Reefs Of Eilat Research Articles

Response of fluorescence morphs of the mesophotic coral Euphyllia paradivisa to ultra-violet radiation

Euphyllia paradivisa is a strictly mesophotic coral in the reefs of Eilat that displays a striking color polymorphism, attributed to fluorescent proteins (FPs). FPs, which are used as visual markers in biomedical research, have been suggested to serve as photoprotectors or as facilitators of photosynthesis in corals due to their ability to transform light. Solar radiation that penetrates the sea includes, among others, both vital photosynthetic active radiation (PAR) and ultra-violet radiation (UVR). Both types, at high intensities, are known to have negative effects on corals, ranging from cellular damage to changes in community structure. In the present study, fluorescence morphs of E. paradivisa were used to investigate UVR response in a mesophotic organism and to examine the phenomenon of fluorescence polymorphism. E. paradivisa, although able to survive in high-light environments, displayed several physiological and behavioral responses that indicated severe light and UVR stress. We suggest that high PAR and UVR are potential drivers behind the absence of this coral from shallow reefs. Moreover, we found no significant differences between the different fluorescence morphs’ responses and no evidence of either photoprotection or photosynthesis enhancement. We therefore suggest that FPs in mesophotic corals might have a different biological role than that previously hypothesized for shallow corals.

Repetitive sex change in the stony coral Herpolitha limax across a wide geographic range

Sex change has been widely studied in animals and plants. However, the conditions favoring sex change, its mode and timing remain poorly known. Here, for the first time in stony corals, we report on a protandrous (youngest individuals are males) repetitive sex change exhibited by the fungiid coral Herpolitha limax across large spatial scales (the coral reefs of Japan, Jordan and Israel) and temporal scales (2004–2017). In contrast to most corals, this species is a daytime spawner (08:00–10:00 AM) that spawned at the same time/same date across all the study sites. The sporadically scattered populations of H. limax among the coral reefs of Eilat (Israel) and Aqaba (Jordan) exhibited significantly slower growth, earlier sex change, and lower percentages of reproduction and sex change in comparison to the densely aggregated populations in Okinawa (Japan). At all sites, sex ratio varied among years, but was almost always biased towards maleness. Growth rate decreased with size. We conclude that comparable to dioecious plants that display labile sexuality in response to energetic and/or environmental constraints, the repetitive sex change displayed by H. limax increases its overall fitness reinforcing the important role of reproductive plasticity in the Phylum Cnidaria in determining their evolutionary success.

Upper mesophotic depths in the coral reefs of Eilat, Red Sea, offer suitable refuge grounds for coral settlement

Due to increasing frequency of disturbances to shallow reefs, it has been suggested that Mesophotic Coral Ecosystems (MCEs, 30–150 m depth) may serve as a refuge for corals and a source of larvae that can facilitate the recovery of shallow degraded reefs. As such, they have received increased attention in the past decade, yet remained understudied regarding recruitment dynamics. Here we describe coral recruitment dynamics on settlement tiles and their adjacent natural habitats (10 m vs. 50 m depths) in Eilat, over a period of 5.5 years. The tiles were deployed along three sites onto 18 racks (3 at each depth and at each site). Recruitment patterns varied both temporally and spatially, ending up to two-fold higher juvenile density and higher recruitment rates at mesophotic sites. Settlement surface preference changed with depth, favoring exposed surfaces in mesophotic waters and cryptic surfaces in shallow waters. Juvenile assemblages differed between depths and were distinct from adjacent natural habitats. Over half of the recruited genera overlapped between depths. We suggest that Eilat MCEs serve as a larval sink, providing settlement grounds for shallow-reef propagules. In view of their significance, we call for the protection of these unique and distinct deep-reef habitats.

Artificial reefs as a means of spreading diving pressure in a coral reef environment

Recreational diving damages coral reefs despite heightened environmental awareness. However, divers prefer preserved coral reefs and therefore reef degradation presents an economic loss. Artificial reefs were suggested among a range of tools to mitigate and reduce divers' negative impact on coral reefs.Coral reefs in Eilat (northern tip of the Red Sea) are among the most densely dived reefs in the world, with an estimated number of dives of up to 350,000 dives a year. At least 7 artificial reefs were deployed in the coastal waters of Eilat, however the divers' visitation on these reefs is not tracked regularly.We found that more than one third of the total dives take place on artificial reefs in Eilat. The divers prefer to vary their diving sites and possess a desire to diversify and expand their diving experience. Thus, the divers are also willing to dive a on artificial reefs, and this is true for both novice and experienced divers. This indicates that artificial reefs can draw divers from natural reefs, thus reducing diving pressure and allowing more sustainable levels of diving on natural coral reefs. This leads us to a conclusion that artificial reefs may be useful in modern reef conservation approaches.

Evaluating the attractiveness and effectiveness of artificial coral reefs as a recreational ecosystem service

Artificial reefs are increasingly being used around the globe to attract recreational divers, for both environmental and commercial reasons. This paper examines artificial coral reefs as recreational ecosystem services (RES) by evaluating their attractiveness and effectiveness and by examining divers' attitudes toward them. An online survey targeted at divers in Israel (n = 263) indicated that 35% of the dives in Eilat (a resort city on the shore of the Red Sea) take place at artificial reefs. A second study monitored divers' behavior around the Tamar artificial reef, one of the most popular submerged artificial reefs in Eilat, and juxtaposed it with divers' activities around two adjacent natural reefs. Findings show that the average diver density at the artificial reef was higher than at the two nearby natural knolls and that the artificial reef effectively diverts divers from natural knolls. A third study that examined the attitudes towards natural vs. artificial reefs found that the artificial reefs are considered more appropriate for training, but that divers feel less relaxed around them. By utilizing the RES approach as a framework, the study offers a comprehensive methodology that brings together the aesthetic, behavioral, and attitudinal aspects in terms of which artificial reefs can be evaluated.

Search for mesophotic octocorals (Cnidaria, Anthozoa) and their phylogeny: I. A new sclerite-free genus from Eilat, northern Red Sea.

This communication describes a new octocoral, Altumia delicata gen. n. & sp. n. (Octocorallia: Clavulariidae), from mesophotic reefs of Eilat (northern Gulf of Aqaba, Red Sea). This species lives on dead antipatharian colonies and on artificial substrates. It has been recorded from deeper than 60 m down to 140 m and is thus considered to be a lower mesophotic octocoral. It has no sclerites and features no symbiotic zooxanthellae. The new genus is compared to other known sclerite-free octocorals. Molecular phylogenetic analyses place it in a clade with members of families Clavulariidae and Acanthoaxiidae, and for now we assign it to the former, based on colony morphology. The polyphyletic family Clavulariidae is, however, in need of a thorough revision once the morphological distinctions among its phylogenetically distinct clades are better understood.

Reproductive strategies of the coral Turbinaria reniformis in the northern Gulf of Aqaba (Red Sea)

Here we describe for the first time the reproductive biology of the scleractinian coral Turbinaria reniformis studied during three years at the coral reefs of Eilat and Aqaba. We also investigated the possibility of sex change in individually tagged colonies followed over a period of 12 years. T. reniformis was found to be a stable gonochorist (no detected sex change) that reproduces by broadcast spawning 5–6 nights after the full moon of June and July. Spawning was highly synchronized between individuals in the field and in the lab. Reproduction of T. reniformis is temporally isolated from the times at which most other corals reproduce in Eilat. Its relatively long reproductive cycle compared to other hermaphroditic corals may be due to the high reproductive effort associated with the production of eggs by gonochoristic females. Sex ratio in both the Aqaba and Eilat coral populations deviated significantly from a 1:1 ratio. The larger number of males than of females may provide a compensation for sperm limitation due to its dilution in the water column. We posit that such sex allocation would facilitate adaptation within gonochoristic species by increasing fertilization success in low density populations, constituting a phenomenon possibly regulated by chemical communication.

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.

Reproduction, abundance and survivorship of two Alveopora spp. in the mesophotic reefs of Eilat, Red Sea.

Although the study of coral reproduction has advanced tremendously over the last few decades, a particular gap exists in our knowledge of the reproductive modes of corals from ‘mesophotic coral ecosystems’ (MCEs) found at 30–150 m depth. Here, we report for the first time on the reproductive patterns, living cover, and survivorship under different light treatments of two scleractinian species from the MCEs of Eilat, Red-Sea: Alveopora allingi and A. ocellata. Both species are found exclusively within MCEs and are high in both abundance and relative cover. These species display a synchronous gametogenic cycles with consecutive oocyte growth and development. Peak of reproductive activity occurs in late summer (September-October), typified by accelerated oocyte growth, coinciding with the rise in seawater temperature. Estimates of fecundity show mean monthly maxima of 48.5 ± 26.3 and 23.5 ± 11.8 (Mean ± SE) oocytes per cm2 for A. allingi and A. ocellata respectively, prior to spawning. A comparison of light and temperature regimes in the shallow vs. MCE environments is presented, and the response of these species to changes in these parameters is discussed. A call encouraging the much-needed studies on the sexuality and reproductive modes of MCE coral species is expressed.

Reproductive features of the Red Sea octocoral Sarcophyton auritum Verseveldt & Benayahu, 1978 are uniform within generic boundaries across wide biogeographical regions

The octocoral Sarcophyton auritum Verseveldt & Benayahu, 1983, is considered endemic to the Red Sea. We investigate here for the first time its distribution on the Eilat reefs and its sexual reproductive features. Quantitative surveys revealed S. auritum is relative rarity with the Morisita index indicating that the colonies exhibit a clumped distribution, frequently growing in groups. This spatial distribution may result from the species’ reproductive features. S. auritum was found to be gonochoric. Female colonies demonstrated a prolonged oogenic cycle (18–21 months), featuring two size groups of oocytes, each presenting a separate developmental cycle. The male spermatogenetic cycle was shorter (8–10 months), with one developmental cycle at a time. Colonies spawned annually on a single night, demonstrating an intraspecific synchronized spawning. The spawning occurred on a full-moon night in July. Cleavage of the embryos can be equal or unequal, resulting in the respective formation of regular blastulae along with bizarre-shaped embryos that subsequently develop into the planulae. The findings indicate that the reproductive features of Sarcophyton soft corals are consistent within the genus, thus supporting the tested hypothesis of the study that among reef soft corals these features are consistent within generic boundaries across all Indo-Pacific regions studied so far.

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

AbstractThe 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.

Grazing Effects of Fish versus Sea Urchins on Turf Algae and Coral Recruits: Possible Implications for Coral Reef Resilience and Restoration

Herbivory is an important structuring factor in coral reefs, influencing seaweed abundance, competitive interactions between seaweeds and corals, and coral reef resilience. Despite reports of a drastic increase in the cover of benthic algae and turf dominancy in the coral reefs of Eilat, Red Sea, very little is known about the factors responsible for this phenomenon or the possible effects of herbivory on turf algae and coral recruits. Here, we examine the effects of herbivory by experimentally exposing turf algae and coral recruits to grazing activities of herbivorous fish and sea urchins. Using remote video cameras to document removal of algae and coral spats, we show that the main grazing impact is due to daily grazing by fishes, whereas the significant impact of sea urchins is mainly expressed in their adverse effect on the survival of coral recruits, with a relatively low effect on algal biomass. These findings contribute to our understanding of the factors influencing turf algae establishment and proliferation, and the survival of coral recruits on the coral reefs of Eilat. The clear differences between the impact of herbivorous fish and that of sea urchins, on the Eilat reefs, have critical implications for reef resilience and restoration measures.

A new species of the genus Boltenia (Ascidiacea) from the Red Sea

Between 2003 and 2008 during surveys and collection of ascidians along the Red Sea coast of Israel several specimens of an undescribed species of Boltenia were collected by SCUBA from man-made structures at 1–20 m depth. This is the first species of the genus Boltenia described from the Red Sea. We name the new species Boltenia yossiloya in honor of Professor Yossi Loya, a world renowned researcher of the coral reefs of Eilat.

Macroalgae in the coral reefs of Eilat (Gulf of Aqaba, Red Sea) as a possible indicator of reef degradation

The current state of health of the coral reefs in the northern Gulf of Aqaba (Red Sea), notably the Eilat reefs, is under debate regarding both their exact condition and the causes of degradation. A dearth of earlier data and unequivocal reliable indices are the major problems hinder a clear understanding of the reef state. Our research objective was to examine coral–algal dynamics as a potential cause and an indication of reef degradation. The community structure of stony corals and algae along the northern Gulf of Aqaba reveal non-seasonal turf algae dominancy in the shallow Eilat reefs (up to 72%), while the proximate Aqaba reefs present negligible turf cover (<6%). We believe that turf dominancy can indicate degradation in these reefs, based on the reduction in essential reef components followed by proliferation of perennial turf algae. Our findings provide further evidence for the severe state of the Eilat coral reefs.

Spatial and temporal photoacclimation of Stylophora pistillata: zooxanthella size, pigmentation, location and clade

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 384:107-119 (2009) - DOI: https://doi.org/10.3354/meps08036 Spatial and temporal photoacclimation of Stylophora pistillata: zooxanthella size, pigmentation, location and clade Gidon Winters1,2,4,*, Sven Beer1, Batsheva Ben Zvi1, Itzik Brickner3, Yossi Loya3 1Department of Plant Sciences, Tel Aviv University, Tel Aviv 69978, Israel 2The Inter-University Institute of Eilat, PO Box 469, Eilat 88103, Israel 3Department of Zoology and the Porter School for Environmental Studies, Tel Aviv University, Tel Aviv 69978, Israel 4Present address: Institute for Evolution and Biodiversity, Westfälische Wilhelms-Universität, Hüfferstrasse 1, 48149 Münster, Germany *Email: wintersg@post.tau.ac.il ABSTRACT: Photoacclimation of the symbiotic hermatypic coral Stylophora pistillata was studied both for colonies growing at different depths (1 to 20 m) sampled within the same season (‘spatial photoacclimation’) and for colonies growing at the same depth (5 m) but sampled throughout the year (‘temporal photoacclimation’). Specimens were darker and had increased chlorophyll densities (chlorophyll per coral surface area) under low-light conditions caused both by increased depth and, in shallow-growing specimens, by the winter season. However, while increased depth involved increased zooxanthella chlorophyll content, acclimation to low irradiances by shallow-growing corals during the winter mostly involved an increase in algal density. In shallow-growing corals, both zooxanthella chlorophyll content and coral chlorophyll density fluctuated seasonally in correlation with light more than with nitrogen or temperature. This could be related to the fact that reefs in Eilat, Israel, are exposed to more solar radiation than many other reefs in the world. Histological analyses of high-light corals showed that zooxanthellae were located deeper inside the host tissue and were smaller in diameter compared to zooxanthellae from low-light corals. Additionally, while deep-water colonies hosted clade C zooxanthellae, colonies growing in shallow waters, both in high- and very low-light environments, hosted clade A. These clade differences were found to affect coral physiology, as examined in a short-term thermal stress experiment, with clade-A colonies having higher thermal resilience than clade-C colonies. Taken together, our results show evidence of different mechanisms that help adjust the light-capturing abilities of S. pistillata zooxanthellae to spatial and temporal changes in irradiance. KEY WORDS: Spatial photoacclimation · Temporal photoacclimation · Stylophora pistillata · Zooxanthella clade · Zooxanthella location · Zooxanthella pigments Full text in pdf format PreviousNextCite this article as: Winters G, Beer S, Zvi BB, Brickner I, Loya Y (2009) Spatial and temporal photoacclimation of Stylophora pistillata: zooxanthella size, pigmentation, location and clade. Mar Ecol Prog Ser 384:107-119. https://doi.org/10.3354/meps08036Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 384. Online publication date: May 29, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Population dynamics of a coral reef ascidian in a deteriorating environment

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 367:163-171 (2008) - DOI: https://doi.org/10.3354/meps07579 Population dynamics of a coral reef ascidian in a deteriorating environment N. Shenkar*, O. Bronstein, Y. Loya Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel *Email: levinn@post.tau.ac.il ABSTRACT: In the coral reefs of Eilat, a newly described colonial ascidian, Botryllus eilatensis, has been observed overgrowing dead coral skeletons and rapidly colonizing artificial substrates. To study overgrowth dynamics and the relationship between coral morphology, size, and orientation and ascidian overgrowth we monitored (monthly) the interaction of 50 to 70 tagged coral colonies with B. eilatensis. The rate of B. eilatensis overgrowth on corals was influenced by the coral’s morphology and orientation combined with a seasonal appearance of the ascidian. During spring, the average ascidian cover was 27 ± 4.6 % (mean ± SE), decreasing rapidly during the summer months when sexual reproduction took place. This seasonality is linked to the vertical mixing phenomenon that occurs in Eilat every winter. Moreover, fragments of B. eilatensis translocated to a nutrient-rich site increased 3-fold in size and exhibited higher survivorship rates in comparison to the fragments at the original site. Increased anthropogenic activity, particularly the eutrophication occurring along the Israeli coasts, creates favorable conditions for filter-feeding organisms such as ascidians, providing them with an advantage in competition for space over reef-building corals and other organisms. KEY WORDS: Eutrophication · Red Sea · Tunicates · Filter-feeding Full text in pdf format PreviousNextCite this article as: Shenkar N, Bronstein O, Loya Y (2008) Population dynamics of a coral reef ascidian in a deteriorating environment. Mar Ecol Prog Ser 367:163-171. https://doi.org/10.3354/meps07579 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 367. Online publication date: September 11, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Habitat selection and the colonization of new territories by Chromis viridis

The settlement and recruitment patterns of Chromis viridis were followed during three consecutive seasons along the reefs of Eilat, Red Sea. The findings, based on intensive field surveys and a translocation experiment, indicated a strong and repeatable preference for some, but not other, colonies of the branching coral Acropora eurystoma; with significantly more larvae settling onto preferred colonies that house conspecific adults and juveniles. Furthermore, these findings showed that, given high recruitment rates, settlement‐site selection could drive migration by adults and older juveniles. As only some C. viridis schools received direct settlement, it was suggested that settlement‐driven migration is responsible for the replenishment of those schools that do not receive settlement and to the colonization of previously unoccupied coral colonies.

Coral recruitment to the reefs of Eilat, Red Sea: temporal and spatial variation, and possible effects of anthropogenic disturbances

The accelerating deterioration of the coral reefs of Eilat has raised debate over the exact causes and how they affect the reefs. The hypothesis of the present study was that a low recruitment rate of reef-building coral species may play an important role in the decline of the Eilat reefs. Our goal was to assess spatial and temporal recruitment patterns in Eilat, focusing on examining the possible impact of human activities. The results of coral recruitment to 10 series of ceramic tiles on metal racks, revealed very low overall recruitment relative to other geographical regions. In addition, we found that recruitment rates and recruit survival were lowest at sites closest to the major eutrophication sources in Eilat. The low recruitment rates may be chronically too low to compensate for the elevated coral mortality rates of recent years. The significant differences between the present study and a similar study carried out during the same period using a different method, emphasize the crucial need for a standardized method for recruitment assessment in coral reefs worldwide.

Do clades of symbiotic dinoflagellates in scleractinian corals of the Gulf of Eilat (Red Sea) differ from those of other coral reefs?

The symbiotic association between corals and zooxanthellae has been a major contributing factor in the success of reef-building corals. Most of these endocellular microalgal symbionts belong to the dinoflagellate genus Symbiodinium. However, considerable genetic diversity was revealed within this taxon, as is evident in the several clades of Symbiodinium found in association with hermatypic corals all over the world. The coral reefs of Eilat (Aqaba), where winter temperature minima of 21 °C are close to threshold values that prevent reef development, are among the northernmost reefs in the world. Furthermore, due to the circulation patterns of the Gulf, the extremely high evaporation, and lack of any riverine inputs, the Gulf's waters are highly saline (40.5‰). In spite of the extreme location, a high diversity of coral species has been reported in this area. In this study, using PCR, we specifically amplified zooxanthellae 18S ribosomal DNA from symbionts of 11 coral species, and analyzed it with respect to RFLP and DNA sequence. Of the several clades described from the same coral hosts in other localities, only A and C were found in the present study. Symbiodinium populations in the host examined from Eilat were different relative to other parts of the world. This distribution is discussed in relation to reproduction strategy: broadcasting versus brooding. Based on our results, we suggest that clade A is transferred through a closed system. As mass bleaching in the Gulf has never been observed, we suggest that the adaptive mechanisms presumably favoring clade diversity were not yet significant in our relatively cool area.

Nutrient enrichment caused by in situ fish farms at Eilat, Red Sea is detrimental to coral reproduction

Recent studies report conflicting results concerning the effects of eutrophication on coral reproduction. The present study examines reproductive effort in the brooding coral Stylophora pistillata exposed to chronic eutrophication caused by in situ fish cages (FC) in the northern Gulf of Eilat (Aqaba). Histological studies of 20 S. pistillata colonies transplanted to each of two study sites, one close to the nutrient enriched FC site and the other at a reference site (IUI), 8 km southwest of the FC site, show that, overall, corals from the FC site have a significantly higher percentage of polyps containing oocytes and testes than corals from the IUI site. However, average oocyte size and the percentage of oocytes reaching the size at which fertilization occurs (i.e., >200 μm) were both significantly greater in colonies at the IUI site compared to the FC site. As the reproductive season progressed, colonies at the IUI site exhibited a decrease in the percentage of polyps containing oocytes, concomitant with an increase in the number of polyps containing planulae, indicating successful development of oocytes into planulae. In contrast, in colonies at the FC site oocyte numbers were greatest at the end of the reproductive season, and overall, numbers of planulae were significantly lower compared with the IUI colonies, suggesting relative failure of oocyte maturation, fertilization and ensuing larval development. The significantly higher lipid content found during the reproduction season in IUI colonies compared with FC colonies corroborates this assertion. This data strongly suggest that nutrients released from the fish farms have adverse effects on successful production of larvae of S. pistillata. In view of the recent severe deterioration of the coral reefs of Eilat and their present critical state of health, the only chance for their renewal is the use of immediate, prudent and rational protection measures against all man-made perturbations.