Synchronous reproduction of corals in the Red Sea

Multi-species synchronous spawning was first described on reefs off the east and west coast of Australia. In contrast, locally abundant species in the northern Red Sea and the central Pacific have little overlap in the time of reproduction. Consequently, the idea developed that high levels of spawning synchrony both within and among species was largely confined to Australian reefs. Here, we show that gamete maturity in colonies of the genus Acropora was highly synchronous in the Red Sea. In early April 2008, at two locations separated by 300 km, 13 of 24 species sampled had mature colonies, and a further 9 species had immature colonies. In late April–early May 2008, all colonies sampled had no oocytes, indicating colonies had spawned a few days after the full moon of 20 April 2008. Similarly, in 2009, 99% of colonies from 17 species at Hurghada were mature in late April, and all were empty in early May. Spawn slicks suggested many of these colonies had released gametes three night prior to the full moon on 8 May 2009. This level of synchrony in gamete maturity is among the highest ever recorded and similar to that typically recorded in Acropora assemblages on Australian reefs. While further work is required to document the night of gamete release, these data strongly suggest that high levels of spawning synchrony are a regular feature of these Red Sea coral assemblages and that multi-species spawning occurs on or around the full moon in April and/or May.     

Organic matter release by dominant hermatypic corals of the Northern Red Sea

Particulate organic matter (POM) and dissolved organic carbon (DOC) release by six dominant hermatypic coral genera (Acropora, Fungia, Goniastrea, Millepora, Pocillopora and Stylophora) were measured under undisturbed conditions by laboratory incubations during four seasonal expeditions to the Northern Red Sea. In addition, the influence of environmental factors (water temperature, light availability and ambient inorganic nutrient concentrations) was evaluated. Particulate organic carbon (POC) and particulate nitrogen (PN) release were always detectable and genus-specific, with Stylophora releasing most POM (6.5 mg POC and 0.5 mg PN m⁻² coral surface area h⁻¹) during all seasons. The fire coral Millepora released significantly less POM (0.3 mg POC and 0.04 mg PN m⁻² coral surface area h⁻¹) than all investigated anthozoan genera. The average POC:PN ratio of POM released by all coral genera was 12 ± 1, indicating high carbon/low nitrogen content of coral-derived organic matter. POM release showed little seasonal variation, but average values of POC and PN release rates correlated with water temperature, light availability and ambient nitrate concentrations. DOC net release and elevated DOC:POC ratios were detectable for Acropora, Goniastrea and Millepora, revealing maximum values for Acropora (30.7 mg DOC m⁻² coral surface area h⁻¹), whilst predominant DOC uptake was observed for Pocillopora, Fungia and Stylophora. Depth-mediated light availability influenced DOC fluxes of Acropora and Fungia, while fluctuations in water temperature and ambient inorganic nutrient concentrations showed no correlation. These comprehensive data provide an important basis for the understanding of coral reef organic matter dynamics and relevant environmental factors.     

Characterization of black band disease in Red Sea stony corals

Microbial communities associated with black band disease (BBD) in massive stony corals from the Northern Red Sea (Eilat) were examined for the first time using molecular tools and microscopy. A high microbial diversity was revealed in the affected tissue in comparison with the healthy area of the same colony. Microscopy revealed the penetration of cyanobacteria into the coral mesoglea and adjacent tissues. Cyanobacterial sequences from Red Sea BBD-affected corals formed a cluster with sequences previously identified from black band and red band diseased corals from the Indo-Pacific and Caribbean. In addition, 11 sequences belonging to the genus Vibrio were retrieved. This group was previously documented as pathogenic to corals. Sulfate-reducing bacteria, a group known to be associated with BBD and produce toxic sulfide, were studied using specific primers for the amplification of the dissimilatory sulfite reductase gene (dsrA). This technique facilitated and improved the resolution of the study of diversity of this group. All the sequences obtained were closely related to sequences of the genus Desulfovibrio and 46% showed high homology to Desulfovibrio desulfuricans. The complex nature of BBD and the lack of success in isolating a single causative agent suggest that BBD may be considered a polymicrobial disease.     

Monogenean infestations and mortality in wild and cultured Red Sea fishes

Hyperinfection by the gill-infesting monogeneanAllobivagina sp. (Microcotylea) caused mass mortalities in juveniles ofSiganus luridus cultured in seawater earthen ponds and holding tanks in Eilat (Gulf of Aqaba, Red Sea). Other species ofSiganus and adults ofS. luridus cultured in the same systems acquired a low intensity of infestation. Most hyperinfected fish were emaciated and anaemic with hematocrit values below 10 %. Skin and mouth infestations by the monogeneanBenedenia monticelli (Capsaloidea) caused mass mortalities in grey mullets (Mugilidae). These mortalities occurred in large individuals in wild populations ofLiza carinata from lagoonal habitats in the Gulf of Suez and in most species of grey mullets cultured in Eilat. The intensity of infestation correlated positively with severity of infestation, and the common sites of infestation corresponded with areas of severe pathological alterations. Spontaneous recovery followed the climax of an epizootic, both for infestedS. luridus and infested grey mullets. Decline in infestation coincided with remission of the pathological signs.     

Carbonate production by scleractinian corals at Aqaba,Gulf of Aqaba,Red Sea

Summary In a fringing reef at Aqaba at the northern end of the Gulf of Aqaba (29°26′N) growth rates, density, and the calcification rate ofPorites were investigated in order to establish calculations of gross carbonate production for the reefs in this area. Colony accretion ofPorites decreases with depth as a function of decreasing growth rates. The calcification rate ofPorites is highest in shallow water (0–5 m depth) with 0.9 g·cm⁻²·yr⁻¹ and falls down to 0.5 g·cm⁻²·yr⁻¹ below 30 m. Scleractinian coral gross production is calculated from potential productivity and coral coverage. It is mainly dependent on living coral cover and to a lesser extent on potential productivity. Total carbonate production on the reef ranged from 0 to 2.7 kg/m² per year, with a reef-wide average of 1.6 kg/m² perycar. Maximum gross carbonate production by corals at Aqaba occurs at the reef crest and in the middle fore-reef from 10 to 15 m water depth. Production is low in sandy reef parts. Below 30 m depth values still reach ca. 50% of shallow water values. Mean potential production of colonies and gross carbonate production of the whole reef community at Aqaba is lower than in tropical reefs. However, carbonate production is higher than in reef areas at the same latitude in the Pacific, indicating a northward shift of reef production in the Red Sea.     

Susceptibility of central Red Sea corals during a major bleaching event

A major coral bleaching event occurred in the central Red Sea near Thuwal, Saudi Arabia, in the summer of 2010, when the region experienced up to 10–11 degree heating weeks. We documented the susceptibility of various coral taxa to bleaching at eight reefs during the peak of this thermal stress. Oculinids and agaricids were most susceptible to bleaching, with up to 100 and 80 % of colonies of these families, respectively, bleaching at some reefs. In contrast, some families, such as mussids, pocilloporids, and pectinids showed low levels of bleaching (<20 % on average). We resurveyed the reefs 7 months later to estimate subsequent mortality. Mortality was highly variable among taxa, with some taxa showing evidence of full recovery and some (e.g., acroporids) apparently suffering nearly complete mortality. The unequal mortality among families resulted in significant change in community composition following the bleaching. Significant factors in the likelihood of coral bleaching during this event were depth of the reef and distance of the reef from shore. Shallow reefs and inshore reefs had a higher prevalence of bleaching. This bleaching event shows that Red Sea reefs are subject to the same increasing pressures that reefs face worldwide. This study provides a quantitative, genus-level assessment of the vulnerability of various coral groups from within the Red Sea to bleaching and estimates subsequent mortality. As such, it can provide valuable insights into the future for reef communities in the Red Sea.     

High CO2 detrimentally affects tissue regeneration of Red Sea corals

Ocean acidification (OA) from rising atmospheric carbon dioxide (CO₂) is threatening the future of coral reef ecosystems. Mounting experimental evidence suggests that OA negatively impacts fundamental life functions of scleractinian corals, including growth and sexual reproduction. Although regeneration is regarded as a chief life function in scleractinian corals and essential to maintain the colony’s integrity, the effect of OA on regeneration processes has not yet been investigated. To evaluate the effects of OA on regeneration, the common Indo-Pacific corals Porites sp., Favia favus, Acropora eurystoma, and Stylophora pistillata were inflicted with lesions (314–350 mm², depending on species) and incubated in different pCO₂: (1) ambient seawater (400 µatm, pH 8.1), (2) intermediate (1,800 µatm, pH 7.6), and (3) high (4,000 µatm, pH 7.3) for extended periods of time (60–120 d). While all coral species after 60 d had significantly higher tissue regeneration in ambient conditions as compared to the intermediate and high treatments, reduction in regeneration rate was more pronounced in the slow-growing massive Porites sp. and F. favus than the relatively fast-growing, branching S. pistillata and A. eurystoma. This coincided with reduced tissue biomass of Porites sp., F. favus, and A. eurystoma in higher pCO₂, but not in S. pistillata. Porites sp., F. favus, and S. pistillata also experienced a decrease in Symbiodinium density in higher pCO₂, while in A. eurystoma there was no change. We hypothesize that a lowered regenerative capacity under elevated pCO₂ may be related to resource trade-offs, energy cost of acid/base regulation, and/or decrease in total energy budget. This is the first study to demonstrate that elevated pCO₂ could have a compounding influence on coral regeneration following injury, potentially affecting the capacity of reef corals to recover following physical disturbance.     

Phylogenetic diversity of bacteria associated with the mucus of Red Sea corals

Coral reefs are the most biodiverse and biologically productive of all marine ecosystems. Corals harbor diverse and abundant prokaryotic communities. However, little is known about the diversity of coral-associated bacterial communities. Mucus is a characteristic product of all corals, forming a coating over their polyps. The coral mucus is a rich substrate for microorganisms. Mucus was collected with a procedure using sterile cotton swabs that minimized contamination of the coral mucus by surrounding seawater. We used molecular techniques to characterize and compare the bacterial assemblages associated with the mucus of the solitary coral Fungia scutaria and the massive coral Platygyra lamellina from the Gulf of Eilat, northern Red Sea. The bacterial communities of the corals F. scutaria and P. lamellina were found to be diverse, with representatives within the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria and Epsilonproteobacteria, as well as the Actinobacteria, Cytophaga-Flavobacter/Flexibacter-Bacteroides group, Firmicutes, Planctomyces, and several unclassified bacteria. However, the total bacterial assemblage of these two corals was different. In contrast to the bacterial communities of corals analyzed in previous studies by culture-based and culture-independent approaches, we found that the bacterial clone libraries of the coral species included a substantial proportion of Actinobacteria. The current study further supports the finding that bacterial communities of coral mucus are diverse.     

Carbohydrate composition of mucus from scleractinian corals from the central Red Sea

Coral Reefs - Coral mucus is continuously released by most corals and acts as an important protective barrier and as a substrate for host-associated microbial communities due to its complex...     

Some toxicological characteristics of three venomous soft corals from the Red Sea

Three common Red Sea soft corals (Cnidaria: Anthozoa), Nephthea sp, Dendronephthya sp and Heteroxenia fuscescens sting humans. Nematocyst venoms of each animal are lethal to mice and hemolytic to human erythrocytes. However, these hemolysins are partially inhibited by known anti-hemolytic agents. Venoms and their gel chromatography-separated fractions have different dermonecrosis and vasopermeability potency in mouse skin. The venom of Heteroxenia fuscescens (Hf) was more lethal (LD50: 0.7 mg/kg), with one prominent 97-kDa protein fraction (LD50: 0.55 mg/kg). Hf venom was more hemolytic, more dermonecrotic, and had more vasopermeable factors than that of the two other species. SDS polyacrylamide gel electrophoresis of soft coral whole venoms and fractions showed different protein molecular masses ranging from 200 to less than 6 kDa. High IgG titers were assayed from venom-sensitized mice blood sera. Enzyme-linked immunosorbent assays (ELISA) marked significant immunological cross-reaction between the studied soft coral venoms and their bioactive fractions.     

Space partitioning by stony corals soft corals and benthic algae on the coral reefs of the northern Gulf of Eilat (Red Sea)

The major faunistic and floristic components occupying space on the coral reefs of the northern Gulf of Eilat (Red Sea) are stony corals, soft corals and benthic algae. The percent living coverage of the three components and the relative abundance of the different species of each component were studied by line transects, on the reef flats and the upper forereef zones of nine localities. A wider and higher range of living coverage values of stony corals were recorded at the upper fore-reef zones (18.30–49.09%) compared with the reef flats (5.50–31.66%) at the different stations. The most abundant stony corals on the reef flats areCyphastrea microphthalma, Stylophora pistillata, Favia favus, Porites lutea, Platygyra lamellina and the hydrozoanMillepora dichotoma. The fire coralM. dichotoma dominates the upper fore-reef zone in most of the stations. The average percent living coverage of soft corals on the reef flats ranged between 0.20 and 17.06%, and on the upper fore-reef zones between 1.68 and 15.13%. Seventy percent of the total living coverage of the soft coral community is contributed by 2 to 3 species. They tend to form large monospecific carpets, such as those composed ofSinularia sp.,Sarcophyton glaucum andLobophytum pauciflorum. The common benthic algae on the coral reef studied occur as turfs or macroscopic noncalcareous algae. They play a significant role in occupying space, especially on the reef flats. The most abundant algae recorded in all localities are the turfsSphacelaria tribuloides, Jania sp. and the macroscopic non-calcareous algaeTurbinaria elatensis andColpomenia sinuosa. Comparison between reef flats and upper fore-reef zones, in terms of average living cover of stony corals, shows that the variation among the reef flats is grater than the variation among the upper fore-reef zones. However, there is no significant variation in the average living coverage of soft corals between these two zones. Annual living-coverage values of algae on the reef flats are significantly higher than those of the upper fore-reef zones. Extremely low tides occurring periodically but unpredictably at Eilat cause mass mortality of the benthic communities on the reef flats reopening new spaces for settlement. The coexistence of stony corals, soft corals and algae on the reef ecosystem is due to different biological properties of each component. Opportunistic life histories of certain stony corals and most algae enable quick colonization of newly opened spaces. Lack of predators, high tolerance against abiotic factors and ability to form large aggregates of colonies are suggested as possible factors supporting the existence of soft corals in shallow water. Biological factors such as competition, predation and grazing pressure play an increasingly important role in controlling space utilization by the components studied with the advancement of succession.     

Recruitment,mortality, and resilience potential of scleractinian corals at Eilat,Red Sea

Events of mass coral bleaching and mortality have increased in recent decades worldwide, making coral recruitment more important than ever in sustaining coral-reef ecosystems and ensuring their resilience. During the last four decades, the coral reefs of Eilat have undergone severe deterioration due to both anthropogenic and natural causes. Recruitment failure has been frequently suggested as one of the main mechanisms underlying this deterioration. Here we assess the demographic replenishment and resilience potential of the local reefs, i.e., the potential for new sexually derived corals to recruit and exceed the community’s mortality rate. We present a detailed analysis of coral community demography, obtained by means of high-resolution photographic monitoring of permanently marked plots. Coral spats as small as 1 mm were documented and the detailed dynamics of coral recruitment and mortality were recorded, in addition to other common ecological measurements. The cumulative quantity of recruited individuals was twofold to fivefold higher than total mortality. The most significant predictor variable for coral recruitment among all ecological parameters measured was the available substrate for settlement, and the survival of recruited corals was correlated with reef structural complexity. Two consecutive annual reproductive seasons (June–September of each year) with high recruitment rates were monitored. Combined with the high survival of recruits and the increase in coral live cover and abundance, the findings from this study indicate an encouraging potential for recovery of these reefs.

     

Spatial and seasonal reef calcification in corals and calcareous crusts in the central Red Sea

The existence of coral reef ecosystems critically relies on the reef carbonate framework produced by scleractinian corals and calcareous crusts (i.e., crustose coralline algae). While the Red Sea harbors one of the longest connected reef systems in the world, detailed calcification data are only available from the northernmost part. To fill this knowledge gap, we measured in situ calcification rates of primary and secondary reef builders in the central Red Sea. We collected data on the major habitat-forming coral genera Porites, Acropora, and Pocillopora and also on calcareous crusts (CC) in a spatio-seasonal framework. The scope of the study comprised sheltered and exposed sites of three reefs along a cross-shelf gradient and over four seasons of the year. Calcification of all coral genera was consistent across the shelf and highest in spring. In addition, Pocillopora showed increased calcification at exposed reef sites. In contrast, CC calcification increased from nearshore, sheltered to offshore, exposed reef sites, but also varied over seasons. Comparing our data to other reef locations, calcification in the Red Sea was in the range of data collected from reefs in the Caribbean and Indo-Pacific; however, Acropora calcification estimates were at the lower end of worldwide rates. Our study shows that the increasing coral cover from nearshore to offshore environments aligned with CC calcification but not coral calcification, highlighting the potentially important role of CC in structuring reef cover and habitats. While coral calcification maxima have been typically observed during summer in many reef locations worldwide, calcification maxima during spring in the central Red Sea indicate that summer temperatures exceed the optima of reef calcifiers in this region. This study provides a foundation for comparative efforts and sets a baseline to quantify impact of future environmental change in the central Red Sea.

     

Taphonomic signatures on modern molluscs and corals from Red Sea coast,southern Saudi Arabia

Bioeroded gastropod, bivalve and coral specimens (n = 570) were collected from the Jazan area, Saudi Red Sea coast, from which 22 ichnospecies of 8 ichnogenera were identified and illustrated. These traces were produced by clionid sponges (Entobia geometrica, E. ovula, E. cf. goniodes, E. cretacea, E. laquea, E. cf. paradoxa and E. isp.), duraphagous drillers (Oichnus ovalis, O. paraboloides, O. simplex and O. isp.), endolithic bivalves (Gastrochaenolites cf. dijugus, G. lapidicus, G. torpedo and G. isp.), polychaete annelids (Caulostrepsis taeniola, C. isp., Maeandropolydora sulcans, M. isp. and ?Trypanites isp.), acorn barnacles (Rogerella isp.), and vermetid gastropods (Renichnus isp.). The seashells act as hard substrate for colonization by serpulid worm, bivalves, bryozoans, and barnacles. Ichnogenus Entobia was most abundant (56.1%), followed by Gastrochaenolites (25.4%), Caulostrepsis (5.3%), Trypanites (4.2%), Maeandropolydora (3.2%), Oichnus (2.8%), Renichnus (1.9%), and Rogerella (1.0%). Oichnus occurred on the thin-shelled and smooth molluscs, while most Gastrochaenolites borings were found in the larger and thicker seashells as a suitable substrate for the settlement of polychaetes, lithophages, naticids, mytilids, and vermetids. Presence of annelid traces among radial ribs and at the siphonal areas of bivalves is indicative of nutrient capturing from water flow during the lifetime of these bivalves, within a shallow, high energy marine environment, where disarticulation, fragmentation, and abrasion of the seashells were abundantly observed.     

In situ measured seasonal variations in F v/F m of two common Red Sea corals

Pulse amplitude modulated (PAM) fluorometry has been suggested as a tool for estimating environmental stresses on corals. However, information regarding natural changes in maximal quantum yields (F _v/F _m) of corals during “normal” (i.e. non-bleaching) years has been limited. In this study, seasonal variations in F _v/F _m for Stylophora pistillata and Favia favus, measured in situ, correlated with seasonal changes in solar irradiance but not in sea temperature. Interactions between sea temperature and irradiance were further studied by growing these corals and Pocillopora damicornis under controlled conditions. Exposure to high light with normal or high temperatures resulted in lower F _v/F _m values than exposure to low light at both temperatures. Thus, high irradiances may cause decreased F _v/F _m values in corals at least as much as, if not more than, high temperatures. Such seasonal variations should be taken into account when using PAM fluorometry as a diagnostic tool for predicting coral bleaching.     

Spawning of coral reef invertebrates and a second spawning season for scleractinian corals in the central Red Sea

Recent coral spawning observations in the central Red Sea show that most scleractinian species release their gametes in the spring, with a majority of species spawning in April. There is, however, a lack of reproductive data for several other coral species, as well as a general lack of data for other invertebrates. Here, we document the detailed timing of spawning for 13 scleractinian coral species, one sea anemone, and six echinoderms from an inshore reef off the coast of Thuwal, Saudi Arabia, in the spring between April and June 2014. Furthermore, inferred from the presence of mature gametes, we report the month of spawning for three additional coral species in the spring. Seven scleractinian coral species were inferred to release their gametes in a second reproductive season, in the autumn, between September and November. This is the first report of a second spawning season in the Arabian region. Biannual spawning has so far been reported on the Great Barrier Reef, in Western Australia, in Indonesia, in Malaysia, in Palau, in Thailand, in Taiwan, and in Western Samoa.     

Red Sea corals under Artificial Light Pollution at Night (ALAN) undergo oxidative stress and photosynthetic impairment

Coral reefs represent the most diverse marine ecosystem on the planet, yet they are undergoing an unprecedented decline due to a combination of increasing global and local stressors. Despite the wealth of research investigating these stressors, Artificial Light Pollution at Night (ALAN) or “ecological light pollution” represents an emerging threat that has received little attention in the context of coral reefs, despite the potential of disrupting the chronobiology, physiology, behavior, and other biological processes of coral reef organisms. Scleractinian corals, the framework builders of coral reefs, depend on lunar illumination cues to synchronize their biological rhythms such as behavior, reproduction and physiology. While, light pollution (POL) may mask and lead de‐synchronization of these biological rhythms process. To reveal if ALAN impacts coral physiology, we have studied two coral species, Acropora eurystoma and Pocillopora damicornis, from the Gulf of Eilat/Aqaba, Red Sea, which is undergoing urban development that has led to severe POL at night. Our two experimental design data revealed that corals exposed to ALAN face an oxidative stress condition, show lower photosynthesis performances measured by electron transport rate (ETR), as well as changes in chlorophyll and algae density parameters. Testing different lights such as Blue LED and White LED spectrum showed more extreme impact in comparison to Yellow LEDs on coral physiology. The finding of this work sheds light on the emerging threat of POL and the impacts on the biology and ecology of Scleractinian corals, and will help to formulate specific management implementations to mitigate its potentially harmful impacts.