Floating and fixed artificial habitats: Spatial and temporal patterns of benthic communities in a coral reef environment

While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column.     

Effect of an exotic prey on the feeding pattern of a predatory snail

The mussel Brachidontes pharaonis, which invaded the Mediterranean from the Red Sea about 120 years ago, has recently become abundant in many midlittoral and some infralittoral rocky habitats along the Israeli rocky shore. We investigated the influence of B. pharaonis, as a novel prey, on the foraging patterns of the large whelk Stramonita haemastoma in the field, and examined food preferences in the laboratory. S. haemastoma has shifted from indigenous species to feeding on the novel mussel when abundant. The whelk prefers to prey upon the invasive mussel over all indigenous species offered (e.g. barnacles and mussels), probably due to its larger size. In the midlittoral zone, the foraging activity of S. haemastoma is considerably low even where refuges are readily available (incisioned-rocks) and food density is high (mainly B. pharaonis). Higher proportions of whelks are actively foraging in the infralittoral zone but usually on smaller prey, mostly barnacles. We suggest that this differential foraging activity in the two zones is related to the degree of exposure to wave action. The midlittoral is inherently more exposed to wave action than the infralittoral, where sea conditions are more benign and the whelks may enjoy longer activity periods.     

Epimenia arabica spec, nov., a Solenogaster (Mollusca) Feeding on the Alcyonacean Scleronephthya corymbosa (Cnidaria) from Shallow Waters of the Red Sea

Abstract. The body organization and some biological data of Epimenia arabica , a new species of Sotenogastres of the order Cavibelonia , are presented. The species is described based on four large-sized specimens (13–21 cm × 0.7-1 cm) from three different localities off the coast of the Sinai Peninsula (Red Sea). It feeds on Scleronephthya corymbosa V erseveldt & C ohen ( Octocorallia: Alcyonacea ), generally at depths of 2–5 meters.     

Can artificial reefs mimic natural reef communities? The roles of structural features and age

In light of the deteriorating state of coral reefs worldwide, the need to rehabilitate marine environments has greatly increased. Artificial reefs (ARs) have been suggested as a tool for reef conservation and rehabilitation. Although successions of AR communities have been thoroughly studied, current understanding of the interactions between artificial and natural reefs (NRs) is poor and a fundamental question still to be answered is that of whether AR communities can mimic adjacent NR communities. We suggest three alternative hypotheses: Neighboring ARs and NRs will (1) achieve a similar community structure given sufficient time; (2) be similar only if they possess similar structural features; (3) always differ, regardless of age or structural features. We examined these hypotheses by comparing the community structure on a 119-year old shipwreck to a neighboring NR. Fouling organisms, including stony and soft corals, sponges, tunicates, sea anemones and hydrozoans were recorded and measured along belt transects. The ahermatypic stony coral Tubastrea micrantha dominated vertical AR regions while the soft corals Nephthea sp. and Xenia sp. dominated both artificial and natural horizontal surfaces. Our results support the second hypothesis, indicating that even after a century an AR will mimic its adjacent NR communities only if it possesses structural features similar to those of the natural surroundings. However, if the two differ structurally, their communities will remain distinct.     

Parity and disparity between two Chama oysters: the reproductive biology of the Indo-Pacific C. pacifica Broderip,invasive to the Mediterranean Sea; and C. savignyi Lamy,indigenous to the Red Sea

The Indo-Pacific oyster Chama pacifica Broderip, 1835 (Mollusca, Bivalvia, Chamidae) is rarely found in the Northern Red Sea reefs of Eilat (Gulf of Aqaba), where it is outnumbered by its indigenous congener, Chama savignyi Lamy, 1921. The influx of Eritrean biota from the Red Sea into the Mediterranean Sea via the Suez Canal has led to the formation of massive Chama oyster beds along the Eastern Mediterranean shore. However, unlike the Northern Red Sea, the Eastern Mediterranean Chama beds are dominated by C. pacifica oysters, whereas C. savignyi is absent from this region. In an attempt to understand this difference in their respective distribution, the reproductive biology of both species was compared. Histological analysis of the male and female gonads, monitored monthly from March 2009 to August 2010 in both regions, revealed a similar reproductive cycle, comprising six stages: onset of gametogenesis, advanced gametogenesis, ripe, ready to spawn, spent and sexual rest. Female gonads demonstrated an additional, seventh stage – restoration, coinciding with inferred spawning of ripe gametes. Both species were found to be dioecious spawners, with a single, annual, temperature-dependent inferred spawning period. Chama pacifica was found to reproduce efficiently in maximal Mediterranean seawater temperatures not experienced by the Northern Red Sea Chama populations. This study demonstrates the high invasive potential of an oyster species despite its rarity in its source region.     

Pre- and post-1998 ENSO records of shallow-water octocorals (Alcyonacea) in the Chagos Archipelago

When compared, principal octocorals collected in the Chagos Archipelago before and after the 1998 ENSO shared many common taxa. While a few discontinuities in their biodiversity revealed subtle changes in more persistent genera (Lobophytum, Sarcophyton), some fast-growing “fugitive” genera (e.g. Cespitularia, Efflatounaria, Heteroxenia) disappeared after the ENSO-related coral bleaching. Such transient fugitives might thus be eliminated from soft coral communities on isolated reef systems, possibly in the long term, by events of this nature. The appearance of Carijoa riseii, a species often considered a fouling organism, even an invasive, may well be indicative of reef degradation during the ENSO event. The post-ENSO recovery manifested by this fauna nevertheless gives cause for hope for their survival in the face of climate change.     

Response of the soft coral Heteroxenia fuscescens to ultraviolet radiation regimes as reflected by mycosporine-like amino acid biosynthesis

The variation in mycosporine‐like amino acid (MAA) concentration in the soft coral Heteroxenia fuscescens in relation to changes in ultraviolet radiation (UVR) regimes was investigated at the Gulf of Eilat, northern Red Sea. Solar radiation (300–700 nm) was measured for different depths and seasons. The UVR irradiance was measured to a depth of 25 m on the reef. The mean attenuation coefficient for UV‐B measured in winter was twofold that of the summer value. Separation of H. fuscescens extracts by reverse‐phase isocratic high‐performance liquid chromatography revealed a single MAA compound, palythine (λ_max = 320 nm). Possible seasonal changes in MAAs in colonies of H. fuscescens along a depth gradient were examined on different dates. Palythine concentrations in the colonies were significantly higher in summer than in the other seasons particularly in shallow water. Possible changes in MAA content in colonies of H. fuscescens as a result of UVR protection, were determined by experiments conducted for periods of 1 week, 1 month and 3 months, at a depth of 5 m. In these experiments colonies were removed from the natural substrate and placed underwater, protected from UVR by a PVC filter. Significant differences between UV‐exposed and protected colonies of H. fuscescens were found only in the 3‐month experiment conducted during the summer. These findings demonstrate that UVR is an important environmental factor regulating MAA biosynthesis in the soft coral H. fuscescens.     

Metamorphosis of Heteroxenia fuscescens planulae (Cnidaria: octocorallia) is inhibited by crude oil: a novel short term toxicity bioassay

By using TPA (12-tetra-decanoyl-phorbol-13-acetate) an artificial inducer for metamorphosis, it was possible to determine the effect of crude oil on settlement and metamorphosis of planulae of the soft coral Heteroxenia fuscescens. In the absence of crude oil, TPA induced metamorphosis in 97% of these planulae. The effect of crude oil on metamorphosis and appearance of deformed primary polyps was concentration dependent. Only 50% of the planulae grown in experimental vessels with crude oil at a concentration of 0.1 ppm covering the bottom and walls of the vessels underwent metamorphosis when triggered by TPA. Of those planulae exposed to 100 ppm of the pollutant only 3% metamorphosed after being induced by TPA. Furthermore, oil film on the water surface was less toxic to the larvae than the crude oil covering the bottom and walls of the experimental vessels. Some of the oil treated planulae died, while others remained viable, looked normal, but did not metamorphose after being presented with TPA. These findings suggest that even at very low concentrations crude oil affects larvae of H. fuscescens preventing their settlement and metamorphosis. Therefore it is possible that oil spills affect coral recruitment by decreasing the viability and the settlement of coral planulae. This assay represents a new sensitive bioindicator to detect the impact of oil pollution on tropical and subtropical marine environments.     

Recruitment of benthic organisms onto a planned artificial reef: shifts in community structure one decade post-deployment

Most artificial reef (AR) studies have examined the early colonization stages of benthic communities, while only a few have monitored the development of AR communities beyond the initial successional phases and evaluated the time scale needed for such development. In addition, despite the proliferation of AR studies, comparative studies between artificial and natural reefs (NRs) are scarce. We present here the monitoring results of initial (1-2 year) and progressed (10 year) stages of the developing benthic communities of a purpose-planned AR submerged at Eilat, Israel (Red Sea), and compare them to its adjacent NR. Visual surveys of macro-invertebrates were conducted on the initial stages and coral communities were characterized at the progressed stage, using belt transects. The results demonstrate a distinct shift in species composition of the AR communities along the monitoring periods: from a soft coral dominated community, comprised mainly of Dendronephthya hemprichi, in initial developmental stages of up to two years post-deployment, to a community dominated by the sponge Crella cyatophora at year 10. Distinct differences in coral species count, living cover and diversity were found between the AR and its neighboring NR. We estimate the time frame required to develop a progressed diverse AR community to be well over a decade, even in tropical ecosystems. The factors shaping the species composition of purpose-designed ARs in a coral reef environment, including structural design, spatial orientation, depth and age, are discussed.     

Coral reefs of the Glorieuses Islands,western Indian Ocean

The benthic fauna on reefs around the Glorieuses Islands, a small and protected Indian Ocean archipelago northwest of Madagascar, was surveyed in November 2015, focusing particularly on the orders Alcyonacea (soft corals and gorgonians) and Scleractinia (stony corals). The species richness of both groups was rather low for a protected, relatively pristine environment in the region. Though certain soft ‘fugitive’ alcyonacean species were noticeably abundant, other soft corals were rare. Sediment-tolerant faviid corals were abundant among the scleractinians. The sediment around the reefs was fine-grained and white, and appeared to be derived from abundant green macroalgae Halimeda and coralline seaweeds. The abundance of these, in turn, might have been attributable to nutrient enrichment from guano deposited on one of the islands by migratory seabirds, causing the aforementioned anomalies in coral biodiversity and abundance.