was most generalised (occupying 3 species of Acropora more frequently than expected). G. reticulatus was a zone specialist that preferred deeper water regions. Less specialised species were able to use substitute host corals, which enabled them to maintain extraordinarily high abundance. G. histrio, for example, preferred the rare A. digitifera, but was common in the very abundant A. acuminata, although proportionally fewer breeding pairs were established in the latter. When compared to the western Pacific, G. histrio showed a more generalised behaviour in the northern Red Sea, and different coral species served as host corals; the latter also holds true for the even more generalised G. rivulatus. Hence, species of Gobiodon appear to alter host-use and degree of specialisation on a global scale. KEY WORDS: Gobiodon spp. · Acropora spp. · Gobiidae · Habitat associations · Abundance · Reef fish · Coral reefs · Red Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Conductivity‐temperature‐depth tracer and direct current measurements collected in the northern Red Sea in February and March 1999 are used to study the formation of deep and bottom water in that region. Historical data showed that open ocean convection in the Red Sea can contribute to the renewal of intermediate or deep water but cannot ventilate the bottom water. The observations in 1999 showed no evidence for open ocean convection in the Red Sea during the winter 1998/1999. The overflow water from the Gulf of Aqaba was found to be the densest water mass in the northern Red Sea. An anomaly of the chlorofluorocarbon component CFC‐12 observed in the Gulf of Aqaba and at the bottom of the Red Sea suggests a strong contribution of this water mass to the renewal of bottom water in the Red Sea. The CFC data obtained during this cruise are the first available for this region. Because of the new signal, it is possible for the first time to subdivide the deep water column into deep and bottom water in the northern Red Sea. The available data set also shows that the outflow water from the Gulf of Suez is not dense enough to reach down to the bottom of the Red Sea but was found about 250 m above the bottom.

Holocene sea levels at the Gulf of Aqaba, northern Red Sea

Spatial patterns of marine Synechococcus diversity across ocean domains have been reported on extensively. However, much less is known of seasonal and multiannual patterns of change in Synechococcus community composition. Here we report on the genotypic diversity of Synechococcus populations in the Gulf of Aqaba, Northern Red Sea, over seven annual cycles of deep mixing and stabile stratification, using ntcA as a phylogenetic marker. Synechococcus clone libraries were dominated by clade II and XII genotypes and a total of eight different clades were identified. Inclusion of ntcA sequences from the Global Ocean Sampling database in our analyses identified members of clade XII from beyond the Gulf of Aqaba, extending its known distribution. Most of the Synechococcus diversity was attributed to members of clade II during the spring bloom, while clade III contributed significantly to diversity during summer stratification. Clade XII diversity was most prevalent in fall and winter. Clade abundances were estimated from pyrosequencing of the V6 hypervariable region of 16S rRNA. Members of clade II dominated Synechococcus communities throughout the year, whereas the less frequent genotypes showed a pattern of seasonal succession. Based on the prevailing nutritional conditions we observed that clade I members thrive at higher nutrient concentrations during winter mixing. Clades V, VI and X became apparent during the transition periods between mixing and stratification. Clade III became prominent during sumeer stratification. We propose that members of clades V, VI, and X, and clade III are Synechococcus ecotypes that are adapted to intermediate and low nutrient levels respectively. This is the first time that molecular analyses have correlated population dynamics of Synechococcus genotypes with temporal fluctuations in nutrient regimes. Since these Synechococcus genotypes are routinely observed in the Gulf of Aqaba we suggest that seasonal fluctuations in nutrient levels create temporal niches that sustain their coexistence.