Oceanography and reefs of recent and Paleozoic tropical epeiric seas

Summary The Java Sea, one of the few modern tropical epeiric seas, is used as an analogue to examine oceanography, stratigraphy, and reefs of Devonian strata in the Appalachian and Michigan Basins. Nearshore patch reefs and offshore “pinnacle” reefs occur in both the Java Sea and the Emsian-Eifelian Onondaga Formation in the Appalachian Basin. Nearshore patch reefs also occur in the Eifelian Formosa Reef Limestone in the Michigan Basin. The Java Sea is characterized by quasi-estuarine circulation, in which runoff and rainfall exceed evaporation. Nutrient and organic matter influx from land and from estuarine upwelling contribute to organic rich facies during transgressions and sea level highstands. Similarly, we propose that high runoff from the Appalachian Mountains and from the Laurentian craton contributed to slightly reduced salinity in the Appalachian basin, including possible density stratification during Middle Devonian highstands. By contrast, the Michigan Basin was characterized by antiestuarine circulation, in which evaporation exceeded combined runoff and rainfall. Contemporaneous Emsian-Eifelian strata in the Michigan Basin are dolomite and dolomitic limestone, rather than cherty and muddy limestone typical of the Appalachian basin. Reef composition generally reflects oceanographic circulation regime within the epicontinental seas we examine. Nearshore reefs of the modern Java Sea and the Onondaga Formation (Appalachian Basin) are dominated by multilobate submassive, dendroid, and phaceloid corals, and virtually no platy corals or tabular stromatoporoids. Multilobate and phaceloid corals are better able to accommodate muddy sedimentation. By contrast, offshore pinnacle reefs of the Java Sea and nearshore reefs of the Formosa Reef Limestone are dominated by platyAcropora (modern) or tabular and laminar stromatoporoids (Devonian). The scarcity of tabular stromatoporoids, and the dominance of phaceloid corals and dendritic branching corals, in the Onondaga Formation (Appalachian Basin) are herein explained by localized high productivity conditions driven by quasi-estuarine circulation, rather than cool water. Quasi-estuarine circulation or localized topographic upwelling leading to highly productive coastal environments may be responsible for other Paleozoic examples of apparent cool-water carbonate deposition within the tropics, including the Ordovician of Eastern Canada.     

Level-bottom brachiopod communities in the Middle Devonian of New York

Depositional environments of the Onondaga Limestone from central to southeastern New York are found to be normal, subtidal marine, due to the absence of characteristic supratidal or intertidal sedimentary features and the presence of a typical, diverse, marine level-bottom community framework. Post-mortem transport has not been extensive, as evidenced by low articulation ratios, lack of abraded valves, and complete ontogenetic gradations within species, which precludes large scale winnowing. Sedimentation rates appear to have been greatest in eastern New York where the Onondaga Limestone reaches a thickness almost three times that of the strata in central New York. Shaly beds in the central area represent periods of cessation of carbonate deposition rather than an influx of clastic material. Deposition terminated with the onset of deeper water characterized by a westerly advance of terrigenous sedimentation (the Marceilus Shale of the Hamilton Group). Nine brachiopod communities can be recognized in the Onondaga Limestone. There is a strong correlation between sediment-substrate and community type, reflecting the sedimentologic control of brachiopod community distribution. Sandy facies, cherty limestones and coral biostromes and bioherms are associated with inner-neritic deposition in Edgecliff time; argillaceous lime muds and lime sands are characteristic of mid-neritic deposition in Nedrow to Moorehouse time; and highly argillaceous lime muds are associated with outer-nerittc deposition in Seneca time.     

Middle Ordovician reefs of Norway

The Middle Ordovician reefs of Norway were the first to develop in the western part of the Balto-scandian epicontinental sea and are the earliest coral-stromatoporoid reefs so far reported in Europe. Small patch reefs in the Steinvika Limestone, Langesund-Skien district, consist mainly of algae, echinoderms, corals and stromatoporoids. Bryozoans, molluscs, arthropods and brachiopods are also present. The reefs developed on pelmatozoan-rich substrates and are organically zoned, consisting of a pioneer community of stemmed echinoderms and sheet algae, a high-diversity intermediate community dominated by fasciculate corals and a low diversity climax community of massive corals and stromatoporoids. These communities are interpreted as the seral stages of an autogenic ecological succession. Small patch reefs are also present in the laterally equivalent Mjøsa Limestone, Toten and Nes-Hamar districts. These are organically very similar to those in the Steinvika Limestone and developed in an identical way. A large complex, consisting of several reefs, is also present in the Mjøsa Limestone. Unlike the reefs elsewhere, which developed within shallow inshore areas, this complex developed at the outer edge of the inshore shelf. The outstanding feature of the complex is the main reef forming the offshore limit which is totally dominated by stromatoporoids and lacks a sequential development. This is due to the influence of the harsher environment at the shelf edge.     

Corals reef of the Upper Oligocene-Lower Miocene, of Turrialba, Costa Rica

The outcrops at Jesús Maria (Turrialba, Cartago Province, Costa Rica) present limestone sequences 12 to 30 m thick (packstones: biolithites, biomicrites; and wackstones: biosparites, biomicrosparites), sandstones and conglomerates of Upper Oligocene-Lower Miocene age, correlated to the Punta Pelada Formation. The limestones are characterized by patch reefs with an irregular distribution and a reduced lateral extension (50 m), composed of corals (40%), calcareous algae and foraminiferans (30%), mollusks (20%), and in minor amounts fragments of barnacles, decapods, echinoderms and bryozoans. They consisted of low diversity communities possibly due to diverse geographical, geological and tectonic factors: a narrow continental shelf, very shallow and isolated environments, sea level fluctuations, and exposure to clastic sedimentation associated with intermitent volcanic activity. Equity was also low, with corals making up 40% of all macrofossils, and one species, Antiguastrea cellulosa, as predominant (80% of the corals present). These bioconstructions were developed in an open circulation lagoon environment with transitions, in several occasions, to shallower environments represented by elastic sediments.     

Turbulence-controlled succession in Middle Devonian reefs of eastern New York State

Wolosz. T. H. 1992 07 15: Turbulence-controlled succession in Middle Devonian reefs of eastern New York State.
The Edgecliff Member ol the Middle Devonian Onondaga Formation contains numerous reefs comprised of two distinct facies. The Phaceloid Colonial Rugosan Facies consists of thickets and mounds, while the Favositid/Crinoidal Sand facies occurs as flank beds surrounding rugosan mounds and as low shield-shaped banks interbedded with thickets of the colonial rugosan facics. Three of these reefs - the North Coxsackie. Albrights and Roberts Hill reefs - have been studied in order to determine the factors that controlled their development and their preserved paleocommunity succession. Both the Roberts Hill and Albrights reefs display well-developed rugosan mounds with an internal succession of rugosan genera. The North Coxsackie reef is a crinoidal sand bank with rugosan thickets and a back-reef satellite mound. Based on the lithology of the underlying limestone in which the reefs are rooted, the North Coxsackie reef is considered to have grown in a shallow-water environment, landwards of the two other reefs. Successional sequences or partial sequences are common to the three reefs, and are found to be reversible - a response attributed to changes in sea-level. As a result, the successions preserved in these reefs are interpreted as having been controlled by degree ol water turbulence.     

Diversity and relative abundance of corals, octocorals and sponges at Jaragua National Park, Dominican Republic

The Jaragua National Park is located in a remote area to the SW coast of the Dominican Republic. Fishing and mining are the major human activities. The main reef formations of the Park include: (a) long bank reefs (spur and groove) growing as bands over the platform and running in a SW-NW direction at 12-25 m depth, (b) well developed, deep, fringing reefs at the platform edge (drop-off) areas which could extend from 10 to 45 m depth, and (c) small patch reefs and poorly developed coral-octocoral-sponge-algal communities in shallow platforms near shore, rocky bottoms, and over the submerged walls of the uplifted reef. Nine reef localities were surveyed between Cabo Beata and Bahia Honda using Scuba diving to inventory the diversity and relative abundance of scleractinian corals, octocorals and sponges. Fringing reefs were surveyed starting at the bottom (30 m) and swimming in a zig-zag pattern (50 m on each side) to shallower areas. Bank reefs were surveyed by swimming in zig-zag across the spur-groove formation along 500 m. Sponges were the most diverse group with 83 species in 50 genera followed by the scleractinian corals with 56 species in 26 genera and the octocorals with 47 species in 15 genera. New records included eight coral species, 29 octocoral species and 59 sponges. The diversity, species composition and abundance of particular groups varied across the different localities. Northern reefs within the park and the Los Frailes Island offshore had the highest live cover, relative abundance and diversity for the three groups. In general, the Jaragua National Park had the highest diversity of corals, octocorals and sponges reported for the Dominican Republic and rank amongst the highest reported for the northern Caribbean. It is recommended that the area be protected and that fishing activities be regulated or eliminated altogether.     

Diversity, composition and structure of Late Eocene shelf-edge coral associations (Nago Limestone, Northern Italy)

Summary During the Late Eocene, shelf-edge patch reefs developed on the western margin of the Lessini Shelf. The coral fauna, studied in the Nago Limestone type locality, is described and interpreted for the first time, and provides further data for better understanding of the generally poorly known Eocene reef communities. Facies analysis was carried out across the shallowing upward succession that characterizes the well exposed type-section of the Nago Limestone. Four distinct facies are identified and a detailed qualitative-quantitative investigation has been applied to the coral-bearing facies in particular, in order to describe and quantify the distribution and palaeoecological zonation of corals. By a comparison of sedimentological and palaeoecological data, it is possible to reconstruct a depositional model of the Nago Limestone at its type locality. In particular, the palaeoecological study clearly reveals that corals change with depth in taxonomic composition, in percentage and proportion within the framework and in growth form, allowing the definition of a relative depth coral zonation. Three coral associations are recognized from the base to the top of the shallowing upward sequence. These differ from each other in the relative abundance of main reefbuilders, in the growth form exhibited by corals in growth position and in the density of the reef framework. These variations are interpreted as responses to major environmental controls which prevailed during the deposition of the different facies (mainly light intensity and hydrodynamic energy). The coral speciesActinacis rollei Reuss is the most abundant and ubiquitous coral of the Nago Limestone. Its adaptation to low-light levels is described here for the first time, confirming the high plasticity of this important Paleogene reef-builder. The results of the present study are finally compared with data from other Middle-Late Eocene European reef sites and some common features are inferred.     

Upper Permian (Murghabian) rugose corals from Oman (Ba’id area,Saih Hatat): Community structure and contributions to reefbuilding processes

Summary Coral-dominated communties are rare in Upper Permian reefs. The study of Murghabian rugose and tabulate corals from allochtonous carbonates (‘Oman exotics’) of the Hawasina Complex and autochthonous carbonates of the Saih Hatat area/Arabian Platform (Oman) provides evidence for a significant contribution of rugose corals to the formation of Late Permian reefs. The corals are described with respect to taxonomy, microfacies and community structure. 8 genera and 7 species were recognized.Monothecalis minor n.sp.,Praewentzelella regulare n.sp. andWentzelella katoi magna n.ssp. are new. The corals represent three communities: (1)Praewentzelella community (Hawasina Complex), (2) cerioid coral community (Hawasina Complex), and (3)Waagenophyllum community (Hawasina Complex and Saih hatat). The corals from the Hawasina Complex and the Saih Hatat flourished in significantly different environments: Rugosa from the Hawasina Complex are representatives of reefs, whereas their counterparts from the Saih Hatat lived in level-bottom communities. Coral-bearing reefal boundstones are characterized by a diverse assemblage of sphinctozoans, inozoans, chaetetids, bryozoans, crinoids,Tubiphytes, Archaeolithoporella and algae. These communities produced bafflestones or framestones and were part of a sponge reef complex. The level-bottom community of the Saih Hatat is low-diverse only comprising rugose and tabulate corals. These of isolated colonies locally acted as bafflers.     

A Paleocene coral—algal—sponge reef from southwestern Alabama and the ecology of Early Tertiary reefs

The Late Paleocene Salt Mountain Limestone from southwestern Alabama is a coral-algal-sponge buildup which further characterizes the faunal makeup of early post-Cretaceous reefs. Thin sectioning has disclosed a variety of lithologies, including large foram-algal packstone, algal bindstone, and sponge bafflestone. A low-diversity fauna of massive scleractinian corals caps the sequence, but may be developed intermittently throughout the section as well. The constructional importance of coralline algae and the low diversity of scleractinian corals are characteristic of Paleocene reefs in general. Sponges, however, are virtually unknown in earliest Tertiary sediments. Their abundance in the Salt Mountain demonstrates not only their local contribution to Early Tertiary reefs, but may also reflect an opportunistic response of sponges as reef constructors following the extinction of oligotrophic, rudist-coral reef communities of the Late Cretaceous. □ Paleocene, reef, paleoecology, sponges, extinction.     

Ramp morphology controlling the facies differentiation of a Late Ordovician reef complex at Bachu,Tarim Block,NW China

A carbonate ramp in the shallow‐marine northwestern part of the Central Tarim Uplift, Bachu, NW China, exhibits an extraordinary Late Ordovician reef complex along the Lianglitag Mountains, exposed for a distance of about 25 km. Seven localities within the ‘Middle Red Limestone’ of the Upper Member of the Lianglitag Formation (Katian, Late Ordovician) illustrated the changes in biofacies and lithofacies: northern, seaward‐directed patch reefs are replaced towards the south by coeval grain banks. The patch reef units are dominated by microbial and calcareous algal components. The reefs at the northernmost locality are knoll‐shaped, kalyptra‐shaped or irregularly shaped with sizes of individual reefs increasing from about 2 m in height and diameter. Stratigraphically upward, reefs notably expand to larger structures by several mounds coalescing; they are generally about 10 m thick and tens of metres in lateral extent. The maximum thickness of the main patch reef is more than 30 m, and its diameter is around 100 m. The reefal units turn into biostromes with gentler relief southward and still further south grade into banks composed of peloids and coated grains. The southernmost locality is still a shallow‐water bank, and the coastline is not documented in the study area. The present evidence indicates that the Late Ordovician palaeo‐oceanography provided a number of environments for the optimal growth of carbonate build‐ups; microbial‐calcareous algal communities could thrive in areas where the innovative metazoan reef frameworks consisting of corals and stromatoporoids did not play a significant role. The ramp morphology, especially changes in water depth, controlled the configuration of the reef complex.     

High macroalgal cover and low coral recruitment undermines the potential resilience of the world's southernmost coral reef assemblages

Coral reefs are under increasing pressure from anthropogenic and climate-induced stressors. The ability of reefs to reassemble and regenerate after disturbances (i.e., resilience) is largely dependent on the capacity of herbivores to prevent macroalgal expansion, and the replenishment of coral populations through larval recruitment. Currently there is a paucity of this information for higher latitude, subtropical reefs. To assess the potential resilience of the benthic reef assemblages of Lord Howe Island (31°32'S, 159°04'E), the worlds' southernmost coral reef, we quantified the benthic composition, densities of juvenile corals (as a proxy for coral recruitment), and herbivorous fish communities. Despite some variation among habitats and sites, benthic communities were dominated by live scleractinian corals (mean cover 37.4%) and fleshy macroalgae (20.9%). Live coral cover was higher than in most other subtropical reefs and directly comparable to lower latitude tropical reefs. Juvenile coral densities (0.8 ind.m(-2)), however, were 5-200 times lower than those reported for tropical reefs. Overall, macroalgal cover was negatively related to the cover of live coral and the density of juvenile corals, but displayed no relationship with herbivorous fish biomass. The biomass of herbivorous fishes was relatively low (204 kg.ha(-1)), and in marked contrast to tropical reefs was dominated by macroalgal browsing species (84.1%) with relatively few grazing species. Despite their extremely low biomass, grazing fishes were positively related to both the density of juvenile corals and the cover of bare substrata, suggesting that they may enhance the recruitment of corals through the provision of suitable settlement sites. Although Lord Howe Islands' reefs are currently coral-dominated, the high macroalgal cover, coupled with limited coral recruitment and low coral growth rates suggest these reefs may be extremely susceptible to future disturbances.     

Regional and local variability in recovery of shallow coral communities: Moorea,French Polynesia and central Great Barrier Reef

Coral communities at Moorea, French Polynesia, and on the Great Barrier Reef (GBR), Australia, were severely depleted by disturbances early in the 1980s. Corals were killed by the predatory starfish Acanthaster planci, by cyclones, and/or by depressed sea level. This study compares benthic community structure and coral population structures on three disturbed reefs (Vaipahu-Moorea; Rib and John Brewer Reefs-GBR) and one undisturbed reef (Davies Reef-GBR) in 1987–89. Moorea barrier reefs had been invaded by tall macrophytes Turbinaria ornata and Sargassum sp., whereas the damaged GBR reefs were colonised by a diverse mixture of short macrophytes, turfs and coralline algae. The disturbed areas had broadly similar patterns of living and dead standing coral, and similar progress in recolonisation, which suggests their structure may converge towards that of undisturbed Davies Reef. Corals occupying denuded areas at Vaipahu, Rib and John Brewer were small (median diameter 5 cm in each case) and sparse (means 4–8 m^-2) compared to longer established corals at Davies Reef (median diameter 9 cm; mean 18 m^-2). At Moorea, damselfish and sea urchins interacted with corals in ways not observed in the GBR reefs. Territories of the damselfish Stegastes nigricans covered much of Moorea's shallow reef top. They had significantly higher diversity and density of post-disturbance corals than areas outside of territories, suggesting that the damselfish exerts some influences on coral community dynamics. Sea urchins on Moorea (Diadema setosum Echinometra mathaei, Echinotrix calamaris) were causing widespread destruction of dead standing coral skeletons. Overall, it appears that the future direction and speed of change in the communities will be explicable more in terms of local than regional processes.     

Die Korallenfauna des Korallenooliths (Oxfordium, Oberjura, NW-Deutschland): Zusammensetzung, Stratigraphie und regionale Verbreitung

The stratigraphie and regional distribution of Oxfordian scleractinian reef corals in the Korallenoolith Formation (NW German Malm Group) is described from the Süntel, Deister, Kleiner Deisler and Osterwald Mountains. In the study area four horizons with (par-) autochthonous corals are developed two of which can be traced region-wide (Untere Korallenbank Member andflorigemma-Bank Member / Obere Korallenbank Member). The coral fauna of the biostromes, forming the Untere Korallenbank Member, is impoverished and dominated by ubiquitous r-strategists. In contrast, the reefal bioconstruetions of theflorigemma-Bank Member show a high variability in their regional appearances, partly forming highly diverse coral associations. The highest diversity is developed in the patch reefs from the Obere Korallenbank Member of the Osterwald Mountains (about 40 species). Corals are an important part of the Korallenoolith fauna. Altogether, 20 species belonging to 15 genera have been identified which were formerly unknown from NW German Oxfordian successions.     

Early Devonian reefs at Reefton, New Zealand: guilds, origin and paleogeographic significance

Study of 35 systematically collected and 10 semi‐random samples (about 100 cm 2 each) from one outcrop of the Lankey Limestone (Emsian) near Reefton, New Zealand indicates that it is a reef framestone built by tabulate (4? spp.) and clonal rugose (one sp.) corals, two species of stromatoporoids, a few bryozoans (2? spp.) and crinoids. The guild structure of the reef community and data on skeleton orientation and growth direction further indicate that there was relatively minor biostratonomic alteration of the original community. Skeletons are either in growth position or tipped, toppled or even overturned, but they have remained in situ. Other clone‐rich Lankey Limestone outcrops in the Reefton area support the notion of an upper shelf reef system and stratigraphic and sedimentologic data suggest that it was located near the Gondwana margin at a paleolatitude of about 35°S.     

Paleoecologic,temporal, and spatial analysis of early Silurian Reefs of the Chicotte Formation,Anticosti Island,Quebec, Canada

Summary Reefs of the Lower Silurian Chicotte Formation are the largest and most faunally diverse known on Anticosti Island, Quebec. They reach up to 25 m in thickness and 250 m in diameter and are present predominantly at two intervals, forming a lower and upper reef cluster. Remnants of bioherms are represented on the present-day wave-cut terrace as 60 to 100 m diameter, subcircular erosional depressions known as Philip structures or as outcrop. The bioherms were relatively low structures, with approximately 3 to 5 m maximum synoptic relief, some of which developed on hardgrounds and possible paleokarst surfaces of crinoidal wackestone and packstone. Dominant skeletal framework builders and sediment producers within all of the reefs are laminar to low domical stromatoporoids, colonial cerioid and fasciculate rugose corals, colonial tabulate corals, and cryptostome bryozoans. Vertical zonation of reef biota is evident within well-exposed reefs of the lower reef cluster. Three to four stages are recognizable:1) a low-diversity tabulate coral-dominatedpioneering community including large tabulate coral colonies (halysitids and favositids), and few stromatoporoids (clathrodictyids, ecclimadictyids), fasciculate rugosans, large generally monotypic stalked crinoids, and shelly benthos (brachiopods, few ostracodes and trilobites);2) an intermediate- to high-diversity, mixed tabulate coral-stromatoporoid-dominatedreef-core community;3) a slightly lower diversity stromatoporoid-tabulate coral-dominatedclimax community with laminar coenitids and alveolitids; and,4) in a few localities, a capping, low-diversity tabulatecoral-dominated (alveolitid and coenitid), and stromatoporoid-bearing community comprising laminar forms. Amelioration of Early Silurian climates, following Late Ordovician glaciation, allowed gradual reestablishment of extensive shallow-water reef growth, by mainly new and increasingly diverse genera and species of metazoans. Reef development within the Chicotte Formation coincided with global, widespread development of latest Llandovery and earliest Wenlock reefs in subtropical to tropical areas. Chicotte reefs have broad characteristics, in terms of overall biotic composition, vertical successions recognized, and paleogeographic setting, similar to those of equivalent and slightly younger age from intracratonic settings in Baltica (Gotland, Sweden and Estonia) and central and northern Laurentia (Midcontinent, U.S.A.; Hudson Bay, Canada; and North Greenland, Denmark).     

Response of triassic reef coral communities to sea-level fluctuations, storms and sedimentation: Evidence from a spectacular outcrop (Adnet, Austria)

Summary The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg Austria has been repeatedly referred to as one of the most spectacular examples of an ancient ‘autochthonous’ coral reef structure. The ‘Tropfbruch’ quarry is probably the best outcrop for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach (combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater detail with data from modern coral reefs investigated by corresponding quantitative surveys. Three unconformities and three well-defined ‘reef growth stages’ reflecting the vertical and lateral development of the reef structure were differrentiated using transects: Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ and the great thickness of this interval. The massive coralPamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branchingRetiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean algaDiplopora adnetensis and by the decreasing size ofRetiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as a major control mechanism. Stage 2, separated from stage 1 by an unconformity caused by partial subaerial exposure and karstification, is characterized by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform. Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment led to a reduction of reef growth. Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the input of platform sediment. The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by small-scale sea level changes, storm activity and sedimentation. The vertical changes in reef community structures correspond to a sequence of ‘allogenic replacements’. The Adnet reef structure should not be regarded as a general model of Alpine Upper Rhaetian reefs, because of the particular setting of the patch reef. Only the ‘capping beds’ of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria similar to Adnet. Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of theRetiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity of corals subsequent to breaks in settlement, segration patterns of corals indicating ‘contact avoidance’, toppling of large coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water depths.     

Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C*. Despite the high temperature in this lake (> 0.5 degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.     

The history of Devonian-Carboniferous reef communities: Extinctions,effects, recovery

Summary Analysis of the taxonomic composition, diversity and guild structure of five “typical” reef and mud mound communities ranging in age from Late Devonian-Early Carboniferous indicates that each of these aspects of community organization changed dramatically in relation to three extinction events. These events include a major or mass extinction at the end of the Frasnian; reef communities were also effected by less drastic end-Givetian and mid-late Famennian extinctions of reef-building higher taxa. Peak Paleozoic generic diversities for reef-building stromatoporoids and rugose corals occurred in the Eifelian-Givetian; reef-building calcareous algal taxa were longranging with peak diversity in the Devonian. These three higher taxa dominated all reef-building guilds (Constructor, Binder, Baffler) in the Frasnian and formed fossil reef communities with balanced guild structures. The extinction of nearly all reef-building stromatoporoids and rugose corals at the end of the Frasnian and the survival of nearly all calcareous algac produced mid-late Famennian reef communities dominated by the Binder Guild. Despite the survival of most calcareous algae and tabulate corals, the mid-late Famennian extinction of all remaining Paleozoic stromatoporoids and nearly all shelf-dwelling Rugosa brought the already diminished Devonian reef-building to a halt. These Devonian extinctions differ from mass extinctions by the absence of a statistically significant drop in taxonomic diversity and by their successional and cumulative effects on reef communities. Tournaisian mud mounds contain communities markedly different from the frame-building communities in Late Devonian and Visean reefs. Mound-building biotas consist of an unusual association dominated by erect, weakly skeletonized members of the Baffler Guild (chiefly fenestrate Bryozoa; Pelmatozoa) and laterally expanded, mud-binding algae/stromatolites and reptant Bryozoa. The initial recovery to reefs with skeletal frameworks in the Visean was largely due to the re-appearance of new species of abundant colonial rugose corals (Constructor Guild) and fenestrate Bryozoa. This Frasnian-Visean evolution in the taxonomic composition and structure of the reef-building guilds is also expressed by abrupt changes in biofacies and petrology of the reef limestones they produced. Thus, “typical” Frasnian reef limestones with balanced guild structures are framestones-boundstones-bafflestones, Famennian reefs are predominantly boundstones, Tournaisian mud mounds are bafflestones and Visean reefs are bafflestones-framestones.     

Microbial diversity associated with four functional groups of benthic reef algae and the reef-building coral Montastraea annularis

The coral reef benthos is primarily colonized by corals and algae, which are often in direct competition with one another for space. Numerous studies have shown that coral-associated Bacteria are different from the surrounding seawater and are at least partially species specific (i.e. the same bacterial species on the same coral species). Here we extend these microbial studies to four of the major ecological functional groups of algae found on coral reefs: upright and encrusting calcifying algae, fleshy algae, and turf algae, and compare the results to the communities found on the reef-building coral Montastraea annularis. It was found using 16S rDNA tag pyrosequencing that the different algal genera harbour characteristic bacterial communities, and these communities were generally more diverse than those found on corals. While the majority of coral-associated Bacteria were related to known heterotrophs, primarily consuming carbon-rich coral mucus, algal-associated communities harboured a high percentage of autotrophs. The majority of algal-associated autotrophic Bacteria were Cyanobacteria and may be important for nitrogen cycling on the algae. There was also a rich diversity of photosynthetic eukaryotes associated with the algae, including protists, diatoms, and other groups of microalgae. Together, these observations support the hypothesis that coral reefs are a vast landscape of distinctive microbial communities and extend the holobiont concept to benthic algae.