Settlement ecology of scleractinian corals of the Northeastern Tropical Pacific

Coral Reefs - Reproduction and recruitment are essential processes for the continued success of coral communities. Islas Marias Archipelago is considered a connectivity node among coral communities...     

New records of ahermatypic scleractinian corals from the Kuril Islands

Four species of caryophyllid scleractinians, Caryophylla ambrosia, C. scobinosa, C. alaskensis, and Polymyces montereyensis, were recorded for the first time in the Sea of Okhotsk off the Kuril Islands. These findings extend the range for the species, of which three had previously been considered to be restricted to the tropical and warm Indopacific waters. These data will supplement regional reports on the bottom fauna of the most fertile and extensively commercially exploited continental shelf region of the North Pacific.Original Russian Text Copyright © 2004 by Biologiya Morya, Latypov.     

Regulation of release of antibacterials from stressed scleractinian corals

Recently, we showed that mechanical stress on scleractinian (stony) corals caused a rapid release of antibacterial material (referred to as coral antibacterial activity, or CAA), which killed various bacterial species, including the coral pathogen Vibrio coralliilyticus . We now report on studies on the regulation of CAA release from stressed scleractinian corals. Corals can repeatedly release highly active CAA as a result of sequential stress inductions. Coral fragments were transferred 19 times from one beaker into another with a stress induction each time after 10 min. There was a decrease in the level of antibacterial activity released during the first four to five transfers. After the fifth transfer, the corals kept releasing CAA for the rest of the experiment with no significant decrease. Apparently, the release of CAA is downregulated by feedback inhibition, depending on the concentration of CAA in the surrounding water. By separating CAA-treated V. coralliilyticus from the surrounding water, it was shown that CAA was bound irreversibly to bacterial cells in a stoichiometric manner. Approximately 4 × 10² bacterial cells were sufficient to bind 1 U of CAA. Resident coral bacteria were more resistant to CAA than bacteria isolated from seawater, suggesting an ecological role for CAA. CAA release was obtained from corals after removal of the mucus layer, and the mucus itself contained antibacterial activity.     

Hormones and reproduction in scleractinian corals

Most broadcast spawning scleractinian corals synchronously release gametes during a brief annual spawning period. In southern Taiwan, the mass spawning of scleractinians occurs in lunar mid-March. The exact cues triggering this annual phenomenon remain unclear. A scleractinian coral, Euphyllia ancora has been selected as a model for the hormones and reproduction studies. Testosterone (T) and estradiol (E2) in free and glucuronided forms were identified and consistently detected in coral polyps throughout the year. Peak levels of free E2, glucuronided E2 and T were obtained in the coral tissue just prior to spawning. The presence of specific aromatase activity was demonstrated in coral tissue. Higher concentrations of free E2 than glucuronided E2 were detected in the coral tissue throughout the year. In contrast, higher levels of glucuronided E2 than free E2 and glucuronided T were found in seawater during mass coral spawning. Furthermore, immunoreactivity and biological activity of immunoreactive gonadotropin-releasing hormone (irGnRH) was detected and quantified in coral tissue. Coral extracts (irGnRH) and mammalian (m)GnRH agonist had a similar dose-dependent effect on luteinizing hormone (LH) release in black porgy fish pituitary cells (in vitro). Peak levels of irGnRH were detected during the spawning period. In in vivo experiments, mGnRH agonist time- and dose-dependently stimulated aromatase activity, as well as the levels of T and E2 in free and glucuronided forms in coral. In conclusion, our data suggest that irGnRH and glucuronided E2 may play important roles in the control of reproduction and mass spawning in corals.     

Nucleotide sequences of highly repetitive DNA from scleractinian corals

The staghorn coral genome contains 5% of a satellite DNA, consisting of 80 to 300 x 10(3) copies of a 118-bp repeat unit per haploid Acropora genome.     

Reassessing evolutionary relationships of scleractinian corals

The widely accepted family tree of Scleractinia published by Wells, based on a combination of morphological coral taxonomy and the fossil record, has recently been revised by Veron. It is now possible to test the validity of some of the conclusions reached by these and other authors by the use of molecular techniques. This paper reviews the results to date. Studies of ribosomal DNA have shown that the Scleractinia are monophyletic, i.e. derived from the same ancestral taxon. Extensions of this same data set now indicate that the Poritidae and Dendrophylliidae, with their fossil antecedents, may each warrant separate suborder status. They further suggest (a) that the Suborder Faviina (faviids, mussids and their allies) should probably be retained as a monophyletic group and (b) that Wells' original account of the isolated position of the Pocilloporidae and Astrocoeniidae is correct. These conclusions all accord with Veron's family tree. However, the Fungiina, even after removal of the Poritidae, are unlikely to be a monophyletic group at suborder level. The molecular data further show that externally observable morphological characters used in the taxonomy of extant corals distinguish families more reliably than do internal micro-skeletal characters frequently used in coral palaeontology.     

Carbohydrate composition of mucus from scleractinian corals from the central Red Sea

Coral Reefs - Coral mucus is continuously released by most corals and acts as an important protective barrier and as a substrate for host-associated microbial communities due to its complex...     

Metabolism of estrogens and androgens by scleractinian corals

Estrogens and androgens are steroids that act as reproductive hormones in vertebrates. These compounds have also been detected in reef-building corals and other invertebrates, where they are hypothesized to act as bioregulatory molecules. Experiments were conducted using labeled steroid substrates to evaluate metabolism of estrogens and androgens by coral homogenates. GC-MS analysis of 13C-labeled steroids showed that Montipora capitata coral homogenates or fragments could convert estradiol to estrone and testosterone to androstenedione and androstanedione, evidence that M. capitata contains 17beta-hydroxysteroid dehydrogenase and 5alpha-reductase. When homogenates from three coral species and symbiotic dinoflagellates (zooxanthellae) were incubated with tritiated steroid substrates, metabolites separated by thin-layer chromatography confirmed that 17beta-hydroxysteroid dehydrogenase activity occurred in all species tested. NADP+ was the preferred cofactor in dehydrogenation reactions with coral homogenates. Reduction of estrone and androstenedione occurred at lower rates and aromatization of androgens was not observed. It is unclear whether estrogens detected previously in coral tissues are produced endogenously or sequestered in coral tissue from dietary or environmental sources. Previous studies have demonstrated that corals can take up estrogens from the water column overlying coral reefs. Considered in total, these observations suggest corals could alter the concentration or form of steroids available to reef organisms.     

Larval development of certain gamete-spawning scleractinian corals

Embryogenesis and larval development were documented in 19 species of hermatypic scleractinians which release gametes during the summer coral spawning season on the Great Barrier Reef. Cleavage of fertilized eggs began approximately 2 h after spawning in all species, and gave rise to blastulae after 7–10 h. Endoderm formation in Platygyra sinensis was by invagination, and this appeared to occur in all species studied. All species observed at 36 h after spawing were mobile and full mobility was reached by 48 h. Settlement of planulae placed in aquaria occurred between 4 and 7 days after fertilization. These results suggest that larval corals produced by most gamete-releasing coral species are likely to be dispersed away from the parent reef.     

Environmental influences on skeletal banding in eastern Pacific (Panama) corals

The timing of skeletal band formation and concomitant changes in calcification rates and linear skeletal extension were investigated in Pavona corals growing under two distinct thermal regimes along the Pacific coast of Panama: fluctuating, marked by seasonal upwelling (Gulf of Panama) and stable, nonupwelling (Gulf of Chiriqui). The purpose of this study was to test the hypothesis that banding in corals is largely mediated by seasonal variations in temperature (Highsmith 1979). Our results indicate that the timing of band formation is synchronous at these two environmentally distinct locations. The low density (LD) portion of the annual band is accreted over a five month period (January–June) and represents an increase in linear skeletal extension (mm/mo.) as well as a marked increase in calcification rate (g CaCO₃ · cm^-2 · mo^-1) relative to the high density portion which forms over the remaining seven month period (July through December). In contrast to the predictions of the Highsmith model these findings indicate that variations in light levels rather than fluctuation in temperature is a better correlate to changes in skeletal density. Qualitatively, banding patterns were similar at the two sites; however, higher growth rates (particularly with respect to the LD band) for Pavona clavus in the Gulf of Panama indicate that lower water temperatures and higher productivity, or both, may be responsible for quantitative differences in banding between sites. We found that formation of the HD band corresponds to lower light levels and the production of gametes. We propose that banding in corals is a complex phenomenon governed by endogenous processes (e.g. reallocation of energy from growth to reproduction) which may be mediated by exogenous factors (e.g light and productivity).     

Free-living scleractinian corals on reefs of the Seychelles Islands

Thirty-nine species of unattached scleractinian corals that belong to 22 genera of 9 families were found on the Seychelles reefs. Variations of the colony form of corals living on soft sediments under continuous wave action are described. Irrespective of their initial growth form and taxonomic position, corals assume a form close to spherical. Because of the worldwide deterioration of coral reefs, the adaptation to changing ecological conditions by reef-building corals needs to be studied.     

Different algal symbionts explain the vertical distribution of dominant reef corals in the eastern Pacific

Symbiotic reef corals occupy the entire photic zone; however, most species have distinct zonation patterns within the light intensity gradient. It is hypothesized that the presence of specific symbionts adapted to different light regimes may determine the vertical distribution of particular hosts. We have tested this hypothesis by genetic and in situ physiological analyses of the algal populations occupying two dominant eastern Pacific corals, over their vertical distribution in the Gulf of California. Our findings indicate that each coral species hosts a distinct algal taxon adapted to a particular light regime. The differential use of light by specific symbiotic dinoflagellates constitutes an important axis for niche diversification and is sufficient to explain the vertical distribution patterns of these two coral species.     

Ontogeny of 'epithecal' and septal structures in scleractinian corals

The ontogenetic development of a solitary scleractinian coral, Flabellum distinctum Edwards & Haime, has been studied in serial thin section, with special attention being paid to epithecal nature in relation to septal growth. The term 'epitheca' has been confusingly used for two different skeletal structures: epitheca ( sensu stricto ) and marginotheca. The latter is here newly proposed. 'epitheca' is defined as a calcareous investment developed on the outside of other skeletal structures of a corallite. It can be distinguished from the marginotheca in section by lacking a dark line (calcification centre) and by being unrelated to the formation of septa. 'marginotheca' defines the outer margin of the main skeletal structures of a corallite. It has a dark line which functionally coincides with that of the eutheca. It is of primary origin, preceding formation of septa and provides the origin of the septa. The marginotheca is one of the more important and fundamental skeletal structures for coral classification.     

Extinction and recovery patterns of scleractinian corals at the Cretaceous-Tertiary boundary

The extinction and recovery of scleractinian corals at the Cretaceous-Tertiary (K-T) boundary was analyzed based on a global database of taxonomically revised late Campanian to Paleocene coral collections. In contrast to earlier statements, our results indicate that extinction rates of corals were only moderate in comparison to other marine invertebrates. We have calculated a 30% extinction rate for Maastrichtian coral genera occurring in more than one stratigraphic stage and more than one geographic region. Reverse rarefaction suggests that some 45% of all coral species became extinct. Photosymbiotic (zooxanthellate) corals were significantly more affected by the extinction than azooxanthellate corals; colonial forms were hit harder than solitary forms, and among colonial forms an elevated integration of corallites raised extinction risk. Abundance, as measured by the number of taxonomic occurrences, had apparently no influence on survivorship, but a wide geographic distribution significantly reduced extinction risk. As in bivalves and echinoids neither species richness within genera nor larval type had an effect on survivorship. An indistinct latitudinal gradient is visible in the extinction, but this is exclusively due to a higher proportion of extinction-resistant azooxanthellate corals in higher-latitude assemblages. No significant geographic hotspot could be recognized, neither in overall extinction rates nor in the extinction of endemic clades.More clades than previously recognized passed through the K-T boundary only to become extinct within the Danian. These failed survivors were apparently limited to regions outside the Americas. Recovery as defined by the proportional increase of newly evolved genera, was more rapid for zooxanthellate corals than previously assumed and less uniform geographically than the extinction. Although newly evolved Danian azooxanthellate genera were significantly more common than new zooxanthellate genera, the difference nearly disappeared by the late Paleocene suggesting a more rapid recovery of zooxanthellate corals in comparison to previous analyses. New Paleocene genera were apparently concentrated in low latitudes, suggesting that the tropics formed a source of evolutionary novelty in the recovery phase.     

Searching for new morphological characters in the systematics of scleractinian reef corals: comparison of septal teeth and granules between Atlantic and Pacific Mussidae

Recent molecular analyses have challenged the traditional classification of scleractinian corals at all taxonomic levels suggesting that new morphological characters are needed. Here we tackle this problem for the family Mussidae, which is polyphyletic. Most of its members belong to two molecular clades composed of: (1) Atlantic Mussidae and Faviidae (except Montastraea) and (2) Pacific Mussidae (Cynarina, Lobophyllia, Scolymia, Symphyllia) and Pectiniidae. Other Pacific mussids (e.g. Acanthastrea) belong to additional clades. To discover new characters that would better serve as phylogenetic markers, we compare the skeletal morphology of mussid genera in different molecular‐based clades. Three sets of characters are considered: (1) macromorphology (budding; colony form; size and shape of corallites; numbers of septal cycles), (2) micromorphology (shapes and distributions of septal teeth and granules), and (3) microstructure (arrangement of calcification centres and thickening deposits within costosepta). Although most traditional macromorphological characters exhibit homoplasy, several new micromorphological characters are effective at distinguishing clades, including the shapes and distribution of septal teeth and granules, the area between teeth, and the development of thickening deposits. Arrangements of calcification centres and fibres differ among clades, but the fine‐scale structure of thickening deposits does not.     

Rethinking the phylogeny of scleractinian corals: a review of morphological and molecular data

Scleractinian corals, which include the architects of coral reefs, are found throughout the world's oceans and have left a rich fossil record over their 240 million year history. Their classification has been marked by confusion but recently developed molecular and morphological tools are now leading to a better understanding of the evolutionary history of this important group. Although morphological characters have been the basis of traditional classification in the group, they are relatively few in number. In addition, our current understanding of skeletal growth and homology is limited, and homoplasy is rampant, limiting the usefulness of morphological phylogenetics. Molecular phylogenetic hypotheses for the order, which have been primarily focused on reef-building corals, differ significantly from traditional classification. They suggest that the group is represented by two major lineages and do not support the monophyly of traditional suborders and most traditional families. It appears that once a substantial number of azooxanthellate taxa are included in molecular phylogenetic analyses, basal relationships within the group will be clearly defined. Understanding of relationships at lower taxonomic levels will be best clarified by combined analyses of morphological and molecular characters. Molecular phylogenies are being used to inform our understanding of the evolution of morphological characters in the Scleractinia. Better understanding of the evolution of these characters will help to integrate the systematics of fossil and extant taxa. We demonstrate how the combined use of morphological and molecular tools holds great promise for ending confusion in scleractinian systematics.     

The enidom: an index of aggressive proficiency in scleractinian corals

This study of ten Indo-Pacific and Caribbean scleractinian corals explains their relative aggressive proficiencies in terms of their cnidoms. Species ranging from aggressive to subordinate, on an established hierarchy, were studied. Size, number and distribution of each cnida type were quantified. A marked relationship between number of nematocysts per polyp and aggressive proficiency was demonstrated. The recorded differences in aggressive proficiency between the Indo-Pacific and Caribbean corals are discussed in terms of cnidom differences. In two species a significant trend in linear distribution of nematocysts along mesenterial filaments was recorded, with a distinct zonation of the different nematocyst types along the length of the filament.