Heteroxenia Fuscescens Research Articles

Motility of zooxanthellae isolated from the Red Sea soft coral Heteroxenia fuscescens (Cnidaria)

Unicellular dinoflagellate algae are among the best examples of organisms that exhibit biological clocks. This study examined the effect of light regime on rhythmicity of motility in the symbiotic dinoflagellate Symbiodinium sp., freshly isolated from the soft coral Heteroxenia fuscescens (Ehrenberg). Freshly isolated algal cells, placed under a 12-h L:12-h D cycle, exhibited motility with a diel rhythm. This motility occurred only during the period of illumination and lasted 8–9 h, with a peak at 2.5–4 h after lights on. Algal cells placed in an inverted light regime inverted their motility pattern. The response to the L/D regime was very precise, and even a 1-h shift backward or forward affected initiation of motility and time of its maximal peak. When placed in either constant light or dark, algal motility ceased until the L/D cycle was restored. These findings suggest that the rhythm is entrained by light cues and is not due to an endogenous circadian rhythm. Further, we provide evidence that the presence of juvenile hosts does not affect the algal motility pattern. These results offer the first evidence for the lack of impact by the host on rhythmicity of motility of free-living algal cells. The motility pattern found in freshly isolated algae may indicate the presence of light-induced diel rhythmicity in yet-to-be described free-living Symbiodinium.

Development and survivorship of zooxanthellate and azooxanthellate primary polyps of the soft coral Heteroxenia fuscescens: laboratory and field comparisons

The zooxanthellate Red Sea soft coral Heteroxenia fuscescens releases aposymbiotic planulae nearly all year round, with higher numbers in the summer than in other seasons. After metamorphosis, primary polyps become infected with symbiotic dinoflagellates (zooxanthellae), derived from the ambient seawater. This study compares aspects of development and survivorship of metamorphic stages of H. fuscescens in relation to onset of infection by the algal symbionts in the laboratory and the field. We revealed no distinct differences in the timing and sequence of morphogenetic events during metamorphosis between zooxanthellate and azooxanthellate primary polyps in the laboratory. In the field, the polyps exhibited higher developmental synchronization during the first days after metamorphosis compared to the laboratory-reared ones, probably as result of a rapid and synchronized onset of metamorphosis in the former. Later, there were no distinct differences in these parameters between the laboratory-reared zooxanthellate polyps and those in the field. Although the symbiotic state did not appear to affect developmental sequence or timing, it did increase host survivorship. In the laboratory, the survivorship of zooxanthellate primary polyps was significantly higher compared to azooxanthellate ones. Therefore, the symbiotic state appears to be ultimately important in overall survivorship. The survivorship of zooxanthellate primary polyps developed from planulae released during the summer months was higher compared to those from other seasons, thus strengthening existing evidence that the summer is the most favorable season for the breeding and development of H. fuscescens sexual progeny. Comparisons between laboratory-reared zooxanthellate primary polyps and naturally settled animals in the field showed a higher survivorship in the laboratory, possibly due to unfavorable conditions commonly occurring in the field. Our findings indicate that H. fuscescens represents an appropriate model system for study of acquisition of algae by aposymbiotic offspring and the impact of the process on their development and survivorship.

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 (LD 50: 0.7 mg/kg), with one prominent 97-kDa protein fraction (LD 50: 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.

Soft-coral natural chimerism: a window in ontogeny allows the creation of entities comprised of incongruous parts

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 231:91-99 (2002) - doi:10.3354/meps231091 Soft-coral natural chimerism: a window in ontogeny allows the creation of entities comprised of incongruous parts Yael Barki1,2, Daniel Gateño1, Dan Graur2, Baruch Rinkevich1,* 1Minerva Center for Marine Invertebrate Immunology and Developmental Biology, National Institute of Oceanography, Israel Oceanographic & Limnological Research, PO Box 8030, Haifa 31080, Israel 2Department of Zoology, Tel Aviv University, Ramat Aviv 69978, Israel *Corresponding author. E-mail: buki@ocean.org.il ABSTRACT: Chimerism, the evolutionary perplexing outcome of fusion between conspecific individuals, is widely documented in nature. Several reports assign a variety of benefits to the state of chimerism, especially in cases of fusions between kins, rating a chimera as a congruous entity. For the first time, we describe here a follow-up study on chimeras of soft corals that occur only between ontogenetically immature conspecifics, prior to development of a histocompatibility recognition system. Four soft coral species from the Red Sea were investigated: Nephthea sp., Heteroxenia fuscescens, Parerythropodium fulvum fulvum and Clavularia hamra. Co-settlement of planulae resulted in high frequencies of spontaneous allogenic fusions between primary polyps. Tissue fusion between allogenic partners was confirmed histologically. During the observation periods (up to 450 d) chimeras were detached, or chimerism resulted in the death of 1 or more partners, or in morphological resorption of the partners. The results also document slower growth and growth-retarding disorders such as disruption of the structural patterns of polyp budding and polyp configuration. These cumulative effects were only manifested by individuals comprised of incongruous components. Such chimeras are likely to be less suited to field conditions than genetically homogeneous individuals, raising the ecological-evolutionary question of why soft-coral chimeras arise in the first place. We propose that juvenile cnidarian chimerism represents a case in which ontogenetic allorecognition is not infallible, and that it is further promoted by the gregarious settlement of larvae characteristic of many coral species. KEY WORDS: Allorecognition · Chimeras · Eilat · Evolution · Soft corals Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 231. Online publication date: April 23, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Biochemical composition, metabolism, and amino acid transport in planula-larvae of the soft coral Heteroxenia fuscescens.

We determined the monthly percentage of biochemical components in planulae of the soft coral Heteroxenia fuscescens, for a 3-year period, and evaluated the findings in relation to seasonal fluctuations in water temperature. We determined the biochemical profile and metabolic rate of aging planulae and examined the possible absorption of dissolved organic material (DOM) from the water by the planulae. Our study is the first to present a long-term biochemical profile of planulae. They contained an average of 2.2% ash, 51.5% lipid, 33.6% protein, and 1.3% carbohydrate. Calculation of the average energetic content of a planula revealed a value of 1. 63 J planula(-1). Significant seasonal differences in planulae weight were noted between the summer and the other seasons. A significant decrease (41%) from the initial weight, 0.029 mg, took place in the planulae dry weight within 15 days. Significant decreases over time were also found in lipid (50%) and carbohydrate (83%) concentration but not in protein (20%). Metabolic rates of a planula was 0.06 microl O(2) planula(-1) hr(-1). The study shows for the first time that a soft coral planulae can take up dissolved free amino acids from seawater. Even though each of the amino acids was initially present at equimolar concentrations, there was a much faster uptake for the neutral, nonpolar amino acids, than for polar and basic ones. The potential contribution to the metabolic demand of planulae, from the uptake of amino acids, is estimated to be 11%. It is suggested that this uptake does not appear to be due to energetic considerations, but may have a more significant impact on their nitrogen budget.

Temporal variation in lipid, protein and carbohydrate content in the Red Sea soft coral Heteroxenia fuscescens

Heteroxenia fuscescens is a common zooxanthellate soft coral on the shallow reefs of the Gulf of Eilat, northern Red Sea. Its main nutritional sources are the uptake of dissolved organic material (DOM) and carbon fixation by its symbiotic algae (zooxanthellae). Recent studies have indicated that although colonies of H. fuscescens release planulae all year round, their fecundity was subject to seasonal changes. In this study the monthly per cent of ash, lipid, protein and carbohydrate in the coral tissue over a three year period was determined. It was found that the tissues of colonies of H. fuscescens contained a monthly per cent mean of 8.8±4 ash (without sclerites), 11±3.5 lipid, 19.2±6.4 protein, and 0.6±0.01 carbohydrate (N=36). This study is the first to present such values based on long term investigation of the biochemical profile of a coral, thus enabling an examination of temporal variability in biochemical composition among seasons and successive years. The results indicated seasonal fluctuations in lipid and protein content, while variation in the biochemical composition among years was expressed only in the protein content. The mean energetic content of H. fuscescens was relatively high at 23.3±1.2 kJ g−1 dry weight (DW). A significant difference in the energetic content of H. fuscescens was found among seasons. It is suggested that the increase in nutrient levels following the annual mixing event at the Gulf of Eilat and the raised light levels led to high energetic content during summer, which may reflect the increase in the number of embryos and developing planulae in H. fuscescens colonies. Furthermore, it is suggested that in the Gulf of Eilat seasonal fluctuations in the abiotic features of the water may have an impact on the biochemical composition and energetic content of the studied species.

Reproduction in the Red Sea soft coral Heteroxenia fuscescens : seasonality and long-term record (1991 to 1997)

Heteroxenia fuscescens is a common zooxanthellate soft coral on the shallow reefs in the Gulf of Eilat, northern Red Sea. In the Red Sea, during its prolonged planulation, H. fuscescens is subjected to a seasonal environmental regime that alternates between stratified warm summer waters and upwelling of low-temperature winter waters. To examine the possible relationship between these seasonal fluctuations and the reproductive characteristics of H. fuscescens, we monitored its breeding activity for a 6-year period, including the percentage of colonies releasing planulae, number of planulae released per colony per night (fecundity), planula size and percentage of released deformed planulae. During summer and fall the combined average percentage of planulating colonies of H. fuscescens was significantly higher than in winter and spring. In addition, fecundity was greater during the summer than the rest of the year. Planulae released during summer were longer, with almost zero percent deformation. During the rest of the year they were shorter, with a higher percentage of deformation. The current study indicates that although H. fuscescens reproduces all year round, the quantity and quality of its reproductive features are subject to seasonal variability. In the Gulf of Eilat seasonal changes in the abiotic features of the water may have an impact on its reproduction. During summer, primary productivity reaches a distinctive maximum up to a depth of about 40 m. The winter upwelling waters introduce nutrients from the depths into the upper 200 m, and especially into the major primary productivity zone, thereby triggering the annual phytoplankton bloom. Because colonies of H. fuscescens gain nutritional benefit from uptake of organic material dissolved in the water and by carbon fixation by zooxanthellae, we␣suggest that the seasonal fluctuations in the species' reproductive traits are related to these fluctuations in nutrient and light levels.

Metamorphic processes in the soft corals Heteroxenia fuscescens and Xenia umbellata: The effect of protein kinase C activators and inhibitors

Summary During the life cycle of marine invertebrates, including corals with benthic and planktonic phases, embryogenesis leads to a free swimming larva which has to find a suitable habitat to settle and metamorphose. Initial settlement and induction of metamorphosis of benthic marine invertebrate larvae are generally determined by interaction of external biochemical and/or physical factors. In a preliminary study we showed that the phorbol ester 12-o-tetra-decanoyl-phorbol-13-acetate (TPA) induces metamorphosis in six Red Sea coral species. Phorbol esters are known to activate the enzyme protein kinase C (PKC) and therefore play an important role in studying the phosphatidy linositol signal (PI) transduction system. The potency of several phorbol esters to induce metamorphosis in planulae of the Red Sea soft coral species Heteroxenia fuscescens and Xenia umbellata was examined to find further indications for the involvement of PKC in anthozoan metamorphosis. All tested phorbol esters, 12-o-tetra-decanoyl-phorbol-13-acetate, phorbol-12, 13-didecanoate, 12-retinoyl-phorbol-13-acetate and phorbol-12, 13-dibutyrate triggered metamorphosis in planulae of both species in a concentration-dependent way. The maximum levels of metamorphosis achieved varied from 30% to 100%, depending on both the species tested and the phorbol ester applied, using concentrations ranging from 10−7 to 10−9 mol/l except for 12-retinoyl-phorbol-13-acetate. In addition, the response of planula fragments to artificial inducers was studied. Our results indicate that the different cnidarian taxa not only respond to a variety of metamorphic cues, but also possess divergent mechanisms for reception and transmission of metamorphic inducers. Phloretin, an inhibitor of mammalian PKC, completely blocked phorbol ester-induced metamorphosis in Heteroxenia fuscescens planulae. Data which indicate the presence of PKC-related enzymes as the biochemical base for metamorphosis are now documented for species of the cnidarian classes Hydrozoa, Scyphozoa and Anthozoa. Based on our results, and the work of other authors, we therefore suggest that the phosphatidy linositol-signaling pathway might represent the general mechanism which regulates metamorphosis in cnidarians.

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.

Longevity, competence and energetic content in planulae of the soft coral Heteroxenia fuscescens

The longevity and competence period of the azooxanthellated planulae of the soft coral Heteroxenia fuscescens, a common shallow-reef inhabitant on the Red Sea reefs, were studied for the first time. The caloric content of the planulae in the course of their life is determined and its possible significance for the longevity and competence periods is considered. H. fuscescens planulae are able to metamorphose immediately upon release and tend to settle adjacent to their parent colonies. The current study presents evidence for absence of a pre-competence period. A maximal longevity of 50 days and a competence of 49 days were recorded, providing an effective dispersal time which encompasses virtually the entire lifespan of the planulae. A monthly variation was found in longevity and competence, possibly temperature related; significantly higher metamorphosis rates occurred during the hotter months of the year, indicating the occurrence of additional temporal variations related to the species reproduction. During late stages of the experiments most of the planulae underwent partial metamorphosis, probably due to a lack of necessary inducers for settlement. It is hypothesized that these polyps may obtain zooxanthellae through their mouth opening, thus acquiring the energy to extend their pelagic life, until they encounter such settlement inducers. Two-day old planulae had a caloric content of 0.58 ± 0.05 cal × planula −1; which decreased gradually with age, to a minimum of 0.35 ± 0.005 cal × planula −1 in 16-day old planulae. H. fuscescens has a wide distribution along the eastern coast of Africa, probably due to the longevity and competence of its planulae.

The natural release of amino acids from the symbiotic coral Heteroxenia fuscescens (Ehrb.) as a function of photosynthesis

Amino acid release from colonies of the symbiotic soft coral Heteroxenia fuscescens (Ehrb.) was studied as a function of photosynthesis. The rate of net DFAA release averaged 1 μmol·100 mg −1 autozooid dw·h −1 indicating that de novo synthesis by the zooxanthellae exceeds the demand of both symbionts and host. The dark release corresponded to 1–2% of the light rate. In nutrient poor environments, such as tropical reefs, surplus production of dissolved organic compounds could be of trophic importance for other auto- and heterotrophic organisms. In calculating the amount of organic C transferred from zooxanthellae to the host, it has to be taken into account that surplus as asimilates are not necessarily utilized by the host.

Polyp dimorphism and functional, sequential hermaphroditism in the soft coral Heteroxenia fuscescens (Octocorallia)

Polyp dimorphism and functional, sequential hermaphroditism in the soft coral Heteroxenia fuscescens (Octocorallia)

Development of planulae within a mesogleal coat in the soft coral Heteroxenia fuscescens

Embryology of the hermaphroditic and dimorphic alcyonacean Heteroxenia fuscescens has been examined by scanning electron microscopy and light microcopy. Initial embryonic development in this octocoral occurs while the embryos migrate freely inside the anthocodiae and the tentacles. Immature planulae are extruded externally into intersiphonozooid spaces, where they mature. All stages of planular morphogenesis, from egg to planula, occur while the embryo is coated by the original egg mesogleal coat derived from the parent colony. Hatching from this mesogleal coat occurs as late as immediately prior to planulation. H. fuscescens demonstrates highly specialized brood care involving the retention of embryos in internal polyp cavities as well as in external spaces. This highly specialized brood care, coupled with the embryo coating, may provide better protection for the embryo and greater fecundity for the colony.

Expulsion of zooxanthellae by symbiotic cnidarians from the Red Sea

The expulsion of zooxanthellae by octocorals (Xenia macrospiculata and Heteroxenia fuscescens), the scleractinian coral Stylophora pistillata, and the hydrocoral Millepora dichotoma, was measured in the field. The numbers expelled did not exceed 0.1% of the total standing stock of symbiotic algae per day, the rate of expulsion was less than 4% of the rate at which cells are added to symbiotic populations, and the carbon lost represented 0.01% of the total carbon fixed on a daily basis. Expulsion of zooxanthellae is therefore not a significant sink for fixed carbon in these symbiotic associations. In contrast to field populations, expulsion by X. macrospiculata increased 5-fold or more in the laboratory, suggesting that laboratory conditions may introduce stress.

Zooxanthellae providing assimilatory power for the incorporation of exogenous acetate in Heteroxenia fuscescens (Cnidaria: Alcyonaria)

The soft coral Heteroxenia fuscescens (Ehrb.) and its isolated zooxanthellae (endosymbiotic dinoflagellates) were investigated with particular regard to uptake and utilization of exogenously supplied 14C-acetate in the light and in the dark. The incorporation of 14C from 14C-acetate into the host tissue and into the zooxanthellae was consistently much higher in the light than in the dark. The incorporated 14C-acetate was rapidly metabolized by the host and algae and was recovered from different assimilate fractions. The major proportion of radiocarbon from metabolized 14C-acetate was located in host tissue. The CHCl3-soluble fraction composed of diverse lipids showed the strongest 14C-labelling. Zooxanthellae isolated prior to incubation accounted for about 80% of the acetate incorporation recorded for zooxanthellae in situ (in vivo). It is concluded from a comparison of acetate incorporation and conversion under light and dark conditions that most of the lipid reserve of the host tissue originates from fatty acids, which are synthesized within the algal symbionts and are then translocated to the heterotrophic partner via extrusion. The acetate units needed for lipid synthesis are obtained by absorption of free acetate from dissolved organic matter (DOM) in the seawater as well as by photosynthetic assimilation of inorganic carbon. Thus, in H. fuscescens, lipogenesis is operated as a light-driven process to which the zooxanthellae considerably contribute assimilatory power by performing fatty acid synthesis and translocation of lipid compounds to their intracellular environment (host cell). A metabolic scheme is proposed to account for the different pathways of carbon conversion observed in H. fuscescens. The incubations took place in August 1980 and the analytical part from October 1980 to January 1984.

Functional autotrophy of Heteroxenia fuscescens (Anthozoa: Alcyonaria): carbon assimilation and translocation of photosynthates from symbionts to host

The association of the alcyonarian Heteroxenia fuscescens (Ehrb.) with its cytosymbiotic algae shows structural and physiological adaptations optimizing the living together of the two partners as one functional unit. To enhance the energetic contribution of the autotrophic partner, the organization of the heterotrophic partner bears typical plant-like imprints. Up to 20% of the inorganic C photosynthetically fixed was translocated to the host (=2 mg C mg d.w.-1 d-1). This net C gain by the host is used for anabolic purposes including the deposition of storage material. Especially the wax-esters and triglycerides of the host-in contrast to those of the symbionts-were intensively labelled. The in-vivo14C-fixation of zooxanthellae is more than double the in-vitro fixation. In both symbionts and host, the lipids show the highest relative 14C-incorporation. In particular the polyol component was strongly labelled. After 120 min of continuous incubation, approximately 40 labelled intracellular metabolites were detectable in the ethanol/water soluble fractions of zooxanthellae. Glycerol is the main low-molecular weight carbohydrate being transferred. This is corroborated by the deacylation of lipids of the host.

Epidermal nutrition of the alcyonarian Heteroxenia fuscescens (Ehrb.): absorption of dissolved organic material and lost endogenous photosynthates.

The trophic strategies were studied of Heteroxenia fuscescens living in shallow tropical waters. Structural and physiological adaptations show that particulate food is of less nutritional importance than the uptake of organic material dissolved in the sea, the utilization of assimilates of cytosymbiotic algae (zooxanthellae) and even the symbionts themselves. The external and internal surfaces of the tentacles are enlarged by featherlike pinnules, on the one hand facilitating the epidermal uptake of dissolved organic compounds and on the other offering wellilluminated spaces in which large numbers of zooxanthellae can be 'cultivated'.Zooxanthellae expelled from gastrodermal cells may be taken up by the mesenteric filaments of the dorsal mesenteries, where they are often decomposed and utilized. The transport of photo-assimilates from the gastrodermis to the epidermis through the mesogloea takes place at a low rate. Most of the released assimilates of the symbionts appear in the coelenteron. One fraction of these assimilates is distributed within the gastric channel system and can be taken up by developing stages living there; another fraction reaches the epidermis extracorporally via the pharynx and the sea. Thus both the pharynx and the epidermis absorb these photo-assimilates. The epidermal uptake capacity serves two main purposes: (1) active uptake and incorporation of external organic material dissolved in the sea; (2) reabsorption of internal, self-produced organic material, i.e. reduction of the loss of endogenous compounds escaping from the gastric cavity necessarily due to the polyfunctionality of the coelenteron.

Effects of Iranian crude oil on the red sea octocoral heteroxenia fuscescens

Acute toxicity and sublethal effects of Iranian crude oil on colonies of the Red Sea octocoral Heteroxenia fuscescens were studied under static and continuous flow assay conditions. Static toxicity bioassays conducted in small (3 litre) jars at 41% 0 salinity and 22°C showed that the concentration of crude oil added at the start fatal to 50% of the test colonies in 96 h was 12 ml/litre. Colonies surviving exposure to high sublethal levels of crude oil were adversely affected both during treatment and afterwards. Tank tests conducted in large (1500 litre), deep (2 m) containers and flowing sea water demonstrated that Heteroxenia were more resistant to crude oil than when assayed in jars; no deaths were observed in tanks during exposure for 168 h to initial concentrations of 10 ml/litre (15 litres added at surface). Tank assays demonstrated a depth protective effect; the number of colonies exhibiting signs of stress decreased with increasing distance from the oil film at the surface. Gas chromotographic analysis of the hydrocarbon composition of Heteroxenia exposed to high sublethal levels of crude showed that petroleum derived hydrocarbons were incorporated into tissues. The highest level of pollutant hydrocarbons found in these colonies was about 1% of their endogenic hydrocarbon content. It is concluded that while crude oil may not be acutely toxic to Heteroxenia, exposure to high sublethal oil levels may result in long term deleterious effects.