Marginal tentacles of the corallimorpharian Rhodactis rhodostoma. 1. Role in competition for space

The corallimorpharian Rhodactis rhodostoma (Ehrenberg, 1934) forms aggregations that dominate patches on some coral reef flats in the Red Sea. The outcomes and mechanisms of competition for space between this corallimorpharian and other sessile organisms are poorly understood. Polyps of R. rhodostoma were observed to overgrow zoanthids, hydrozoan corals, sponges and encrusting macroalgae on a fringing reef at Eilat, northern Red Sea. R. rhodostoma polyps also damaged, and in some cases overgrew, reef-building corals in the families Poritidae, Acroporidae and Pocilloporidae, most of which form branching colonies with small polyps that are subordinate in coral competitive hierarchies. In contrast, most stony corals in the families Faviidae and Mussidae had standoff interactions with R. rhodostoma, in which they prevented the corallimorpharians from damaging them or approaching closer than 1 to 3 cm. The latter corals are ranked at the top of competitive hierarchies for Indo-Pacific corals, and they form massive colonies of large polyps which may develop aggressive organs termed sweeper tentacles. Some soft corals that exude allelopathic chemicals also avoided overgrowth by the corallimorpharians. Tentacles along the oral disk margin of R. rhodostoma polyps were swollen and bulbous during contacts with cnidarians. These bulbous marginal tentacles had significantly thicker ectoderm and a higher proportion of holotrichous nematocysts than did the normally filiform marginal tentacles of R. rhodostoma polyps. It is concluded that, on the reef flat at Eilat, this corallimorpharian damages and overgrows a variety of sessile competitors, including branching stony corals, via the application of specialised marginal tentacles filled with penetrating nematocysts. R. rhodostoma is an intermediate competitor in the aggressive hierarchy among Indo-Pacific Anthozoa, including the reef-building corals. Received: 1 July 1998 / Accepted: 24 March 1999     

Complexity of coral interactions: Influence of time,location of interaction and epifauna

The potential role of competition for space in a community depends on the arrangement of interaction relationships. A survey (255 m²) of the interactions between corals (Scleractinia) on a Caribbean reef (depth 10–30 m) indicated the outcome of 17–35% of the aggressive and defensive interactions to be unpredictable. Experiments on the reef (depth 7–13 m) with pairs of interacting corals — Madracis mirabilis (Duchassing & Michelotti), Agaricia agaricites (L), Montastrea annularis (Ellis & Solander), Eusmilia fastigiata (Pallas) — showed that, after the initial contest through extracoelenteric digestion, there are at least two additional processes which can result in a reversal of dominance: interference by epifauna and sweeper tentacle development. Moreover, the impact of extracoelenteric digestion and the extent of sweeper tentacle development varied over the surface of the corals. Employing laboratory and field experiments to distinguish between the impact of extracoelenteric digestion, epifauna behaviour and sweeper tentacles, we show the three processes combined to explain the coral interaction process in toto. The outcome of the interaction process on the reef depends on numerous, partly unpredictable, variables, including mode of contact and effects of position. Consequently, patterns of community organization resulting from spatial competition will be slow to emerge and easily erased prematurely by disturbances.     

Antimicrobial activity of Red Sea corals

Scleractinian corals and alcyonacean soft corals are the two most dominant groups of benthic marine organisms inhabiting the coral reefs of the Gulf of Eilat, northern Red Sea. Antimicrobial assays performed with extracts of six dominant Red Sea stony corals and six dominant soft corals against marine bacteria isolated from the seawater surrounding the corals revealed considerable variability in antimicrobial activity. The results demonstrated that, while the majority (83%) of Red Sea alcyonacean soft corals exhibited appreciable antimicrobial activity against marine bacteria isolated from the seawater surrounding the corals, the stony corals had little or no antimicrobial activity. From the active soft coral species examined, Xenia macrospiculata exhibited the highest and most potent antimicrobial activity. Bioassay-directed fractionation indicated that the antimicrobial activity was due to the presence of a range of compounds of different polarities. One of these antibiotic compounds was isolated and identified as desoxyhavannahine, with a minimum inhibitory concentration (MIC) of 48 μg ml⁻¹ against a marine bacterium. The results of the current study suggest that soft and hard corals have developed different means to combat potential microbial infections. Alcyonacean soft corals use chemical defense through the production of antibiotic compounds to combat microbial attack, whereas stony corals seem to rely on other means.     

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     

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     

Possible effects of water pollution on the community structure of Red Sea corals

The community structure and species diversity of hermatypic corals was studied during 1969–1973, in two reef flats in the northern Gulf of Eilat, Red Sea: the reef flat of the nature reserve at Eilat, which is chronically polluted by oil and minerals, and a control reef, located 5 km further south, which is free from oil pollution. In 1969, the nature reserve and the control reef had similar coral community structure. In September, 1970, both reefs suffered approximately 90% mortality of corals, as a result of an unexpected and extremely low tide. In 1973 the control reef was “blooming” with a highly diverse coral community, while almost no signs of coral recolonization have been observed at the nature reserve, and it is significantly lower in diversity. It is suggested that phosphate eutrophication and chronic oil pollution are the major man-made disturbances that interfere with coral colonization of the reef flat at the nature reserve. Although no direct evidence is provided that oil damages hermatypic corals, the data strongly suggest that chronic oil spills prevent normal settlement and/or development of coral larvae. It is possible that chronic oil, pollution results in either one or a combination of the following: (1) damage to the reproductive system of corals; (2) decreased viability of coral larvae; (3) changes in some physical properties of the reef flat which interfere with normal settlement of coral larvae.     

Biology of small juveniles of the tropical holothurian Actinopyga echinites: growth,mortality, and habitat preferences

Several morphological, physiological and ecological experiments on the general biology of small juveniles (drained body weight=0.09 to 17.34 g) of Actinopyga echinites (Jäger 1833) (Echinodermata, Holothuroidea) were conducted between August 1991 and July 1992 at Bise reef flat, Okinawa, southern Japan. Supplementary experiments were carried out at the laboratory. The experiments were designed with a view to potential stock enhancement projects of A. echinites and other commercially exploited tropical sea cucumbers of the coral reef zone. During the enclosure experiments, the average percentage of drained body weight to fresh body weight of the juveniles was 48.3%. The specimens displayed a growth rate of 1500% during the 11-mo period. Their drained body weight increased from 0.87 to 12.82 g. The juveniles' internal and skeletal morphology differed considerably from the morphology of adult A. echinites. Two new types of skeletal spicules were discovered. Individual growth of all spicule types monitored differed notably, and shrinkage was observed for the two newly discovered types. Relative frequency of the spicule types within the skeletons changed with increasing body weights of the individuals. The juveniles of A. echinites displayed a strong habitat preference for plate-like substrate types such as eroded limestone or dead coral plates. Skeletons of Acropora spp. were accepted at a much lower rate. Weight-frequency distributions of the specimens on varying substrate types and between various times of the day showed significant differences. Cryptic behaviour of the juveniles was observed at all times of the day. Natural mortality of the holothurians, excluding predation and minor dislodgement effects, was low at 0.6% mo^–1. When predation effects were introduced to the experiments, mortality reached a rate of 0.3% mo^–1. The average percentage of predation effects within the natural mortality total was 76.8%. Juvenile A. echinites exhibited a maximum short-distance migration speed of 9 cm h^–1. This was two orders of magnitude slower than the speed observed in adults (900 cm h^–1) when differences in total body length were taken into consideration. The holothurians had two activity peaks during the 4-h periods monitored, around sunrise and sunset, respectively.     

Marginal tentacles of the corallimorpharian Rhodactis rhodostoma. 2. Induced development and long-term effects on coral competitors

Polyps of the corallimorpharian Rhodactis rhodostoma (Ehrenberg, 1934) form aggregations that monopolise patches of space on the shallow reef flats of some Red Sea coral reefs. Some of these polyps bear specialised bulbous marginal tentacles (BMTs) where they contact cnidarian competitors. BMTs differ from the normally filiform marginal tentacles (FMTs) of R. rhodostoma, and appear to develop from them. However, their morphogenesis and long-term impacts on spatial competition with reef corals are unknown. We experimentally induced contacts between R. rhodostoma polyps and colonies of the branching stony coral Acropora eurystoma on a shallow coral reef at Eilat, northern Red Sea. During the first 24 d of contact, the A. eurystoma colonies extruded mesenterial filaments that damaged the tissues of the corallimorpharian polyps. After 18 d,>90% of R. rhodostoma individuals had developed BMTs, which resulted in a reversal in the direction of competitive damage. During the subsequent 1.5 years of observation, the corallimorpharians maintained well-developed BMTs, unilaterally damaged the tissues of A. eurystoma, and in some cases moved onto the stony coral skeletons and partially overgrew them. BMTs developed from FMTs in a series of four distinct stages, accompanied by significant changes in their morphology, cnidom, and density of nematocysts. Isolated control polyps did not develop BMTs or show any signs of damage. In contrast, corallimorpharian polyps transplanted into contact with colonies of the massive stony coral Platygyra daedalea began to develop sporadic BMTs, but were unilaterally and severely damaged by the corals, and started to disappear within 21 d, after the corals developed sweeper tentacles. We conclude that long-term outcomes of competition between R. rhodostoma and reef-building corals depend largely on the relative aggressive reach of the competitive mechanisms developed by each species. As a consequence, this corallimorpharian is an intermediate competitor in the aggressive hierarchy among Indo-Pacific reef corals. This study confirms that R. rhodostoma polyps may actively damage and overgrow some stony corals, leading to the formation of an almost continuous blanket of polyps in large patches of some shallow reef flats. Received: 15 July 1998 / Accepted: 24 March 1999     

Phototaxis in Fungiidae corals (Scleractinia)

Corals within the scleractinian family Fungiidae were observed to move toward light (positive phototaxis). Negative phototactic movement was not observed in any of the specimens tested. On sandy substratum, Diaseris distorta moved faster (max. speed of 3 cm h^-1) than other species. Although D. distorta has symbiotic algae, phototactic movement also was observed both in bleached corals and in those treated with a specific inhibitor (dichlorophenyl dimethyl urea) of photosynthesis. D. distorta was phototactic even on a glass plate, and climbed up a steep slope (up to 30°). Based on experiments with Fungia fungites and D. distorta, soft tissues at the peripheral region of the dise seem to be responsible for movement via peristalsis. It is suggested that positive phototaxis in symbiontbearing fungiid corals is an important trait for selection of favorable habitats.     

Community structure and species diversity of hermatypic corals at Eilat,Red Sea

This study investigates the community structure of reefbulding corals in terms of species composition, zonation and diversity patterns, as well as possible factors affecting the observed distributions. The study was carried out by a series of line transects run underwater with SCUBA apparatus from the reef flat to a depth of 30 m. The reefs of Eilat are of the fringing type, with seleractinian corals as the most important hermatypic organisms. The different zones of the reef are analyzed on the basis of topographical characteristics of the reef, as well as from the numerical data on abundance and living coverage, using cluster analysis of all transects surveyed. The present knowledge concerning species diversity is reviewed and analyzed in the context of hermatypic coral data. Three different diversity indices (the species count, Simpson's index and Shannon and Weaver's index) were calculated for estimating the diversity obtained on different zones of the reef. It was found that there is a successive increase in diversity of hermatypic corals from shallow water to a depth of 30 m. Species diversity and living voverage of corals were significantly greater in steeper zones as compared to flatter zones of the reef. A possible explanation for this phenomenon is the accumulation of sediments in the flat zones. It is proposed that the severe and umpredictable nature of the reef flat may account for low abundance and living coverage of corals. It is also proposed that deep-water species which do not invade shallow water are species which have developed high specialization to their local environment. The idea that light intensity is a significant factor in calcium-carbonate deposition by scleractinian corals is supported by field measurements of individual colonies at different depths.This paper is part of a thesis submitted to the State University of New York at Stony Brook in partial fulfillment of the requirements for a Ph. D. degree.     

Ecological and biological phenomena influencing coral-species composition on the reef tables at Eilat (Gulf of Aqaba,Red Sea)

Observations performed on coral colonies damaged during a very low tide on the shallow-water reef tables at Eilat (Red Sea), showed that most colonies are able to regenerate if parts of the living tissue remain intact on the skeletons. Brain-like corals, such asFavia favus andPlatygyra lamellina, were found to be more resistant to dessication than the delicate bush-like forms. It was also observed that the exposed skeletons of corals were immediately covered by a successive group of algae with a rich invertebrate epifauna among them. It is postulated that unpredicted extreme low water, occurring once in several years, could be the factor that prevents crowding on the reef tables, thus keeping high the level of coralspecies diversity.Supported, in part, by a grant from the Smithsonian Institution, USA. SFC-70074.This paper was presented at the Intecol Symposium held in Dubrovnik in March, 1972.     

Chronology of lead pollution contained in banded coral skeletons

Lead concentrations relative to calcium within dated subsamples of hermatypic (reef-building) coral skeletons from St. Croix, US Virgin Islands, record ambient pollution levels. Concentrations within a coral from a polluted reef (395 ng g^-1) average five-fold higher than within a coral from a pristine site (87 ng g^-1). The lead chronologies of both corals show a significant increase in concentration towards the present during the past 26 yr (1954–1980). The increase in lead concentration in the coral from the pristine site is suggested to represent the increase in lead availability from global pollution. Coral skeletons offer the probability of development into tools for longterm chemical recorders of levels of lead and possibly other metals or compounds in seawater.     

Respiration rate and cost of swimming for Antarctic krill,<Emphasis Type="Italic"> Euphausia superba</Emphasis>, in large groups in the laboratory

Constructing realistic energy budgets for Antarctic krill, Euphausia superba, is hampered by the lack of data on the metabolic costs associated with swimming. In this study respiration rates and pleopod beating rates were measured at six current speeds. Pleopod beating rates increased linearly with current speed, reaching a maximum of 6 beats s^–1 at 17 cm s^–1. There was a concomitant linear increase in respiration rate, from 1.8 mg O₂ g_D^–1 h^–1 at 3 cm s^–1 to 8.0 mg O₂ g_D^–1 h^–1 at 17 cm s^–1. The size of the group tested (50, 100 and 300 krill) did not have a significant effect on pleopod beating rates or oxygen consumption (ANCOVA, F=0.264; P>0.05). The cost of transport reached a maximum of 75 J g^–1 km^–1 at 5 cm s^–1, and then decreased with increasing current speed to 29 J g^–1 km^–1. When considered in light of energy budgets for E. superba, these data indicate that the cost of swimming could account for up to 73% of total daily metabolic expenditure during early summer.Communicated by G.F. Humphrey, Sydney     

Spatial and temporal variability in somatic growth of green sea turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) resident in the Hawaiian Archipelago

The somatic growth dynamics of green turtles (Chelonia mydas) resident in five separate foraging grounds within the Hawaiian Archipelago were assessed using a robust non-parametric regression modelling approach. The foraging grounds range from coral reef habitats at the north-western end of the archipelago, to coastal habitats around the main islands at the south-eastern end of the archipelago. Pelagic juveniles recruit to these neritic foraging grounds from ca. 35 cm SCL or 5 kg (~6 years of age), but grow at foraging-ground-specific rates, which results in quite different size- and age-specific growth rate functions. Growth rates were estimated for the five populations as change in straight carapace length (cm SCL year^–1) and, for two of the populations, also as change in body mass (kg year^–1). Expected growth rates varied from ca. 0–2.5 cm SCL year^–1, depending on the foraging-ground population, which is indicative of slow growth and decades to sexual maturity, since expected size of first-time nesters is 80 cm SCL. The expected size-specific growth rate functions for four populations sampled in the south-eastern archipelago displayed a non-monotonic function, with an immature growth spurt at ca. 50–53 cm SCL (~18–23 kg) or ca. 13–19 years of age. The growth spurt for the Midway atoll population in the north-western archipelago occurs at a much larger size (ca. 65 cm SCL or 36 kg), because of slower immature growth rates that might be due to a limited food stock and cooler sea surface temperature. Expected age-at-maturity was estimated to be ca. 35–40 years for the four populations sampled at the south-eastern end of the archipelago, but it might well be >50 years for the Midway population. The Hawaiian stock comprises mainly the same mtDNA haplotype, with no differences in mtDNA stock composition between foraging-ground populations, so that the geographic variability in somatic growth rates within the archipelago is more likely due to local environmental factors rather than genetic factors. Significant temporal variability was also evident, with expected growth rates declining over the last 10–20 years, while green turtle abundance within the archipelago has increased significantly since the mid-1970s. This inverse relationship between somatic growth rates and population abundance suggests a density-dependent effect on somatic growth dynamics that has also been reported recently for a Caribbean green turtle stock. The Hawaiian green turtle stock is characterised by slow growth rates displaying significant spatial and temporal variation and an immature growth spurt. This is consistent with similar findings for a Great Barrier Reef green turtle stock that also comprises many foraging-ground populations spanning a wide geographic range.Communicated by P.W. Sammarco, Chauvin     

Population structure and growth in captivity of the spiny lobsterPanulirus penicillatus from Dahab,Gulf of Aqaba,Red Sea

Panulirus penicillatus (Olivier, 1791) (Decapoda: Palinuridae) is the most common spiny lobster in the Red Sea and is widely distributed in the Indian and Pacific Oceans. Lobsters (n=377) were collected on four occasions during 1986 on the coral reef at Dahab, Sinai, Egypt. Average size of the collected individuals was 70.5±24.6 mm carapace length (CL) for males and 63.2±15.9 mm CL for females. The sex ratio was 1:1.64 males to females. Length increment per molt was inversely correlated with size and ranged from 2.1 mm per molt in the 40 to 50 mm CL size class to less than 1 mm in the 60 to 70 mm CL size class. Average intermolt period was ca. 136 d for all size classes. The relationship between carapace length and body weight was expressed by the equation:W _b=6.43 × 10^–4 × (CL)^2.89.P. penicillatus from Dahab differ in size, sex ratio and growth rate compared to other palinurid populations throughout their range. This might represent the effect of isolation and location at the edge of the geographical range for this species. It may also indicate an adaptation to their unique habitat in the coral reef in comparison to other palinurid species.     

Water flow and prey capture by three scleractinian corals, Madracis mirabilis, Montastrea cavernosa and Porites porites, in a field enclosure

Scleractinian corals experience a wide range of flow regimes which, coupled with colony morphology, can affect the ability of corals to capture zooplankton and other particulate materials. We used a field enclosure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow speeds. Experiments were carried out from 1989 to 1992. Particles (Artemia salina cysts) and naturally occurring zooplankton attracted into the enclosures were used as prey for the corals Madracis mirabilis (Duchassaing and Michelotti) (narrow branches, small polyps), Montastrea cavernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pallas) (wide branches, small polyps). This design allowed corals to be used without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces. Flow speed had significant effects on capture rate for cysts (M. mirabilis), total zooplankton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mirabilis). Zooplankton prey capture increased with prey concentration for M. mirabilis and M. cavernosa, over a broad range of concentrations, indicating that saturation of the feeding response had not occurred until prey density was over 10⁴ items m⁻³, a concentration at least an order of magnitude greater than the normal range of reef zooplankton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most particles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions. The present study confirms laboratory flume results, and field results for other species, suggesting that many coral species experience particle flux and encounter rate limitations at low flow speeds, decreasing potential zooplankton capture rates. Received: 17 September 1996 / Accepted: 22 November 1997     

Heavy metal migration in soils and rocks at historical smelting sites

The vertical migration of metals through soils and rocks was investigated at five historical lead smelting sites ranging in age between 220 and 1900 years. Core samples were taken through metal-contaminated soils and the underlying strata. Concentration profiles of lead and zinc are presented from which values for the distances and rates of migration have been derived. Slag-rich soil horizons contain highly elevated metal concentrations and some contamination of underlying strata has occurred at all sites. However, the amounts of lead and zinc that have migrated from soils and been retained at greater depths are comparatively low. This low metal mobility in contaminated soils is partly attributed to the elevation of soil pH by the presence of calcium and carbonate originating from slag wastes and perhaps gangue minerals. Distances and rates of vertical migration were higher at those sites with soils underlain by sandstone than at those with soils underlain by clay. For sites with the same parent material, metal mobility appears to be increased at lower soil pH. The mean migration rates for lead and zinc reach maxima of 0.75 and 0.46 cm yr^–1 respectively in sandstone at Bole A where the elements have moved mean distances of 4.3 and 2.6 m respectively. There is some evidence that metal transport in the sandstone underlying Bole A and Cupola B occurs preferentially along rock fractures. The migration of lead and zinc is attenuated by subsurface clays leading to relatively low mean migration rates which range from 0.03 to 0.31 cm yr^–1 with many values typical of migration solely by diffusion. However, enhanced metal migration in clays at Cupola A suggest a preferential transport mechanism possibly in cracks or biopores.     

Microhabitat utilisation patterns in cryptobenthic coral reef fish communities

The cryptobenthic reef fish communities from four microhabitats at Orpheus Island, central Great Barrier Reef are described. Eighty-four 0.4m² samples yielded a total of 368 individuals from 42 species in eight families, with a mean density of 11 individuals m^–2 (±1.7SE) and 2.9 species 0.4 m^–2 (±0.2SE). Caves contained the highest number of both individuals (120) and species (26), followed by sand/rubble, soft coral, and open reefs. Microhabitat associations included cave and soft coral specialists. Site fidelity in 71 tagged individuals of 4 species was high, with a mean recapture rate of 53% (±8.4SE) remaining within the ~0.4 m² sampling area after a 48-h period. Behavioural observations also reflect this limited movement, with the dominant mode of behaviour in 7 species being a motionless state (67.5% ±11.6SE), followed by feeding (21.8% ±8.7SE), hiding (6.3% ±1.6SE), and swimming (4.4% ±1.5SE). Two distinct behavioural groups are identified: (1) sedentary forms, characterised by long periods of immobility (5 species); and (2) winnowers, characterised by long feeding bouts (2 species). The fine-scale partitioning of microhabitats, restricted home ranges, and sedentary behaviour of many cryptobenthic reef fish species suggest that this reef fish community exhibits similar patterns of habitat utilisation to their larger reef-fish counterparts, but at a much finer scale.     

Impact of Gold mining on the Environment and Human Health: A Case Study in the Migori Gold Belt, Kenya

The study of gold sites in the Migori Gold Belt, Kenya, revealed that the concentrations of heavy metals, mainly Hg, Pb and As are above acceptable levels. Tailings at the panning sites recorded values of 6.5–510 mg kg^–1 Pb, 0.06–76.0 mg kg^–1 As and 0.46–1920 mg kg^–1 Hg. Stream sediments had values of 3.0–11075 mg kg^–1 Pb, 0.014–1.87 mg kg^–1 As and 0.28–348 mg kg^–1 Hg. The highest metal contamination was recorded in sediments from the Macalder stream (11075 mg kg^–1 Pb), Nairobi mine tailings (76.0 mg kg^–1 As) and Mickey tailings (1920 mg kg^–1 Hg). Mercury has a long residence time in the environment and this makes its emissions from artisan mining a threat to health. Inhaling large amounts of siliceous dust, careless handling of mercury during gold panning and Au/Hg amalgam processing, existence of water logged pits and trenches; and large number of miners sharing poor quality air in the mines are the major causes of health hazards among miners. The amount of mercury used by miners for gold amalgamation during peak mining periods varies from 150 to 200 kg per month. Out of this, about 40% are lost during panning and 60% lost during heating Au/Hg amalgam. The use of pressure burners to weaken the reef is a deadly mining procedure as hot particles of Pb, As and other sulphide minerals burn the body. Burns become septic. This, apparently, leads to death within 2–3 years. On-site training of miners on safe mining practices met with enthusiasm and acceptance. The use of dust masks, air filters and heavy chemical gloves during mining and mineral processing were readily accepted. Miners were thus advised to purchase such protective gear, and to continue using them for the sake of their health. The miners' workshop, which was held at the end of the project is likely to bear fruit. The Migori District Commissioner and other Government officials, including medical officers attended this workshop. As a result of this, the Government is seriously considering setting up a clinic at Masara, which is one of the mining centres in the district. This would improve the health of the mining community.     

Ontogeny of diet changes in a tropical benthic carnivorous fish, Parupeneus barberinus (Mullidae): relationship between foraging behaviour, habitat use, jaw size, and prey selection

Parupeneus barberinus forages on benthic invertebrates using a wide range of foraging modes, including vigorous digging in the substratum, resulting in considerable disturbance to the benthos. Polychaetes were the most important prey item for all size classes, but fishes less than 120 mm total length consumed more small ostracods and nematodes than did larger fishes. Fishes greater than 120 mm total length consumed mostly bivalves, and fishes over 240 mm total length consumed mostly bivalves and crabs. A morphological examination of the feeding apparatus suggested that the size of important prey items consumed was determined by gape height and jaw width. Prey available to different size classes of fishes was determined by combining information on microhabitat use, foraging behaviours, and prey volumes in the substratum. Small fishes spent more time foraging on the reef flat and slope, compared with larger fishes that foraged mostly on the reef edge and base. In addition smaller fishes foraged mostly in the upper 2 cm of sediment, whereas larger fishes often foraged to depths of 10 cm. Selection ratios showed that different size classes of fishes selectively extracted different prey items from the substratum. Small fishes showed a preference for ostracods whereas large fishes selected for bivalves and crabs. Although polychaetes were the dominant prey item for all size classes, they were consistently selected against.