Cnidarian internal stinging mechanism

Stinging mechanisms generally deliver venomous compounds to external targets. However, nematocysts, the microscopic stinging organelles that are common to all members of the phylum Cnidaria, occur and act in both external and internal tissue structures. This is the first report of such an internal piercing mechanism. This mechanism identifies prey items within the body cavity of the sea anemone and actively injects them with cytolytic venom compounds. Internal tissues isolated from sea anemones caused the degradation of live Artemia salina nauplii in vitro. When examined, the nauplii were found to be pierced by discharged nematocysts. This phenomenon is suggested to aid digestive phagocytic processes in a predator otherwise lacking the means to masticate its prey.

Bidirectional sex change in mushroom stony corals

Sex change occurs when an individual changes from one functional sex to another. The direction of sex change occurs mainly from male to female (protandry) or vice versa (protogyny), but sometimes may be bidirectional (repetitive). Here, for the first time in stony corals, we report on a protandrous sex change exhibited by two mushroom corals, Fungia repanda and Ctenactis echinata, with the latter also exhibiting bidirectional sex change. Compared with C. echinata, F. repanda exhibited relatively earlier sex change, significantly slower growth and higher mortality rates, in accordance with sex-allocation theory. Sex ratio in both the species was biased towards the first sex. The bidirectional sex change displayed by C. echinata greatly resembles that of dioecious plants that display labile sexuality in response to energetic and/or environmental constraints. We posit that, similar to these plants, in the studied corals, sex change increases their overall fitness, reinforcing the important role of reproductive plasticity in scleractinian corals in determining their evolutionary success.

Ascidian recruitment patterns on an artificial reef in Eilat (Red Sea)

Although ascidians are conspicuous members of the fouling community not much is known regarding their recruitment patterns in coral reefs. A 1-year study was carried out along the Red Sea coast of Israel to examine the effects of season and spatial distribution on ascidian recruitment to artificial marine structures. In general, autumn and spring were characterized by higher coverage with a significantly higher percentage of cover of Didemnum granulatum in autumn and higher numbers of Herdmania momus in spring. These species contributed the most to similarity between treatments consequently setting the pattern for each group (colonial and solitary). Halocynthia spinosa had significantly higher numbers during winter and Phallusia nigra was absent in spring and winter. H. momus showed a preference for horizontal surfaces. P. nigra and Ascidia cannelata showed a preference for floating units. It is concluded that the ascidian recruitment patterns are species-specific and vary between seasons, orientation and position on the substrata and in the water column.

Coral disease diagnostics: what's between a plague and a band?

Recently, reports of coral disease have increased significantly across the world's tropical oceans. Despite increasing efforts to understand the changing incidence of coral disease, very few primary pathogens have been identified, and most studies remain dependent on the external appearance of corals for diagnosis. Given this situation, our current understanding of coral disease and the progression and underlying causes thereof is very limited. In the present study, we use structural and microbial studies to differentiate different forms of black band disease: atypical black band disease and typical black band disease. Atypical black band diseased corals were infected with the black band disease microbial consortium yet did not show any of the typical external signs of black band disease based on macroscopic observations. In previous studies, these examples, here referred to as atypical black band disease, would have not been correctly diagnosed. We also differentiate white syndrome from white diseases on the basis of tissue structure and the presence/absence of microbial associates. White diseases are those with dense bacterial communities associated with lesions of symbiont loss and/or extensive necrosis of tissues, while white syndromes are characteristically bacterium free, with evidence for extensive programmed cell death/apoptosis associated with the lesion and the adjacent tissues. The pathology of coral disease as a whole requires further investigation. This study emphasizes the importance of going beyond the external macroscopic signs of coral disease for accurate disease diagnosis.

The Coral Probiotic Hypothesis

Emerging diseases have been responsible for the death of about 30% of corals worldwide during the last 30 years. Coral biologists have predicted that by 2050 most of the world's coral reefs will be destroyed. This prediction is based on the assumption that corals can not adapt rapidly enough to environmental stress-related conditions and emerging diseases. Our recent studies of the Vibrio shiloi/Oculina patagonica model system of the coral bleaching disease indicate that corals can indeed adapt rapidly to changing environmental conditions by altering their population of symbiotic bacteria. These studies have led us to propose the Coral Probiotic Hypothesis. This hypothesis posits that a dynamic relationship exists between symbiotic microorganisms and environmental conditions which brings about the selection of the most advantageous coral holobiont. Changing their microbial partners would allow the corals to adapt to changing environmental conditions more rapidly (days to weeks) than via mutation and selection (many years). An important outcome of the Probiotic Hypothesis would be development of resistance of the coral holobiont to diseases. The following evidence supports this hypothesis: (i) Corals contain a large and diverse bacterial population associated with their mucus and tissues; (ii) the coral-associated bacterial population undergoes a rapid change when environmental conditions are altered; and (iii) although lacking an adaptive immune system (no antibodies), corals can develop resistance to pathogens. The Coral Probiotic Hypothesis may help explain the evolutionary success of corals and moderate the predictions of their demise.

Energy integration between the solitary polyps of the clonal coral Lobophyllia corymbosa

Clonal integration in the coral Lobophyllia corymbosa was studied from two perspectives: transfer of carbon among clonemates and allorecognition. This coral forms colonies in the early post-metamorphic stages. In later ontogeny, the tissues interconnecting polyps die,transforming the colony into a clone of solitary polyps. These polyps continue to live in close proximity but without tissue continuity. Isolated polyps labeled with radioactive carbon in the light showed oriented transfer of assimilates towards adjacent, injured polyps. No significant transfer of carbon was observed towards intact, isogeneic polyps or allogeneic polyps. Grafting of coral tissues resulted in intra-clonal fusion, but only when polyps were previously sectioned. Allogeneic sectioned grafts were always rejected. Intact polyps were unresponsive towards isogeneic and allogeneic counterparts when grafted. Our results show that isolated Lobophylliapolyps not only recognize their clonemates as such, but also help them when necessary, although no tissue continuity exists between them.

The mitochondrial 60-kDa heat shock protein in marine invertebrates: biochemical purification and molecular characterization

Sessile marine invertebrates undergo constant direct exposure to the surrounding environmental conditions, including local and global environmental fluctuations that may lead to fatal protein damage. Induction of heat shock proteins (Hsps) constitutes an important defense mechanism that protects these organisms from deleterious stress conditions. In a previous study, we reported the immunological detection of a 60-kDa Hsp (Hsp60) in the sea anemone Anemonia viridis (formerly called Anemonia sulcata) and studied its expression under a variety of stress conditions. In the present study, we show that the sponge Tetilla sp. from tidal habitats with a highly variable temperature regime is characterized by an increased level of Hsp60. Moreover, we show the expression of Hsp60 in various species among Porifera and Cnidaria, suggesting a general importance of this protein among marine invertebrates. We further cloned the hsp60 gene from A viridis, using a combination of conventional protein isolation methods and screening of a complementary deoxyribonucleic acid library by polymerase chain reaction. The cloned sequence (1764 bp) encodes for a protein of 62.8 kDa (588 amino acids). The 62.8-kDa protein, which contains an amino terminal extension that may serve as a mitochondrial targeting signal, shares a significant identity with mitochondrial Hsp60s from several animals but less identity with Hsp60s from either bacteria or plants.

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 microm) 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.

Coastal coal pollution increases Cd concentrations in the predatory gastropod Hexaplex trunculus and is detrimental to its health

Parameters of environmental health, including paracellular permeability of external epithelia, functional state of lysosomes and the level of metallothioneins (MTs), were examined using fluorescent markers and vital microfluorometry in different tissues of the marine gastropod, Hexaplex trunculus, from a coal-polluted and coal-free site. Vital microfluorometrical examinations exhibited enhanced paracellular permeability of external epithelia to the anionic marker, fluorescein (FLU), lower lysosomal accumulation of neutral red (NR) as well as higher levels of MTs, when compared with epithelia of gastropods from the coal-free site. Those differences were particularly marked in the foot epithelium, which is in direct contact with the substrate. In addition, cadmium was measured by ICP-AES in the hepatopancreas of gastropods sampled from the coal-polluted site and two coal-free sites. Significantly higher levels of Cd were found in gastropod hepatopancreas from the coal-polluted site. In addition, two months feeding experiments conducted in aquaria containing: (a) coal pieces covered by barnacles; (b) natural rocks covered by barnacles; and (c) natural rocks with barnacles + bare coal pieces, demonstrated significant increase of Cd concentration in the hepatopancreas of the gastropods exposed to coal. We suggest that coal in the marine environment has detrimental effects on marine gastropods, both directly through contact with the organisms and indirectly through the food web.

Deterioration Index (DI): a suggested criterion for assessing the health of coral communities

The extensive deterioration of coral reefs worldwide highlights the importance of creating efficient monitoring methods to best assess their state of health. At present, several suggested parameters serve such indicators. None of these, however, is well accepted as reliably representing reef community health. In the present study we examine a new approach based on the ratio between mortality and recruitment rates of branching corals, which we term 'Deterioration Index' (DI). It aims at providing a quantitative indication of the state of health of reef-building coral communities. The method was developed and tested on 16 coral communities on artificially laid rocks along the coast of Eilat, Red Sea (Gulf of Aqaba). In contrast to frequently used indices (i.e. mortality rate, abundance and species richness), which did not demonstrate a consistent result in comparing disturbed vs. undisturbed coral communities, the DI revealed significant differences between these communities. Our results suggest that the use of the DI may enable the detection of disturbed coral communities in one instance monitoring, where the other parameters had failed. The DI, therefore, may provide a comparable quantitative assessment of the deterioration process and its intensity in a coral community. We propose the DI approach as an efficient and applicable tool for coral reef monitoring.

The marine fireworm Hermodice carunculata is a winter reservoir and spring-summer vector for the coral-bleaching pathogen Vibrio shiloi

Vibrio shiloi, the causative agent of bleaching of the coral Oculina patagonica in the Mediterranean Sea, is present in all bleached O. patagonica corals in the summer (25-30 degrees C), but can be not detected in the coral during the winter (16-20 degrees C). Furthermore, the pathogen can not survive in O. patagonica at temperatures below 20 degrees C. Using fluorescence in situ hybridization (FISH) with a V. shiloi-specific oligonucleotide probe, we found that the marine fireworm Hermodice caranculata is a winter reservoir for V. shiloi. Worms taken directly from the sea during the winter contained approximately 10(8) V. shiloi per worm by FISH analysis. However, colony-forming units (cfu) revealed only 4.1-18.3 x 10(4) V. shiloi per worm, indicating that approximately 99.9% of them were in the viable-but-not-culturable (VBNC) state. When worms were infected with V. shiloi, most of the bacteria adhered to the worm within 24 h and then penetrated into epidermal cells. By 48 h, less than 10(-4) of the intact V. shiloi in the worm gave rise to colonies, suggesting that they differentiated inside the worm into the VBNC state. When worms infected with V. shiloi were placed in aquaria containing O. patagonica, all of the corals showed small patches of bleached tissue in 7-10 days and total bleaching in 17 days. This is the first report of a reservoir and vector for a coral disease.

Endolithic algae: an alternative source of photoassimilates during coral bleaching

Recent reports of worldwide coral bleaching events leading to devastating coral mortality have caused alarm among scientists and resource managers. Differential survival of coral species through bleaching events has been widely documented. We suggest that among the possible factors contributing to survival of coral species during such events are endolithic algae harboured in their skeleton, providing an alternative source of energy. We studied the dynamics of photosynthetic pigment concentrations and biomass of endoliths in the skeleton of the encrusting coral Oculina patagonica throughout a bleaching event. During repeated summer bleaching events these endolithic algae receive increased photosynthetically active radiation, increase markedly in biomass, and produce increasing amounts of photoassimilates, which are translocated to the coral. Chlorophyll concentrations and biomass of endoliths were 4.6 +/- 1.57 and 1570 +/- 427 microg cm(-2) respectively, in skeletons of relatively healthy colonies (0-40% bleaching) but up to 14.8 +/- 2.5 and 4036 +/- 764 microg cm(-2) endolith chlorophyll and biomass respectively, in skeletons of bleached colonies (greater than 40% bleaching). The translocation dynamics of (14)C-labelled photoassimilates from the endoliths to bleached coral tissue showed significantly higher 14C activity of the endoliths harboured within the skeletons of bleached corals than that of the endoliths in non-bleached corals. This alternative source of energy may be vital for the survivorship of O. patagonica, allowing gradual recruitment of zooxanthellae and subsequent recovery during the following winter.

The effect of gravity on coral morphology

Coral morphological variability reflects either genetic differences or environmentally induced phenotypic plasticity. We present two coral species that sense gravity and accordingly alter their morphology, as characterized by their slenderness (height to diameter) ratio (SR). We experimentally altered the direction (and intensity) of the gravitational resultant force acting along or perpendicular to the main body axis of coral polyps. We also manipulated light direction, in order to uncouple gravity and light effects on coral development. In the experiments, vertically growing polyps had significantly higher SR than their horizontal siblings even when grown in a centrifuge (experiencing different resultant gravitational forces in proximal and distal positions). Lowest SR was in horizontal side-illuminated polyps, and highest in vertical top-illuminated polyps. Adult colonies in situ showed the same pattern. Gravitational intensity also affected polyp growth form. However, polyp volume, dry skeleton weight and density in the various centrifuge positions, and in aquaria experiments, did not differ significantly. This reflects the coral's ability to sense altered gravity direction and intensity, and to react by changing the development pattern of their body morphology, but not the amount of skeleton deposited.

The 60-kDa heat shock protein (HSP60) of the sea anemone Anemonia viridis: a potential early warning system for environmental changes

Expression of heat shock proteins (HSPs) is often correlated with adaptation to environmental stress. We examined the role of HSP60 (60 kDa) in acclimatization to thermal stress in the sea anemone Anemonia viridis. Using monoclonal antibodies, we identified HSP60 in sea anemones for the first time, and showed that its expression varied with changes in seawater temperature (SWT). Anemonia viridis displayed high levels of HSP60 when extreme temperatures prevailed in stressful habitats such as tidal pools. Specimens sampled from different temperature layers in the same tidal pool differed in their levels of HSP60. Specimens from subtidal zones exhibited a seasonal pattern of expression of HSP60, according to the seasonal SWT. The level of HSP60 was significantly higher in the summer (SWT, 31 degrees C) than in other seasons throughout the year. This study suggests the use of HSP60 expression as a tool for stress detection in marine invertebrates.

Vibrio shiloi sp. nov., the causative agent of bleaching of the coral Oculina patagonica

The aetiological agent of bleaching of the coral Oculina patagonica was characterized as a new Vibrio species on the basis of 16S rDNA sequence, DNA-DNA hybridization data and phenotypic properties, including the cellular fatty acid profile. Based on its 16S rDNA and DNA-DNA hybridization, the new Vibrio species is closely related to Vibrio mediterranei. The name Vibrio shiloi sp. nov. is proposed for the new coral-bleaching species, the type strain being AK1T (= ATCC BAA-91T = DSM 13774T).

Role of endosymbiotic zooxanthellae and coral mucus in the adhesion of the coral-bleaching pathogen Vibrio shiloi to its host

Vibrio shiloi, the causative agent of bleaching the coral Oculina patagonica in the Mediterranean Sea, adheres to its coral host by a beta-D-galactopyranoside-containing receptor on the coral surface. The receptor is present in the coral mucus, since V. shiloi adhered avidly to mucus-coated ELISA plates. Adhesion was inhibited by methyl-beta-D-galactopyranoside. Removal of the mucus from O. patagonica resulted in a delay in adhesion of V. shiloi to the coral, corresponding to regeneration of the mucus. DCMU inhibited the recovery of adhesion of the bacteria to the mucus-depleted corals, indicating that active photosynthesis by the endosymbiotic zooxanthellae was necessary for the synthesis or secretion of the receptor. Further evidence of the role of the zooxanthellae in producing the receptor came from a study of adhesion of V. shiloi to different species of corals. The bacteria failed to adhere to bleached corals and white (azooxanthellate) O. patagonica cave corals, both of which lacked the algae. In addition, V. shiloi adhered to two Mediterranean corals (Madracis and Cladocora) that contained zooxanthellae and did not adhere to two azooxanthellate Mediterranean corals (Phyllangia and Polycyathus). V. shiloi demonstrated positive chemotaxis towards the mucus of O. patagonica. The data demonstrate that endosymbiotic zooxanthellae contribute to the production of coral mucus and that V. shiloi infects only mucus-containing, zooxanthellate corals.