Relationship of Vibrio species infection and elevated temperatures to yellow blotch/band disease in Caribbean corals

The bacterial and temperature factors leading to yellow blotch/band disease (YBD), which affects the major reef-building Caribbean corals Montastrea spp., have been investigated. Groups of bacteria isolated from affected corals and inoculated onto healthy corals caused disease signs similar to those of YBD. The 16S rRNA genes from these bacteria were sequenced and found to correspond to four Vibrio spp. Elevating the water temperature notably increased the rate of spread of YBD on inoculated corals and induced greater coral mortality. YBD-infected corals held at elevated water temperatures had 50% lower zooxanthella densities, 80% lower division rates, and a 75% decrease in chlorophyll a and c2 pigments compared with controls. Histological sections indicated that the algal pyrenoid was fragmented into separate segments, along with a reconfiguration and swelling of the zooxanthellae, as well as vacuolization. YBD does not appear to produce the same physiological response formerly observed in corals undergoing temperature-related bleaching. Evidence indicates that YBD affects primarily the symbiotic algae rather than coral tissue.     

The effects of elevated temperature on the photosynthetic efficiency of zooxanthellae in hospite from four different species of reef coral: a novel approach

Bleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are known as zooxanthellae, and/or loss of algal pigments. The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, Agaricia lamarki, Agaricia agaricites and Siderastrea radians was examined by pulse-amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (30–36°C). Zooxanthellae within M. annularis and A. lamarki were found to be more sensitive to elevated temperature, virtually complete disruption of photosynthesis being noted during exposure to temperatures of 32 and 34°C. The photosynthetic efficiency of zooxanthellae within S. radians and A. agaricites decreased to a lesser extent. Differences in the loss of algal cells on an aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the non-invasive PAM technique with whole-cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbionts within different species of coral. Zooxanthellae within M. annularis appear to be more susceptible to heat-induced damage at or near the reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non-photochemical pathways, thereby protecting the photosystem from damage during heat exposure.     

Functional significance of genetically different symbiotic algae Symbiodinium in a coral reef symbiosis

The giant sea anemone Condylactis gigantea associates with members of two clades of the dinoflagellate alga Symbiodinium, either singly or in mixed infection, as revealed by clade-specific quantitative polymerase chain reaction of large subunit ribosomal DNA. To explore the functional significance of this molecular variation, the fate of photosynthetically fixed carbon was investigated by (14)C radiotracer experiments. Symbioses with algae of clades A and B released ca. 30-40% of fixed carbon to the animal tissues. Incorporation into the lipid fraction and the low molecular weight fraction dominated by amino acids was significantly higher in symbioses with algae of clade A than of clade B, suggesting that the genetically different algae in C. gigantea are not functionally equivalent. Symbioses with mixed infections yielded intermediate values, such that this functional trait of the symbiosis can be predicted from the traits of the contributing algae. Coral and sea anemone symbioses with Symbiodinium break down at elevated temperature, a process known as 'coral bleaching'. The functional response of the C. gigantea symbiosis to heat stress varied between the algae of clades A and B, with particularly depressed incorporation of photosynthetic carbon into lipid of the clade B algae, which are more susceptible to high temperature than the algae of clade A. This study provides a first exploration of how the core symbiotic function of photosynthate transfer to the host varies with the genotype of Symbiodinium, an algal symbiont which underpins corals and, hence, coral reef ecosystems.     

Preliminary evidence for tissue retraction as a factor in photoprotection of corals incapable of xanthophyll cycling

In a 6-h experiment where xanthophyll inter-conversion was blocked by the inhibitor dithiothreitol (DTT), corals in full sunlight showed a significant increase in oxidative damage and cnidarian antioxidant enzyme concentrations compared with controls. By comparison, antioxidant enzyme concentrations did not increase within the symbiotic algae. In addition, the normal reduction in steady state chlorophyll fluorescence (F_t) and maximum fluorescence (F_m′), in response to increased irradiance, was initially suppressed in the DTT-treated corals, but after 6 h, both parameters had reduced to levels similar to controls with a functional xanthophyll cycle. Extreme host retraction was observed in corals treated with DDT in full sunlight compared with untreated corals in full sunlight and DTT-treated corals in dim irradiance. These results suggest that the coral host is capable of using behavioural (tissue retraction) and biochemical defences (antioxidant enzymes) to protect the symbiotic algae under high natural irradiance when the xanthophyll cycle is absent. While these defences could not prevent oxidative damage, nonetheless, algal numbers and algal chlorophyll levels were not affected.     

Resilience and acclimation to bleaching stressors in the scleractinian coral Porites cylindrica

‘Resilience’, the capacity of the coral symbiosis with dinoflagellate algal symbionts (‘zooxanthellae’) to recover after bleaching, is a little-studied but crucial aspect of coral responses to bleaching stressors. This study investigated the response of the zooxanthella population in the coral Porites cylindrica after bleaching either naturally on a shallow subtidal reef or experimentally in response to elevated temperature and darkness. Coral resilience was influenced by the nature and duration of the stressor. Corals strongly bleached by natural stressors were less resilient than those that had been partially bleached; and a similar recovery profile was obtained for corals experimentally bleached by exposure to elevated temperature, in which recovery was slower for corals thermally-stressed 96 h than for 72 h. The opposite trend was evident for corals exposed to darkness, indicating that the bleaching trigger had a strong impact on coral resilience. When P. cylindrica recently recovered from bleaching was subjected to a repetition of bleaching stressors, it did not display acclimation, i.e. experience-mediated acquisition of resistance to bleaching stressors. The zooxanthella populations in all corals tested throughout the experiments were typed by PCR-RFLP as clade C, indicating that coral responses were not accompanied by any substantial change in zooxanthella composition at the cladal level.     

Relationship of Vibrio Species Infection and Elevated Temperatures to Yellow Blotch/Band Disease in Caribbean Corals

The bacterial and temperature factors leading to yellow blotch/band disease (YBD), which affects the major reef-building Caribbean corals Montastrea spp., have been investigated. Groups of bacteria isolated from affected corals and inoculated onto healthy corals caused disease signs similar to those of YBD. The 16S rRNA genes from these bacteria were sequenced and found to correspond to four Vibrio spp. Elevating the water temperature notably increased the rate of spread of YBD on inoculated corals and induced greater coral mortality. YBD-infected corals held at elevated water temperatures had 50% lower zooxanthella densities, 80% lower division rates, and a 75% decrease in chlorophyll a and c₂ pigments compared with controls. Histological sections indicated that the algal pyrenoid was fragmented into separate segments, along with a reconfiguration and swelling of the zooxanthellae, as well as vacuolization. YBD does not appear to produce the same physiological response formerly observed in corals undergoing temperature-related bleaching. Evidence indicates that YBD affects primarily the symbiotic algae rather than coral tissue.     

Hyperdiversity of Genes Encoding Integral Light-Harvesting Proteins in the Dinoflagellate Symbiodinium sp

The superfamily of light-harvesting complex (LHC) proteins is comprised of proteins with diverse functions in light-harvesting and photoprotection. LHC proteins bind chlorophyll (Chl) and carotenoids and include a family of LHCs that bind Chl a and c. Dinophytes (dinoflagellates) are predominantly Chl c binding algal taxa, bind peridinin or fucoxanthin as the primary carotenoid, and can possess a number of LHC subfamilies. Here we report 11 LHC sequences for the chlorophyll a-chlorophyll c ₂-peridinin protein complex (acpPC) subfamily isolated from Symbiodinium sp. C3, an ecologically important peridinin binding dinoflagellate taxa. Phylogenetic analysis of these proteins suggests the acpPC subfamily forms at least three clades within the Chl a/c binding LHC family; Clade 1 clusters with rhodophyte, cryptophyte and peridinin binding dinoflagellate sequences, Clade 2 with peridinin binding dinoflagellate sequences only and Clades 3 with heterokontophytes, fucoxanthin and peridinin binding dinoflagellate sequences.     

Application of chlorophyll fluorescence technique in the study of coral symbiotic zooxanthellae micro-ecology

Mutualistic relationship between coral polyps and their symbiotic zooxanthellae living within their tissues are the most essential features of a coral reef ecosystem. In this symbiotic system, the coral polyps provide a protected habitat, carbon dioxide and nutrients needed for photosynthesis to zooxanthellae; in turn, the symbiotic zooxanthellae provide food as products of photosynthesis to coral polyps. The Photosynthesis of zooxanthellae is therefore an important process of this symbiotic system as well as the development of the whole coral reef ecosystem. The recent application of chlorophyll fluorescence technique in the study of the zooxanthellae’s photosynthesis has greatly improved our understanding on the micro-ecology of corals and the symbiotic zooxanthellae. This paper summarizes the recent progress as the following aspects: (1) The ecological characteristics of the photosynthesis of symbiotic zooxanthellae, such as the diurnal and seasonal changes in the photochemical efficiency of the zooxanthellae, and the relationship between zooxanthellae photosynthesis and the world-wide coral bleaching. (2) The mechanism of corals acclimating to the changes of irradiance via spatial and temporal photoacclimations, including the corals’ photobiology; zooxanthella size, pigmentation, location and clade, and the relationship between light extremes and the corals’ metabolism and calcification. (3) The understanding of the response of zooxanthellae to various environmental stresses, such as long-term changes in the chlorophyll fluorescence of bleached and recovering corals; the tolerance of corals to thermal bleaching; the changes to photosystem II of symbiotic zooxanthellae after heat stress and bleaching. Due to the above findings, the chlorophyll fluorescence values of those coral species sensitive to environmental changes have been utilized as indicators of coral health as well as the status of coral reef ecosystems. In summary, the chlorophyll fluorescence technique has great potential in the understanding, monitoring, protecting and managing coral reefs.     

Optical spectra and pigmentation of Caribbean reef corals and macroalgae

 Coastal reef degradation and widespread bleaching of corals, i.e. loss of pigments and/or symbiotic zooxanthellae, is increasing globally. Remote sensing from boats, aircraft or satellites has great potential for assessing the extent of reef change, but will require ground-verified spectral algorithims characteristic of healthy and degraded reef populations. We collected seven species of Caribbean reef corals and also representative macroalgae from reefs near Lee Stocking Island, Bahamas and quantified their pigments using high performance liquid chromatography. We also measured the fluorescence and reflectance spectra of corals and macroalgae using an in situ benthic spectrofluorometer. In visibly pigmented (unbleached) coral from 4 to 5 m depth, the mean (±SD) surface density of pigments (3.0±1.3 μg chlorophyll-a cm^-2 and 2.1±0.7 μg peridinin cm^-2) was similar between colonies of the same species, but differed among species. The mean quantity of pigment per zooxanthella (1.8±0.9 pg chl-a cell^-1 and 1.4±0.7 pg peridinin cell^-1) also differed among species and sometimes between colonies of the same species. Chl-a and peridinin densities per surface area of coral were positively correlated. When excited with blue light (480 nm), macroalgae and corals had typical chlorophyll fluorescence with a peak at 680 nm and a smaller shoulder peak at 730 to 740 nm. Most corals, unlike macroalgae, also had distinct fluorescence peaks between 500 and 530 nm. In visibly bleached corals 680 nm fluorescence was greatly reduced in amplitude. Pigmented coral, under natural lighting conditions, had a reflected light peak at about 570 nm. Reflectance increased over all wavelengths in bleached corals, with the greatest increase at the wavelengths where chlorophyll and accessory pigments absorb light, i.e. 670 and 450 to 550 nm. Both fluorescence and reflectance spectra appear promising to remotely differentiate between pigmented and bleached coral and between coral and macroalgae. Accepted: 15 March 1999     

Bio-optical modeling of photosynthetic pigments in corals

The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c ₂, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c ₂. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes.     

Repair machinery of symbiotic photosynthesis as the primary target of heat stress for reef-building corals

In a coral-algae symbiotic system, heat-dependent photoinhibition of photosystem II (PSII) leads to coral bleaching. When the reef-building coral Acropora digitifera was exposed to light, a moderate increase of temperature induced coral bleaching through photobleaching of algal pigments, but not through expulsion of symbiotic algae. Monitoring of PSII photoinhibition revealed that heat-dependent photoinhibition was ascribed to inhibition of the repair of photodamaged PSII, and heat susceptibility of the repair machinery varied among coral species. We conclude that the efficiency of the photosynthesis repair machinery determines the bleaching susceptibility of coral species under elevated seawater temperatures.     

Light absorption by carotenoid peridinin in zooxanthellae cell and setting down of hermatypic coral to depth

Carotenoid peridinin absorbs ocean light which could penetrate deep into the water. Absolute and relative contents of symbiotic dinoflagellatae zooxanthellae are increased with depth of habitat of germatypic corals. To estimate whether the presence of peridinin in corals is chromatic adaptation or not, the absorbance of solar radiation by different amounts of peridinin and chlorophyll in natice zooxanthellae cells was evaluated. Calculations have shown that at the great depths the peredinin absorbance corresponds to 42% of total cell absorbance and that the increase of light absorbance correlating with changes of its spectral characteristics is entirely determined by presence of this carotenoid. The increase of amount of peridinin in cell is as much important as important the increase of all other pigments taken together. However, at the same time selective and preferential accumulation of peridinin and the change of its native state in the limits naturally occurred in zooxanthellae cells have only low impact on the light absorbance. The presence of peridinin could be considered as manifestation of chromatic adaptation of organism. The comparison of light absorption by zooxanthellae with different content of peridinin (or without peridinin) reveals that this pigment expands the habitat of hermatypic corals in ocean waters at 8-17 meters into the deep.     

Specificity is rarely absolute in coral-algal symbiosis: implications for coral response to climate change

Some reef-building corals have been shown to respond to environmental change by shifting the composition of their algal symbiont (genus Symbiodinium) communities. These shifts have been proposed as a potential mechanism by which corals might survive climate stressors, such as increased temperatures. Conventional molecular methods suggest this adaptive capacity may not be widespread because few (～25%) coral species have been found to associate with multiple Symbiodinium clades. However, these methods can fail to detect low abundance symbionts (typically less than 10-20% of the total algal symbiont community). To determine whether additional Symbiodinium clades are present, but are not detected using conventional techniques, we applied a high-resolution, real-time PCR assay to survey Symbiodinium (in clades A-D) from 39 species of phylogenetically and geographically diverse scleractinian corals. This survey included 26 coral species thought to be restricted to hosting a single Symbiodinium clade ('symbiotic specialists'). We detected at least two Symbiodinium clades (C and D) in at least one sample of all 39 coral species tested; all four Symbiodinium clades were detected in over half (54%) of the 26 symbiotic specialist coral species. Furthermore, on average, 68 per cent of all sampled colonies within a given coral species hosted two or more symbiont clades. We conclude that the ability to associate with multiple symbiont clades is common in scleractinian (stony) corals, and that, in coral-algal symbiosis, 'specificity' and 'flexibility' are relative terms: specificity is rarely absolute. The potential for reef corals to adapt or acclimatize to environmental change via symbiont community shifts may therefore be more phylogenetically widespread than has previously been assumed.     

Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C*. Despite the high temperature in this lake (> 0.5 degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.     

Quantification of total and particulate dimethylsulfoniopropionate (DMSP) in five Bermudian coral species across a depth gradient

The symbiotic dinoflagellate microalgae of corals (Symbiodinium spp.) contain high concentrations of dimethylsulfoniopropionate (DMSP), a multifunctional metabolite commonly found in many species of marine algae and dinoflagellates. A photoprotective antioxidant function for DMSP and its breakdown products has often been inferred in algae, but its role(s) in the coral–algal symbiosis remains elusive. To examine potential correlations between environmental and physiological parameters and DMSP, total DMSP (DMSP_t, from the host coral and zooxanthellae), particulate DMSP (DMSP_p, from the zooxanthellae only), coral surface area, and total protein, as well as zooxanthellae density, chlorophyll concentration, cell volume and genotype (i.e., clade) were measured in five coral species from the Diploria-Montastraea-Porites species complex in Bermuda along a depth gradient of 4, 12, 18, and 24 m. DMSP_t concentrations were consistently greater than DMSP_p concentrations in all species suggesting the possible translocation of DMSP from symbiont to host. D. labyrinthiformis was notably different from the other corals examined, showing DMSP_p and DMSP_t increases (per coral surface area or tissue biomass) with increasing water depth. However, overall, there were no consistent depth-related patterns in DMSP_p and DMSP_t concentrations. Further research, investigating dimethylsulfide (DMS), dimethylsulfoxide, and acrylate levels and DMSP-lyase activity in correlation with other biomarker endpoints that have been shown to be depth (i.e., temperature and light) responsive are needed to substantiate the significance of these findings.     

PHOTOSYNTHESIS IN SOME ALCYONACEAN CORALS

Burkholder , Paul R., and Lillian M. Burkholder . (Brooklyn Botanic Garden, Brooklyn, New York.) Photosynthesis in some Alcyonacean corals. Amer. Jour. Bot. 47(10) : 866–872. Illus. 1960.—Quantitative production of oxygen in bottles, and amounts of chlorophyll and carotenoid pigments were studied in selected species of Alcyonacean corals, the stony coral Porites, porites, and turtle grass, Thalassia testudinum, in Puerto Rico. Photosynthetic production exceeds the consumption of oxygen in combined respiration of the corals and their contained algal zooxanthellae, both in short-term light experiments and over 24 hr. of natural, alternating day and night. Observations of oxygen production in 8 species of corals, exposed to full sunlight in 1 ft. of water, gave assimilation values of 0.9 mg. O₂ (equivalent to 0.27 mg. C fixed) per mg. chlorophyll a per hour. A maximum assimilation value of 1.56 was observed in Antillogorgia turgida. From data on the increased oxygen it was calculated that from 0.33 to 1.65 mg. residual fixed carbon per g. of fresh coral were accumulated in Porites porites and Antillogorgia turgida during a day and night period of 24 hr. Photosynthesis of turtle grass in the same environment was more than 3 times the rate of these corals. The zooxanthellae contain carotenoids in abundance, along with chlorophylls a and c. On a unit of chlorophyll a basis, the photosynthetic systems of corals appear to be less active in reduction of carbon dioxide in bottles than some other photosynthetic systems of the sea, such as turtle grass and phytoplankton observed under optimum conditions.     

Effect of inorganic and organic nutrient addition on coral–algae assemblages from the Northern Red Sea

Previous studies in fringing reefs of the Northern Red Sea demonstrated that the in-situ competition of corals and algae in natural assemblages is highly variable between seasons displaying fast overgrowth of corals by benthic reef algae in fall that follows close to equilibrium between both groups of organisms in summer. This may be caused by up to 5-fold higher inorganic nutrient and 6-fold higher organic nutrient concentrations in fall and winter, thereby potentially promoting algae and cyanobacteria growth with concomitant phase shift. A long term mesocosm experiment (duration: 90 days) was conducted in order to study the effect of dissolved inorganic (ammonium, phosphate, nitrate, and mix of all three) and organic (glucose) nutrient addition onto the competitive process in the dominant coral–algae assemblages of the Northern Red Sea involving branching corals of the genus Acropora and a typical consortium of benthic turf algae. Nutrients were added in 3-fold higher concentrations compared to the annual averages, and the parameters algal growth, extension of bleached area on corals, tissue colour change and chlorophyll a concentrations were monitored at regular intervals over experimental duration. This revealed that elevated ammonium concentrations and elevated organic nutrient concentrations stimulate algal growth, while coral tissue pigmentation and chlorophyll a content were significantly decreased. But only in the elevated organic nutrient treatment all effects on corals were significantly pronounced when assembled with benthic turf algae. Supplementary logger measurements revealed that O₂ water concentrations were significantly lower in the elevated organic nutrient mesocosm compared to all other treatments, confirming side-effects on microbial activity. These findings indicate that organic nutrient input into coral reefs can affect physiology and metabolism of both corals and benthic turf algae. Reinforcing interaction between both groups of organisms along with involvement of microbes may facilitate phase shifts in coral reef ecosystems.     

Visibly healthy corals exhibit variable pigment concentrations and symbiont phenotypes

Understanding the natural variability of photosynthetic pigment ranges and distributions in healthy corals is central to evaluating how useful these measurements are for assessing the health and bleaching status of endosymbiotic reef-building corals. This study examined the photosynthetic pigment variability in visibly healthy Porites lobata and Porites lutea corals from Kaneohe Bay, Hawaii and explored whether pigment variability was related to the genetic identity or phenotypic characteristics of the symbionts. Concentrations of the photosynthetic pigments chlorophyll a, peridinin, chlorophyll c ₂ , diadinoxanthin, diatoxanthin, β,β-carotene and dinoxanthin were quantified using high-performance liquid chromatography (HPLC). Pigment concentrations were found to range 1.5–10 fold in colonies of each species at similar depths (0–2, 2–4, 10–15 and 19–21 m). Despite the high pigment variability, pigment ratios for each species were relatively conserved over the 0–21 m depth gradient. The genetic identity of the symbiont communities was examined for each colony using 18S nuclear ribosomal DNA (nrDNA) restriction fragment length polymorphisms. All colonies contained symbionts belonging to clade C. The density and phenotypic characteristics of the symbionts were explored using flow cytometry, and fluorescence and side scatter (cell size) properties revealed phenotypically distinct symbiont subpopulations in every colony. The symbiont subpopulations displayed pigment trends that may be driven by acclimatization to irradiance microenvironments within the host. These results highlight the biological complexity of healthy coral–symbiont associations and the need for future research on pigments and symbiont subpopulation dynamics.     

Algal genotype and photoacclimatory responses of the symbiotic alga Symbiodinium in natural populations of the sea anemone Anemonia viridis

As an approach to investigate the impact of solar radiation on an alga–invertebrate symbiosis, the genetic variation and photosynthetic responses of the dinoflagellate algal symbiosis in an intertidal and a subtidal population of the sea anemone Anemonia viridis were explored. Allozyme analysis of the anemones indicated that the two populations were genetically very similar, with a Nei''s index value of genetic identity (I) of 0.998. The algae in all animals examined were identified as Symbiodinium of clade a by PCR-RFLP analysis of the small subunit ribosomal RNA gene. The symbiosis in the two populations did not differ significantly in algal population density, chlorophyll a content per algal cell or any photosynthetic parameter obtained from studies of the relationship between photosynthesis and irradiance. We conclude that there is not necessarily genetic variation or photosynthetic plasticity of the symbiotic algae in Anemonia viridis inhabiting environments characterized by the different solar irradiances of the subtidal and intertidal habitats.     

Diurnal changes in photochemical efficiency and xanthophyll concentrations in shallow water reef corals : evidence for photoinhibition and photoprotection

 Diurnal patterns of photoinhibition have been identified in seven species of shallow water reef corals from the Andaman Sea, off the west coast of Thailand, using pulse amplitude fluorometry. Photochemical efficiency (F_v/F_m) and quantum yield (ΔF/F_m∑) of symbiotic dinoflagellates within the corals declined after dawn to reach a minimum between midday and early afternoon, recovering to former dawn levels by early evening. Parallel studies on the xanthophylls diadinoxanthin (Dn) and diatoxanthin (Dt), and their inter-conversion, also revealed a strong diurnal pattern as well as inverse correlations between the xanthophyll ratio Dt/(Dn+Dt) and F_v/F_m and ΔF/F_m′. These findings suggest a photoprotective function for these pigments. Accepted: 18 March 1999