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.     

Mangrove fish-communities in tropical Queensland,Australia: Spatial and temporal patterns in densities,biomass and community structure

Regular daylight sampling over 13 mo (February 1985–February 1986) in and adjacent to intertidal forested areas, in small creeks and over accreting mudbanks in the mainstream of a small mangrove-lined estuary in tropical northeastern Queensland, Australia, yielded 112 481 fish from 128 species and 43 families. Species of the families Engraulidae, Ambassidae, Leiognathidae, Clupeidae and Atherinidae were numerically dominant in the community. The same species, with the addition ofLates calcarifer (Latidae).Acanthopagrus berda (Sparidae) andLutjanus agentimaculatus (Lutjanidae) dominated total community biomass. During high-tide periods, intertidal forested areas were important habitats for juvenile and adult fish, with grand mean (±1 SE) density and biomass of 3.5±2.4 fish m^–3 and 10.9±4.5 g m^–3, respectively. There was evidence of lower densities and less fish species using intertidal forests in the dry season (August, October), but high variances in catches masked any significant seasonality in mean fish biomass in this habitat. On ebb tides, most fish species (major families; Ambassidae, Leiognathidae, Atherinidae, Melanotaeniidae) moved to small shallow creeks, where mean (±1 SE) low-tide density and biomass were 31.3±12.4 fish m^–2 and 29.0±12.1 g m^–2, respectively. Large variances in catch data masked any seasonality in densities and biomasses, but the mean number of species captured per netting in small creeks was lowest in the dry season (July, August). Species of Engraulidae and Clupeidae, which dominated high-tide catches in the forested areas during the wet season, appeared to move into the mainstream of the estuary on ebbing tides and were captured over accreting banks at low tide. Accreting banks supported a mean (±1 SE) density and biomass of 0.4±0.1 fish m^–2 and 1.7±0.3 g m^–2, respectively, at low tide. There were marked seasonal shifts in fish community composition in the estuary, and catches in succeeding wet seasons were highly dissimilar. Comparison of fish species composition in this and three other mangrove estuaries in the region revealed significant geographic and temporal (seasonal) variation in fish-community structure. Modifications and removal of wetlands proposed for north Queensland may have a devastating effect on the valuable inshore fisheries of this region, because mangrove forests and creeks support high densities of fish, many of which are linked directly, or indirectly (via food chains) to existing commercial fisheries.Contribution No. 493 from the Australian Institute of Marine Science     

Quantitative distribution of herbivorous reef fishes in the Gulf of Aqaba (Red Sea)

The distribution of the main herbivorous fishes (Acanthuridae, Scaridae, Siganidae) was studied across a coral reef of the Jordanian coast in the Gulf of Aqaba (Red Sea). Visual counts were realized by diving along transects (200 m long and 5 m wide), parallel to the shore, at 10 stations located from the lagoon to 40 m deep on the outer reef slope. Herbivorous reef fishes reach their highest abundance on the reef front, where 234 fishes were counted per 1,000 m². Their density decreases on the reef flat, with an average of 150 fish 1,000 m^-2, and is lowest on the outer reef slope (69 fish 1,000 m^-2). Surgeonfishes form 63% of the herbivorous ichthyofauna, parrotfishes 35%, and rabbitfishes 2%. Families and species display different distributions according to biota. The Acanthuridae dominate on the reef flat, whereas the Scaridae are more numerous on the outer reef slope. The evolution of the social structure of the main species was observed: the adults generally school in the lagoon and on the reef flat, but are mainly solitary on the reef slope. The distribution of juvenile individuals is more restricted: they are concentrated on the reef front and on the upper part of the reef slope.This study is part of a cooperation programme between the University of Nice (France) and the University of Jordan, to study the ecology of the coral reefs and the surrounding waters of the Jordanian coast (Gulf of Aqaba, Red Sea)     

Among-habitat variation in herbivory on Sargassum spp. on a mid-shelf reef in the northern Great Barrier Reef

Herbivory is widely acknowledged as a key process determining the benthic community structure and resilience of coral reefs. Despite numerous studies that have examined herbivory across reef gradients in the Caribbean, few studies have directly quantified this process on Pacific reefs. Bioassays of two species of erect macroalgae (Sargassum swartzii and S. cristaefolium) were used to quantify variation in grazing intensity across seven habitats of varying depth and wave exposure on a mid-shelf reef in the northern Great Barrier Reef. Removal rates of Sargassum varied significantly among habitats, with both species displaying broadly similar patterns. The shallow habitats on the exposed aspect of the reef (i.e. reef crest, flat and back reef) experienced the highest reductions in mass (81.4–91.6% day⁻¹) for both S. swartzii and S. cristaefolium, while the deeper exposed habitats (reef slope and base) displayed the lowest reductions (3.8–13.4% day⁻¹) over a 24 h period. In contrast, the grazing intensity varied between the two species in the three habitats on the leeward aspect of the reef. Reductions in mass remained relatively high for S. swartzii on the patch reef and sheltered reef base and flat (62.7–76.5% day⁻¹) but were considerably lower for S. cristaefolium (37.9–63.5% day⁻¹) across the same habitats. Surprisingly, the rates of removal of Sargassum displayed no relationship with the density or biomass of roving herbivorous fishes or those species known to consume erect macroalgae, either collectively or independently. These results suggest that the relationship between browsing rates and herbivorous fish biomass is complex and may be driven by species that are underestimated in visual surveys. Direct quantification of browsing intensity using assays revealed a different pattern to inferences based on herbivore densities and highlights the potential difficulties of evaluating ecosystem processes based on visual census data alone.     

Direct versus indirect methods of quantifying herbivore grazing impact on a coral reef

Two methods were used to assess the grazing impact of roving herbivorous fishes across a coral reef depth gradient within Pioneer Bay, Orpheus Island, Great Barrier Reef. The first technique employed was a method traditionally used to quantify herbivory on coral reefs via the (indirect) inference of herbivore impact from biomass estimates and reported feeding rates. The second method (one of a range of direct approaches) used remote underwater video cameras to film the daily feeding activity of roving herbivores in the absence of divers. Both techniques recorded similar patterns and relative levels of herbivore biomass across five reef zones at the study site. Indirect estimates of the grazing impact across the reef depth gradient of the three predominant species of herbivore broadly coincided with levels quantified directly by remote underwater video, indicating that, to a large extent, presence does correspond to function. However, the video data suggested that, for individual species in particular reef zones, the absolute level of impact may be less than that inferred from presence. In the case of the parrotfish Scarus rivulatus, the video recordings suggested that, at the reef crest, an average of 52% (±18 SE) of each m² area of reef would be grazed each month, compared with an area of 109% (±41 SE) suggested by inferring grazing activity from presence alone. Potential biases associated with remote video recorders may explain some of the discrepancy between values. Overall, the results suggest that, for some fish groups, the indirect method of inferring function from presence can provide a good indication of relative levels of herbivore impact across a coral reef. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Extreme genetic diversity and temporal rather than spatial partitioning in a widely distributed coral reef fish

Mitochondrial control region (HVR-1) sequences were used to identify patterns of genetic structure and diversity in Naso vlamingii, a widespread coral reef fish with a long evolutionary history. We examined 113 individuals from eight locations across the Indo-Pacific Ocean. Our aims were to determine the spatial scale at which population partitioning occurred and then to evaluate the extent to which either vicariance and/or dispersal events have shaped the population structure of N. vlamingii. The analysis produced several unexpected findings. Firstly, the genetic structure of this species was temporal rather than spatial. Secondly, there was no evidence of a barrier to dispersal throughout the vast distribution range. Apparently larvae of this species traverse vicariance barriers that inhibit inter-oceanic migration of other widespread reef fish taxa. Thirdly, an unusual life history and long evolutionary history was associated with a population structure that was unique amongst coral reef fishes in terms of the magnitude and pattern of genetic diversity (haplotype diversity, h = 1.0 and nucleotide diversity π = 13.6%). In addition to these unique characteristics, there was no evidence of isolation by distance (r = 0.458, R ² = 0.210, P = 0.078) as has also been shown for some other widespread reef species. However, some reductions in gene flow were observed among and within Ocean basins [Indian–Pacific analysis of molecular variance (AMOVA), Φ _st = 0.0766, P < 0.05; West Indian–East Indian–Pacific AMOVA Φ _st = 0.079, P < 0.05]. These findings are contrasted with recent studies of coral reef fishes that imply a greater degree of spatial structuring in coral reef fish populations than would be expected from the dispersive nature of their life cycles. We conclude that increased taxon sampling of coral reef fishes for phylogeographic analysis will provide an extended view of the ecological and evolutionary processes shaping coral reef fish diversity at both ends of the life history spectrum.     

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

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

Bioerosion of coral reefs by two Hawaiian parrotfishes: species, size differences and fishery implications

Parrotfishes can be significant bioeroders and sediment producers on coral reefs. We quantified the bioerosion rates of two similarly sized Hawaiian parrotfishes with two different feeding modes (Scarus rubroviolaceus—a scraper and Chlorurus perspicillatus—an excavator). The results showed that feeding modes did not affect bioerosion rates but that bioerosion rates were size dependent, with largest individuals (S. rubroviolaceus 45–54 cm FL) bioeroding up to 380 ± 67 kg ind⁻¹ year⁻¹. The size for onset of bioerosion capabilities for both species was 15 cm. Grazing by the two species consumed 60% of the carbonate production of the fore reef area, suggesting that large parrotfishes in Hawaii are ecologically important bioeroders. As individual large S. rubroviolaceus contributed disproportionately more to bioerosion and sediment production than the equivalent biomass of smaller conspecifics, management strategies designed to retain normal reef bioerosion rates should seek to preserve the historical size structure of S. rubroviolaceus populations and to especially protect the larger size classes.     

Differential movement patterns and site fidelity among trophic groups of reef fishes in a Hawaiian marine protected area

We tracked the long-term movements of 70 parrotfishes, surgeonfishes and goatfishes captured inside a small (1.3 km²) marine protected area (MPA: Kealakekua Bay Marine Life Conservation District, Hawaii) by implanting them with small transmitters and deploying underwater monitoring devices inside the bay and along 100 km of the adjacent west Hawaii coastline. Individual fish were detected inside Kealakekua Bay for up to 612 days but many were detected for much shorter periods (median = 52 days). There were species-specific differences in the scale of movements and habitats used, but most fish utilized between 0.2 and 1.6 km of coastline, and individuals of each species showed some degree of diel habitat shift. A wide variety of reef fishes captured inside the MPA swam back and forth across an MPA boundary intersecting continuous reef (i.e., this boundary was porous to reef fish movements), but only 1 of 11 species tagged crossed a wide sandy channel inside Kealakekua Bay suggesting that this feature may function as a natural barrier to movements. Results indicate relatively small MPAs (<2 km of coastline) could provide effective, long-term protection for multi-species assemblages of reef fishes provided that boundaries are situated along major habitat breaks (e.g., large sand channels between reefs) that may serve as natural barriers to reef fish movements. It is crucial that a multi-species approach be used when assessing MPA effectiveness.     

Variability in nursery function of tropical seagrass beds during fish ontogeny: timing of ontogenetic habitat shift

Seagrass beds are often considered to be important nurseries for coral reef fish, yet the effectiveness of these nursery functions (refuge and food availability) at different juvenile stages is poorly understood. To understand how the demands of juvenile fish on seagrass nursery functions determines the timing of ontogenetic habitat shifts from seagrass beds to coral reefs, we conducted visual transect survey and field tethering and caging experiments on three different sizes of the coral reef fish Pacific yellowtail emperor (Lethrinus atkinsoni) during its juvenile tenure in seagrass beds at Ishigaki Island, southern Japan. The study showed that although the number of individual L. atkinsoni juveniles decreased by >90 % during their stay in the seagrass nursery, the shelter and/or food availability functions of the nursery, at least for a juvenile size of approximately 5 cm total length (TL), provided the best survival and growth option. The timing of ontogenetic migration to coral reefs of larger fish (>8 cm TL) was attributed to foraging efficiency for larger food items in different habitats. Overall, the function of the seagrass bed nursery changed with juvenile body size, with marginally higher survival and significantly greater growth rates during early juvenile stages in seagrass beds compared to coral reefs. This would contribute to the enhancement in the number of individuals eventually recruited to adult populations.     

A new apparatus for force measurement in marine bioadhesion

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

Habitat biodiversity as a determinant of fish community structure on coral reefs

Increased habitat diversity is often predicted to promote the diversity of animal communities because a greater variety of habitats increases the opportunities for species to specialize on different resources and coexist. Although positive correlations between the diversities of habitat and associated animals are often observed, the underlying mechanisms are only now starting to emerge, and none have been tested specifically in the marine environment. Scleractinian corals constitute the primary habitat-forming organisms on coral reefs and, as such, play an important role in structuring associated reef fish communities. Using the same field experimental design in two geographic localities differing in regional fish species composition, we tested the effects of coral species richness and composition on the diversity, abundance, and structure of the local fish community. Richness of coral species overall had a positive effect on fish species richness but had no effect on total fish abundance or evenness. At both localities, certain individual coral species supported similar levels of fish diversity and abundance as the high coral richness treatments, suggesting that particular coral species are disproportionately important in promoting high local fish diversity. Furthermore, in both localities, different microhabitats (coral species) supported very different fish communities, indicating that most reef fish species distinguish habitat at the level of coral species. Fish communities colonizing treatments of higher coral species richness represented a combination of those inhabiting the constituent coral species. These findings suggest that mechanisms underlying habitat-animal interaction in the terrestrial environment also apply to marine systems and highlight the importance of coral diversity to local fish diversity. The loss of particular key coral species is likely to have a disproportionate impact on the biodiversity of associated fish communities.     

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.     

Defining Critical Habitats of Threatened and Endemic Reef Fishes with a Multivariate Approach

Understanding critical habitats of threatened and endemic animals is essential for mitigating extinction risks, developing recovery plans, and siting reserves, but assessment methods are generally lacking. We evaluated critical habitats of 8 threatened or endemic fish species on coral and rocky reefs of subtropical eastern Australia, by measuring physical and substratum‐type variables of habitats at fish sightings. We used nonmetric and metric multidimensional scaling (nMDS, mMDS), Analysis of similarities (ANOSIM), similarity percentages analysis (SIMPER), permutational analysis of multivariate dispersions (PERMDISP), and other multivariate tools to distinguish critical habitats. Niche breadth was widest for 2 endemic wrasses, and reef inclination was important for several species, often found in relatively deep microhabitats. Critical habitats of mainland reef species included small caves or habitat‐forming hosts such as gorgonian corals and black coral trees. Hard corals appeared important for reef fishes at Lord Howe Island, and red algae for mainland reef fishes. A wide range of habitat variables are required to assess critical habitats owing to varied affinities of species to different habitat features. We advocate assessments of critical habitats matched to the spatial scale used by the animals and a combination of multivariate methods. Our multivariate approach furnishes a general template for assessing the critical habitats of species, understanding how these vary among species, and determining differences in the degree of habitat specificity. Definición de Hábitats Críticos para Peces Arrecifales Amenazados y Endémicos Mediante un Método Multivariado     

Predicting structural complexity of reefs and fish abundance using acoustic remote sensing (RoxAnn)

This study determined whether the acoustic roughness of Caribbean reef habitats is an accurate proxy for their topographic complexity and a significant predictor of their fish abundance. Fish abundance was measured in 25 sites along the forereef of Glovers Atoll (Belize). At each site, in situ rugosity (ISR) was estimated using the “chain and tape” method, and acoustic roughness (E1) was acquired using RoxAnn. The relationships between E1 and ISR, and between both E1 and ISR and the abundance of 17 common species and the presence of 10 uncommon species were tested. E1 was a significant predictor of the topographic complexity (r ² = 0.66), the abundance of 10 common species of surgeonfishes, pomacentrids, scarids, grunts and serranids and the presence of 4 uncommon species of pomacentrids and snappers. Small differences in E1 (i.e. ∆0.05–0.07) reflected in subtle but significant differences in fish abundance (~1 individual 200 m⁻² and 116 g 200 m⁻²) among sites. Although we required the use of IKONOS data to obtain a large number of echoes per site, future studies will be able to utilise RoxAnn data alone to detect spatial patterns in substrate complexity and fish abundance, provided that a minimum of 50 RoxAnn echoes are collected per site.     

Method of estimating the standing stock of Trochus niloticus incorporating Landsat satellite data,with application to the trochus resources of the Bourke Isles,Torres Strait,Australia

The habitat of Trochus niloticus in the Bourke Isles, Torres Strait, was classified into areas of a Landsat image, using high-ratio values of green (Band 2) to red (Band 3) light, along the windward reef margins. These shallow-water (< 15 m) areas have a coral and rubble/algal pavement cover, which constitutes the optimal habitat for this gastropod. The habitat was sampled to estimate the abundance of T. niloticus. The proportion of commercial-sized individuals was estimated by measuring the basal width of all individuals in a sample. A multistage sample design incorporating three spatial scales -100 m² (transect), 1500 m² (site) and 1 km² (reef) — was used to provide variance estimates for sample-design optimisation and to provide data on the spatial variation of abundance. Most variation (68%) in abundance was within reefs and was attributable to differences in reef cover. Variations in abundance and time costs for sampling 2 and 4 m transects were compared; the 2 m transect was more efficient than the 4 m transect. The abundance estimates were combined with habitat-area estimates and the proportion of commerical-sized individuals was estimated at a standing stock of 186000 (24% precision), or 14 t of commerical-sized T. niloticus.     

Use of pelagic prey subsidies by demersal predators in rocky reefs: insight from movement patterns of lingcod

Allochthonous subsidies of energy and nutrients can affect community structure in patchy marine habitats, including rocky reefs, and their ecological consequences may depend on the mechanism of energy transfer. Lingcod (Ophiodon elongatus) are demersal predators that trophically link nearshore rocky reefs with offshore pelagic habitats through consumption of pelagic fishes. We quantified lingcod habitat use and movement patterns to make inferences about the temporal and spatial conditions under which lingcod may acquire pelagic prey. Lingcod maintained small home ranges (21,272 ± 13,630 m²) within a rocky reef in the San Juan Archipelago, Washington; eight of nine individuals used rocky habitat exclusively. Depths occupied by lingcod (0–50 m) coincided with pelagic fish distribution on the rocky reef; however, diel patterns in lingcod activity varied inversely with occurrence of pelagic fishes on the reef. Our findings suggest that the pelagic subsidy to lingcod is not strongly mediated through directed off-reef foraging by lingcod.     

Fission and its effect on population structure of Holothuria atra (Echinodermata: Holothuroidea) in Taiwan

Populations of Holothuria atra Jaeger occurring at Wanlitung and Nanwan were sampled monthly at spring tide from March 1990 to February 1992 in southern Taiwan. At Wanlitung, small individuals with evidence of fission and regeneration were abundant in shallow tidepools on the wide reef flats (density: 98±40 ( ± SD) 100 m^-2, body weight: 6 to 182 g). At Nanwan, large individuals with no evidence of fission were sparse in deep tidepools and narrow flats [density: 0.24±0.07 ( ± SD) 100 m^{- 2}, body weight: 351 to 1400 g]. At Wanlitung, fission occurred throughout the year with an average monthly fission frequency of 4.5%, peaking at 18% in September 1990 and 16% in August 1991. Fission was accomplished by revolving, twisting, and stretching of the body, resulting in two unequal fragments. The minimal weight of 3007 individuals measured during 1 yr at Wanlitung was 6 g. All ten individuals weighing 6 to 9 g ( ± SD = 6.7 ± 1.1) 100 m^{- 2} showed evidence of regeneration from fission products. Nine large individuals (>500 g) transferred from Nanwan to Wanlitung and 50 small individuals (<100 g) transferred from Wanlitung to Nanwan in February 1991 showed no evidence of fission during the following year. Fission occurs in small individuals living in shallow tidepools, suggesting that fission probably is triggered by a stressful environment resulting from solar radiation at the unusually low water level of spring tide. Fission of H. atra at Wanlitung results in a population consisting of small individuals.     

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.     

Ecology of Conus on eastern Indian Ocean fringing reefs: Diversity of species and resource utilization

The most diverse assemblages of the genus Conus known occur on fringing coral reefs in Thailand and Indonesia. As many as 27 congeneric species of these gastropods inhabit a single reef; in all, we examined 1,350 individuals of 48 species. Several attributes of the populations we observed conform to expectations of a model of ecological characteristics of bench and reef Conus proposed by Kohn (1971a). Number of species (S) averaged 15, and species diversity (H″) averaged 2.3 in the most heterogeneous habitat type — topographically complex, subtidal reef platforms (Type III habitat). Both species richness and evenness of distribution of individuals among species contribute strongly to H″. Fewer congeners and greater numerical dominance by single species characterize more homogeneous habitats. On subtidal reef platforms with large areas of sand substrate and less coral limestone (Type I–III habitat), mean values were S=10, and H″=1.6. In the one intensively studied, truncated reef-limestone platform (Type II–III intermediate habitat), S=13 and H″=1.4. Summed population density of all Conus species in Type III and I–III habitats is similar (0.02 to 0.05 individuals /m²) and comparable to estimates from similar habitats elsewhere in the Indo-West Pacific region. Mean density (0.7/m²) and other population attributes in Type II–III habitat more closely resemble those of Type II than Type III habitats in general. We combined analysis of species diversity and other attributes of assemblages in habitats of different environmental complexity with analysis of microhabitat and food-resource utilization, in order to demonstrate the extent to which specialization on different resources occurs in assemblages differing in diversity and habitat type. In the habitats studied, co-occurring species of Conus specialized to a greater extent on different prey species than on different microhabitat patches, but degree of microhabitat specialization was greater than in similarly complex habitats with assemblages of lower diversity elsewhere in the Indo-West Pacific region. While most Conus species preyed primarily on a different species or higher taxon of polychaetes, diets are not more specialized or dissimilar than in similar habitats elsewhere. Degree of specialization on different prey is not correlated with Conus species diversity in the different types of habitats studied. The data lead to the conclusion that differential predation is as important — and differential microhabitat utilization is more important — in permitting coexistence of potentially competing congeners, compared with conditions in habitats of comparable heterogeneity that support fewer congeners farther from the center of the Indo-West Pacific region. Pairwise comparisons of congeners indicate that many species pairs have low or no overlap in both microhabitat and food utilization. Members of species pairs with high overlap in microhabitat utilization typically eat different prey organisms, and those with similar diets typically occupy different habitats or microhabitats. This applies to molluscivorous as well as vermivorous species. Information on the diets of 11 species is reported here for the first time. Of 48 Indo-West Pacific Conus species whose food is now known, 35 prey on polychaetes, 2 on enteropneusts, 6 on gastropods, and 5 on fishes. Vermivorous Conus prey on relatively few of the polychaete species present in the environments. Species eaten represent only 12% of a total estimated polychaete population density of 27,000 individuals /m². Certain very abundant polychaetes may be protected from predation by Conus by their small size, others by their long tubes. Two new aspects of size-selective predation by Conus are reported: (1) Although comparisons of predation rate with prey standing-crop suggest that food is plentiful, selective predation on the largest prey individuals present suggests that only small proportions of prey-species populations may have large enough body size to repay foraging effort by the Conus present; (2) composition of the diet changes qualitatively with increase in body size in several vermivorous Conus species; shifting by larger individuals to larger prey species could be documented in C. ebraeus.