Distribution,abundance, and substrate preferences of demersal reef zooplankton at Lizard Island Lagoon,Great Barrier Reef

Demersal zooplankton, those plankton which hide within reef sediments during the day but emerge to swim freely over the reef at night, were sampled quantitatively using emergence traps planced over the substrate at Lizard Island Lagoon, Great Barrier Reef. Densities of zooplankton emerging at night from 6 substrate types (fine, medium, and coarse sand, rubble, living coral and reef rock) and from 5 reef zones (seaward face, reef flat, lagoon, back reef, and sand flat) were determined. A large population of nocturnal plankton including cumaceans, mysids, ostracods, shrimp, isopods, amphipods, crustacean larvae, polychaetes, foraminiferans and copepods are resident members of the reef community at Lizard Island. The mean density of plankton emerging throughout the reef was 2510±388 (standard error) zooplankton/m² of substrate. Biomass averaged 66.2±5.4 mg ash-free dry weight/m² of substrate. Demersal zooplankton exhibited significant preferences for substrate types and reef zones. The highest mean density of zooplankton emerged from coral (11,264±1952 zooplankton/m²) while the lowest emerged from reef rock (840±106 zooplankton/m²). The density of demersal plankton was six times greater on the face than in any other zone, averaging 7900±1501 zooplankton/m². Copepods dominated samples collected over living coral and rubble while foraminiferans, ostracods and decapod larvae were most abundant from sand. Plankton collected with nets at night correlated only qualitatively with plankton collected in emergence traps from the same location. Although abundant, demersal plankton were not numerous enough to meet the metabolic needs of all corals at Lizard Island Lagoon. Demersal plankton appear especially adapted to avoid fish predation. The predator-avoidance strategies of demersal plankton and maintenance of position on the reef are discussed. Our results indicate that much of the zooplankton over coral reefs actually lives on the reef itself and that previous studies using standard net sampling techniques have greatly underestimated plankton abundance over coral reefs.     

Variation in emergence of parasitic and predatory isopods among habitats at Lizard Island, Great Barrier Reef

Gnathiid isopods are one of the most abundant groups of ectoparasites on coral reef fishes. They, and other isopods, have been shown to significantly affect the health and behaviour of many reef fish. Whether isopod emergence differs among habitats on coral reefs is not known. In this study, we measured emergence rates of parasitic isopods (Gnathiidea and Flabellifera) in six habitats at two sites at Lizard Island during new moon periods in March and December 2004. Isopods were collected from the periphery and centres of micro-reefs, patch reefs, continuous reefs, and from inter-reefal habitats (sand or rubble) with 1 m² emergence traps. Sites (Casuarina and Coconut Beach) were located on opposite sides of Lizard Island. Live gnathiids were collected with light traps in November 2005 to investigate species differences between sites. At both sites, the most abundant gnathiid species was exclusive to that site. More gnathiid larvae emerged at night, and emergence of fed gnathiids (pranizae) and flabelliferan isopods was almost exclusively nocturnal. Diurnal emergence was greater at Coconut Beach than Casuarina Beach. Although emergence counts were not consistently affected by parameters such as habitat, site, or sampling period, gnathiid size and feeding state were. Where significant differences existed, gnathiids were larger and more often fed over reef borders than centrally. We suggest first stage larvae (Z1) have the largest influence on total abundance and are patchily distributed in accordance with adults from which they have recently hatched. As later stage larvae depend on fish, more successful (fed) and older larvae are found on the edges of reefs where appropriate hosts may be more abundant, or predation is lower. Gnathiids were over-dispersed in all habitats investigated, including apparently homogeneous beds of coral rubble and sand. This indicates that their distributions may be better predicted by very fine scale differences in substrate or that aggregations are the result of gregariousness and may be difficult to predict on the basis of substrate. Emergence traps collected comparatively few parasitic flabelliferan isopods. This community differed greatly from the previously described community of scavenging isopods at Lizard Island. These differences are probably the result of differences in trapping methodology.     

Tolerance of estuarine benthic diatoms to high concentrations of ammonia,nitrite ion,nitrate ion and orthophosphate

A carbon-14 assimilation method was used to determine action spectra and photosynthesis versus irradiance (P versus I) curves of natural populations of phytoplankton and zooxanthellae from a coral reef fringing Lizard Island in the Australian Barrier Reef. The action spectra were related to the phytoplankton species composition. The curves showed shade adaptation in phytoplankton from deeper waters and in the zooxanthellae. Rates of photosynthesis of zooxanthellae were shown to be highly but variably dependent on their host organisms. Photosynthetic production by zooxanthellae was about 0.9 gC m^-2 day^-1, which is about three times higher than phytoplankton production in the waters close to the reef.     

Sexual reproduction in Acropora (Isopora) (Coelenterata: Scleractinia)

In contrast to the seasonal gamete and planula production of Acropora (Isopora) palifera on Heron Island reef (Lat. 23° S), populations on Lizard Island reef (Lat. 14° S), sampled in 1979, 1981 and 1983, and Salamaua and Busama reefs (Lat. 7° S), sampled from 1980 to 1983, planulated year-round. Intensive sampling of colonies at Salamaua and Busama showed that gametes ripened at two-month intervals and that up to six cycles of gametes and larvae could be produced by an individual colony. Gametes of only a portion of the population — usually close to 50% — ripened each month. The Salamaua population, on average, produced fewer and smaller planulae than the Heron Island population during each two-monthly reproductive cycle. Hypotheses correlating the annual periodicity of breeding in marine animals with latitudinal variation of temperature were tested. In general, the time of breeding in A. palifera at Heron Island reef is much more restricted than theories based on latitudinal variations of water temperature would predict. It is hypothesized that, in the near subtropical environment of Heron Island reef, this species has evolved a life-history strategy that limits the amount of energy allocated to reproduction and allocates more energy to growth.     

Documenting Loss of Large Trophy Fish from the Florida Keys with Historical Photographs

Abstract:  A loss of large vertebrates has occurred in aquatic and terrestrial ecosystems, but data to measure long-term population changes are sparse. Historical photographs provide visual and quantitative evidence of changes in mean individual size and species composition for groups of marine fish that have been targeted by sport fishing. I measured such trends for 13 groups of recreationally caught "trophy" reef fish with photographs taken in Key West, Florida, from 1956 to 2007. The mean fish size declined from an estimated 19.9 kg (SE 1.5) to 2.3 kg (SE 0.3), and there was a major shift in species composition. Landings from 1956 to 1960 were dominated by large groupers ( Epinephelus spp.), and other large predatory fish were commonly caught, including sharks with an average length of just <2 m. In contrast, landings in 2007 were composed of small snappers ( Lutjanus spp. and Ocyurus chrysurus ) with an average length of 34.4 cm (SE 0.62), and the average length of sharks declined by more than 50% over 50 years. Major declines in the size of fish caught were not reflected in the price of fishing trips, so customers paid the same amount for a less-valuable product. Historical photographs provide a window into a more pristine coral reef ecosystem that existed a half a century ago and lend support to current observations that unfished reef communities are able to support large numbers of large-bodied fish.     

In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces: Serranidae)

Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s⁻¹) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s⁻¹). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between 2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80% (4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between 5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first. Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance of predators and settlement seem to rely on vision. Received: 7 July 1998 / Accepted: 26 January 1999     

Particle interception,transport and rejection by the feather star Oligometra serripinna (Echinodermata: Crinoidea), studied by frame analysis of videotapes

Suspension feeding by a stalkless crinoid (Oligometra serripinna) was studied at Lizard Island, Australia, in 1985. The crinoids were placed in a laboratory flume with a slow, unidirectional current of seawater. Nutritive and non-nutritive particles (15 to 180 m) were introduced upstream from the crinoid, and feeding behavior was recorded at high magnifications on videotape for frame analysis. These direct observations showed that each intercepted particle (whether a dejellied clam egg, Sephadex bead or latex sphere) contacts a single, evidently adhesive tube foot and is rapidly transferred to the pinnular food groove by a bend of the tube foot. The tube foot bends in about 0.1 s and returns to its extended position in 1 to 2 s. Spheres less than 20 m in diameter cause only the intercepting tube foot to bend. In contrast, larger spheres cause the coordinated bending of the intercepting tube foot plus many of the neighboring tube feet: the stimulus spreads through the reacting group of tube feet at about 1 cm s^-1. After transfer to the pinnular food groove, the nutritive particles (dejellied clam eggs) travel at about 1 cm min^-1 to the arm axis and thence down the arm food groove at about 4 cm min^-1 to the mouth; in contrast, non-nutritive particles (Sephadex beads and latex spheres) are discarded from the pinnular food groove between 1 and 30 s after capture. Tube-foot bending is presumably triggered when arriving particles (whether nutritive or non-nutritive) are detected by sensory cells in the tubefoot epithelium: mechanoreception by itself appears sufficient to initiate bending, although chemoreception may modify the reaction. Then, soon after captured particles have been transferred to the pinnular food groove, the crinoid discards those judged unsuitable (probably by contact chemoreceptors in the food-groove epithelium). Clam eggs with intact jelly layers temporarily hang up on tube feet they contact and then float away in the curent: the jelly evidently interferes with mechanoreception and/or chemoreception by the tube-foot epithelium. Some previous studies of crinoid feeding have suggested that particles are trapped in extensive nets or strands of mucus: we found no evidence for this in O. serripinna, which captures particles predominantly be the direct interception method of the aerosol filtration model.     

Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations

The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s⁻¹ to 100.8 cm s⁻¹ (mean=37.3 cm s⁻¹), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.     

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.     

Temporal and spatial variation in bacterial production in the water column over a coral reef

Production and doubling times of the bacterial populations in the water around and over the reefs at Lizard Island, Great Barrier Reef were measured during summer and winter, 1982 and 1983. Bacterial productivity, determined from the rate of tritiated thymidine incorporation into DNA, was high over the reef flats and a Thalassia hemprichii sand flat (28 to 58 g Cl^-1 d^-1). Bacterial growth rates increased during the day and fell at night over the reef flats and seagrass bed. Growth rates were slower over the reef front and in open water. Doubling times ranged from about 2 d in the open water to about 3 h over the reef flat in summer. As numbers did not increase, grazing was probably intense on the reef flats. Growth rates were much slower in winter. The main source of organic nutrient used by the bacteria was probably mucus released following photosynthesis in the corals. The cyanobacterium Synechococcus sp. was sometimes very numerous, especially in summer when 2×10⁸ cells l^-1 were recorded in one water mass. The number of bacteria was also very high in summer, with values ranging from 1×10⁹ to 2.5×10⁹l^-1.     

Density-dependent habitat selection and performance by a large mobile reef fish.

Many exploited reef fish are vulnerable to overfishing because they concentrate over hard-bottom patchy habitats. How mobile reef fish use patchy habitat, and the potential consequences on demographic parameters, must be known for spatially explicit population dynamics modeling, for discriminating essential fish habitat (EFH), and for effectively planning conservation measures (e.g., marine protected areas, stock enhancement, and artificial reefs). Gag, Mycteroperca microlepis, is an ecologically and economically important warm-temperate grouper in the southeastern United States, with behavioral and life history traits conducive to large-scale field experiments. The Suwannee Regional Reef System (SRRS) was built of standard habitat units (SHUs) in 1991-1993 to manipulate and control habitat patchiness and intrinsic habitat quality, and thereby test predictions from habitat selection theory. Colonization of the SRRS by gag over the first six years showed significant interactions of SHU size, spacing, and reef age; with trajectories modeled using a quadratic function for closely spaced SHUs (25 m) and a linear model for widely spaced SHUs (225 m), with larger SHUs (16 standardized cubes) accumulating significantly more gag faster than smaller 4-cube SHUs (mean = 72.5 gag/16-cube SHU at 225-m spacing by year 6, compared to 24.2 gag/4-cube SHU for same spacing and reef age). Residency times (mean = 9.8 mo), indicative of choice and measured by ultrasonic telemetry (1995-1998), showed significant interaction of SHU size and spacing consistent with colonization trajectories. Average relative weight (W(r)) and incremental growth were greater on smaller than larger SHUs (mean W(r) = 104.2 vs. 97.7; incremental growth differed by 15%), contrary to patterns of abundance and residency. Experimental manipulation of shelter on a subset of SRRS sites (2000-2001) confirmed our hypothesis that shelter limits local densities of gag, which, in turn, regulates their growth and condition. Density-dependent habitat selection for shelter and individual growth dynamics were therefore interdependent ecological processes that help to explain how patchy reef habitat sustains gag production. Moreover, gag selected shelter at the expense of maximizing their growth. Thus, mobile reef fishes could experience density-dependent effects on growth, survival, and/or reproduction (i.e., demographic parameters) despite reduced stock sizes as a consequence of fishing.     

Productivity of bacteria and microalgae and the effect of grazing by holothurians in sediments on a coral reef flat

Bacterial productivity in sandy sediments on reef flats at Lizard Island, Great Barrier Reef was determined from the rate of incorporation of tritiated thymidine into DNA. The study was conducted during January 1982 and July 1983. A small diurnal increase occurred in sediments having a dense population of microalgae. Bacterial production was 120 to 370 mg C m^-2 d^-1 in summer on reef flats, which was equivalent to 30–40% of primary production by benthic microalgae. In winter, rates of primary production by benthic microalgae and secondary production by bacteria were about one-half to one-fifth of those in summer. There was much variation in production, due to patchiness in the distribution of benthic microbes, especially microalgae. Doubling times for the bacteria in surface sediment were 1 to 2 d in summer and 4 to 16 d in winter on the reef flats. These high productivity values for bacteria indicated that a net input of organic matter to the sediment was needed to support the growth of bacteria. Sediment bacteria thus have a very important role in transforming organic matter on the reef flats. Grazing by Holothuria atra depressed both primary production and bacterial production. It was estimated that these holothurians ate about 10 to 40% of bacterial carbon produced each day in summer, and thus have an important role in the carbon cycle. Harpacticoid copepods were numerically important components of the benthic meiofaunal community and probably had a significant impact on bacterial density as grazers.     

Tube-worm-sediment relationships in populations of Pectinaria gouldii (Polychaeta: Pectinariidae) from Barnegat Bay,New Jersey,USA

Pectinaria gouldii (Verrill), which lives for 1 year in Barnegat Bay, New Jersey, constructs over its lifetime a conical tube of increasingly large sand grains, regardless of surrounding sediment characteristics. However, the rate of increase of mean grain size of the tube and the population density of the worm vary with sediment type. The distribution of this species is limited by sediment composition. Worms of equal length will always have equal anterior tube apertures, although the thickness of the tube walls may be unequal. Tube surface-area, worm dry weight, and tube weight all increase as a power function of tube length. The conical shape and increasing mass of the tube impose an upper limit to worm growth, but do not interfere with worm mobility.     

Sediment-rejection efficiency of 22 species of Australian scleractinian corals

Sediment-rejection rates of 22 Australian midshelf coral species were studied in situ between March and July 1988 at Lizard Island, Great Barrier Reef. Rejection rates of non-branching species were positively correlated with calice size and were faster for fine (63 to 250 m) than for coarse (500 to 1000 m) sediment at influxes of 200 mg/cm². Increasing water turbulence was a more important influence on rejection rates for some species than for others. Most replicates of most species cleared all sediment in 2 d. Of those that did not, some Favia stelligera and Leptoria phrygia showed partial tissue death within 48 h, and Gardineroseris planulata showed partial tissue death within 6 d. Montipora aequituberculata, Porites lobata and P. lutea tolerated sediment for at least 6 d, and exhibited extensive tissue bleaching, but these tissues recovered after sediment removal. Sediment-rejection efficiency and sediment tolerance are not directly related, and wide interspecific differences may occur in both. These findings are correlated with differences in sediment-rejection mechanisms and with ecological distributions on the reef.     

Local variation in mortality rates and life-expectancy estimates of the coral-reef fish Centropyge bicolor (Pisces: Pomacanthidae)

Mortality rates of the coral reef fish Centropyge bicolor were based on the disappearance of known individual fish. Data were collected over three years from 1978 at four sites around Lizard Island, Queensland, Australia. To measure disappearance, membership of 36 harems (comprising about 150 fish at any one time) was determined at bimonthly intervals. Mortality rates varied significantly among the four study areas. A tenfold difference in mean mortality occurred between two of the areas. The ranking of areas according to mortality rate was similar for 1978–1979 and 1979–1980. The ranking of areas was again similar for 1980–1984 when mortality rates were determined from an additional census in June 1984. Average further life-expectancy of mature fish based on mortality rates varied from 1 yr in one study area to 5 to 13 yr in a different area.     

Daily feeding rates in herbivorous labroid fishes

Estimates of daily feeding rates were obtained for two groups of herbivorous labroid fishes, one confined to cold water and the other to tropical reef environments. These were the family Odacidae, represented by Odax pullus from New Zealand waters, (Goat Island Bay: Latitude 36° South; on the northeastern coast of New Zealand) and the family Scaridae, represented by Scarus rivulatus, S. schlegeli and S. sordidus from the northern Great Barrier Reef (Lizard Island; a mid-shelf reef at 14° South latitude). Observations on the odacid were made in 1984 and in 1992, and on the scarids in 1984 and 1988. O. pullus displayed a diurnal feeding pattern in which the rates (expressed as bites min^-1) are greatest early in the day. The mean combined feeding rate for three size groups (juveniles, subadults and adults) peaked (average of 2.9 bites) from 06.00 to 08.00 hrs and declined fourfold to a combined average of 0.7 bites min^-1 by midday. The greatest mean feeding rate recorded was 3.7 bites min^-1, with an overall mean of 1.8 bites min^-1. For subadults and adults there were consistent trends in feeding, with subadults feeding at a greater rate than adults and both groups displaying a decline in feeding rate during the day. The change in feeding rate with time of day was statistically significant in both groups. The pattern for juvenile O. pullus was different from that in the two larger size groups in that juveniles did not show a uniform decline in feeding with time of day. For scarids, the daily feeding rate varied by site, but the pattern was similar for all species, characterised by initial low rates increasing to higher but variable levels by midday. The influence of both site of feeding and time of day on feeding rate was confirmed by analysis. The overall mean values for each species were 20.1 bites min^-1 for S. rivulatus, 19.7 bites min^-1 for S. schlegeli and 14.9 bites min^-1 for S. sordidus. For scarids, the peak feeding rates varied from 19.3 to 32.8 bites min^-1, with overall rates from 14.9 to 21.1 bites min^-1. Estimates of activity and movement patterns during feeding were obtained for O. pullus. Distance moved per unit time was highly variable, 0.1 to 47.5 m min^-1, with a mean of 8.5 m min^-1 (SD=9.9). Trends in movement among sexes and size classes were obscured by the variable movement patterns of individual fishes.     

Reef coral reproduction in the eastern Pacific: Costa Rica,Panamá, and Galápagos Islands (Ecuador). II. Poritidae

A comparative study of the reproductive ecology of the zooxanthellate, scleractinian corals Porites lobata Dana and P. panamensis Verrill was conducted from 1985 to 1991 in eastern Pacific reef environments that were severly impacted by the 1982–1983 El Niño warming events. P. lobata, a presumed broadcast spawner of large colony size, is widely distributed in the equatorial eastern Pacific, whereas P. panamensis, a brooder of small colony size, is abundant only on some reefs in Panamá. Both species were gonochoric with nearly 1:1 sex ratios in large study populations except for P. lobata at Caño Island that had 14% hermaphroditic colonies. Mature, unfertilized oocytes contained numerous zooxanthellae in both Porites species, and all planula developmental stages contained zooxanthellae in P. panamensis. Year-round sampling revealed high proportions of colonies with gonads, ranging from 30 to 68% in P. lobata and from 60 to 68% in P. panamensis. No clear relationship between numbers of reproductive colonies and the thermal stability of the habitat was evident in P. lobata: percent colonies with gonads at non-upwelling sites was 48 to 68% at Caño Island (Costa Rica) and Uva Island (Panamá), and at upwelling sites 30 to 50% at Saboga Island and Taboga Island (Panamá), and the Galápagos Islands (Ecuador). Similarly, 90% of all P. panamensis colonies were reproductive at Uva Island (a non-upwelling site), and 86% were reproductive at Taboga Island (an upwelling site). Upwelling at Taboga Island is seasonal, nevertheless P. panamensis produced mature gonads or planulae over most of the year (11 mo), whereas P. lobata exhibited reproductive activity during only 2 mo (May and June). No clear lunar periodicity was observed in P. panamensis (Taboga Island), but a high proportion of P. lobata showed increased gonadal development around full and new moon, especially at Caño and Uva Islands. Estimated fecundities were relatively high for P. lobata at Caño (4000 eggs cm^-2 yr^-1) and Uva (5200 eggs cm^-2 yr^-1) Islands, and notably low (70 to 110 eggs cm^-2 yr^-1) in the Galápagos Islands. P. panamensis mean fecundity at Taboga Island was 720 planulae cm^-2 yr^-1 or 4.0 mm³ cm^-2 yr^-1, which was lower than the egg volume production of P. lobata at Caño and Uva Islands (7.0 to 10.0 mm³ cm^-2 yr^-1). The capacity of P. lobata and P. panamensis to reproduce sexually supports the notion that eastern Pacific coral reef recovery may not be dependent on long-distance dispersal from central Pacific areas. However, sexual recruits of P. lobata are absent or uncommon at all eastern Pacific study sites while recruits of P. panamensis were common to abundant only at the Uva Island study site. Asexual fragmentation in P. lobata augments recruitment locally, but plays no role in P. panamensis recruitment.     

Reproduction in five species of crinoids at Lizard Island,Great Barrier Reef

Reproduction in five species of crinoids [Himerometra bartschi (A. H. Clark), H. robustipinna (P. H. Carpenter), Cenometra bella (Hartlaub), Colobometra perspinosa (P. H. Carpenter), and Oligometra serripinna (P. H. Carpenter)] was studied at Lizard Island, Queensland, over 24 mo, from April 1981 to March 1983 (except for O. serripinna —June 1981 to March 1983). All five species of crinoids were dioecious, although a few instances of synchronous hermaphroditism were noted in H. bartschi, C. perspinosa, and O. serripinna. Gonad morphology and the sequence of developmental stages were similar in each species. Within individuals, gametogenesis was synchronous in gonads both along and between arms, except in some proximal and distal genital pinnules in which gonads never matured. Within a species, there was a degree of synchrony of gametogenesis in a sample, but the level of gametogenic activity varied considerably between years. A high level of continuous reproductive activity was observed in H. bartschi, H. robustipinna, Cenometra bella, and Colobometra perspinosa from about mid-summer to early/mid-winter, while O. serripinna probably had a bimodal reproductive cycle with peaks around February and June. There was a significant 1:1 male:female sex ratio in the populations sampled, and unsexable individuals were significantly smaller (as determined by maximum arm length) than either sexable males or females.     

Biomass of suspended bacteria over coral reefs

The biomass of bacteria suspended in water flowing over coral reefs at Lizard Island and Yonge Reef (Northern Great Barrier Reef) was estimated by measurement of muramic acid. Values ranged from 20 mg C m^-3 in the open water up to about 60 mg C m^-3 over the reef flat. Direct counts of total numbers of free bacteria were made for comparison. Values of around 2.0x10⁹ cells g^-1 muramic acid showed that there was a good agreement between direct counts and muramic acid content of free bacteria in the open water. In samples containing suspended particulate matter, ratios of direct counts to muramic acid concentration were lower, because bacteria on particles could not be counted. Thus, these ratios were used to indicate the proportions of bacteria attached to particles. Changes in the biomass and numbers of bacteria were determined in water masses identified either by a drogue or fluorescein, as they moved across the reefs. In the zone on the outside of the reef, the number of free bacteria decreased compared to open sea water, but total biomass increased, showing that particulate matter containing bacteria was thrown up into suspension. About 50% of bacteria were attached to particles. Water flowing over the reef flats contained much particulate material with bacteria attached. Bacteria constituted between about 5 and 20% of particulate organic carbon.