Coral Pocillopora Damicornis Research Articles

Stimulation of fat-body production in the polyps of the coralPocillopora damicornis by the presence of mutualistic crabs of the genusTrapezia

A mutualism exists between the xanthid crabs of the genusTrapezia and their host corals,Pocillopora damicornis. It has previously been established that these obligate coral residents benefit the coral hosts by defending them against echinoderm predators and by increasing the survival of polyps located deep between the coral branches. In turn, the corals apparently benefit the crabs by producing lipid-filled structures on which the trapezid crabs feed; these fat bodies may contain some of the lipid which in previous studies of coral metabolism has been termed “excess”. It was determined by experiments conducted at the Hawaii Institute of Marine Biology that the presence of crabs in colonies ofP. damicornis stimulates the polyps to produce the lipid-filled fat bodies; removal of crabs causes corals to cease producing fat bodies. A structure very similar to the fat bodies ofP. damicornis has been reported inAcropora durvillei. Both of these coral genera ordinarily possess xanthid-crab mutualists. This association between branching corals and crustaceans may have evolved because corals of these genera provide shelter among their branches and because these shallow-water corals are evidently capable of releasing lipid which is excess to the corals' metabolic needs, but which can be utilized by the crabs.

Sediment and the settlement of larvae of the reef coralPocillopora damicornis

The larval settlement rate of the Indo-Pacific reef coral,Pocillopora damicornis, on bare glass was compared with the rate on glass covered with measured amounts and area of fine sediment. Larval settlement in all sediment treatments was significantly less than on bare glass. Sediment cover of 95% completely prevented settlement. There was no increase in settlement when sediment cover was reduced from 90% to 50% of the glass surface area. If planulae of many coral species behave in a similar fashion in nature, sedimentation at a level that only partially covers the substrate and that is not directly harmful to adult colonies could significantly reduce larval recruitment by inhibiting settlement.

Diurnal patterns of skeleton formation in Pocillopora damicornis (Linnaeus)

Scanning, transmission and X-ray microanalytical electron microscopy were used to investigate the skeleton, organic matrix and calicoblastic ectoderm of the reef coral Pocillopora damicornis over a diurnal cycle. All skeletal surfaces, both during day and hight, are “fasciculate” except for skeletal spines on the branch tip apex at night where small (0.5 μm) fusiform crystals are deposited. X-ray microanalysis shows that the fusiform crystals and needle-shaped crystals that compose the fasciculi are distinct forms of calcium carbonate. Demineralization of the skeleton reveals an organic matrix with two components which are related to the formation of fusiform crystals and fasciculi. During the day the calicoblastic ectoderm overlying all skeletal surfaces is 1–3 μm thick. At night ultrastructural evidence suggests that skeletal deposition occurs only on those skeletal spines at the branch tip apex which are growing parallel with the branch growth axis. The calicoblastic ectoderm overlying apical skeletal spines at night shows a greater degree of cellular activity, and is thicker, than calicoblastic ectoderm overlying both other skeletal surfaces at night ( 6 μm) and all skeletal surfaces during the day ( 3 μm). The deposition of fusiform crystals on skeletal spines at the branch tip apex is proposed to promote deposition of fasciculi during the day, relative to other skeletal surfaces, providing a mechanism determining apical growth of branch tips. The results are discussed with respect to previous concepts of skeletal deposition in scleractinian corals.

Patterns of formation and the ultrastructure of the larval skeleton of Pocillopora damicornis

The growth and development of the tissues and skeleton of settled larvae of the reef coral Pocillopora damicornis (Linnaeus), collected in December 1983 from Ko Phuket, Thailand, were investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. The rate of development of larval skeletons was very variable, preventing the chronological sequencing of skeletal growth. However, four growth stages in the development of a complete larval skeleton from first settlement were identificd: Stage 1, deposition of the first elements of the basal plate upon settlement; Stage 2, completion of basal plate, and deposition of skeletal spines and ridges in positions corresponding to the septal cycles; Stage 3, formation of the corallite wall and septal and costal cycles; Stage 4, the complete larval skeleton which represented the maximum growth attained eight days after settlement. The configuration of the larval tissues, particularly the aboral ectoderm, mirrored the four developmental stages. The deposition of the larval skeleton was correlated with the metamorphosis of the aboral ectoderm from a columnar to a squamous morphology. The basal plate of the larval skeleton had two layers of crystals orientated perpendicular to each other. The architecture of the complete larval skeleton is described and compared to that of the adult skeleton of P. damicornis. The results are discussed with respect to previous concepts of the formation of the larval skeleton of scleractinian corals and coral calcification.

Coral populations Fringing Islands: Larval Connections

The ubiquitous Indo-Pacific coral Pocillopora damicornis utilises two modes of larval dispersal; one operates over short distances and involves a brooded, asexually-produced, planula; the second acts over longer distances and involves a sexual propagule. When examined genetically, larval connections between definable populations were weaker between fringing reefs around an island than they were between patch reefs in an embayment of similar dimensions. Differing regimes of water circulation were inferred to explain this pattern. One implication for management is that populations on fringing reefs are more likely to contain singularities than those on patch reefs and will thus contribute more to the total genetic diversity within a species.

Metals in Pocillopora damicornis exposed to tin smelter effluent

Metal concentrations in tissues and skeleton of the coral Pocillopora damicornis were compared from intertidal reefs adjacent to a tin smelter at Phuket, Thailand. Tissue concentrations of ten metals were significantly higher for corals collected at the tin smelter than at control reefs, 1 km distant. Elevated tissue metal concentrations were considered not to be derived from particulate material but probably from solution. Analyses of skeletal material revealed no differences in metal concentrations between study sites. The implications of elevated tissue metal concentrations are discussed in relation to reduced growth rates and low abundance of branching coral species at the reef adjacent to the tin smelter when compared to the control reefs.

Energetics, competency, and long-distance dispersal of planula larvae of the coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus) were collected from Enewetak Atoll, Marshall Islands, in 1980–1981) and Kaneohe Bay, Hawaii, in 1982. Their planula larvae contained 17% protein, 70% lipid, and 13% carbohydrate by dry weight. Calculations based on stored energy reserves and daily metabolic expenditure indicate that planulae could survive approximately 100 d and still settle successfully. Competency experiments demonstrated that larvae settled and metamorphosed after 103 d. This period of time is sufficient to allow immigration of larvae from the Central Pacific to the eastern Pacific, and supports the hypothesis of long-distance dispersal of larvae for the origin of present eastern Pacific populations of P. damicornis.

Linear extension rate is independent of colony size in the coral Pocillopora damicornis

Measurements of the skeletal extension rate of branches of the reef coral Pocillopora damicornis showed that the linear extension rate is independent of colony size for colonies from 1.9 to 19 cm in diameter. Analysis of existing data from Western Australia, Samoa, the Great Barrier Reef and Hawaii supports the finding that linear extension is not related to colony size in this species.

Mortality and growth of juvenile coral Pocillopora damicornis (Linnaeus)

Early mortality in cohortsof the coral Pocillopora damicornis (Linnaeus) was monitored under experimental conditions on a reef in order to evaluate effects of sedimentation, grazing, predation and competition. Corals that settled in dishes in the laboratory were placed on the reef flat about 3 days after metamorphosis. Six different conditions were tested in each series of experiments: orientation of dishes (upward, vertical and downward) by with and without protection against potential grazers by covering the dish with a net. Survival of juvenile corals on both protected and unprotected dishes facing upward was lower than in the vertical or downward direction. Under the vertical facing and protected conditions, algal growth was more intensive and algae trapped sediment; mortality of juvenile corals by algae and sedimentation increased gradually. In the uprotected and vertical conditions, algal growth on the surface was removed constantly by grazing invertebrates and fishes and the juvenile corals were removed or killed as well. On the downward facing dishes, survivorship of juveniles was relatively high in both protected and unprotected conditions. This habitat attracted many sessile animals that killed some juveniles by competition. Thus, juvenile corals survived better in experimentally manipulated microhabitats not affected by direct sedimentation, not exposed to direct grazing activity, and not occupied by rapidly growing filamentous algae.

LIPID DECLINE IN STRESSED CORALS AND THEIR CRUSTACEAN SYMBIONTS

Total lipid levels, determined by the phosphosulphovanillin colorimetric method, declined significantly in ramose scleractinian corals and their xanthid crab symbionts during the 1983 El Niño warming event on the Pacific coast of Panamá. This decline was observed in a controlled laboratory experiment, employing host corals (Pocillopora damicornis) and obligate crab symbionts (Trapezia corallina and Trapezia ferruginea), concurrently with morbidity and mortality observed on coral reefs in the field. Lipid levels decreased from 0.59% (dry weight) to 0.34% in normal versus affected and dead corals, and from 4.54% (dry weight) to 1.20% in normal versus affected and dead crabs in a two-week period. Lipid depletion in corals accompanied the loss of zooxanthellae and increased morbidity and death; in crabs, a decrease in the number of egg-carrying females, a high emigration rate, a slight increase in mortality, and a decline in defensive behavior occurred. These findings suggest that symbiotic crabs were deprived of food from their coral hosts who initially lost zooxanthellae, an event correlated with the prolonged El Niño sea warming.

Cycles of gametogenesis and plantation in the coral Pocillopora damicornis

Cycles of gametogenesis and plantation in the coral Pocillopora damicornis

Night irradiance and synchronization of lunar release of planula larvae in the reef coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus), which is known to release planula larvae on a monthly cycle, was grown in full daytime solar irradiance, but with four treatments of night irradiance: (1) natural night irradiance, (2) shifted-phase (total darkness during nights of full moon with artificial irradiance at lunar intensity on nights of new moon), (3) constant full moon (full lunar irradiance every night), and (4) constant new moon (total darkness every night). The reproductive cycle of the corals held in the “shifted-phase” treatment moved out of synchrony with the cycle of corals exposed to a natural lunar cycle of night irradiance. Two previously described “types” of P. damicornis were tested. The “Type Y” normally start releasing larvae at full moon, with peak production at third quarter. In the shifted-phase treatment they began releasing planulae at new moon (artificial full moon), with peak production at first quarter. The “Type B” corals, that normally start releasing planulae at new moon with peak production at first quarter, began to release planulae at full moon (artificial new moon), with peak production at third quarter. Populations of corals grown either in the constant full moon or constant new moon treatment quickly lost synchronization of monthly larva production, although production of planulae continued. Thus spawning is synchronized by night irradiance.

Genetic differentiation amongst populations of the coral Pocillopora damicornis off southwestern Australia

An electrophoretic study of genetic differentiation amongst local populations of the reef-coral Pocillopora damicornis was used to group coral heads into units defined as the area of effective dispersal of a clone, and termed “colonies”. For reefs off southwestern Australia, colonies were usually under a few hundred metres in extent. Although most new recruits within a colony were derived asexually, sexually produced propagules acted to connect populations outside the boundaries of a colony. Such connections were weak, and allelic frequencies varied considerably over a few kilometres. The primary agent of genetic differentiation was suggested to be the small effective population size resulting from the asexual proliferation of a few genotypes at any site. The effective number of genotypes per colony was approximately six. Asexual reproduction appears also to limit gene flow and accentuate selection in this species.

Genetical structure within populations of the coral Pocillopora damicornis

Genetic variation of allozymes within populations of Pocillopora damicornis from southwestern Australia was consistent with a primary role of local asexual proliferation of clones in population maintenance. Populations were composed typically of two to four multilocus genotypes accounting for 40 to 80% of individuals, with the remainder assigned to genotypes occasionally in twos or threes but more commonly singly. In the three populations where recruitment was examined genetically, 84% of all first-year recruits was assigned to clones represented in the population's resident adults. The majority of these recruits came from the most highly-replicated of the adult clones. The observed genotypic diversity was, on average, about half that calculated to occur for the same allelic frequencies in a sexually-reproducing population with free recombination. Despite the prevalence of asexual reproduction, both through planulae and fragments, the existence of a sexual mode of reproduction was inferred from the high level of variation produced by pooling populations, the existence of novel genotypes and the concordance of clonal gene frequencies at many sites with the predictions of Hardy-Weinberg equilibria.

Fauna Associated with the Coral Pocillopora damicornis at the Southern Limit of its Distribution in Western Australia

In a study of the fauna of Pocillopora damicornis from three sites at two temperate latitudes on the Western Australia coast, we collected ninetyfour species of coral symbionts, including fifty-four species of decapod crustaceans. Nine of these species are known to be obligate symbionts of living pocilloporid corals throughout the Indo-West Pacific region. At least four other species are known to be non-specifically dependent on living coral with a similarly widespread distribution. Of the remaining eighty-one species, four are known only from living and dead coral, sixty are known from a variety of reef habitats and only facultatively associated with coral, and seventeen have undescribed habits. Although regional species diversity, estimated by species richness, at these two temperate latitudes was less than that reported for some tropical sites, we could find no consistent trend of decreasing diversity with increasing latitude particularly when sample size and size of region were taken into account. More significantly, there was no consistent difference in local species diversity as measured by number of species per unit coral volume between temperate and tropical sites. We conclude that the diversity of the fauna associated with P. damicornis depends as much on the specific characteristics of the site as on latitudinal position.

Effects of light and dark treatments on feeding by the reef coral Pocillopora damicornis (Linnaeus)

The feeding capability of Pocillopora damicornis (Linnaeus) was measured by exposing segments of the same colony to different densities of Artemia salina (L.) nauplii and determining the number of ingested prey. Feeding is directly related to prey density. No plateau in feeding capability was observed over the range of prey densities used. The effects of reduced photosynthesis on feeding capability and tissue dry weight were also examined in colonies maintained in unfiltered running sea water. Tissue samples from clonal segments of Pocillopora damicornis colonies maintained in a covered (dark) sea table for 2 days or 15 to 17 days weighed significantly less than equivalent samples from segments maintained in a normal (light) sea table. Segments maintained in a darkened sea table for over 2 wk were unable to ingest as many Artemia nauplii as their light table equivalents. These data indicate that the amount of Zooplankton available to the colonies in the sea table was insufficient to meet their metabolic requirements and that feeding in Pocillopora damicornis was dependent upon energy derived from photosynthesis by the zooxanthellae.

Spatial and temporal patterns of recuruitment of juvenile coral reef fishes to coral habitats within ?One Tree Lagoon?, great barrier reef

Recruitment of juvenile fishes to coral grids, each comprising 4 colonies of 3 species of coral (Acropora formosa, Seriatopora hystrix and Pocillopora damicornis), was examined at 4 widely separated sites within the lagoon of “One Tree Reef” over two successive summers and intervening months (November 1976–January 1978). Recruitment was highly seasonal, with most recruitment occurring during summer. For many species, numbers settling differed greatly from year to year with total numbers (over all sites) differing as much as an order of magnitude between summers. Many fish species demonstrated marked preference among the three coral species as settling sites. The distribution of each of the 20 commonest species across the 4 lagoon sites differed significantly from a random pattern. Differences of an order of magnitude were common in the numbers of a given species recruited to different sites. Each site was preferred by at least one species. In each of 5 cases examined, the pattern of settlement of the species across the 4 sites changed significantly from one summer to the next. The distribution of recruits of a number of species corresponded to the distribution of adults, but for other species there was no correspondence. It is concluded that, at the spatial scale examined, patterns of recruitment of some taxa are consistently more variable than those of other taxa. The implications of spatial variability of recruitment for the distribution of adult fish is discussed and the importance of being able to discriminate such “natural” variability from other kinds of change is stressed.

Stable isotopes in a branching coral monitor seasonal temperature variation

Reef corals, both fossil and recent, are potentially useful monitors of the surface ocean ‘climate’. Because coral reefs flourish only in relatively warm water1,2, the very presence of reef corals constrains the estimation of local temperature ranges. Studies of hermatypic corals have shown that coral growth rate3–8, density band formation (in some species)9–15, and stable isotopic composition14–23, all respond to variations in water temperature and light intensity. We have measured the stable isotopic composition of specimens of the branching reef coral Pocillopora damicornis which have grown in the field while seawater temperatures were continuously recorded. Detailed oxygen isotope profiles of branches of this species indicate that seasonal changes in temperature and seawater isotopic composition are precisely recorded. Isotopic profiles may be used to estimate growth rates of branching corals, which lack annual density banding. The method provides a technique for high resolution palaeoclimatic reconstruction of seasonal temperature ranges and accurate estimation of rates of reef carbonate production.

Community structure of the fauna associated with the coral Pocillopora damicornis (L.) on the Great Barrier Reef

The structure and composition of the infauna of the coral P. damicornis in the Capricorn Group, Great Barrier Reef, is examined. A total of 40 coral heads were sampled from four localities on two reefs and 951 individuals of 101 species were extracted. This is five times the species collected from P. damicornis in previous studies. A comprehensive species list is provided. Infauna was dominated by only a few species, 20 species accounting for 78% of individuals and 36 species recorded only as single individuals. Crustacea was the dominant taxon present, comprising 72% of species and 86% of individuals. Number of species and number of individuals show significant regressions with size of coral heads. Differences in physical environment at the four sites did not affect species diversity within coral heads. However, several common species only occurred within particular habitats. Species diversity is discussed briefly in relation to the behaviour of resident symbionts, random pelagic settlements of larvae, the size of target corals and habitat heterogeneity in coral heads.

Communication and coexistence in a coral community

A large number of biotic relationships among dissimilar organisms is characteristic of tropical coral reefs. Such relationships involve at least four of the 16 species associated with the coral Pocillopora damicornis (L.) at Heron Island on the Great Barrier Reef. Behavioural interactions among the most conspicuous resident species (2 fish, 1 crab and 1 shrimp) were studied in the field under natural and experimental conditions. The inhabitants have the potential to harass, capture and eat, or exclude one another from the coral habitat but a system of signals among the residents facilitates coexistence and maintains the integrity of the community. The signals include contact and shivering movements by the fish which apparently inform the crustaceans of the fish's resident status.