Small Coral Reef Research Articles

Conventional tagging and acoustic telemetry of a small surgeonfish, Zebrasoma flavescens, in a structurally complex coral reef environment

Passive acoustic telemetry and conventional tag/re-sight techniques were used to study daily movement patterns of adult yellow tang, Zebrasoma flavescens, over a period of months. Range testing and visual observations revealed the limitations of using small acoustic transmitters to monitor movements of small coral reef fish in a topographically complex and noisy coral reef environment. Visual observations of conventionally tagged and albino fish suggest individuals return each day to forage over the same few hundred m2 of shallow, turf algae dominated boulder and reef flat habitat for periods of at least weeks to months. Acoustic telemetry data suggest lower frequency of repeated use of daytime foraging, nighttime refuge and sunset spawning sites. However, integration of observation and acoustic telemetry data revealed that many fish were not detected while they were within the empirically tested range of the receivers. These observations indicate that data from passive acoustic telemetry can underestimate the frequency and duration of repeated use of specific areas. Yellow tang adults made daily crepuscular migrations of up to 600 m between foraging and spawning or sheltering sites at consistent times relative to sunset and sunrise. While there was high individual variability in migration distance, almost all individuals moved in the same direction (from south to north) at sunset. This study provided valuable information for evaluating ongoing fishery management efforts using marine protected areas in Hawaii.

Géomorphologie de Tromelin, océan Indien

Tromelin is a small coral reef island (1 km 2) located in the Indian Ocean, approximately 440 km east of Madagascar and 580 km north of La Réunion. Despite the presence of a permanent Météo France weather station on Tromelin since the 1950 s, a detailed geomorhological study of the island has never been undertaken. In this paper, we describe results from the 2008 field season, which enabled us to map and describe seven geomorphological zones on the atoll. (1) Tromelin's bathymetry is characterised by a pronounced submarine slope, which attains depths of 1000 m at only 2.5 km from the island's coastline. This geomorphology is typical of volcanic hotspots. (2) A coral platform borders the emerged crown of the island. This platform is exposed at low tide and has been fashioned in an ancient Pleistocene substratum. The substratum has been eroded by abrasive marine action to its present shape since the stabilisation of relative sea level around 6000 years ago. Erosion of the reef yields most of the biogenic sediment supply to the island. (3) The upper foreshore is characterised by outcrops of beachrock. These formations show a stratfication in slabs and dip gently towards the sea in the same manner as the contemporary clastic sediments. (4) Tromelin's beaches are divided into three sub-units, which reflect the different energy dynamics around the island, in addition to the transfer of sediment from the windward to the leeward side: (i) the southern storm beaches are characterised by coral blocks reworked during episodic high-energy events; they form boulder ramparts. Four perched rampart ridges have been recorded at ∼1 m, ∼3 m, ∼4.5 m and ∼7 m above mean sea level; (ii) transitional beaches are observed between the south and the north, constituting storm blocks and coarse sands and gravels; and (iii) sandy beaches are noted on the northern leeward side, comprising rounded gravels and coarse sands. The northern tip of the island is characterised by a sand spit (∼125 × ∼225 m), whose geometry varies based on the seasonal and meteo-marine contexts. (5) On Tromelin, a number of dune formations are observed. These are best developed in the north of the island due to the south-north translation of clastic sediments by aeolian wind action, and the trapping of sands by the well-developed vegetation. The height of the dunes varies between 10 cm (the southern micro-dunes) to 250 cm in the Northeast of Tromelin. (6) Exceptional waves have deposited storm tracts up to 250 m from the foreshore zone, comprising coarse gravels and coral blocks. The storm tract deposits are most prevalent on the windward side of the island, due not only to the high-energy dynamics, but also to the absence of vegetation cover in this area. (7) The southern depression covers an area of ∼40,000 m 2. At its lowest point it is only 1.2 m above sea level.

Experimental evidence for density‐dependent reproductive output in a coral reef fish

AbstractWe tested for density‐dependent reproduction in a small coral reef fish using field manipulations of density and observational data. Males of the study species, the bridled goby (Coryphopterus glaucofraenum Gill), defend benthic nest sites, within which they spawn with females, and females can spawn repeatedly over an extended breeding season. In small areas, usually only a single male nested at any one time regardless of how many males were present, so the probability of nesting was inversely proportional to density. Nesting males were almost always the largest in the vicinity, suggesting that, for males whose home ranges overlap, social interactions dictate opportunities to nest. Both the per capita rate at which clutches were laid and the number of eggs produced per clutch declined with increasing density, so the per capita rate of egg production was also density dependent. All three measures of fecundity were better predicted by numerical density (numbers per unit area) than biomass (mass of fish per unit area), and were well described as an inverse function of the number of gobies in the vicinity. A simple hypothesis consistent with these results is that a constant number of females spawn, regardless of density. Alternately, the effect of crowding may depend primarily on the number of interacting individuals and affect all females relatively equally. This density dependence could thus contribute to population regulation at the spatial scale over which populations become reproductively closed.

Evaluation of effective groundwater recharge of freshwater lens in small islands by the combined modeling of geoelectrical data and water heads

In small islands, a freshwater lens can develop due to the recharge induced by rain. Magnitude and spatial distribution of this recharge control the elevation of freshwater and the depth of its interface with salt water. Therefore, the study of lens morphology gives useful information on both the recharge and water uptake due to evapotranspiration by vegetation. Electrical resistivity tomography was applied on a small coral reef island, giving relevant information on the lens structure. Variable density groundwater flow models were then applied to simulate freshwater behavior. Cross validation of the geoelectrical model and the groundwater model showed that recharge exceeds water uptake in dunes with little vegetation, allowing the lens to develop. Conversely, in the low‐lying and densely vegetated sectors, where water uptake exceeds recharge, the lens cannot develop and seawater intrusion occurs. This combined modeling method constitutes an original approach to evaluate effective groundwater recharge in such environments.

SPATIAL DENSITY DEPENDENCE SCALES UP BUT DOES NOT PRODUCE TEMPORAL DENSITY DEPENDENCE IN A REEF FISH.

Field experiments provide rigorous tests of ecological hypotheses but are typically of short duration and use small spatial replicates. We assessed empirically whether the results of experiments testing for density dependence applied at larger spatial domains and explained temporal population dynamics. We studied a small coral reef fish, the goldspot goby (Gnatholepis thompsoni), in the Bahamas. We assessed the effects of interactions with conspecifics and with an ecologically similar species, the bridled goby (Coryphopterus glaucofraenum). Two density manipulations on small reef patches revealed that goldspot goby mortality over one month increased as conspecifics became crowded. On five large natural reefs, we correlated the initial year-class density of both species (annual larval settlement) with the subsequent decline of goldspot goby year-classes for five years. Mortality was correlated with conspecific density among reefs for all years, but not among years for all reefs. Thus, spatial density dependence in mortality scaled up qualitatively from small patches to entire reefs but was not associated with temporal density dependence. Our results support the conclusion that field experiments may be extrapolated to larger spatial domains with care, but that using small spatial comparisons to predict temporal responses is difficult without knowing the underlying biological mechanisms.

Satellite remote sensing of Spratly Islands using SAR

Spratly Islands, located in the southern part of the South China Sea (SCS), consist of more than 100 small islands, coral reefs and banks. Remote sensing is the only way to obtain a synoptic view of all of the islands in such a large area. It has been demonstrated that satellite synthetic aperture radar (SAR) imagery is a very powerful tool for monitoring meso‐scale and small‐scale ocean processes in a large area. In this study, satellite SAR images were used to study the ocean environment in the area of Spratly Islands. The aim was to understand the capability of satellite remote sensing to monitor ocean processes and provide information for future field studies. Two sets of high‐resolution European Remote Sensing satellite (ERS)‐2 SAR images over the entire Spratly Islands area were collected in April and December 2005. The ocean features were identified/extracted from the SAR images to overlay the bathymetric map for comparison. Some case studies of SAR mapping on Spratly Islands are described and issues regarding existing navigation charts are discussed.

THE EXTENDED LONGEVITY OF A SMALL CORAL REEF SERRANID; A LESSON FROM CEPHALOPHOLIS CYANOSTIGMA (BLUE SPOT ROCK COD) OF THE CENTRAL GREAT BARRIER REEF, AUSTRALIA

The blue spot rock cod, Cephalopholis cyanostigma, is a small common coral reef serranid that forms a significant proportion of the discarded by-catch in the Great Barrier line fishery. Samples were obtained by spear and line fishing at Orpheus Island (range 114- 294 mm FL, mean = 226 mm, n = 137) and from Pelorus Island (range 120-285 mm FL, mean = 214 mm, n = 125). Sagittal otoliths were used to obtain age-based parameter estimates for the populations at each island. Analysis of marginal increments on monthly samples suggested that a single opaque band was deposited annually during November - December. Recaptures of three fishes (9,18, and 24 years old) in July and November 1997, five years after injection of oxytetracycline, further corroborated our conclusion that band formation was annual. The maximum age in our samples of 31 years suggested that the blue spotted rock cod was one of the longest lived serranids documented to date. The von Bertalanffy growth function provided the best description of the pattern of growth for populations at both islands with high coefficients of determination (R2 = 0.86 and 0.82 for Orpheus and Pelorus islands, respectively). Female population of both sites grew relatively slow, not reaching asymptotic size until 7-10 yrs. Statistical comparisons on male and female growth patterns were not significant, however. There were significant differences in growth parameters between islands with C. cyanostigma on average growing larger at Orpheus Island (L?= 258 mm and K= 0.22) compared with Pelorus Island (L?=244 mm and K = 0.25). These age-based population parameter estimates indicated that C. cyanostigma was considerably longer lived than expected for a small coral reef serranid and further demonstrated the utility of age-based methods in studies of the demography of tropical reef fish. The implication for conservation and fisheries management of small tropical serranids is that species with similar population parameters are likely to sustain much lower levels of fishing mortality than previously thought.

What do we know about Eilat (Red Sea) reef degradation? A critical examination of the published literature

During the last four decades, the coral reef at Eilat, northern Red Sea, has undergone major changes. Increasing impacts from human activities, coupled with those from natural disasters, have set off its current poor state. Here, I critically overview the salient features for Eilat's reef degradation published since the 1960s. Although this reef is one of the most intensively studied small coral reef worldwide, the literature elucidates that the available results are exceedingly fragmented, offering only scanty knowledge for the causes and pathways of the reef deterioration. During the years, 1975–2000, scarcely any reef evaluation had been done and the reef at Eilat was not well characterized to establish baseline data for future evaluations and for analyzing the trends. Even the follow up studies on the extreme low tide episode (occurred during 1970) are limited and localized, and cannot be used as a model case in calibrating Eilat reef status. Natural forces affecting the reef at Eilat are understood only vaguely, and coral assemblages/recruitments, even between neighboring sites, vary markedly in any studied biological-ecological parameter. The importance of the complex networks of interactions between algae, their grazers and corals for structuring coral assemblages, were overlooked, and massive algal growths were mistakenly attributed to anthropogenic impacts alone. Whereas, no long-term study can provide much indication for future prospects, at present, the tourist industry is probably the major cause for reef decline. Surprisingly, the literature further unveils at some sites various ecological properties, such as species diversity and densities of coral species and colonies, similarly to the values recorded decades ago and reveals that the paucity of information has led to conclusions unsubstantiated by robust sets of experiments. At this stage, therefore, decisive conclusions pertaining to the causes and pathways of Eilat reef degradation cannot be reached. Four future prospectuses are outlined, including the need for implementation of active restoration measures.

Life-history characteristics of coral reef gobies. II. Mortality rate, mating system and timing of maturation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 290:223-237 (2005) - doi:10.3354/meps290223 Life-history characteristics of coral reef gobies. II. Mortality rate, mating system and timing of maturation V. Hernaman1,3,*, P. L. Munday2 1Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand2School of Marine Biology and Aquaculture, James Cook University, Townsville, Queensland, Australia3Present address: School of Biological Sciences, Victoria University, PO Box 600, Wellington, New Zealand *Email: vhernaman@xtra.co.nz ABSTRACT: High adult mortality rate is expected to select for early maturation. However, physiological constraints or size-related reproductive benefits might select for delayed maturation, especially in small-bodied species. Additionally, the mating system and the relative intensity of mate competition can modify the timing of maturation. Here, we investigate the influence of mortality rate and mating system on the timing of maturation in 5 species of small coral reef goby that are either polygynous (Asterropteryx semipunctatus and Istigobius goldmanni) or monogamous pair-spawners (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis). All 5 species experienced high annual adult mortality rates with annual survivorship of ≤2.3%. The mean size at maturity, compared to maximum adult size, was smaller than is typical for fishes, indicating selection for early maturity in all of these species. The season of growth had little effect on size at maturity, but had a considerable effect on age at maturity, with summer-growing individuals exhibiting a younger mean age at maturity than winter-growing individuals. As predicted, males of the 3 monogamous pair-spawning species matured earlier and smaller than females (A. bynoensis and A. phalaena) or at the same time as females (V. muralis), but contrary to expectation, males of the 2 polygynous species (A. semipunctatus and I. goldmanni) did not mature later and at a larger size than females. Overall, the timing of maturation in these species is consistent with predictions from general life-history theory, however, the sex-specific timing of maturation may be influenced by body size constraints and the mating system. KEY WORDS: Maturity · Mortality · Life history · Body size · Gobiidae · Mating system Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 290. Online publication date: April 13, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

PREDATORS, PREY REFUGES, AND THE SPATIAL SCALING OF DENSITY-DEPENDENT PREY MORTALITY

We tested the biological cause of density-dependent mortality in the bridled goby (Coryphopterus glaucofraenum), a small coral reef fish, and evaluated whether this knowledge allowed us to detect density dependence at different spatial scales in natural habitats. To identify the biological cause of density dependence, we manipulated both population density and the availability of shelter (crevices used as refuges from predators) in small plots of continuous reef. We detected strong density-dependent mortality in plots with few refuges, but mortality was density independent in plots with abundant refuges, indicating that limited shelter causes density dependence. Predator density was unrelated to the density of gobies and refuges, suggesting that predators displayed a type III functional response in patches with few refuges. In a second experiment, we manipulated goby density within replicate plots of three sizes (4, 16, and 64 m2) that varied naturally in the availability of refuges. If refuge availability was ignored, mortality appeared to be density independent at all scales. If, however, plots were grouped by refuge availability, mortality was density dependent in plots with few refuges, but low and density independent in plots with many refuges at all spatial scales. Understanding the mechanism of density dependence (refuge shortage) was thus required to measure the strength of density dependence in natural, spatially variable, habitat. We suggest that density dependence was detectable in plots of different sizes because the relationships between the densities of gobies, refuges, and goby predators were similar across the spatial scales we studied. Our work demonstrates that identifying the biological interactions that cause density dependence, and characterizing the spatial domains at which those interactions operate, will be important to accurately assess the effects of density dependence on population dynamics.

Impact of ectoparasites on the demography of a small reef fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 248:305-309 (2003) - doi:10.3354/meps248305 Impact of ectoparasites on the demography of a small reef fish Rachel J. Finley*, Graham E. Forrester Department of Biological Sciences, 100 Flagg Road, University of Rhode Island, Kingston, Rhode Island 02881-0816, USA *Email: rpet3012@postoffice.uri.edu ABSTRACT: In marine systems, empirical studies demonstrating effects of macroparasites on host population dynamics are relatively few. We tested the effects of a copepod macroparasite infecting the gills of a small coral reef fish, the bridled goby Coryphopterus glaucofraenum. Fish that were naturally infected and uninfected were tagged as individuals and tracked in the field for 5 mo. Parasitism was associated with an increase in gill ventilation rate, and a reduction in feeding. More importantly, parasitized fish showed significantly reduced growth (by 66%) and gonad mass (by 68%) compared to uninfected fish, and parasitism increased instantaneous mortality by a factor of 1.8. Since the prevalence of infection was higher in areas of high goby density, parasite-induced mortality is a possible cause of host density dependence. These results imply a major effect of parasitism on host population dynamics and suggest that parasitism warrants closer attention by marine ecologists. KEY WORDS: Pharodes tortugensis · Coryphopterus glaucofraenum · Host-parasite interaction · Parasitic gill copepod Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 248. Online publication date: February 20, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

A new genus of small coral-reef goby (Teleostei: Gobiidae) from the Indo-west Pacific, with discussion of its relationships

A new genus and species, Minysicya caudimaculata, is created for a small coral reef gobiine known so far from the Yaeyama Islands, Ryukyu Archipelago, Japan; Scott Reef off northern Western Australia; Lizard Island, Queensland; and the Tuamotu Islands, French Polynesia. Phylogenetic analysis shows that Minysicya n. gen. forms a monophyletic group with five other genera including Bryaninops and Pleurosicya (commensal on various invertebrates and plants), but has fewer of the specialisations exhibited by the other genera.

A quantitative framework to evaluate the attraction?production controversy

Artificial reefs have been proposed as a tool to mitigate impacts on natural reefs, augment natural fish production, and divert detrimental harvesting activities from sensitive natural habitats. The efficacy of this strategy depends on the extent to which artificial reefs contribute to new production or simply redistribute fish during or after settlement. Small coral reef fishes are ideal study subjects because redistribution is most likely during the larval stage, given limited dispersal of benthic stages. We develop a model that incorporates the simultaneous effects of habitat augmentation, competition among reefs for larval settlers, and post-settlement density-dependence, and propose two experimental approaches for evaluating the effects of artificial reefs on local production of natural reefs. One is based on small-scale studies using replicated patch reefs, the other on unreplicated studies using larger reefs and the Before-After-Control-Impact Paired Series (BACIPS) design. Using field data for six fish species, we estimated spatial and temporal variance and thus statistical power of both designs. Power varied among species, but in most cases was sufficiently high to detect local reductions in density of 10–40% with modest levels of replication (6–20 patch reefs or sampling dates). 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Rapid Smothering of Coral Reef Organisms by Muddy Marine Snow

Estuarine mud, when resuspended in nutrient-rich near-shore water, aggregates to marine snow, and within minutes to hours can exert detrimental or even lethal effects on small coral reef organisms. In a pilot study, estuarine mud was suspended in near-shore and off-shore waters of the Great Barrier Reef to a final concentration of 170 mg l −1. The short-term responses of a coral ( Acropora sp.) and coral-inhabiting barnacles (subfamily Pyrgomatidae), exposed to either near-shore or off-shore water, were microscopically observed and video recorded. In the off-shore water treatment, flocculation was minor, and aggregate sizes were c. 50 μm. The organisms were able to clean themselves from these small settling aggregates at low siltation (<0·5 mg cm −2), and struggled and produced mucus only at high siltation (4–5 mg cm −2). In contrast, in near-shore, nutrient-enriched waters, the suspended mud aggregated into large sticky flocs of marine snow (200–2000 μm diameter). The organisms responded to a thin coat of deposited flocs with vigorous cleaning by cirri and tentacle beating. After 5 min struggle, the barnacle stopped moving, calanoid copepods were entangled in the aggregates, and thick layers of mucus were exuded by the coral polyps. Both barnacle and copepods died after <1 h exposure; a short time compared with natural occurrences of marine snow deposition on coral reefs. Enhanced nutrient concentrations are known to contribute to enhance biologically mediated flocculation. This pilot study suggests that the concentration of suspended mud, and extent of stickiness and flocculation, can synergistically affect reef benthos organisms after short exposure. The enclosed macro video recordings clearly visualize these effects, and help convey the important implications for managers: that inshore reefs of the Great Barrier Reef cannot be sustainably managed without managing the adjacent land.

Arrecifes del Tortoniense inferior en la Cuenca de Granada, Cordillera Bética, España

A small coral reef, together with oyster biostromes, of lower Tortonian age occurs north of Albunuelas in the Granada Basin (Betic Cordillera, Spain). These reefs were deposited south of a Betic island in a coastal area. The lensoid coral reef is made up of Tarbellastraea and Porites heads, intensely bored by Lithophaga. The corals grew on a bank of large oysters that colonised conglomerates. Banks of smaller oysters (O. edulis) grew on silts in more distal areas. Fossil assemblages indicate high ambient nutrient content. The hermatypic corals record a warm climatic phase in the early Tortonian in the western Mediterranean.

Factors Influencing the Juvenile Demography of a Coral Reef Fish

A notable recent development in marine ecology has been the suggestion that the size of demersal populations is limited and that patterns in demersal abundance are determined by the settlement of pelagic larvae (recruitment). Here I examine some factors potentially limiting and determining population density in a small coral reef fish. An experimental study of the demography of juveniles of a small planktivorous damselfish, the humbug Dascyllus aruanus (Pomacentridae), was done at One Tree Reef, southern Great Barrier Reef, Australia. Recently settled fish were transplanted to replicate units of habitat at three lagoonal sites. The interactive effects of initial recruit density, the presence of adults, and supplemental feeding on the growth, survival, migration, and maturation of the recruits were examined over the following 10 mo. Migration was apparently rare and thus unimportant. Effects of the factors on the growth and survival of recruits were complex. Survival of recruits was generally inversely related to their density but enhanced in the presence of adults. Average survival also varied among locations. Mean growth was generally depressed at high recruit densities and in the presence of adults but was enhanced by supplemental feeding. Maturation was related to size and so was influenced by effects on growth. The results suggest that regulatory interactions and shortages of food may limit the size of adult populations via their effect on growth rates. Effects of the factors on survival were slight. Total abundance may thus be limited primarily by recruitment unless effects on growth are ultimately translated to effects on demersal mortality. As a result of the effects on survival, there was some modification of the initial pattern of recruit abundance. The importance of these effects in determining patterns of abundance in unmanipulated populations depends on variation in recruitment at similar scales. The number of recruits entering the adult population under different treatments was highly modified from the pattern of initial recruit density. The number of recruits that became mature by the end of the experiment was totally unrelated to their initial density. In addition, that number was reduced in the presence of adults, and was limited by the availability of food. The results suggest that complex effects of these factors on juvenile demography can modify recruitment patterns at small spatial scales. They also suggest that these factors may have different effects on the adult and total demersal populations. In general terms, both recruitment and postrecruitment processes influence patterns in abundance.

In situ survival of Vibrio cholerae and Escherichia coli in tropical coral reefs

Vibrio cholerae and Escherichia coli were inoculated into membrane diffusion chambers and placed around two small coral reef islands in Puerto Rico and monitored for 5 days. Several chambers were also buried in the sands of one of the reefs. Both E. coli and V. cholerae densities declined by 2 orders of magnitude, as measured by direct particle counts with a Coulter Counter (Coulter Electronics, Inc., Hialeah, Fla.). However, the density of neither bacteria changed dramatically when the same samples were analyzed by epifluorescent direct counts. Differences in the two direct count methods were accounted for by changes in cell morphology that occurred in both bacteria after exposure to seawater. Morphological changes occurred more rapidly in E. coli compared with those in V. cholerae. Bacteria in chambers exposed to sediment did not show significant changes in morphology and had only a slight decline in density. Physiological activity declined by more than 40% for both bacteria within 24 h. The decline in activity was less severe in the sediments. Tropical coral reef sands and turtle grass beds were shown to be less stressful environments for V. cholerae and E. coli than would have been predicted from temperature and microcosm studies. V. cholerae can survive the in situ conditions of a tropical coral reef and could become a source of bacterial contamination for fish and shellfish in this environment. The simultaneous monitoring of E. coli levels established that this bacteria can not be used as an indicator of V. cholerae or other fecal-borne pathogens in coral reef environments because of the greater stress these environments put on E. coli. Both bacteria could be of greater public health importance in tropical marine areas than previously imagined.

Sedimentologic Succession of Uplifted Coral Community, Urvina Bay, Isabela Island, Galapagos Archipelago, Ecuador: ABSTRACT

In March 1954, along the west-central coast of Isabela Island, an upward movement of magma suddenly raised Urvina Bay over 6 m and exposed several square kilometers of carbonate deposits covering a young aa lava flow (around 1000 years old). Results from 6 transect lines across the uplift, 30 cores, and 10 trenches describe the sedimentologic and ecologic transition from barren basalt to diverse carbonate sediments with small coral reefs. Along horizontal transects spanning from 0 to 7 m paleowater depth, there is a seaward progression from beaches, mangroves, and basalt to thick deposits (> 1.6 m) of carbonate sands and small coral reefs. Variation in water depth, degree of wave exposure, and irregularity of the aa lava topography provided many microhabitats where coral, calcareous algae, and mollusks settled and grew. Eight hermatypic coral species are found throughout the shelf, and three species (i.e., Pavona clavus, Pocillopora damicornis, and Porites lobata) produced five small, isolated, monospecific, coral-reef frameworks. The vertical section seen in cores and trenches shows that calcium carbonate increased upward, whereas volcanic sediments decreased; however, episodic layers occur with high concentrations of basaltic sands. In vertical samples from the central portion of the shelf, the coral population changedmore » from small, isolated colonies of Psammocora (Plesioseris) superficalis near the basalt basement to large reef-forming colonies of Pocillopora damicornis farther upsection. Reefs of the Galapagos Islands are small and less diverse than most Pacific reefs. Nonetheless, understanding their temporal successional development should throw light on the origin and history of larger oceanic reefs in the Pacific.« less

Sedimentology and paleoecology of Upper Ordovician mounds of Anticosti Island, Quebec

Relatively thin organic buildups in the Ellis Bay Formation of Anticosti Island developed in a shallow subtidal regressive marine shelf environment during the Late Ordovician. The Ellis Bay Formation has been subdivided into six members by Bolton. Two buildups, one in each of members 4 and 6, were studied in detail. The member 6 mud mound on the Salmon River (8 m thick) is bound by calcareous algae, stromatoporoids, and corals, and consists of a micritic bafflestone core capped by crinoidal lime grainstone. Early marine cementation permeated nearly all of the primary porosity. Cathodoluminescence indicates at least five stages of cementation of the mound. Constructive mound development was terminated by progressively shallowing, agitated marine conditions.The member 4 mound is a small coral (ecological) reef exposed on the Vaureal River.

Triassic Carbonate Buildups of The Dolomites, Northern Italy: ABSTRACT

In the Middle Triassic of the Dolomites of northern Italy thick carbonate bodies (1,000 m) of relatively restricted extension are surrounded, and in places covered, by volcanic rocks and clastic sediments. These bodies, characterized at the periphery by inclined beds dipping basinward (15-35°), are formed by massive carbonates, mostly crystalline dolomite (Schlern Dolomite); in many places the massive facies is replaced laterally by stratified carbonate rocks. Organisms in the massive dolomite are uncommon (some corals, a few pelecypods and crinoidal plates) and poorly preserved; in the massive limestones and in the bedded carbonate rocks, calcareous algae, crinoids, mollusks, rare corals, foraminifers, and ostracods are present. The central part of the buildups lies directly on a biostromal blanket dolomite (Serla Dolomite) which extends throughout the region. A sequence of cherty micritic limestone (Livinallongo Formation), in places nodular or bituminous, End_Page 836------------------------------ lies lateral to the core between the Serla Dolomite and the Schlern Dolomite; between the buildups this sequence is covered directly by volcanics (prevalently latites) and other volcanoclastic rocks. Prevalently terrigenous sediments (Raibl Formation) ended Middle Triassic sedimentation and disconformably overlie the carbonate masses. In the literature, from the last century until the most recent papers, the carbonate buildups have been interpreted as coral reefs with internal lagoons (the bedded parts); the volcanics and the associated sediments filling the interreef basins have been regarded as contemporary with the reefs. The Dolomites became famous as a classic region for paleoreefs and spectacular lateral facies changes (heteropic contacts). The following data are from a new detailed field examination and sedimentologic analysis. The massive part of the buildups is prevalently mud-supported grainstone (pelletoid and skeletal grains) and is characterized by the presence of reef tufa (fibrous carbonate in cavities with irregular, in many places lobate, walls). the stratified part consists of thick beds of mud-supported grainstone (pelletoids). The grainstone is commonly burrowed, has crinoids and algae (Diplopora), and has thin interbeds of laminated micrites, common pisolites, intraclastic breccias, sheet cracks, and tepee structures. The boundaries between carbonate bodies and surrounding volcanoclastic rocks are abrupt, without transitional facies; the bodies interfinger with the underlying Livinallongo Formation whi h, in the transition zone, contains abundant, commonly graded breccias. In places the upper part of the buildups interfingers with muddy carbonate sediments that end the basin sequence. These data suggest a different interpretation from the classic one. On the higher parts of the basal blanket dolomite, banks of shallow-water carbonate sediments developed and grew. These carbonate banks were exposed periodically, keeping pace with subsidence, and reached thicknesses of about 1,000 m. A starved-basin sequence was deposited in progressively deeper waters to a maximum depth of about 800 m. Later the products of the submarine volcanic eruptions filled interbank depressions rather quickly, literally suffocating some buildups and fossilizing their primary morphology. At the end of the Middle Triassic the almost complete topographic leveling caused a renewal of the carbonate sedimentation which led to the development of slightly raised banks and, in places, small coral reefs. End_of_Article - Last_Page 837------------