Simulation of recovery of pre-disturbance size structure in populations of Porites spp. damaged by the crown of thorns starfish Acanthaster planci

Outbreaks of the crown of thorns starfish Acanthaster planci (L.) have caused high levels of mortality and injury in corals on the Great Barrier Reef. In surveys conducted in 1985 and 1986, it was estimated that a quarter of the massive Porites spp. corals surveyed at five reefs — John Brewer, Rib, Potter, Feather and Green Island — had been killed outright. In addition, there was minor to severe injury to colonies throughout the coral's size range. A population model was used to evaluate this damage. The evaluations were based on simulations of the time necessary for prior abundances of large colonies (>2 m diam) to be re-established and on simulations of the number of additional disturbances the populations could withstand before becoming locally extinct. The affect of recurrent disturbances on populations receiving recruits was also simulated. Assuming no further disturbance, the model predicts minimum recovery times in excess of 50 yr for most of the populations, and 9 to 100 yr for sub-populations within reefs. For populations subjected to repeated disturbance every 10 to 30 yr, it predicted that all large colonies would soon be lost unless there was both low background mortality and a major recruitment of Porites spp. between outbreaks. In the worst-case scenario of failed recruitment and high background mortality, four of the five populations could withstand as few as two to three additional disturbances equivalent to those earlier in this decade.     

Lipid content of some Caribbean corals in relation to depth and light

Three procedures for the extraction of coral lipids were compared and a rapid and effective method for future use is suggested. This method was used to measure the lipid content of the branching coral Porites porites (Pallas) and the massive corals Montastrea annularis (Ellis and Solander) and Siderastrea siderea (Ellis and Solander) during July and August 1991. P. porites and M. annularis were sampled on two fringing reefs, each characterised by different water quality affecting light transmission, and at depths of down to 30 m on a barrier reef on the west coast of the island. m. annularis contained, on average, 29% of dry weight as lipid, and there were no significant differences in lipid levels between corals sampled on either fringing reef at 3 and 6 m, or between fringing reefs and the barrier reef at 13, 20 or 30 m depth. Five samples were also taken from a single massive colony of S. siderea at 3 m on a fringing reef and at 13, 20 and 30 m depth on the barrier reef. Values for lipid ranged from 26 to 35% of dry tissue weight. P. porites from 3 and 6 m depth on both fringing reefs contained the same amount of lipid (11% of dry tissue weight). However, at 13 m depth on the barrier reef this coral contained significantly less lipid (8.5% of dry tissue weight). This difference may be attributable to a higher nutritional intake by P. porites on the fringing reefs.     

Plankton inhabiting the surface layer of the southern and southwestern lagoon of New Caledonia

In the southern and southwestern coral reef lagoon of New Caledonia and the adjacent oceanic waters, 42 neuston samples were collected from the upper surface layer (0 to 10 cm) along nine transects from the coast to the coral barrier reef and the open ocean immediately beyond the reef, in March and April 1979. There was a progressive numerical decrease in zooplankton densities from the coast to the reef and from the reef to the open sea. Generally, 80 to 95% of the surface plankton consisted of holoplankton and 5 to 20% of meroplankton. Zooplankton was very abundant in littoral bays with a marked eutrophication. In a few samples collected in very shallow waters close to coral patches, cladocerans were numerous and constituted up to 75% of the total plankton, whilst in other samples collected above greater depths, copepods made up 60 to 85% of the total plankton. In the coral reef lagoon of south and southwest New Caledonia, typically hyponeustonic copepods (pontellids) often comprised 5% of the total copepod populations.     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.     

Settlement and recruitment of sea urchins (Strongylocentrotus spp.) in a sea-urchin barren ground and a kelp bed: are populations regulated by settlement or post-settlement processes?

I sampled recruitment of very small sea urchins (Strongylocentrotus spp.) by using the anesthetic magnesium chloride to remove individuals from substrata collected in sea-urchin barren grounds (barrens) and kelp beds at Naples Reef near Santa Barbara, California, USA. Preliminary sampling found low numbers of newly settled individuals(<0.6 mm test diam) from April–July in 1984 and 1985, and in April, 1986. In early May, 1986, I found many newly settled seaurchins (0.3 to 0.6 mm, 5 to 17 d old), and I compared the densities of the cohort on several types of natural substrata in barrens and kelp-bed habitats. Newly settled individuals of both purple sea urchins (S. purpuratus) and red sea urchins (S. franciscanus) were present in similar, high densities (1 000 S. purpuratus m^-2) on foliose red algal turf, a dominant substratum ofthe kelp bed, and on crustose coralline algae, the dominant substratum of an adjacent barrens. Larvae of S. purpuratus reared and tested in the laboratory showed high rates of settlement on both red algal turf and on crustose coralline algae, but significantly lower rates on rock. Larvae also settled in response to a partiallypurified extract of coralline algae. The reduced settlement on natural rock surfaces relative to either algal treatment and the significant settlement in response to the extract of coralline algae indicate that larvae discriminate between natural substrata and probably respond to a settlement cue other than, or in addition to, a simple microbial (bacterial) film. The similar densities of young recruits of S. purpuratus on dominant substrata of barrens and kelp bed show that, at least in this case, differential settlement cannot explain the high densities of sea urchins in the barrens habitat. Movement between barrens and kelp bed is unlikely given the small sizes of the newly recruited sea urchins relative to the large distances often involved. Reduced post-settlement mortality of newly settled individuals in the barrens remains the most likely mechanism leading to the higher densities of sea urchins in barrens relative to kelp-bed habitats.     

In situ thermal dynamics of shallow water corals is affected by tidal patterns and irradiance

We studied the diel variation of in situ coral temperature, irradiance and photosynthetic performance of hemispherical colonies of Porites lobata and branching colonies of Porites cylindrica during different bulk water temperature and tidal scenarios on the shallow reef flat of Heron Island, Great Barrier Reef, Australia. Our study presents in situ evidence that coral tissue surface temperatures can exceed that of the surrounding water under environmental conditions typically occurring during low tide in shallow reef or lagoon environments. Such heating may be a regular occurrence on shallow reef flats, triggered by the combined effects of high irradiance and low water flow characteristic of low Spring tides. At these times, solar heating of corals coincides with times of maximum water temperature and high irradiance, where the slow flow and consequent thick boundary layers impede heat exchange between corals and the surrounding water. Despite similar light-absorbing properties, the heating effect was more pronounced for the hemispherical P. lobata than for the branching P. cylindrica. This is consistent with previous laboratory experiments showing the evidence of interspecific variation in coral thermal environment and may result from morphologically influenced variation in convective heat transfer and/or thermal properties of the skeleton. Maximum coral surface warming did not coincide with maximum irradiance, but with maximum water temperature, well into the low-tide period with extremely low water flow in the partially drained reef flat, just prior to flushing by the rising tide. The timing of low tide thus influences the thermal exposure and photophysiological performance of corals, and the timing of tidally driven coral surface warming could potentially have different physiological impacts in the morning or in the afternoon.     

Biochemical evidence for absence of feeding in puerulus larvae of the Western rock lobster Panulirus cygnus (Decapoda: Palinuridae)

Changes in energy-reserves during the transition from phyllosoma through peurulus to juvenile in the Western rock lobster Panulirus cygnus (George, 1962) were studied by means of carbon: nitrogen analysis. Specimens were collected by means of plankton nets and puerulus collectors along the Western Australian coastline between July 1992 and January 1993. Reserves are accumulated during the last phyllosoma stage and are consumed during the puerulus stage. These observations support the hypothesis that the puerulus is a non-feeding stage. Based on basal metabolic rate and observed changes in reserves, the natant puerulus stage is calculated to last a maximum of 21.6d. When the estimated cost of swimming is taken into account, the duration is reduced to perhaps a week. The latter time-span corre-sponds with field observations that both abundance of planktonic pueruli in oceanic waters and inshore settlement of pueruli peak in the week around new moon. At 18°C, the puerulus metamorphoses to the first juvenile stage within 12.8 d after settlement; at 23°C this is reduced to 8.3 d. After settlement, puerulus larvae have an energetic advantage at elevated temperatures; the increased cost of metabolism is compensated by an accelerated development. The natant puerulus, however, appears to be slightly disadvantaged energetically at elevated temperatures; both C:N ratio and ash-free dry weight of pueruli just after settlement show a decreasing trend as the water temperature increases. The effect of water temperature and the distance from the edge of the continental shelf to the shore on consumption of energy reserves might provide a mechanism to partially explain temporal and spatial patterns in puerulus settlement.     

Growth trajectories of corallites and ages of polyps in massive colonies of reef-building corals of the genus Porites

Massive colonies of the reef-building coral genus Porites were collected at inshore, midshelf and shelf-edge reefs in the central section of the Great Barrier Reef in November 1987. These colonies were comprised of 4 species: P. lobata, P. lutea, P. solida and P. mayeri. X-radiographs made of skeletal slices cut from the skeletons displayed the annual density-banding pattern characteristic of massive corals, and appeared to show corallites within each slice. The average age of the 36 colonies was 41±12 yr (mean±SD). The images of corallites displayed by the X-radiographs were not images of actual corallites, but approximated the position and size of actual corallites. Consequently, X-radiographs provide information about the formation and growth trajectories of corallites, and about the history of the polyps which deposited the corallites. Individual corallites were always normal to the growth surface. The growth surface of the colonies became bumpy when they reached 50 to 80 mm in height and, as a result, corallites took on a fan-shaped arrangement within a bump. New corallites were initiated at the summit of each bump and grew upwards and outwards. Thus, growth of colonies resulted in corallites becoming increasingly displaced from the summit of a bump. The X-radiographs showed that corallite growth becomes occluded at the bottom of valleys between adjacent bumps. Corallite growth then stops and the associated polyps are probably resorbed. Annual density banding showed that the average age of polyps in these colonies was 2 to 3 yr, average life expectancy 5 yr, and that no polyp was likely to be older than 8 yr. Small but significant variations in polyp longevity between corals from different reefs were probably associated with significant differences in bumpiness of growth surfaces. Even in Porites colonies which have been growing for several centuries, polyp longevity is likely to be 5 yr.     

Spatial and temporal variation in coral recruitment on the Great Barrier Reef: Implications for dispersal hypotheses

Over 15 000 coral recruits were counted on settlement plates from three mid-shelf reefs and six fringing reefs in the northern section of the Great Barrier Reef during two summers (1986 and 1987) and one winter (1987). The density of coral recruits on some settlement plates from a fringing reef was up to 4.88 cm^–2, the highest value ever reported. Mean density of recruits was greater on fringing reefs (81.1 recruits/settlement plate) than on mid-shelf reefs (15.6 recruits/settlement plate), but there was greater spatial variation in abundance of recruits between the fringing reef sites. Other differences between the mid-shelf reefs and the fringing reefs were that different taxa were dominant, and that settlement orientation differed, with mid-shelf recruits settling preferentially on horizontally oriented surfaces and fringingreef recruits preferring vertical surfaces. Of the three midshelf reefs, Green Island reef recorded the highest recruitment rate for each of the two summers, despite having a depauperate adult coral population following predation by the asteroidAcanthaster planci. This suggests that coral larvae frequently travel between reefs. In contrast with an earlier study, there was no consistent difference in abundance of recruits between forereef and backreef locations. Overall, the results indicated great spatial variation in the availability of coral larvae, both on the scale of whole reefs and within-reef habitats.     

The effects of temperature on the growth of juvenile scleractinian corals

Tropical reef corals are well known for their sensitivity to rising temperature, yet surprisingly little is known of the mechanisms through which temperature acts on intact coral colonies. One such mechanism recently has been suggested by the association between the growth of juvenile corals and seawater temperature in the Caribbean, which suggests that temperature causes a transition between isometric and allometric growth scaling in warmer versus cooler years, respectively (Edmunds in Proc R Soc B 273:2275–2281, 2006). Here, this correlative association is tested experimentally for a cause-and-effect relationship. During April and May 2006, juvenile colonies (8–35 mm diameter) of massive Porites spp. from Moorea, French Polynesia, were incubated at warm (27.8°C) and cool (25.7°C) temperatures for 15 days, and their response assessed through the scaling of growth (change in weight) with colony size. The results reveal that the scaling of colony-specific growth (mg colony⁻¹ day⁻¹) was unaffected by temperature, although growth absolutely was greater at the cool compared to the warm temperature, regardless of colony size. This outcome was caused by contrasting scaling relationships for area-specific growth (mg cm⁻² day⁻¹) that were negatively allometric under warm conditions, but independent of size under cool conditions. In April 2007, a 22 days field experiment confirmed that the scaling of area-specific growth in juvenile Porites spp. is negatively allometric at a warm temperature of 29.5°C. Based on strong allometry for tissue thickness, biomass, and Symbiodinium density in freshly collected Porites spp., it is hypothesized that the temperature-dependency of growth scaling in these small corals is mediated by the interaction of temperature with biomass.     

High rates of nitrogen fixation on coral skeletons after predation by the crown of thorns starfish Acanthaster planci

At One Tree Reef, Great Barrier Reef, Australia, between 1983 and 1985, corals killed by the crown of thorns seastar Acanthaster planci L. gave rise to skeletons which were colonised rapidly by blue-green and other algae. For the next 3 to 9 mo these coral skeletons showed over three times more nitrogen fixation (acetylene reduction) than control substratum rates (9 to 32 nmol vs 3 to 10 nmol C₂H₂ cm^-2 h^-1, over all seasons). These values convert to relatively high annual fixation rates of 37 to 127 kg N ha^-1 yr^-1 but, at the low densities of A. planci on One Tree Reef (ca. 0.65 ha^-1), this has little impact on the total nitrogen fixation rate and, as a result, on the level of organic nitrogen in the system. However, it is suggested that on reefs subjected to high aggregations of a. planci such an effect would enhance the level of organic nitrogen and lead to greater primary and secondary production throughout the reef system.     

Cross-shelf distribution of copepods and fish larvae across the central Great Barrier Reef

The distribution of total dry weight of zooplankton, copepod numbers and ichthyoplankton across the outer continental shelf in the central Great Barrier Reef was examined at bi-weekly intervals for three months over summer of 1983. Copepods were sampled (236 m net) within 10 m of the surface and within 10 m of the bottom. Mean densities in surface waters decreased markedly from the mid-shelf to outer shelf and the Coral Sea, but no cross-shelf gradient occurred in the bottom-water. Densities of copepods on the mid-shelf (surface and bottom waters) and in bottom-waters of the outer shelf were typically ca. 400 m^–3. Significantly lower densities (ca. 100 m^–3) occurred in surface waters of the outer shelf, except during outbursts of Acartia australis, when densities in these waters differed little from those elsewhere on the shelf. In oceanic waters, 10 km from the outer shelf station, copepod densities in surface waters were ca. 40 m^–3. Four of the five most abundant copepod taxa in surface waters, Paracalanus spp., Eucalanus crassus, Acrocalanus gracilis and Canthocalanus pauper, tended to be most abundant at the mid-shelf end of the transect. Acartia australis was sporadically very abundant in surface waters of the outer shelf, as was Paracalanus spp. in bottom-water of the outer shelf. An assemblage of Coral Sea species of copepod occurred in bottom-water of the outer shelf during two major intrusions, but not at other times. Densities of all common species varied considerably between cruises. Maximum densities of all common species except A. australis tended to be associated with diatom blooms linked to intrusions but a bloom did not necessarily mean all common species were abundant. Fish larvae included both reef and non-reef taxa, with reef taxa predominating on the outer shelf (approx 2:1 in density of individuals) and non-reef taxa dominating in nearshore samples (approx 2:1). Nine of the ten most abundant taxa analysed showed highly significant variation in numbers among stations and all but one of these also exhibited significant station x cruise interactions. Interactions generally reflected changes in the rank importance of adjacent stations from one cruise to the next or lack of any significant cross-shelf variation on some cruises where overall abundance of the taxa was low.     

Ecological versatility and the decline of coral feeding fishes following climate driven coral mortality

Coral reefs are under threat due to climate-mediated coral mortality, which affects some reef coral genera more severely than others. The impact this has on coral reef fish is receiving increasing attention, with one focal area assessing impacts on fish that feed directly on live coral. It appears that the more specialised a species of corallivore, the more susceptible it is to coral declines. However data are sparse for the Indian Ocean, and little is known about why some corals are preferentially fed upon over others. Here I assess feeding specialisation in three species of coral feeding butterflyfish in the Chagos Archipelago, central Indian Ocean, assess the food quality of the coral genera they target and document patterns of decline in the Seychelles following a severe coral mortality event. Cheatodon trifascialis was the most specialised coral feeder, preferentially selecting for Acropora corals, however, when Acropora was scarce, individuals showed considerable feeding plasticity, particularly for the dominant Pocillopora corals. C. trifasciatus also preferentially fed on Acropora corals, but fed on a much more diverse suite of corals and also displayed some selectivity for Porites. C. auriga is a facultative corallivore and consumed ∼55% live coral, which lies within the wide range of coral dependence reported for this species. C:N ratio analysis indicated Lobophyllia and Acropora have the highest food quality, with Pocillopora having the lowest, which conforms with diet selection of corallivores and helps explain preferential feeding. Obligate specialist feeders displayed the greatest declines through coral mortality in the Seychelles with obligate generalists also declining substantially, but facultative feeders showing little change. Clearly a greater understanding of the species most vulnerable to disturbance, their habitat requirements and the functional roles they play will greatly assist biodiversity conservation in a changing climate.     

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     

Effects of selective settlement and of aggression by residents on distribution of young recruits of two tropical damselfishes

The reef fishes that settled on an array of experimental corals at Lizard Island, Queensland, Australia, were counted during a pulse of recruitment in December 1986. NeitherPomacentrus sp. norP. amboinensis showed any evidence that harassment by residentDascyllus aruanus caused a decrease in persistence during the first day after settlement. LarvalPomacentrus sp. settled selectively on corals without residentD. aruanus. The results forP. amboinensis were ambiguous. Settlers of both species positioned themselves closer to the sand on corals with residentD. aruanus than on unoccupied corals. This could reduce access to planktonic food and increase the risk of predation. Adult aggression may be less important and active selection of settlement sites by larvae may be more important to the distribution of recruits than is suggested by the literature. The presence or absence of particular species should be included among the cues that larval reef fishes use to choose settlement sites.     

Seasonality of coral reproduction in the Dampier Archipelago,northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.     

Ecological studies of the coral predator Acanthaster planci in the south pacific

Ecological surveys involving over 500 man-days between 1966 and 1969 indicate that the coral-eating sea star, Acanthaster planci, is a normal component of the coral reef community throughout the tropical Pacific, and that its abundance in the past has probably been underestimated. The sea star is not uncommon in certain environments, particularly back-reef and lagoon slopes. Sheltered, inner reefs are generally preferred over less protected reefs. Recently reported population explosions of A. planci at Guam and on the Great Barrier Reef of Australia appear to be isolated, widely-separated, local infestations of unknown cause. The infestation on the Great Barrier Reef has not spread beyond the area off Cairns and Innisfail. Approximately 40 of the more than 1000 reefs comprising the Great Barrier Reef complex have been infested heavily.     

Population dynamics of Amphiura chiajei (Echinodermata: Ophiuroidea) in Killary Harbour,on the west coast of Ireland

The infaunal ophiuroid Amphiura chiajei Forbes is a dominant member of the A. chiajei community in Killary Harbour, a fjord-like inlet on the west coast of Ireland. High density populations (700 individuals/ m²) occur in sediments with a silt/clay content of 80 to 90% and organic carbon levels of 5 to 7%. A study of the population dynamics of this species was carried out from November 1985 to October 1988. At the outset, the population consisted of approximately equal numbers of adults and juveniles. By October 1988, the percentage of adults had increased to 95%, with little or no change in the mean annual dersities. However, there was some degree of variability between the mean monthly densities. Such variability may have been due to very low bottom temperatures, resulting in mortality among the older members of the population. Observations suggest that in Killary Harbour the species may attain an age of 10 yr, with an early annual growth rate of 0.5 mm (oral width). Annual recruitment was variable and low, due presumably to intraspecific competition with the adults; recruitment success may be very closely linked to adult mortality. The Killary Harbour findings are considered in the light of what is currently known of similar amphiurid populations in different geographical locations.     

Dinoflagellate infections of Favella panamensis from two North American estuaries

Favella panamensis Kofoid and Campbell, 1929 is seasonally abundant in meso- to polyhaline waters of Chesapeake Bay and Indian River, Florida, USA, where it reaches densities of 10³ cells l^-1. During the summers of 1986–1992. F. panamensis populations of the two estuaries were commonly infected by the parasitic dinoflagellate Duboscquella aspida Cachon, 1964. The intracellular phase of the parasite reached maturity in 21 h (30 °C) and consumed 35% of the host's biomass. Infections were not typically lethal to F. panamensis, but sometimes forced the host from its lorica. Several D. aspida were found in the cytoplasm of many hosts, and the number of parasites infection^-1 was directly related to infection level. Parasite prevalence averaged 24.0 and 11.5% with mean number of parasites infection^-1 being 1.5 and 1.3 for Chesapeake Bay and Indian River samples, respectively. D. aspida was estimated to remove up to 68% of host standing stock d^-1 with a mean of 10% for all samples. The average impact of parasitism on F. panamensis populations was somewhat less than would be expected from copepod grazing.     

Reproduction and reproductive variability in the coral Pocillopora verrucosa from the Republic of Maldives

The sexuality, reproductive mode, and timing of reproduction of Pocillopora verrucosa from the Republic of Maldives, Indian Ocean, were assessed using serial histological sections. These showed that P. verrucosa is an annual simultaneous hermaphrodite, with gonads arranged in two opposing arcs of alternating testes and ovaries, six gonads in each arc. No planulae were observed in any dissection or histological analysis carried out, therefore making brooding unlikely. Broadcast spawning is inferred from the disappearance of mature gametes from samples collected between late March and April 1991. Mean oocyte size at spawning was 53.5 m and mean potential fecundity was 7300 ooctyes cm^-2yr^-1. The reproductive pattern of P. verrucosa in the Maldives is compared to that of the same species in different locations, the short breeding season in March to April occurring earlier in the Maldives than in Red Sea populations. The maximum mean oocyte diameter found in Maldivian specimens was much smaller than elsewhere. The year-to-year variation in numbers of oocytes/polyp within single colonies, and the variation between colonies within the population was significant (p<0.01). Therefore, it is possible that fecundity is not a good variable to use when monitoring stress on coral reefs unless larger numbers of estimates can be routinely made. Some colonies contained immature oocytes at spawning that were not released and continued to grow to approximately twice the size of the spawned oocytes that were presumed to be mature. These unspawned oocytes were oosorbing, and were characterised by the presence of zooxanthellae and large numbers of vacuoles in their cytoplasm. This gradual expansion and oosorption of unspawned oocytes has not been documented previously for corals.