Habitat patchiness and predation modify the distribution of a coral-dwelling damselfish

Fish abundance is often better predicted by microhabitat variables on continuous reefs than on isolated patch reefs. Although this was suggested to stem from reduced post-recruitment relocation, this has not been shown experimentally. We found the relationship between the presence of a coral-dwelling fish, Dascyllus marginatus, and the size of its coral host to differ between corals on continuous reefs and the sparsely distributed corals on sandy bottoms. Empty transplanted corals were colonized exclusively by new recruits when on the sandy bottom, and both by new recruits and post-recruitment dispersal of adults when on the continuous reef. New recruits settled predominantly into small corals, although analyses of recruitment patterns were confounded by low recruitment in the studied years. Both tank experiments and field survey data suggest that the presence of recruits in small corals is at least partially driven by predation by the dottyback, Pseudochromis olivaceus, which lives predominantly in large corals within both habitats. Consequently, we suggest that the relationship between fish presence and coral size differs between the habitats due to coral size dependent predation on recruits and variability in the importance of direct recruitment to replenish fish populations.     

Effects of sheltering fish on growth of their host corals

Stony corals are the foundation species of tropical reefs, and their structures can harbor a diverse range of mutualist taxa that can confer important benefits, including provision of nutrients. Prominent among the associates of branching coral in the genus Pocillopora are groups of zooplanktivorous damselfishes that take refuge in the coral to avoid their predators. In field and laboratory experiments, we explored the effects of colonies of resident damselfishes on growth of their host corals. Laboratory studies revealed a positive relationship between biomass of fish and output of ammonium. In the field, levels of ammonium were significantly elevated in the water surrounding the branches of Pocillopora occupied by colonies of damselfish, particularly in time periods following active feeding by the fish. Experimental manipulation of the presence of fish on host corals during a month-long field experiment revealed that corals hosting fish grew significantly more than those that lacked fish, and coral growth was positively correlated with the biomass of resident fish. The Pocillopora colonies in the field experiment varied in the degree of openness of their branching structure, and dye studies indicated that this affected their ability to retain waterborne nutrients. Together with biomass of resident fish, colony openness explained 76% of the variation in coral growth rate during the experiment. Corals can exhibit considerable morphological variability, and mutualistic fish respond to colony architecture during habitat selection, with some species preferring more open-branched forms. This makes it likely that corals may face tradeoffs in attracting resident fish and in retaining the nutrients they provide.     

Increased mortality and photoinhibition in the symbiotic dinoflagellates of the Indo–Pacific coral Stylophora pistillata (Esper) after summer bleaching

Coral bleaching (the loss of symbiotic dinoflagellates from reef-building corals) is most frequently caused by high-light and temperature conditions. We exposed the explants of the hermatypic coral Stylophora pistillata to four combinations of light and temperature in late spring and also in late summer. During mid-summer, two NOAA bleaching warnings were issued for Heron Island reef (Southern Great Barrier Reef, Australia) when sea temperature exceeded the NOAA bleaching threshold, and a ‘mild’ (in terms of the whole coral community) bleaching event occurred, resulting in widespread S. pistillata bleaching and mortality. Symbiotic dinoflagellate biomass decreased by more than half from late spring to late summer (from 2.5×10⁶ to 0.8×10⁶ dinoflagellates cm² coral tissue), and those dinoflagellates that remained after summer became photoinhibited more readily (dark-adapted F _V : F _M decreased to (0.3 compared with 0.4 in spring), and died in greater numbers (up to 17% dinoflagellate mortality compared with 5% in the spring) when exposed to artificially elevated light and temperature. Adding exogenous antioxidants (d-mannitol and l-ascorbic acid) to the water surrounding the coral had no clear effect on either photoinhibition or symbiont mortality. These data show that light and temperature stress cause mortality of the dinoflagellate symbionts within the coral, and that susceptibility to light and temperature stress is strongly related to coral condition. Photoinhibitory mechanisms are clearly involved, and will increase through a positive feedback mechanism: symbiont loss promotes further symbiont loss as the light microenvironment becomes progressively harsher.     

Plasticity in size and age at maturity in a monogamous fish: effect of host coral size and frequency dependence

The number and maximum body size of the gobioid fish, Paragobiodon echinocephalus, increase with the size of its obligate host coral, Stylophora. Only the largest two individuals breed monogamously in each coral head, and the reproductive success of each spawning is positively correlated with body size. In this study, the plasticity in size and age at maturity in P. echinocephalus was examined. We analyzed life history data from gobies 15–20 mm TL (total length) at their initial marking. Gobies found in larger corals were of lower rank in size order and began to breed later at a larger size, usually upon moving to other corals. The size at maturity ranged widely from 17.2 to 36.0 mm TL. After maturation, growth rates decreased. Mortality, however, was not affected by the timing of maturation. The host coral size did not affect the growth and mortality of marked fish, but the mortality rate of juveniles prior to marking appeared to be higher in smaller corals. The estimated lifetime reproductive success did not differ between the gobies inhabiting corals of different size. Thus the plasticity in size and age at maturity in this species may be maintained by frequency-dependent selection in choosing a host coral size that affects an individual’s social status. Received: 5 April 1995/Accepted after revision: 18 February 1996     

Using three-dimensional surface area to compare the growth of two Pocilloporid coral species

Many facets of coral research require coral colony surface area estimates. This study developed a relationship between the two-dimensional (2D) projected area and the three-dimensional (3D) whole colony surface area for two commonly studied Indo-Pacific coral species: Pocillopora damicornis and Stylophora pistillata. The surface index function was used to measure the growth of colonies in situ around Heron reef on the southern Great Barrier Reef. The results show that while growth between the two species was not significantly different when measured in two dimensions, the 3D area showed significantly different growth rates with S. pistillata growing at almost double the rate of P. damicornis. The study demonstrates that it is possible to make reliable estimates of the 3D surface area of entire colonies of these complex branching coral species, using the plan view of the coral and a pre-determined surface index function. In addition, this study shows that the 3D surface area provides a more useful measure of colony growth than the traditional methods of either 2D area or longest dimension.     

Coral recruitment: a spatio-temporal analysis along the coastline of Eilat,northern Red Sea

Recruitment rates of stony corals to artificial substrates were monitored for 2 years at 20 sites along the coast of Eilat, northern Red Sea, to compare with those recorded at other coral reef locations and to assess variation in recruitment at several spatial scales. Coral recruitment was low compared to that observed on the Great Barrier Reef in Australia, but was similar to levels reported from other high-latitude reef locations. Pocilloporids were the most abundant coral recruits in all seasons. Recruitment was twofold higher during the first year than during the second year of study. There was considerable spatial variability, with the largest proportion of variance, apart from the error term, attributable to differences between sites, at a scale of 10² m. Spearmans ranked correlation showed consistency in spatial patterns of recruitment of pocilloporid corals between years, but not of acroporid corals. During spring, when only the brooding pocilloporid coral Stylophora pistillata reproduces at this locality, most coral recruitment occurred at central and southern sites adjacent to well-developed coral reefs. During summer, recruitment patterns varied significantly between years, with wide variation in the recruitment of broadcasting acroporid corals at northern sites located distant from coral reefs. Settlement was low at all sites during autumn and winter. This work is the first detailed analysis of coral recruitment patterns in the Red Sea, and contributes to the understanding of the spatial and temporal scales of variation in this important reef process.Communicated by O. Kinne, Oldendorf/Luhe     

Assessing stress response of Stylophora pistillata towards oil and phosphate pollution in the Gulf of Aqaba,using molecular and biochemical markers

Crude oil (from oil terminal) and raw phosphate (from phosphate port) pollution are responsible for the lowered health conditions of coral reefs at their vicinity in the Jordanian coast of the Gulf of Aqaba. Both in situ incubations and ex situ laboratory exposure experiments were used to study the effects of those pollutants on corals, by using molecular and biochemical biomarkers in the coral Stylophora pistillata. For ex situ part of the experiment, crude oil and raw phosphate were added to a final concentration of 500?ppm for both pollutants. The DNA damage was assessed by Comet assay, while biochemical stress markers were reassessed by lipid peroxidation (LPO) test. Although the corals looked healthy from outside, the use of stress biomarkers indicated that they are under high pressure at the cellular level. The corals incubated with oil and phosphate had more DNA damage and LPO in comparison with the control samples. The results obtained suggest that the use of stress biomarkers can be used as important prognostic tools for examining the sub-lethal stress on corals before their death.     

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.     

Transplantation of juvenile corals: a new approach for enhancing colonization of artificial reefs

 Coral reefs in the northern Gulf of Eilat are exposed to continuous man-made disturbances, resulting in decreased coral coverage and reduced recruitment at the Nature Reserve of Eilat. The construction of artificial reefs on sandy bottoms is a possible option to decrease diving pressure on natural reefs. In the present study we tested this hypothesis by submerging an experimental artificial reef anchored to the bottom at 18 m depth and floated vertically 3 m below water surface. The reef was composed of PVC plates, attached both vertically and horizontally along a wire. Propagules of two coral species, the stony coral Stylophora pistillata and the soft coral Dendronephthya hemprichi, were transplanted to this artificial reef. Planulae of S. pistillata were obtained during the breeding season, seeded in petri dishes in the laboratory and after 2 wk the dishes were transferred to the experimental artificial reef. Automized fragments of D. hemprichi which had previously settled on 10 × 10 cm PVC plates were transplanted onto the experimental artificial reef. The survivorship of the transplanted D. hemprichi colonies was significantly higher on the lower sides of shallower plates. Survivorship of S. pistillata colonies increased with depth when located on the vertical plates, or on the upper sides of the horizontal plates. The highest survivorship of this coral was on the vertical plates and on the upper sides of the horizontal plates, while very low survivorship was recorded on the lower sides. The results indicate that vertical artificial surfaces offer the optimal biotic and abiotic conditions for the survival of the two examined corals. The vertical plates are characterized by low sed imentation rates, low coverage of turf-algae, minimal grazing by sea urchins and absence of the competitor tunicate Didemnum sp. In addition, the vertical orientation of the experimental plates reduces shading and offers the required light intensity for zooxanthellate corals such as S. pistillata. Only a few studies to date have tried to implement artificial reefs in a coral reef environment. The results of the present study indicate the potential of enhancing recruitment of corals by transplantation of juvenile recruits onto appropriate artificial structures. Maximal survivorship of these recruits is dependent upon the structural features of the artificial reef, which should offer optimal conditions. Received: 25 May 1996 / Accepted: 15 July 1996     

Variation in colony geometry modulates internal light levels in branching corals, <Emphasis Type="Italic">Acropora humilis</Emphasis> and <Emphasis Type="Italic">Stylophora pistillata</Emphasis>

Colonial photosynthetic marine organisms often exhibit morphological phenotypic plasticity. Where such plasticity leads to an improved balance between rates of photosynthesis and maintenance costs, it is likely to have adaptive significance. To explore whether such phenotypic plasticity leads to more favourable within-colony irradiance for reef-building branching corals, this relationship was investigated for two coral species Acropora humilis and Stylophora pistillata, along a depth gradient representing light habitats ranging from 500 to 25 μmol photons m⁻² s⁻¹, during 2006 at Heron Island, Great Barrier Reef (23.44°S, 151.91°E). In the present study changes in flow-modulated mass transfer co-varied with light as a function of depth. In low-light (deep) habitats, branch spacing (colony openness) in A. humilis and S. pistillata was 40–50% greater than for conspecifics in high-light environments. Also, branches of A. humilis in deep water were 40–60% shorter than in shallow water. Phenotypic changes in these two variables lead to steeper within-colony light attenuation resulting in 38% higher mean internal irradiance (at the tissue surface) in deep colonies compared to shallow colonies. The pattern of branch spacing was similar for S. pistillata, but this species displayed an alternate strategy with respect to branch length: shade adapted deep and cave colonies developed longer and thinner branches, allowing access to higher mass transfer and irradiance. Corals in cave habitats allowed 20% more irradiance compared to colonies found in the deep, and had a 47% greater proportion of irradiance compared to colonies in the shallow high-light environment. Such phenotypic regulation of internal light levels on branch surfaces partly explains the broad light niches of many branching coral species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Purification of multiple vitellogenins in grey mullet (<Emphasis Type="Italic">Mugil cephalus</Emphasis>)

Coralliophila abbreviata (Lamarck) is a corallivorous gastropod that lives and feeds on several species of scleractinian coral in the Western Atlantic and Caribbean. Previous studies of C. abbreviata have revealed that snails on branching acroporid corals are larger and consume more tissue than those on massive and plating corals. To ascertain whether snail life-history and fitness are differentially affected by the coral host, an analysis of the age structure and female reproductive output of snail populations on three coral host taxa (Acropora palmata, Diploria spp., and Montastraea spp.) was conducted at four shallow (2–7 m depth) reef sites off Key Largo, Florida in June through August, 2004. Snails were, on average, almost twice as large on A. palmata than on Diploria spp. and Montastraea spp., averaging 30.3 mm shell length, compared to 17.2 and 17.6 mm, respectively. Brood size increased as a power function with female shell length. Females on A. palmata were significantly larger than females on the other two hosts and, therefore, produced more offspring per female. The number of growth striae on the inner surface of the operculum was used to estimate snail age. Estimates of growth rate were obtained by fitting the Gompertz growth function to size-at-age plots and mortality was estimated using growth parameters and size-frequency data. The data suggest that C. abbreviata inhabiting A. palmata are larger than on alternative hosts due to a combination of a faster growth rate and longer life-span. The species is believed to be a protandrous hermaphrodite. The timing of sex change varied among hosts; snails on A. palmata changed sex later at larger sizes relative to those on the other two hosts. Based on these results, it seems probable that C. abbreviata has developed reaction norms for life-history traits, allowing snails to adjust and maximize fitness in the different environments associated with various coral hosts.     

Effects of ambient levels of solar ultraviolet radiation on zooxanthellae and photosynthesis of the reef coral Montipora verrucosa

Paired flat plates of the hermatypic coral Montipora verrucosa from Kaneohe Bay, Oahu, Hawaii, were acclimated to photosynthetically active radiation (PAR) only and to full sunlight (PAR+UV) for several weeks in the summer of 1990. After the acclimation period, photosynthesis, both in PAR-only and PAR+UV as well as dark respiration were measured. Levels of the UV-absorbing compounds, S320, density of zooxanthellae, and chlorophyll a concentration were determined. Corals acclimated in PAR+UV had higher levels of the UV-protective compounds and lower areal zooxanthellae densities than corals acclimated in PAR-only. Chlorophyll a per unit volume of coral host and per algal cell did not differ between corals from the two acclimation treatments. Corals acclimated to PAR+UV displayed higher photosynthesis in full sunlight than corals acclimated to PAR-only, but when photosynthesis was measured in the light regime to which the corals had been acclimated, there were no differences in photosynthesis. Dark respiration was the same for corals from the two acclimation treatments regardless of the light quality immediately preceding the dark period.Contribution No. 902 HIMB     

Rafting of reef corals and other organisms at Kwajalein Atoll

Studies conducted at Kwajalein Atoll (9°N; 168°E) in early 1988 reveal that marine organisms are commonly rafted into the area on drift pumice, drift wood and other flotsam. Coralskeletons on pumice provide the most useful quantitative data because they persist after rafted motile organisms have departed and rafted sessile forms have decomposed or been scavenged. The estimated minimum number of pumice fragments carrying corals into Kwajalein Atoll during its geological history is on the order of 10⁹, with a more realistic estimate in excess of 10¹¹. The estimated number of coral colonies rafted into the atoll would probably have to be increased several-fold if rafting on floating organic materials such as wood, charcoal, nuts and seeds could be determined. In the present study, a typical sample of beached pumice from Kwajalein Atoll contained 10³ coral colonies per m³ of bulk pumice fragments. Major pumice rafting episodes frequently result from volcanic eruptions. Estimates based on the observed K wajalein coral fouling rate and literature values for drift pumice production suggest that 10⁵ colonies could be rafted through the tropics by the smallest reported pumice-producing events and up to 10¹² colonies for large events. In the present study, most of the rafted corals that were recovered belong to species of the genus Pocillopora, but speccics of Porites and Millepora were also collected. Analysis of surface-current data and reported drift patterns for pumice, logs, drift bottles and wrecks suggests that movement of rafted corals and drifting larvae is predominantly from peripheral areas of low coral-species diversity into centers of high coral diversity. Coral diversity centers might be viewed as areas of coral species accumulation rather than centers of coral species origin.     

Reproductive patterns of scleractinian corals in the northern Red Sea

The majority of published accounts on scleractinian coral reproduction are from the tropical Pacific and Caribbean, with very little information known about Red Sea species. This report examines variation in reproductive mode in 24 species of hermatypic corals (belonging to seven families) in the Gulf of Eilat, Red Sea. Eighteen species are hermaphroditic broadcasters, two are hermaphroditic brooders and three are gonochoric broadcasters. In the Pocilloporidae, the gonads project into the body cavity, while in the other six families the gonads reside inside the mesenteries. The number of gonads per polyp in broadcasting species follows family or genus lines. Fecundity (eggs per polyp) increases with polyp size. Brooding species usually exhibit one or two gonads per polyp and each gonad contains only one to three oocytes. Oocyte size varies widely and does not relate to mode of reproduction. The largest oocytes (diameter = 450 μm) occur in the brooding coral Alveopora daedalea and in broadcasting species of the genus Acropora (diameter = 420 μm). Gonad morphology and gonochorism versus hermaphroditism appear to be constrained phylogenetically at the family or genus level. Lastly, this report compares the data presented for Red Sea scleractinian species with the data available on scleractinian corals from other geographical regions. Received: 2 February 1993 / Accepted: 9 March 1998     

Cohabitation of a coral reef sponge and a colonial scyphozoan

A sensitive experimental protocol using cloned corals (hereafter microcolonies) of the branching scleractinian coral Stylophora pistillata and ⁴⁵Ca has been developed to enable reproducible measurements of physiological and biochemical mechanisms involved in calcium transport and compartmentalization during coral calcification. Cloned S. pistillata microcolonies were propagated in the laboratory from small fragments of parent colonies collected in 1990 in the Gulf of Aqaba, Jordan. Cloned microcolonies have several intrinsic properties that help to reduce unwanted biological variability: (1) same genotype; (2) similar sizes and shapes; and (3) absence of macroscopic boring organisms. Errors specifically associated with long-standing problems to do with isotopic exchange were further reduced by producing microcolonies with no skeletal surfaces exposed to the radioisotope-labelled incubation medium. The value of the technique resides principally in its superior ability to elucidate transportation pathways and processes and not in its ability to quantitatively estimate calcium deposition by corals in nature. We describe here a rapidly exchangeable calcium pool in which up to 90% of the radioactive label taken up during incubations is located. This pool (72.9±1.4 nmol Ca mg^-1 protein) is presumably located within the coelenteric cavity as suggested by the following: (1) it has 4-min half-time saturation kinetics; (2) the accumulation of calcium is linearly correlated with the calcium concentration of sea-water; and (3) its insensitivity to metabolic and ion transport inhibitors indicate that membranes do not isolate this compartment. Washout of this large extracellular pool greatly improved estimates of calcium deposition as evidenced by 10 to 40% reduction in coefficients of variation when compared with previous ⁴⁵Ca²⁺ methods described in the literature. Comparisons of calcification measurements simultaneously carried out using the alkalinity anomaly technique and the ⁴⁵Ca protocol described here show that the correlation coefficient of both techniques is close to 1. Unlike previous reports, our ⁴⁵Ca²⁺-derived measurements are slightly lower than those computed from the alkalinity depletion technique.     

Adaptation of solitary corals and their zooxanthellae to low light and UV radiation

Adaptation of solitary corals, Fungia repanda and F. echinata, and their zooxanthellae to low light and ultraviolet light B (UV-B) was studied with respect to changes in their protein contents, photosynthetic pigment contents and the photosynthesis-irradiance (P-I) curves. The corals were collected from 1 to 50 m depths in the Republic of Belau (Paulau) in 1990 and 1991. The chlorophyll a content in a unit surface area of the coral did not change significantly with the depth of the habitat, whereas cellular chlorophyll a in the algae increased with the depth. Zooxanthellae density and protein content in a unit surface area of Fungia spp. decreased with the depth. Photosynthetic parameters normalized by a unit surface area of the Fungia spp., maximum gross photosynthetic rate (P _gmax area^-1) and dark respiration rate (R area^-1), were negatively correlated with the depth, while initial slope of the P-I curve () did not show significant correlation with the depth. Compensation light intensity (Ic) decreased with the depth. In isolated zooxanthellae, P _max chl a ^-1, and R chl a ^-1 decreased with the depth, while _{chl a} was constant. P _gmax cell^-1 and R cell^-1 did not change significantly but _cell increased with the depth. Ic decreased with the depth as in the intact corals. Reduction of protein content in a unit area of the coral from deeper habitat implies decrease of host animal tissues. Reduction of Ic can be explained by decrease of R area^-1, which may be due to the diminution of animal tissues. The photoadaptational response to low light intensity of intact Fungia spp. was found to be a combination of the photoadaptation of symbiotic algae and the decrease of host animal tissue. In order to study their adaptation to ultraviolet (UV) radiation, P-I curves of Fungia spp. and isolated zooxanthellae were analyzed before and after UV-B irradiation. 1 h UV-B irradiation showed no effect on the photosynthetic rate of the shallow water (1 m) corals, while it inhibited the photosynthesis of the deep water (30 m) corals and zooxanthellae isolated from both shallow and deep water corals. These results indicate that the host, Fungia spp., in shallow water have protective mechanism for intense UV-B in their habitat. These photoadaptational mechanisms seem to allow the Fungia spp. to have wide vertical distribution where light intensity spans more than two orders of magnitude.     

Coral mucus stable isotope composition and labeling: experimental evidence for mucus uptake by epizoic acoelomorph worms

Mucus released by scleractinian corals can act as an important energy and nutrient carrier in coral reef ecosystems, and a distinct isotopic signature would allow following the fate of this material. This study investigates the natural C and N stable isotopic signatures of mucus released by four scleractinian coral genera (Acropora, Fungia, Pocillopora and Stylophora) in comparison with those of suspended particulate organic matter (POM) in seawater of a Northern Red Sea fringing coral reef near Aqaba, Jordan. The natural δ¹³C and δ¹⁵N signatures of coral mucus differed significantly from seawater POM for the majority of seasonal comparisons, but were inappropriate for explicit tracing of mucus in the coral reef food web. Thus, a labeling technique using stable isotope tracers (¹³C and ¹⁵N) was developed that produced δ¹³C values of up to 122 ± 5‰ (mean ± SE) and δ¹⁵N of up to 2,100 ± 151‰ in mucus exuded by Fungia corals. ¹³C and ¹⁵N-enriched compounds were rapidly (within 3 h) and light-dependently transferred from the endosymbiotic zooxanthellae to the mucus-producing coral host. The traceability of ¹⁵N-labeled mucus was examined by evaluating its uptake and potential utilization by epizoic acoelomorph Waminoa worms naturally occurring on a range of scleractinian coral taxa. This tracer experiment resulted in uptake of coral mucus by the coral-associated acoelomorphs and further demonstrated the possibility to trace stable isotope-labeled coral mucus by revealing a new trophic pathway in coral reef ecosystems.     

Temporal genetic variation in subpopulations of bicolor damselfish (Stegastes partitus) inhabiting coral reefs in the Florida Keys

In 1986 we observed significant genetic heterogeneity among samples of bicolor damselfish (Stegastes partitus) from geographically proximate coral reefs in the Florida Keys. This result was in contrast to results of virtually all previous studies of coral reef fishes. To assess temporal stability of localized genetic differentiation, we resampled reefs in 1989. Within approximately two generations, allele frequencies at the most differentiated locus,ACO-1 ^*, had changed by as much as 0.65, resulting in almost complete homogeneity between previously differentiated subpopulations. Estimates of 10.78 migrants per generation suggested that high gene flow is the most likely factor responsible for the significant change in allele frequencies. We attribute the original genetic differentiation to a population bottleneck, possibly caused by environmental perturbations such as hurricanes and consequent genetic drift. For reef fishes with pelagic egg and/or larval stages, a growing body of data suggests that: (1) populations are geographically extensive gene pools, and (2) rates of dispersal appear to be high enough to allow for continual repopulation of isolated and/or perturbed coral reef communities.     

Lipids of some Caribbean and Red Sea corals: total lipid,wax esters,triglycerides and fatty acids

The Caribbean reef-building corals Porites porites (Pallas) and Montastrea annularis (Ellis and Solander) and the Red Sea corals Pocillopora verrucosa (Ellis and Solander), Stylophora pistillata (Esper) and Goniastrea retiformis (Lamark) were analysed for total lipid, wax ester and triglyceride content, and fatty acid composition. M. annularis contained about 32% of dry weight as total lipid, whereas much lower values of between 11 and 17% were recorded for the other four species. It is concluded that there is greater variation in coral total lipid than hitherto thought. The total lipid contained a substantial proportion of wax ester (22 to 49%) and triglyceride (18 to 37%). The storage lipids (wax esters and triglycerides) accounted for between 6 and 20% of the dry weight and between 46 and 73% of the total lipid. Variation in lipid content between species could not be attributed to geographical location, but the low values for total lipid in Red Sea corals may in part be due to environmental factors as these samples were collected in winter. All corals analysed contained high levels of saturated fatty acids, the most abundant fatty acids being 16:0, 18:0 and 18:1n-9. Marked differences were observed in polyunsaturated fatty acid (PUFA) content between species, with comparatively low levels of 10 and 11% of fatty acids being recorded in M. annularis and G. retiformis, respectively. The values for the other species ranged between 21 and 37%. Fatty acid composition may vary according to the proportions of fatty acids obtained from diet, algal photosynthesis and synthesis by the animal tissues.     

A new apparatus for force measurement in marine bioadhesion

In an experimental study on the effect of parrotfish (probably Scarus taeniurus) grazing on the structure of benthic reef communities, fishes in densities of 0.6 to 1.5 parrotfish per m² or 9 to 17 g wet weight of fish per m² of feeding surface were found to have an optimum effect, resulting in the greatest benthic species richness and biomass on 2-dimensional surfaces. The presence of refuges (3-dimensional habitats), however, has a greater impact on bemthic community structure (number of species and biomass) than does just the density of parrotfish in such an experimental system. Coral recruitment is enhanced by the presence of refuges and, like coralline algae, is more successful under increased grazing pressure. These optimum densities of parrotfishes relate well to observed field densities where, in a collection from a Hawaiian patch reef, there were 1.1 fish or 10.8 g wet weight of parrotfish per square meter of collection area. The success of coralline algae and corals under high grazing pressure may have important consequences for the stability and structure of modern coral reefs.