Fatty acids of the scleractinian coral Galaxea fascicularis: effect of light and feeding

In order to investigate nutritional interactions in the symbiotic scleractinian coral-zooxanthella association, fatty acids of the coral Galaxea fascicularis were analysed in two groups of cultured microcolonies. The first group was fed with Artemia sp., while the second group was starved. After an initial 1-month period during which both groups were subjected to the same normal light conditions (constant irradiance of 125 E·cm^-2·s^-1 and 14:10 h light:dark), a light cap was used to cover the aquarium and keep all the microcolonies in permanent darkness for 20 days. During the light phase of the experiment it was shown that the nutritional status lead to large variations in the percentage of saturated, mono-unsaturated and polyunsaturated fatty acids. Palmitic acid (C16:0) was the most abundant fatty acid in both groups. Important differences between fed and starved microcolonies occurred during the dark phase of the experiment. In the fed group the dark phase was characterized by a significant increase in polyunsaturated fatty acids. Particularly arachidonic acid (C20:4 n-6) became the most important fatty acid followed by docosatrienoic acid (C22:3 n-3). A slight increase in these two fatty acids was also found in the starved group but the bulk of polyunsaturated fatty acids was significantly decreased. In this group, palmitic acid remained the most important fatty acid while an increased concentration of cis-vaccenic acid (C18:1 n-7) was found at the end of the experiment. The increased concentration of cis-vaccenic acid might indicate that bacteria serve as a source of energy. While the number of zooxanthellae per milligram of protein and the chlorophyll a to protein ratio strongly decreased in the starved microcolonies immediately after the beginning of the dark period, the decrease in fed microcolonies was delayed for about 10 days. Furthermore, after 20 days of dark incubation the chlorophyll a to protein ratio was the same as measured at the beginning of the dark period. This suggests that in the dark the metabolic requirements of the zooxanthellae are in part met from the animal host through a heterotrophic mode of nutrition.Abbreviations CZ cultured zooxanthellae - FAME fatty acid methylester(s) - FDM fed dark microcolonies - FLM fed light microcolonies - MUFA monounsaturated fatty acid(s) - PUFA polyunsaturated fatty acid(s) - SDM starved dark microcolonies - SFA saturated fatty acids - SLM starved-light microcolonies - SW sea water - TFA total fatty acids     

Spatial distribution of calcification and photosynthesis in the scleractinian coral Galaxea fascicularis

The spatial heterogeneity of photosynthesis and calcification of single polyps of the coral Galaxea fascicularis was investigated. Photosynthesis was investigated with oxygen microsensors. The highest rates of gross photosynthesis (Pg) were found on the tissue covering the septa, the tentacles, and the tissues surrounding the mouth opening of the polyp. Lower rates were found on the tissues of the wall and the coenosarc. Calcification was investigated by radioactive tracers. The incorporation pattern of ⁴⁵Ca and ¹⁴C in the corallites was imaged with use of a Micro-Imager. The -images obtained showed that the incorporation of the radioactive tracers coincided with the Pg distribution pattern with the highest incorporation rates found in the corallite septa. Thus, the high growth rate of the septa is supported by the high rates of Pg by the symbiont in the adjacent tissues. The total incorporation rates were higher in light than in dark, however, the distribution pattern of the radioisotope incorporation was not affected by illumination. This further emphasizes the close relation between calcification and photosynthesis.     

Valine uptake by the scleractinian coral Galaxea fascicularis: characterization and effect of light and nutritional status

The characteristics of valine uptake by isolated microcolonies of Galaxea fascicularis (Linnaeus 1758) were studied under various conditions including light, dark and feeding. The results demonstrated the presence of: (1) a linear component which might represent either a diffusional transport or a low-affinity carrier-mediated transport (apparent carrier affinity >250 mol·l^–1), and (2) a high-affinity active carrier-mediated transport (apparent carrier affinity about 5 mol·l^-1). The latter is mediated by two different systems: (i) a Na⁺-dependent carrier, stimulated by light and operative in both fed and unfed polyps, and (ii) a Na⁺-independent carrier, light insensitive and present only in unfed polyps. Competition experiments with other amino acids show that the Na⁺-dependent carrier is highly specific for neutral amino acids, as indicated by the high inhibition constants of basic and acidic amino acids. Our results suggest that the energy supplied by zooxanthellae photosynthates is necessary for the process of amino acid uptake, and that the Na⁺-dependent carrier responsible for valine uptake by G. fascicularis is similar to the B^0,+ system.Abbreviations AA amino acid(s) - AC/HC ratio autotrophic/heterotrophic carbon - ASW artificial sea water - DOM dissolved organic material - HPLC high performance liquid chromatography - K ₁ apparent inhibition constant - K _m apparent affinity of the carrier - SE standard error - V _max maximal rate of absorption     

Calcium associated with a fibrillar organic matrix in the scleractinian coral Galaxea fascicularis

Summary.  Field emission scanning electron microscopy of frozen-hydrated preparations of the scleractinian coral Galaxea fascicularis revealed organic fibrils which have a diameter of 26 nm and are located between calicoblastic ectodermal cells and the underlying CaCO₃ skeleton. Small (37 nm in diameter) nodular structures observed upon this fibrillar organic material possibly correspond to localised Ca-rich regions detected throughout the calcifying interfacial region of freeze-substituted preparations by X-ray microanalysis. We propose that these Ca-rich regions associated with the organic material are nascent crystals of CaCO₃. Significant amounts of S were also detected throughout the calcifying interfacial region, further verifying the likely presence of organic material. However, the bulk of this S is unlikely to be derived from mucocytes within the calicoblastic ectoderm. It is suggested that in the scleractinian coral G. fascicularis, nodular crystals of CaCO₃ establish upon a fibrillar, S-containing, organic matrix within small but distinct extracellular pockets formed between calicoblastic ectodermal cells and skeleton. This arrangement conforms with the criteria necessary for biomineralisation and with the long-held theory that organic matrices may act as templates for crystal formation and growth in biological mineralising systems. Received April 30, 2002; accepted September 11, 2002; published online March 11, 2003     

Intraspecific interactions in a scleractinian coral,Galaxea fascicularis: Induced formation of sweeper tentacles

Sweeper tentacles of Galaxea fascicularis have a different nematocyst composition than do ordinary tentacles. The sweeper tentacles contain many large microbasic b-mastigophores (MbM) instead of the microbasic p-mastigophores (MpM) which are abundant in the acrospheres of ordinary tentacles. There is, however, an intermediate type of tentacle which has both large MbM and MpM. These tentacles may represent those undergoing transformation from ordinary into sweeper tentacles or vice versa. Two polyps isolated from the same colony (syngeneic pairs), or from colonies belonging to different colour morphs (presumed allogeneic pairs), were set about 5 mm apart with tentacles touching, and then maintained for about two months in this position. Tissue fusion was observed only in syngeneic pairs. In some allogeneic combinations, one polyp of the pair was damaged or killed by the other. The dominant polyp developed many sweeper tentacles. In other allogeneic combinations, both polyps survived and no, or only a few, sweeper tentacles were formed. Tissue fusion also failed to occur in the allogeneic combinations.     

Light-dependent fluorescence in the coral Galaxea fascicularis

The concept of ecological stoichiometry has been useful for understanding nutrient dynamics in aquatic food webs; however, the majority of studies have focused on autotrophic systems, leaving detritus-based food webs largely understudied. In addition, most detritus-based studies have explored enrichment in high-gradient, low-nutrient systems, despite the fact that many of the streams most likely to face enrichment (those surrounded by agriculture) are low-gradient and contain inherently higher dissolved nutrient concentrations due to differences in soil type, geomorphology, and atmospheric deposition. Constraints on consumer growth due to consumer-resource imbalances have been documented in these low-nutrient streams, but the extent to which consumer growth may be limited in higher-nutrient, detritus-based streams is unknown. We investigated the impact of dissolved nutrients (N and P) on mayfly growth, using artificial streams simulating a high-nutrient detritus-based system. Mayflies were reared and sampled under two total nutrient concentrations, one meant to mimic a more natural undisturbed (ambient) watershed and one to mimic a disturbed (enriched) watershed. Under each of these conditions two N:P ratios (low and high) were tested. The low N:P treatments produced higher mayfly growth under both ambient and enriched conditions, showing that nutrient limitation can occur even in high-nutrient streams.     

Telomere length of the colonial coral Galaxea fascicularis at different developmental stages

The ability to estimate coral age using soft tissue would be useful for population biology or aging studies on corals. In this study, we investigated whether telomere length can be used to estimate coral age. We applied single telomere length analysis to a colonial coral, Galaxea fascicularis, and estimated telomere lengths of specific coral chromosomes at different developmental stages. If the telomere shortened at each cell division, the telomere length of the coral would be longest in sperm and shortest in adult colonies. However, the mean telomere length of sperm, planula larvae, and polyps was approximately 4 kb, with no significant differences among the developmental stages. The telomerase restriction fragment (TRF) analysis also showed no significant difference in the mean TRF length among the developmental stages. Our results suggested that telomere length is maintained during developmental stages and that estimating the age of colonial coral based on telomere length may not be possible. However, our findings can be used to examine avoidance of aging and rejuvenation during regeneration and asexual reproduction in colonial corals.     

Light-regulated Ca2+ uptake and O2 secretion at the surface of a scleractinian coral Galaxea fascicularis

The surface concentration dynamics of Ca(2+) and O(2) in the scleractinian coral Galaxea fascicularis were investigated by means of 2 mm-sized sensors (mini-electrodes). Mini-electrodes were used to measure the light-regulated uptake of Ca(2+) for calcification, and the secretion of O(2), produced by photosynthesising zooxanthellae, at the surface of the oral ectoderm of Galaxea polyps. The concentration of Ca(2+) measured in the boundary layer of seawater adjacent to the polyp surface was variable but always higher than in bulk seawater in the dark and fell to levels closer to the value in bulk seawater on illumination. The fall in concentration, representing an influx of Ca(2+) into the ectoderm, increased with increasing photosynthetic photon flux density of illumination. The decrease in Ca(2+) concentration on illumination was insensitive to ruthenium red but sensitive to verapamil and acetazolamide. Oxygen secretion at the ectoderm, manifested by an increase in O(2) concentration in the boundary layer, increased on illumination but was not sensitive to any of the inhibitors used in the calcium experiments. The results suggest that Ca(2+) uptake involves calcium channels and is coupled in someway to the uptake of inorganic carbon for calcification. Uptake is also strongly coupled to photosynthesis.     

Precursor structure of egg proteins in the coral Galaxea fascicularis

In the egg of the reef coral Galaxea fascicularis, four proteins (named GfEP-1 to -4) are stored in high abundance. In the present study, a cDNA containing a full-length open reading frame for GfEP-1 was cloned, and the translated protein sequence was compared to the N-terminal sequences of GfEP-2, -3, and -4. GfEP-1 and -2 were shown to be generated by processing of a precursor of 1439 amino acids, and GfEP-3 turned out to be a partial fragment of GfEP-2. The precursor protein contained regions which exhibited similarities to vitellogenins (Vgs) in bilaterian animals (oviparous vertebrates and invertebrates including nematodes, arthropods, and molluscs). This study reports the first cloning and characterization of a full-length cDNA encoding a Vg in a non-bilaterian animal, and argues that the emergence of Vg as a precursor of egg yolk proteins predated the divergence of the cnidarian and bilaterian lineages.     

澄黄滨珊瑚和丛生盔型珊瑚非培养放线菌多样性

【目的】研究澄黄滨珊瑚(Porites lutea)和丛生盔型珊瑚(Galaxea fascicularis)联合放线菌物种多样性。【方法】实验提取两种珊瑚的总DNA,利用放线菌特异性引物对样品总DNA进行扩增,通过构建16S rRNA基因克隆文库和系统发育分析,对三亚鹿回头岸礁区优势物种澄黄滨珊瑚和丛生盔型珊瑚联合放线菌的多样性和群落结构进行研究。【结果】118个从澄黄滨珊瑚克隆文库中随机挑选的阳性克隆子归为58个OTUs,主要分布于酸微菌亚目、棒状杆菌亚目、微球菌亚目、丙酸杆菌亚目和未知类群。丛生盔型珊瑚克隆文库共获得96个序列,归为31个OTUs,主要分布于酸微菌亚目和未知的放线菌类群。多样性指数和稀疏度曲线分析结果显示澄黄滨珊瑚联合放线菌物种多样性比丛生盔型珊瑚更高。【结论】澄黄滨珊瑚和丛生盔型珊瑚拥有较高水平的放线菌物种多样性和复杂的群落结构,并隐藏着大量的高等级放线菌新分类单元。     

Identification of a novel yolk protein in the hermatypic coral Galaxea fascicularis

The reef-building (or hermatypic) coral Galaxea fascicularis (Anthozoa, Hexacorallia, Scleractinia) has an annual reproductive cycle. Females of G. fascicularis release packages (or ;bundles') of eggs for external fertilization, whereas male individuals form bundles consisting of sperm and infertile ;pseudo-eggs' that are thought to confer buoyancy to the male bundle. In the egg of G. fascicularis, four proteins (GfEP-1 to 4) were found to be stored in high abundance, and three of them (GfEP-1, 2 and 3) are generated by processing of a vitellogenin (Vg)-like precursor. In the present study, a cDNA encoding GfEP-4 was cloned and its sequence determined (GenBank/EMBL/DDBJ accession no. AB259859). The amino acid sequence of this protein does not exhibit similarity to known proteins, including Vgs or other yolk proteins found in some invertebrates. The expression of GfEP-4 mRNA was observed in females, and also in the majority of males examined, although expression levels were lower than in females. The GfEP-4 protein was detected in pseudo-eggs, where its concentration was 20-100 times lower than in eggs. In contrast, GfEP-1, 2 and 3 were not detected in pseudo-eggs. A protein (28 kDa) which cross-reacted with anti-GfEP-4 antibodies was detected in eggs of the coral Montipora digitata, suggesting the possibility that homologs of this protein are present in the eggs of other scleractinian corals.     

Effects of the multiple stressors high temperature and reduced salinity on the photosynthesis of the hermatypic coral Galaxea fascicularis

This study investigates the physiological responses in the hermatypic coral Galaxea fascicularis exposed to salinity stress (from 37 ppt to 15 ppt) for 12 h, combined effects of reduced salinity (from 37 ppt to 20 ppt) and two temperatures (26 °C and 32 °C) for 12 h and combined effects of reduced salinity (from 37 ppt to 25 ppt) and two temperatures (26 °C and 29.5 °C) for 10 d. The results demonstrate that the coral is tolerant to 12 h exposure to extremely low salinity (15 ppt). The study also shows that combined effects of temperature and low salinity aggravate the damage on the photosynthesis of the symbiotic dinoflagellates in 12 h exposure to 20 ppt sea water. This study suggests that high temperature (29.5 °C) aggravates the damage of trivially low salinity (30 ppt) on the holobiont (the coral and its symbiotic dinoflagellates) in 10 d exposure. However, high temperature (29.5 °C) may have an antagonistic effect between temperature and low salinity (25 ppt) on metabolism of the holobiont. Based on the above results, we suggest that (1) the true mechanism of corals exposed to combined effects of low salinity and high temperature is complicated. This calls for more studies on different corals. Future studies should aim at investigating long-term low-level stress in order to simulate in situ conditions more accurately; (2) when corals exposed to extremely severe combined stressors for short-term or trivially severe stressors for relative long-term, the combined effects of two stressors (such as low salinity and high temperature) may be negative, otherwise, the effects may be additive.     

Variation in skeletal microstructure of the coral Galaxea fascicularis: effects of an aquarium environment and preparatory techniques

To compare the crystalline microstructure of exsert septa, polyps of the scleractinian coral Galaxea fascicularis were sampled from shallow reef flat colonies, from colonies living at a depth of 9 m, and from colonies kept in a closed-circuit aquarium. Septal crystal structure and orientation was markedly different between corals in the field and in aquaria. In samples collected from deep water, acicular crystals were composed of conglomerates of finer crystals, and skeletal filling was considerably reduced when compared with samples collected from shallow water. Comparisons were also made between septa prepared in sodium hypochlorite (commercial bleach), sodium hydroxide (NaOH), hydrogen peroxide (H(2)O(2)), and distilled water (dH(2)O). Commercial bleach was the most effective solvent for tissue dissolution in investigations of skeletal structure. Samples prepared in NaOH commonly displayed crystalline artefacts, while the use of dH(2)O and H(2)O(2) was labor intensive and often resulted in unclean preparations. Fusiform crystals were seen only on G. fascicularis septa prepared in bleach and on Acropora formosa axial corallites prepared in either bleach or dH(2)O. We suggest that the mechanical agitation and additional washing necessary for samples prepared in dH(2)O, NaOH, or H(2)O(2) resulted in the loss of fusiform crystals from these preparations.     

Deposition of fusiform crystals without apparent diurnal rhythm at the growing edge of septa of the coral Galaxea fascicularis

Recent studies suggest a diurnal periodicity in the deposition of fusiform crystals by scleractinian corals. In order to check whether this is universally true in the Scleractinia, the surface structure of skeletons of Galaxea fascicularis (L.), collected at 3 h intervals over 1 day was observed with a scanning electron microscope. Fusiform crystals 0.3–3 m wide and 0.5–5 m long were found on the growing edges of septa of polyps collected at different times of day. There was no apparent diurnal change in the mean diameter of fusiform crystals. The size distributions of these crystals were almost the same by day (1200 h) and at night (2400 h). Small fusiform crystals which appeared to have been newly deposited were observed on septa collected both during the day and at night. The present study suggests that fusiform crystals are deposited continuously with no diurnal rhythm in G. fascicularis.     

The effect of selected trace metals on the fertilization success of several scleractinian coral species

This study provides new information on the effects of various concentrations of the trace metals copper, lead, zinc, cadmium, and nickel on fertilization success of gametes from the scleractinian reef corals Goniastrea aspera,Goniastrea retiformis, Acropora tenuis, and Acropora longicyathus. The EC50 values (the concentration that reduces the fertilization rate by 50% relative to the control fertilization) for copper effects on fertilization success of these coral species range from 15 to 40 μg/L, which is similar to responses of other marine invertebrates. The EC50 values for lead were 1450–1800 μg/L for the Acropora species, and >2400 μg/L for G. aspera gametes, which indicates that lead was much less toxic than copper. Fertilization responses to zinc and nickel were variable and a significant reduction in fertilization success for A. tenuis gametes was found only at very high cadmium concentrations. The data from this study and other recent research clearly demonstrate that some trace metals impair the fertilization success of gametes from faviid and acroporiid reef corals. Trace metal inputs into reef waters should be limited and controlled to avoid potential interference with sexual reproductive processes of reef corals.     

Effect of zooplankton availability on the rates of photosynthesis, and tissue and skeletal growth in the scleractinian coral Stylophora pistillata

This work investigated the effect of light and feeding on tissue composition as well as on rates of photosynthesis and calcification in the zooxanthellae (zoox) scleractinian coral, Stylophora pistillata. Microcolonies were maintained at three different light levels (80, 200, 300 μmol m⁻² s⁻¹) and subjected to two feeding regimes (starved and fed) over 9 weeks. Corals were fed both natural plankton and Artemia salina nauplii four times a weeks and samplings were made after 2, 5, and 9 weeks. Results confirmed that feeding enhances coral growth rate and increases both the dark and light calcification rates. These rates were 50-75% higher in fed corals (FC; 60±20 and 200±40 nmol Ca²⁺ cm⁻² h⁻¹ for dark and light calcification, respectively) compared to control corals (CC; 30±9 and 124±23 nmol Ca²⁺ cm⁻² h⁻¹). The dark calcification rates, however, were four times lower than the rates of light calcification (independent of trophic status). After 5 weeks, chlorophyll a (chl-a) concentrations were four to seven times higher in fed corals (7-21 μg cm⁻²) than in control corals (2-5 μg cm⁻²). The amount of protein was also significantly higher in fed corals (2.11-2.50 mg cm⁻²) than in control corals (1.08-1.52 mg cm⁻²). Rates of photosynthesis in fed corals were 2-10 times higher (1.24±0.75 μmol O₂ h⁻¹ cm⁻²) than those measured in control corals (0.20±0.08 μmol O₂ h⁻¹ cm⁻²).     

Effects of delayed settlement on post-settlement growth and survival of scleractinian coral larvae

Demographic connectivity requires both the dispersal of individuals between sub-populations, and their subsequent contribution to population dynamics. For planktonic, non-feeding marine larvae, the capacity to delay settlement enables greater dispersal distances, but the energetic cost of delayed settlement has been shown to adversely impact post-settlement fitness in several taxa. Here, we assess whether delayed settlement influences mortality rates or growth rates for the first 6 weeks following settlement of the scleractinian coral, Acropora tenuis. Coral larvae that were settled at 2, 4, and 6 weeks after spawning, and then deployed in the field, showed negligible effects of delayed settlement on post-settlement survival and time to initial budding for colony formation. Between-cohort differences in budding rate appeared to be explained by temporal variation in the post-settlement acquisition of zooxanthellae. The potential for coral larvae to remain in the pelagic zone for increased periods of time with little to no effect on post-settlement survival and growth suggests that the capacity for delayed settlement is likely to have meaningful demographic consequences for broadcast-spawning reef-building corals, and that the predicted trade-off between delayed settlement and post-settlement fitness is less applicable to reef-building scleractinian corals than other taxa with non-feeding larvae.     

The effect of seasonal temperature extremes on sediment rejection in three scleractinian coral species

Sedimentation from resuspension following storm surge is a natural occurrence on coral reefs, and scleractinian corals have adapted to effectively reject sediment. However, it is unclear whether the physical ability to reject sedimentation is affected during seasonal temperature extremes. We acclimated three coral species (Montipora aequituberculata, Lobophyllia corymbosa and Fungia fungites), with different active shedding mechanisms, to three temperature treatments (winter minimum, summer maximum and mean). Corals were then exposed to a sediment rejection experiment in which we measured clearance rates and tissue inflation cycles associated with the clearance of sediment. Temperature impacted clearing rates of M. aequituberculata, which exhibited significantly faster sediment rejection under winter temperatures. Fungia fungites, on the other hand, exhibited significantly higher tissue inflation rates under summer temperatures. Although limited in scope, this study demonstrates that temperature can have a strong effect on the response of corals to sedimentation.     

Skeletal growth, ultrastructure and composition of the azooxanthellate scleractinian coral Balanophyllia regia

The biomineralization process and skeletal growth dynamics of azooxanthellate corals are poorly known. Here, the growth rate of the shallow-water dendrophyllid scleractinian coral Balanophyllia regia was evaluated with calcein-labeling experiments that showed higher lateral than vertical extension. The structure, mineralogy and trace element composition of the skeleton were characterized at high spatial resolution. The epitheca and basal floor had the same ultrastructural organization as septa, indicating a common biological control over their formation. In all of these aragonitic skeletal structures, two main ultrastructural components were present: “centers of calcification” (COC) also called rapid accretion deposits (RAD) and “fibers” (thickening deposits, TD). Heterogeneity in the trace element composition, i.e., the Sr/Ca and Mg/Ca ratios, was correlated with the ultrastructural organization: magnesium was enriched by a factor three in the rapid accretion deposits compared with the thickening deposits. At the interface with the skeleton, the skeletogenic tissue (calicoblastic epithelium) was characterized by heterogeneity of cell types, with chromophile cells distributed in clusters regularly spaced between calicoblasts. Cytoplasmic extensions at the apical surface of the calicoblastic epithelium created a three-dimensional organization that could be related to the skeletal surface microarchitecture. Combined measurements of growth rate and skeletal ultrastructural increments suggest that azooxanthellate shallow-water corals produce well-defined daily growth steps.