Effects of colony size and polyp position on polyp fecundity in the scleractinian coral genus Acropora

This study examined the effects of colony size and polyp position on six variables of polyp fecundity [egg number, egg size, total egg volume, total testis volume, total gonad volume, and gonad ratio (egg volume/testis volume)] in three tabular Acropora corals (Scleractinia), A. hyacinthus, A. japonica, and A. solitaryensis. Samples were collected from various colony sizes (n = 21–30 colonies species^?1), just before the predicted spawning at Kochi, Japan, in 2009. Five replicate polyps were sampled at three positions (center, middle, and outer) from the center to the marginal area in each tabular colony. Results indicated effects of colony size and polyp position on both male and female gonads polyp^?1. A positive effect of colony size was observed on variables of female gonads polyp^?1 (egg number, total egg volume) in A. hyacinthus only, while the positive effect on the variable of male gonads polyp^?1 (total testis volume) was common in all Acropora species, with total testis volume polyp^?1 increasing 2–4-fold from the small (200–400 cm²) to the large size class (5,000–9,000 cm²). Among the polyp positions, lower values were observed mostly in center polyps in A. hyacinthus, while lower values were observed only in outer polyps in the other Acropora species. The distinct patterns between A. hyacinthus and the other two Acropora species suggest different reproductive strategies at the species level. Further studies are needed to confirm the prevalence of these effects in scleractinian corals, which will broaden our understanding of reproductive life history strategies and improve the estimation of reproductive performance.     

Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula

Sentoku, A. & Ezaki, Y. 2011: Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula. Lethaia, Vol. 45, pp. 62–70. Scleractinia display a variety of growth forms, whether zooxanthellate or azooxanthellate, as the consequence of the combined effects of both intrinsic and extrinsic factors. New modules arise in colonial corals through asexual reproduction, including budding and division. The azooxanthellate, branching dendrophylliid Dendrophyllia arbuscula van der Horst 1922 , is a good species to investigate intrinsic regularities in budding, because: (1) the lateral corallites always occur in the vicinity of four primary septa, excluding the two directive primary septa; (2) the two directive septa in lateral corallites tend to be oriented almost perpendicular to the growth orientation of parental corallites; (3) the lateral corallites grow more‐or‐less diagonally upwards; and (4) these regularities are retained from the axial to the derived lateral corallites during colony growth. Accordingly, a colony of apparently complex dendroid corals is formed according to certain universal rules that apply to successive generations of corallites. The presence of two opposite sectors in which budding do not occur seems to be common to other azooxanthellate scleractinian families. Regularities, other than the orientation of the directive septa, are also commonly found at least in other azooxanthellate dendrophylliid genera. These regularities suggest the presence of strict developmental constraints on the asexual reproduction of the Scleractinia, both extant and extinct. These regularities by azooxanthellate scleractinians, as one of the representative colonial metazoan groups, provide us with fundamental data with which we can understand how colonies are constructed. □Azooxanthellate coral, budding, colony, Dendrophyllia arbuscula, regularity.     

Allometric scaling in small colonies of the scleractinian coral Siderastrea siderea (Ellis and Solander)

Although most physiological traits scale allometrically in unitary organisms, it has been hypothesized that modularity allows for isometric scaling in colonial modular taxa. Isometry would allow increases in size without functional constraints, and is thought to be of central importance to the success of a modular design. Yet, despite its potential importance, scaling in these organisms has received little attention. To determine whether scleractinian corals are free of allometric constraints, we quantified metabolic scaling, measured as aerobic respiration, in small colonies (< or =40 mm in diam.) of the scleractinian Siderastrea siderea. We also quantified the scaling of colony surface area with biomass, since the proposed isometry is contingent upon maintaining a constant ratio of surface area to biomass (or volume) with size. Contrary to the predicted isometry, aerobic respiration scaled allometrically on biomass with a slope (b) of 0.176, and colony surface area scaled allometrically on biomass with a slope of 0.730. These findings indicate that small colonies of S. siderea have disproportionately high metabolic rates and SA:B ratios compared to their larger counterparts. The most probable explanations for the allometric scaling of aerobic respiration are (1) a decline in the SA:B ratio with size such that more surface area is available per unit of biomass for mass transfer in the smallest colonies, and (2) the small size, young age, and disproportionately high growth rates of the corals examined. This allometric scaling also demonstrates that modularity, alone, does not allow small colonies of S. siderea to overcome allometric constraints. Further studies are required to determine whether allometric scaling is characteristic of the full size range of colonies of S. siderea.     

Transplantation and cultivation of fragments of coral colonies of various scleractinian species on a reef in Vietnam

Six coral species of the genus Acropora and two species of the genus Porites were studied during experiments on cultivation of reef-building scleractinian corals. The research has established species-specific factors and others affecting regeneration of fragments and growth of new colonies in these coral species. The accretion of donor fragments and new branches averaged from 40 to 160 mm per year, depending on the coral species, colony size, and season of transplantation. An average monthly accretion of medium and larger transplants and growth of new branches were 1.2–1.3 times higher at spring cultivation than at autumn transplanting. When transplanted, coral fragments of medium and larger sizes survived well and showed higher growth rates in all species studied. These transplants developed the highest number of new branches, and their buds and formed the largest colonies. Prolongation of the cultivation time from 1 to 1.5 years caused a 1.2–1.4 fold accretion of transplants.     

Chemical diversity in the scleractinian coral Astroides calycularis

The detailed chemical inspection of the Mediterranean coral Astroides calycularis led to the isolation and structure characterization of two families of alkaloids. Derivatives of orthidine were for the first time isolated from this species. The second family of alkaloids includes the aplysinopsins among which a new derivative is described. The structure was identified on the basis of extensive NMR data interpretation. These results are of chemotaxonomic relevance in order to link this species to the Atlantic Tubastrea aurea.     

Bioaccumulation of zinc in the scleractinian coral Stylophora pistillata

The uptake kinetics of zinc (Zn), an essential nutrient for both photosynthesis and calcification, in the tissue of S. pistillata showed that the transport of Zn is composed of a linear component (diffusion) at high concentrations and an active carrier-mediated component at low concentrations. The carrier affinity (K _m=28 pmol l⁻¹) was very low, indicating a good adaptation of the corals to low levels of Zn in seawater. Zn accumulation in the skeleton was linear; its level was dependent on the length of the incubation as well as on the external concentration of dissolved Zn. There was also a light-stimulation of Zn uptake, suggesting that zooxanthellae, through photosynthesis, are involved in this process. An enrichment of the incubation medium with 10 nM Zn significantly increased the photosynthetic efficiency of S. pistillata. This result suggests that corals living in oligotrophic waters might be limited in essential metals, such as zinc.     

Tissue age affects calcification in the scleractinian coral Madracis mirabilis

In this study, two factorial experiments were used to investigate the role of tissue age in affecting the phenotypic expression of calcification in scleractinian corals. Both experiments tested whether calcification was altered by tissue age and whether corals of different ages exploit plasticity to differing degrees by altering calcification rates under new environmental conditions. To isolate age and size effects, branches of the Caribbean coral Madracis mirabilis were broken into a distal portion that was functionally young and a proximal portion that was functionally old. Fragments were transplanted from a deep (17 m) to a shallow (9 m) site in a Jamaican lagoon to test whether age affected the plasticity of calcification. Both experiments demonstrated that calcification scaled isometrically in the two age groups, and although scaling exponents were indistinguishable statistically among ages, young fragments calcified faster than old fragments. Thus, the effect of age on calcification rate was absolute and independent of size. However, the interactive effect of age and depth was not significant, demonstrating that ability to alter calcification rate (i.e., the extent of phenotypic plasticity for this trait) was unaffected by age. Together, these patterns are consistent with the hypothesis that the proximal modules (i.e., polyps) of M. mirabilis are subject to physiological senescence, as has been reported for other clonal organisms, including algae, fungi, plants, bryozoans, ascidians, and other cnidarians.     

A polypeptide toxin from the coral Goniopora. Purification and action on Ca2+ channels

A polypeptide toxin has been isolated from Goniopora coral with an Mr of 19 000. Goniopora toxin has the following properties: it induces contraction of guinea pig ileum and this contraction is prevented by Ca2+-channel blockers; it stimulates 45Ca2+ influx in cardiac cells in culture and this stimulation is abolished by Ca2+-channel blockers; it prevents binding of (+)-[3H]PN 200-110 to the Ca2+-channel protein of skeletal muscle T-tubule membranes. All these results taken together suggest that Goniopora toxin is a Ca2+-channel activator.     

The cellular stress response of the scleractinian coral <Emphasis Type="Italic">Goniopora columna</Emphasis> during the progression of the black band disease

Black band disease (BBD) is a widespread coral pathology caused by a microbial consortium dominated by cyanobacteria, which is significantly contributing to the loss of coral cover and diversity worldwide. Since the effects of the BBD pathogens on the physiology and cellular stress response of coral polyps appear almost unknown, the expression of some molecular biomarkers, such as Hsp70, Hsp60, HO-1, and MnSOD, was analyzed in the apparently healthy tissues of Goniopora columna located at different distances from the infection and during two disease development stages. All the biomarkers displayed different levels of expression between healthy and diseased colonies. In the healthy corals, low basal levels were found stable over time in different parts of the same colony. On the contrary, in the diseased colonies, a strong up-regulation of all the biomarkers was observed in all the tissues surrounding the infection, which suffered an oxidative stress probably generated by the alternation, at the progression front of the disease, of conditions of oxygen supersaturation and hypoxia/anoxia, and by the production of the cyanotoxin microcystin by the BBD cyanobacteria. Furthermore, in the infected colonies, the expression of all the biomarkers appeared significantly affected by the development stage of the disease. In conclusion, our approach may constitute a useful diagnostic tool, since the cellular stress response of corals is activated before the pathogens colonize the tissues, and expands the current knowledge of the mechanisms controlling the host responses to infection in corals.     

Biomineralization in newly settled recruits of the scleractinian coral Pocillopora damicornis

Calcium carbonate biomineralization of scleractinian coral recruits is fundamental to the construction of reefs and their survival under stress from global and local environmental change. Establishing a baseline for how normal, healthy coral recruits initiate skeletal formation is, therefore, warranted. Here, we present a thorough, multiscale, microscopic and spectroscopic investigation of skeletal elements deposited by Pocillopora damicornis recruits, from 12 h to 22 days after settlement in aquarium on a flat substrate. Six growth stages are defined, primarily based on appearance and morphology of successively deposited skeletal structures, with the following average formation time‐scales: A (<24 h), B (24–36 h), C (36–48 h), D (48–72 h), E (72–96 h), and F (>10 days). Raman and energy dispersive X‐ray spectroscopy indicate the presence of calcite among the earliest components of the basal plate, which consist of micrometer‐sized, rod‐shaped crystals with rhomboidal habit. All later CaCO₃ skeletal structures are composed exclusively of aragonite. High‐resolution scanning electron microscopy reveals that, externally, all CaCO₃ deposits consist of <100 nm granular units. Fusiform, dumbbell‐like, and semispherulitic structures, 25–35 µm in longest dimension, occur only during the earliest stages (Stages A–C), with morphologies similar to structures formed abiotically or induced by organics in in vitro carbonate crystallization experiments. All other skeletal structures of the basal plate are composed of vertically extending lamellar bundles of granules. From Stage D, straight fibrils, 40–45 nm in width and presumably of organic composition, form bridges between these aragonitic bundles emerging from the growing front of fusing skeletal structures. Our results show a clear evolution in the coral polyp biomineralization process as the carbonate structures develop toward those characterizing the adult skeleton. J. Morphol. 275:1349–1365, 2014. © 2014 Wiley Periodicals, Inc.     

A poecilostome copepod parasitic in a scleractinian coral in the moluccas

Wedanus inconstans, n. gen., n. sp., a lichomolgid copepod living in the polyps of the reef coral Goniopora tenuidens (Quelch), is described from Halmahera in the Moluccas. The genus is apparently related to Xenomolgus Humes & Stock, 1972.     

Intracolonial genetic variation in the scleractinian coral Seriatopora hystrix

In recent years, increasing numbers of studies revealed intraorganismal genetic variation, primarily in modular organisms like plants or colonial marine invertebrates. Two underlying mechanisms are distinguished: Mosaicism is caused by somatic mutation, whereas chimerism originates from allogeneic fusion. We investigated the occurrence of intracolonial genetic variation at microsatellite loci in five natural populations of the scleractinian coral Seriatopora hystrix on the Great Barrier Reef. This coral is a widely distributed, brooding species that is at present a target of intensive population genetic research on reproduction and dispersal patterns. From each of 155 S. hystrix colonies, either two or three samples were genotyped at five or six loci. Twenty-seven (~17%) genetically heterogeneous colonies were found. Statistical analyses indicated the occurrence of both mosaicism and chimerism. In most cases, intracolonial variation was found only at a single allele. Our analyses suggest that somatic mutations present a major source of genetic heterogeneity within a single colony. Moreover, we observed large, apparently stable chimeric colonies that harbored clearly distinct genotypes and contrast these findings with the patterns typically observed in laboratory-based experiments. We discuss the error that mosaicism and chimerism introduce into population genetic analyses.     

Metamorphosis of a scleractinian coral in response to microbial biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.     

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.