Carboniferous reef succession of the Panthalassan open-ocean setting: example from Omi Limestone, central Japan

Summary The Carboniferous-Permian (Visean-Midian) Omi Limestone in the Akiyoshi Terrane, central Japan is a large carbonate unit developed on a seamount in the Panthalassa Ocean. As the seamount subsided during Carboniferous and Permian time, the carbonate deposition at the top of a seamount was almost continous. Terrigenous siliciclastic sediments are absent, because the seamount was situated in an open-ocean setting. The lower part of this seamount-type limestone records a nearly continuous Carboniferous reef succession. Sedimentary facies in the Carboniferous part of the Omi Limestone are generally highly diverse, but their diversity varies in each age. The Upper Carboniferous part consists of highly diversified facies including fore reef, reef front, reef crest, sand shoal, and lagoon facies, while a simple facies assemblage, composed only of fore reef, reef front, and sand shoal facies, occurs in the Lower Carboniferous. The Carboniferous reef succession consists of four phases characterized, in ascending order, by the coralbryozoan-crinoid community, problematic skeletal organism-microencruster community, chaetetid-microencruster community, and calcareous algal community. The first phase, comprising the coral-bryozoan-crinoid community, occurs in theEndothyra spp. Zone to theEostaffella kanmerai Zone (Visean to Serpukhovian). This community acted only as sediment-bafflers and/or contributors. The second phase, represented by the problematic skeletal organism-microencruster community, is developed in theMillerella sp. Zone to theAkiyoshiella ozawai Zone (Bashkirian to lowermost Moscovian), and the third phase, comprising the chaetetid-microencruster community, occurs in the overlyingFusulinella biconica Zone (Lower Moscovian). These two communities are characterized by highly diversified reef-building organisms that had the ability to build rigid frameworks. Calcareous algae and incertae sedis such asHikorocodium, solenoporaceans and phylloid algae characterize the fourth phase, which occurs in theBeedeina sp. Zone (Upper Moscovian). The changes of the reef communities were sucessive for a long period of more than 40 m.y., and each community was distributed in various environments. In addition, the continuous subsidence of the isolated seamount resulted in environmental stability. These properties indicate that this succession represents the biotic evolution of reef-building organisms. The problematic skeletal organism-microencruster community and chaetetid-microencruster community of the Late Carboniferous formed wave-resistant and rigid frameworks along with abundant submarine cements. The growth of these reef frameworks resulted in the formation of highly diversified sedimentary facies comparable to those of a modern reef complex. Such reefs are also recognized in the seamount-type Akiyoshi Limestone, but rare on Carboniferous Pangean shelves. Therefore, the formation of these types of reefs appear to be characteristic of open-ocean seamount settings, which differed from epicontinental shelf settings in having no siliciclastic input, being exposed to relatively strong openocean waves and swells, and probably more environmental stability resulting from the relatively continuous subsidence of the seamount.     

Youngest early carboniferous (late Visean) shallow-water patch reefs in eastern Australia (Rockhampton Group, Queensland): Combining quantitative micro- and macro-scale data

Summary Although skeletal organisms have received most of the emphasis in studies on Phanerozoic roef history, the roles of non-skeletal (non-enzymatic) carbonates (e.g., synsedimentary cements, automicrite, microbialite, etc.) in reef framework construction are becoming increasingly better understood. One problem in understanding the role of non-enzymatic carbonates in reef construction has been the difficulty in recognizing them in reef facies. Whereas skeletal organisms commonly can be recognized and documented in the field, non-enzymatic carbonates may be recognizable only in thin section. This paper describes the application of a new sampling technique that allows the quantitative comparison of skeletal macrofauna and flora with associated non-enzymatic carbonates and other microfaunal/microfloral constituents. The technique involves the point counting of thin sections made from small diameter cores that are systematically recovered from grids and line transects that cover a reasonable area (m²) of reef facies. Small, shallow-water patch reefs are abundant in scattered oolitic intervals in the Lower Carboniferous strata of eastern Australia. The youngest known Carboniferous reefs in eastern Australia occur in uppermost Visean strata (limestone FC5) near the top of the Rockhampton Group, approximately 50 km west-northwest of Rockhampton, Queensland. The largest sampled reef was 15 m thick and 42 m in diameter, with synsedimentary relief above the sea floor of at least 2 m during the primary growth phase. The reef occurs within bioclasticoolitic grainstones representing a shallow shelf setting and consists of eight common framework microfacies: 1) coral boundstone; 2) bryozoan boundstone; 3) mixed crinoid-bryozoan boundstone; 4) tubular problematica boundstone; 5) sponge-automicrite boundstone; 6) encrusted thrombolite boundstone; 7) mixed automicrite boundstone; and 8) thrombolitic wackestone-packstone. Reef growth was initiated by automicrite-producing biofilms, sponges and a tubular problematic organism. Primary relief building was accomplished by automicrite-dominated frameworks and lithistid sponges, crinoids, and corals. Large cerioidAphrophyllum coral colonies had a heterogeneous distribution through the reef. The framework of the main relief-bearing portion of the reef consists on average of 44.4% automicrite and automicrite-bound detritus, excluding automicrite-bound sponge body fossils, and at most 19.6% skeletal organisms in growth position (minimum of 7.2%). If sponge body fossils are included as automicrite framework, because they are preserved only as a result of automicrite formation, the percentage of automicrite and bound sediment is 54.9%. A smaller sampled reef consisting of the same basic facies had 39.5% automicrite and automicrite-bound sediment in its fremework (50.2% including sponges) and, at most, 33.4% skeletal organisms in growth position (minimum of 22.7%). The greater volume of skeletal framework in the small reef reflects a greater proportion of large corals. Of framebuilding skeletal organisms, automicrite-preserved lithistid and other sponges and cerioid rugose corals provided the greatest volume. However, crinoid holdfasts were the most widespread skeletal framework components. The dominant framework facies are sponge-automicrite boundstone, encrusted thrombolite, boundstone, mixed automicrite boundstone, and coral boundstone. The reefs are similar in overall framework construction and ecological succession to slightly older Visean reefs in eastern Australia and to some of the late Visean reefs of northern England. Surprisingly, framework similarities also exist between the reefs and certain thrombolite-lithistid-coral reefs of the European Jurassic.     

The influence of prey communities on fish species assemblages on artificial reefs in Puget Sound,Washington

Synopsis Research on eleven artificial reefs in Puget Sound, Washington examined the relative importance of reef-produced prey items to recreationally important reef fish species assemblages. The colonization of potential prey items, and fish species assemblages to ten artificial reefs were examined for the reefs first two to five years, and observations were conducted on an eleventh reef during its forty-ninth productive year. Fish species became more abundant, or were seen more frequently on reef habitats whose substrates had successionally developed from barnalces to algal mats. Fish species most affected by this successional change foraged heavily on organisms which were associated with reef algae. Starfish and nudibranchs. who preyed on the barnacles, were identified as the ‘keystone’ predators of these subtidal reef habitats.     

Structure of reef fish communities in Catalinas Islands and Ocotal beach, North Pacific of Costa Rica

The reefs are heterogeneous systems that maintain a high diversity of organisms. Fish community structure varies within and among reefs, so it would be expected that reef structure and heterogeneity should affect fish communities inhabiting reefs. Four reef patches at Catalinas Islands (Sur, La Pared, Roca Sucia and Sombrero) and one in Ocotal beach (10 degrees 28'45" N; 85 degrees 52'35" W) were studied with visual censuses (July-December 2003). The structure and composition of fishes between Catalinas islands and Ocotal beach were different, and habitat structure and composition explain most of the variance founded. The presence of the fleshy algae Caulerpa sertularioides in Ocotal, and the corals Tubastrea coccinea and Pocillopora spp. at Catalinas Island explained the variability among sites and how it affected fish community structure and composition. The butterfly fish Johnrandallia nigrirostris, damselfish Microspathodon dorsalis, and surgeon fish Prionurus punctatus were directly correlated with the ahermatipic coral Tubastrea coccinea in Roca Sucia reef, while the angel fish Holacanthus passer was associated to reefs with a major percentage of rocky substrate. Other species such as the damselfish Abudefduf troschelli and Halichoeres dispilus were more abundant at Ocotal, where the algae C sertularioides dominated. The number and abundance of reef fishes was directly correlated with the rugosity index at the reefs of Roca Sucia and Ocotal, but not at reefs of La Pared and Sombrero.     

Bioeroders in fossil reefs

Summary Boring algae, fungi and bacteria have been the most constant factor in bioerosion through earth history. Their record reaches back into the middle Precambrian. The only fossil reefs specifically researched for these microendoliths are of Triassic and Upper Jurassic age. Boring worms appear in reefs in the Lower Cambrian. Boring sponges and bivalves first appear also in the lower Paleozoic, but do not become abundant in reefs until the Triassic. Effective substrate excavating grazers are relatively young geologically: Patellids and substrate excavating Echinoids evolved in the Triassic but did not become important bioeroders until the Jurassic or Cretaceous. Scarid fishes are even younger, the oldest representatives having been found in the Miocene. Thus, it seems that the intensity of bioerosion changed significantly during earth history. This may have had consequences for diversity of reef organisms, quality and quantity of reef debris, for diagenesis and record of reef rock.     

Distribution and evolution of Carboniferous reefs in South China

Reefs are sensitive proxies for palaeontological, palaeoenvironmental, and palaeogeographical changes during geological history. In South China, after the collapse of the reef ecosystem during the Frasnian-Famennian and Hangenberg mass extinction events, Carboniferous reefs underwent evolutionary episodes of recovery, decline, and turnover, which were controlled by changes of reef-builders abundance, sedimentary facies, relative sea level, and even global climate. In Tournaisian times, only a few Waulsortian-like banks have been found in Liuzhou, Guangxi without metazoan reefs, which were caused by the lack of reef-builders, such as colonial rugose corals and bryozoans, and the dominant non-carbonate facies (shale, mud stone and sandstone) driven by low relative sea level. The absence of mud mounds in the early Viséan was attributed to the regression event during the Tournaisian-Viséan boundary. During Viséan times, bryozoan-coral reefs in Huishui, Guizhou and Tianlin, Guangxi occurred during a time of increasing biodiversity and carbonate facies resulting from relative sea-level rise. The number of potential reef-builders as colonial rugose coral and bryozoan genera significantly increased in Viséan times in South China. The reef abundance declined during Serpukhovian times in South China and the controlling factors were decreasing abundance of potential reef-builders and developing non-carbonate facies due to a relative sea-level fall. The sedimentary facies were characterized by shale, mud stone, sandstone, and dolostone during this time. A distinct change in reef types occurred after the Mississippian-Pennsylvanian boundary, when phylloid algae and red algae reefs (distributed in Ziyun, Guizhou and Beibuwan, Guangxi) replaced metazoan reefs and became the dominant role in reef ecosystem. This reef turnover event may be triggered by the dramatic relative sea-level fall during the mid-Carboniferous, and continued low relative sea level in South China and global flourish of phylloid and red algae during Pennsylvanian times. Grainstone and dolomitic limestone were the main composition of the platform sedimentary facies in South China during Pennsylvanian times. In addition, global climate cooling and warming, resulted from the waxing and waning of Gondwana glaciation, may also influence the reef evolution in South China, as evidenced from the consistent transgression and regression events and reef evolutionary pattern between South China and globe during the Carboniferous.     

Establishment and development of patch reefs in the intracratonic Ordovician sequence near Chicoutimi, Quebec

Patch reefs occur near the top of the transgressive sequence of Ordovician Trenton Group limestones in the Chicoutimi area of Quebec, eastern Canada. Despite their small sue, these reefs comprise diverse assemblages dominated by bryozoans, corals, stromatoporoids and receptaculitid algae. Pelmatozoans and gastropods are also conspicuous. The reefs were initiated and grew in a fully marine, open shelf setting. Available substrates varied from loose skeletal lenses to soft, firm or hardened bioturbated wackestones, and the earliest stages of reef growth reflect this heterogeneity. Loose or less firm substrates were colonised by bryozoans and pelmatozoans and/or by receptaculitids, which, together with accessory organisms, stabilised the sediments and provided the basis for further reef development. The resultant firmer, slightly elevated substrates provided sites for attachment of stromatoporoids and colonial corals which spread over earlier reef organisms and sediments and dominated the later stages of reef growth. On hardened areas of sediment, stromatoporoids and corals colonised the surface directly and the early stabilising stage of reef growth is absent. The compositions and developmental stages of these Trenton Group reefs are comparable with those seen in broadly contemporaneous and often larger reefs elsewhere, and are among the earliest in which corals played an important role.     

Biotic structure and morphology of patch reefs from South China (Ningqiang Formation, Telychian, Llandovery, Silurian)

Summary Ningqiang Formation (late Telychian, Llandovery, Silurian), characterized by nearly 3000 m of shales in tercalated with carbonates, is situated between Ningqiang (S. Shaanxi Province) to Guangyuan (N. Sichuan Province) adjacent to the northwest margin of the Yangtze Platform. The high diversity “Xiushan Fauna”, and abundant reef development, illustrate a relatively warm and persistent shallo marine environment in these early Silurian sediments. The sequence shows reef radiation after recovery from the end Ordovician mass extinction envents. Multiple horizons of reef-building occurred within a relatively short geological interval and resulted in more than 30patch reefs up to 200 m in diameter and 1–50 m vertically, composed of abundant fossils. Reef biota include frame-building corals, stromatoporoids, bryozoans, and microbialites, and reef-associated oranisms such as crinoids, brachiopods, trilobites, gastropods, nautiloids and ostracods. Three reefrelated biotic associations are recognised: a) reefs dominated by framework with crinoids and microbia; b) reefs dominated by only crinoids and microbia; and c) crinoiddomainated facies. Seven representative reef examples illustrate different morphologies and growth styles. A high terrigenous debris input and shallow epicontinental ramp, which lacked obvious topographic variation, were major controls which resulted in rather simple reefs; sedimentation was apparently the main constraint on lateral and vertical extension of reefs, and prevented large-scale reef complexes developing.     

中国南方二叠纪海绵礁的成礁模式

广泛发育于我国南方碳酸盐岩台地区的二叠纪生物礁,其中绝大多数属于海绵生物礁。从该地区二叠纪海绵生物礁的内部成礁因素分析,即从主要造礁生物－钙质海绵和钙质藻类等的生物学和生态学特征、埋藏和保存特点等方面进行分析,提出了华南二叠纪海绵生物礁主要是由于其主要造礁生物钙质海绵和钙质藻类独特的生物学特征、生态学特征以及它们的共同作用所形成的。此模式与其它地质历史时期生物礁的成礁模式明显不同。     

ECOLOGY AND MORPHOLOGY OF RECENT CORAL REEFS

1. The classical ‘coral reef problem’ concerned the geological relationships of reefs as major topographical features; modern coral studies consider reefs both as complex biological systems of high productivity and as geological structures forming a framework for and being modified by coral growth. 2. Deep borings in reefs have conclusively confirmed the general arguments of Darwin, that oceanic reefs developed by progressive subsidence of their foundations. Darwin failed to take account of Pleistocene changes in sea level and their effect on the present surface features of reefs. Daly's alternative ‘glacial control theory’ was based on false assumptions concerning marine erosion rates during glacial periods, but if sea level during the Holocene was higher than at present, as Daly also supposed, the effects on reef features would be profound. 3. Reefs are complex biological systems in tropical seas, dominated by scleractinian corals. Coral faunas are larger and more diverse in the Indo-Pacific than in the Atlantic. Hermatypic corals are restricted to shallow water by the light requirements of their symbiotic algae, but temperature is a major control of worldwide distributions. Temperature, salinity and sediment tolerances of corals are wider than formerly supposed, and corals can survive brief emersion except when it coincides with heavy rainfall. Water turbulence is an important ecological control, but difficult to measure. 4. The trophic status of corals is still unclear, but in spite of their anatomical and physiological specialization as carnivores it is likely that they derive some nutrient substances from zooxanthellae. Suggestions that filamentous algae in coral heads play a major part in the economy of the corals have not been supported by later work, but biomass pyramids constructed on the basis by Odum and Odum remain the only ones available. Most reefs are apparently autotrophic, with 1500–3500 g. Carbon being fixed per m.² per year. 5. Few animals eat corals, which may account for their success. Important predators are fish and the echinoderm Acanthaster. Quantitative estimates of biogenic erosion of organic skeletons on reefs are high. Fish affect not only corals but other invertebrates, algae and marine phanerogams. 6. Corals may be killed by ‘dark water’, intense rain or river floodwaters, earth movements, human interference and especially hurricanes. Reef recovery after hurricanes may take 10–20 years. 7. In addition to fringing, barrier and atoll reefs, intermediate types are recognised. The main types may consist of linear reefs or faros. Smaller lagoon reefs include pinnacles, patches and platforms, and submerged knolls. Complex cellular or mesh reef patterns are also found. 8. Reefs are conspicuously zoned, both laterally in response to changing exposure to waves to form windward and leeward reefs, and transversely, as a result of steep environmental gradients across reef flats from sea to lagoon. Topographic and ecological zones may be characterized by particular coral species, but these vary widely from reef to reef. A major distinction can be made between reefs with and without algal ridges, which are common on open-ocean trade-wind reefs, in the Indo-Pacific, but are absent on Caribbean reefs and on Indo-Pacific reefs in more sheltered waters. gorgonians are common on Caribbean reefs, alcyonaceans in the Indo-Pacific. 9. Much of the difficulty in comparing reefs stems from the lack of uniformity in surveying methods. Problems of describing the complex three-dimensional patterns of organisms on reefs have yet to be solved, and hence little progress has been made in explanation of these patterns. Explanation in terms of simple environmental controls is inadequate. 10. Understanding the distribution of corals is made more difficult both by taxo-nomic problems and by the plasticity of growth form in different situations. 11. Growth of corals and reefs may be estimated by measuring the growth of individual colonies, measuring rates of calcium carbonate deposition in the skeleton, measuring topographic change on the reef and deducing net rates of reef growth from geological evidence. Massive corals may increase in diameter by 1 cm./year, branches of branching corals may increase in length by 10 cm./year. Study of deposition rates shows variation within colonies, between species, in light and dark, and seasonally. Rates of reef growth extrapolated from colony measurements reach 2–5 cm./year, and contrast with figures as low as 0–02 cm/year averaged over 70 million years from borehole data. Both colony growth rates and geological data suggest worldwide variations in rates of reef growth. 12. In spite of clear evidence of long-continued subsidence, present surface features of reefs, often only thinly veneered by modern corals, have been much affected by recent sea level fluctuations. Many slightly raised reefs at 2–10 m. above sea level date at 90–160 thousand years B.P.; there is evidence for a sea level at about the present level at 30–35 thousand years B.P.; and controversy continues over whether sea level has stood higher than the present at any time since the last sea level rise began about 20,000 years ago. Evidence from many reefs suggests a slightly higher sea level in the last 4000 years, but on other reefs such evidence is lacking. 13. Several reef features (submerged terraces, groove-spur systems, algal ridge, reef flat, reef blocks and reef islands) have been interpreted either as relict features dating from a higher sea level in the last 5000 years, or contemporary features developed in response to present processes. In some cases the evidence is equivocal; in others it is clear that diverse features are being grouped together under the same name. If such features are referable to a higher sea level, this may have been of last Interglacial or even Interstadial age rather than Holocene. 14. A reef consists of a rigid framework defining several major depositional environments within and around it. Sediments are of biological, mainly skeletal origin, except in unusual environments such as the Bahama Banks. The characteristics of sediments derived from organisms depend partly on the breakdown patterns of particular skeletons, partly on transportation and sorting processes. Fine sediments may be either detrital, or physicochemical precipitates. 15. Organisms affect sediments after deposition, by disturbance, transportation and probably comminution. Fish and holothurians have been studied in detail. 16. While new theories of coral reefs are proposed from time to time, the need is less for new theories than for standardised procedures to ensure comparability of reef studies and the identification of variations in reefs both on local and regional scales. While reefs as biological systems adjust relatively rapidly to changes, reefs as geological systems adjust much more slowly. Because of the magnitude and recency of Pleistocene fluctuations in sea level, many biological features of reefs are out of phase with inherited geological features, and this had led to much controversy.     

PROCESSES OF ORGANIC PRODUCTION ON CORAL REEFS

1. The first quantitative studies of production on coral reefs were those of Sargent & Austin who showed that productivity on reefs was considerably higher than in surrounding waters. This high production occurred in spite of nutrient limitation and low productivity of offshore waters. Their conclusions have since been confirmed by numerous other workers in both the Atlantic and the Pacific. 2. Primary production on reefs has been studied by flow respirometry, measuring changes in oxygen or carbon dioxide concentrations in water flowing over reefs. Production of benthic organisms has also been measured in situ by light and dark bottle methods and by radioactive tracer techniques. Production values obtained by the various methods are not identical but their use in combination is to be recommended. 3. Rates of gross primary production on reefs vary between 300–5000 gC/m²/yr. These rates are higher than general oceanic values and as high as those of the most productive marine communities. 4. Sources of primary production include fleshy macrophytes, calcareous algae, filamentous algae on the coral skeletons or calcareous rock, marine grasses and the zooxanthellae within coral tissue. Production values from the various sources fall within the range of production of reefs as a whole. 5. Concentrations of nitrogen and phosphorus in waters flowing over reefs are consistently low. There is evidence to suggest that both these nutrients are recycled rapidly on the reef and that nitrogen is fixed by bacteria and primary producers. 6. In many instances the mass of detritus over coral reefs exceeds the biomass of zooplankton. While the quantitative significance of detritus as food for corals and other benthic organisms has not been evaluated, there is a growing body of evidence to show that this may be the key to understanding secondary production. 7. Opinions differ on the adequacy of zooplankton in satisfying the food requirements of corals and other benthic invertebrates on reefs. The weight of evidence suggests that while there is a removal of zooplankton by benthic organisms, the total biomass carried over the reef is too small to support the energy needs of secondary production. 8. Bacteria are a potential source of energy for secondary production on reefs and are implicated in nitrogen fixation, decomposition and biogeochemical cycling. 9. There is an abundance of sessile invertebrates other than corals on reefs but there are few quantitative data on their importance in secondary production. 10. The biomass of fish on reefs may be very high but the quantitative significance of grazing and predation is not fully established. 11. Studies on the growth of corals themselves have been based on measurements of skeletal accretion. These methods do not lead directly to estimates of reef organic production. Growth rates of corals vary considerably between and within species. 12. Estimates of reef growth have been made from measurements of coral growth and from the flux of calcium carbonate. There is less quantitative information on erosion caused by mechanical damage, by boring organisms and by human pollution. 13. Hydrographic factors influence growth and form of reefs and there is some evidence to show that production is enhanced by conservation of water in lagoonal areas.     

Effects of territorial damselfish on an algal-dominated coastal coral reef

Territorial damselfish are important herbivores on coral reefs because they can occupy a large proportion of the substratum and modify the benthic community to promote the cover of food algae. However, on coastal coral reefs damselfish occupy habitats that are often dominated by unpalatable macroalgae. The aim of this study was to examine whether damselfish can maintain distinctive algal assemblages on a coastal reef that is seasonally dominated by Sargassum (Magnetic Island, Great Barrier Reef). Here, three abundant species (Pomacentrus tripunctatus, P. wardi and Stegastes apicalis) occupied up to 60% of the reef substrata. All three species promoted the abundance of food algae in their territories. The magnitudes of the effects varied among reef zones, but patterns were relatively stable over time. Damselfish appear to readily co-exist with large unpalatable macroalgae as they can use it as a substratum for promoting the growth of palatable epiphytes. Damselfish territories represent patches of increased epiphyte load on macroalgae, decreased sediment cover, and enhanced cover of palatable algal turf.     

Spatial competition among clonal organisms in extant and selected paleozoic reef communities

Summary Occurrences of densely packed benthic organisms in extant reefs are of two types: 1) live-live interactions, where two living organisms interact, and 2) live-dead associations, where only one is alive and uses the other as a substrate. The latter are common in reef deposits due to biostratinomic feedback, i.e. dense skeletal accumulations provide hard substrates for clonal recruitment, thus facilitating greater frequency of live-dead encounters than in lower biomass level-bottom communities dominated by solitary organisms. Differentiating between these two types in ancient reefs is difficult, often impossible. Most live-live interactions among clones in extant reef communities involve competition for space. Clonal spatial competition is divisible into four types: 1) direct-aggressive: encrusting overgrowth; 2) indirect-passive: depriving neighbors of resources, chiefly sunlight, by growth above them; 3) stand-off: avoidance of competition by organisms adopting positions that avoid or minimize direct polyp/zooid contact; and 4) overwhelming: one clone/ species volumetrically or numerically overwhelms the other, meeting minimal resistance. Despite class-order level differences in taxa, our results indicate that extant analogs, based on the arrangement and distortion of skeletons, are valuable for recognizing live-live interactions in Silurian and Carboniferous reefs and interpreting the types of spatial competition represented. Comparison of overhead (plan) views of live-live coral competition in Polynesian reefs with vertical sections of Silurian and Carboniferous sponge-dominated reefs and biostromes suggests that direct-aggressive competition is more common among extant than among Paleozoic reef-builders. Stand-offs showing clone margin distortion and overwhelming with minor skeletal distortion are most common in our fossil examples and probably relate to the dominance of these reefs by sponges. Success by extant sponges in spatial competition is largely due to allelochemical deterrence which may explain the predominance of stand-off and overwhelming confrontations in fossil sponges rather than tentacle-mesentery based direct aggression among extant corals and bryozoans.     

Anisian (middle triassic) buildups of the Northern Dolomites (Italy): The recovery of reef communities after the permian/triassic crisis

Summary After the end-Permian crisis and a global ‘reef gap’ in the early Triassic, reefs appeared again during the early Middle Triassic. Records of Anisian reefs are rare in the Tethys as well as in non-Tethyan regions. Most Anisian reefs are known from the western part of the Tethys but there are only very few studies focused on biota, facies types and the paleogeographical situation of these reefs. From the eastern part of the Tethys, Anisian reefs, reefal buildups or potential reef-building organisms have been reported from different regions of southern China. Most of the Anisian reefs known from western and central Europe as well as from southern China seem to be of middle and late Pelsonian age. The study area is situated in the northern Dolomites (South Tyrol, Italy) southeast of Bruneck (Brunico). It comprises the area between Olang (Valdaora) and Prags (Braies). The study is based on detailed investigations of the regional geology, stratigraphy and lithofacies (R. Zühlke, T. Bechst?dt) as well as on a comprehensive inventory of Anisian reef organisms (B. Senowbari-Daryan, E. Flügel). These data are used in the discussion of the controls on the recovery of reefs during the early Middle Triassic. Most late Anisian reef carbonates studied are represented by allochthonous talus reef blocks of cubicmeter size. Small biostromal autochthonous mounds are extremely rare (Piz da Peres). The reef mounds as well as most of the reef blocks occur within the middle to late Pelsonian Recoaro Formation. They were formed on the middle reaches of carbonate ramps in subtidal depths, slightly above the storm wave base with only moderate water energy. Most lithotypes observed in the reef blocks correspond to sponge and/or algal bafflestones. Low-growing sessile organisms (Olangocoelia (sponge, alga?), sphinctozoan sponges, bryozoans, soleno-poracean algae, corals) and encrusting epibionts (sponges, porostromate algae, cyanophycean crusts, foraminifera, worms, microproblematica) created low cm-sized biogenic structures (bioconstructions) which baffled and bound sediment. Organic framework was only of minor importance; it is restricted to theOlangocoelia lithotype. Framework porosity was small in these reef mounds. Submarine carbonate cements, therefore, are only of minor importance s compared with Permian or Ladinian reefs. The relatively high number of lithotypes encountered in the reef blocks indicates a high biofacies diversity. Regarding the relative frequency, the diverse biota consist in descending order ofOlangocoelia, sponges (sphinctozoans, inozoans, siliceous sponges), bryozoans, porostromate algae and worm tubes. The sphinctozoans are characterized by small, mostly incrusting forms. The numerical diversity (species richness) is low compared with late Permian or Ladinian and late Triassic sphinctozoan faunas occurring within reefs. Following the sponges, monospecific bryozoans (Reptonoditrypa cautica Sch?fer & Fois) are the most common organisms in the reef limestones. Porostromate algae were restricted to areas within the bioconstructions not inhabited by sponges. The low-diverse corals had no importance in the construction of an organic framework. Surprisingly, microbial crusts are rare or even lacking in the investigated Anisian bioconstructions. This is in contrast to late Permian and Ladinian as well as Carnian reefs which are characterized by the abundance of specific organic crusts. The same comes true for‘Tubiphytes’ which is a common constituent in Permian, Ladinian and Carnian reef carbonates but is very rare in the Anisian of the Olang Dolomites. Instead of‘Tubiphytes’ different kinds of worm tubes (spirorbid tubes, Mg-calcitic tubes and agglutinated tubes) were of importance as epifaunal elements. Macrobial encrustations consisting of characteristic successions of sponges, bryozoans, algae, worm tubes and microproblematica seem to be of greater quantitative importance than in Ladinian reefs. Destruction of organic skeletons (predominantly of bryozoans) by macroborers (cirripedia?) is a common feature. The Anisian reef organisms are distinctly different from late Permian and from most Ladinian reef-builders. No Permian Lazarus taxa have been found. New taxa: Sphinctozoan sponges—Celyphia? minima n.sp.,Thaumastocoelia dolomitica n. sp.,Deningeria tenuireticulata n. sp.,Deningeria crassireticulata n. sp.,Anisothalamia minima n.g. n.sp., Inozoan sponges-Meandrostia triassica n.sp. Microproblematica-Anisocellula fecunda n.g. n.sp., Porostromate alga-Brandneria dolomitica n.g. n.sp. Most of our data are in agreement with the model described byFois & Gaetani (1984) for the recovery of reef-building communities during the Ansian but the biotic diversity seems to be considerably higher than previously assumed. Anisian deposition and the formation of the reef mounds within the Pelsonian Recoaro Formation of the Dolomites were controlled by the combined effects of synsedimentary tectonics and eustatic changes in sea-level. During several time intervals, especially the early Anisian (northern and western Dolomites: tectonic uplift), the early Pelsonian (eastern Dolomites: drowning) and the late Illyrian (wide parts of the Dolomites: uplift and drowning), the sedimentation was predominantly controlled by regionally different tectonic subsidence rates. The amount of terrigenous clastic input associated with synsedimentary tectonics (tectonic uplift of hinterlands) had a major influence on carbonate deposition and reef development. The re-appearance of reef environments in the Olang Dolomites was controlled by a combination of regional and global factors (paleogeographic situation: development of carbonate ramps; decreasing subsidence of horst blocks; reduced terrigenous input; moderate rise in sea-level).     

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.     

Sponge-mediated coral reef growth and rejuvenation

Sponges mediate consolidation of Porites furcata rubble on shallow Caribbean reefs by quickly adhering to rubble and stabilizing it until carbonate secreting organisms can grow and consolidate it to the reef. Experimental investigations demonstrate that the entire cycle from (1) temporary binding of rubble by sponges, through (2) rubble consolidation by encrusting coralline algae, to (3) colonization of consolidated rubble by corals, can be completed within 10 months. Bound rubble both adds to vertical reef growth and also provides stable substrata for colonization by corals. Corals that colonize stabilized rubble are damaged less and survive better than on unstable rubble. Rubble that is not temporarily stabilized by sponges does not become bound to the reef, because continuous movement disturbs the consolidation process, and does not provide suitable substrata for settlement and growth of corals. Sponge-mediated consolidation of rubble may increase rates of reef growth and enhance reef recovery after damage. This new role for sponges in reef growth is not obvious from examination of the internal fabric of a reef frame. Spongemediated consolidation may help to explain geographic and temporal differences in growth and morphology among shallow reefs of ramose corals.     

海洋生物礁类型、生态功能及其生态修复

海洋生物礁是由具有造礁能力的海洋生物聚集而成的一种三维礁体结构,其形成改变了海底地貌、增加了不同尺度上的地形复杂性,为其他海洋生物提供了栖息地并维持了生物多样性。近年来,由于自然因素和人为因素影响,海洋生物礁受到了严重威胁,已成为海洋生态保护和修复领域的重要研究对象。综述了海洋生物礁的类型、生态功能及其生态修复的研究进展。根据形成海洋生物礁的优势造礁生物种类,将海洋生物礁分为海藻礁、海绵礁、刺胞动物礁、贝类礁和多毛类礁,其优势造礁生物分别是珊瑚藻和仙掌藻、钙质海绵和硅质海绵、造礁珊瑚、牡蛎、龙介虫。目前国内对海洋生物礁的全面了解相对较少,主要集中在珊瑚礁和牡蛎礁。海洋生物礁的生态功能主要有海岸防护、提供栖息地、净化水体、固碳作用和能量耦合等。全球变暖和海洋酸化等全球气候变化以及海洋污染、破坏性渔业捕捞、海岸工程、水产养殖和敌害生物等自然和人为因素对海洋生物礁构成了严重威胁。海洋生物礁的生态修复方法分为两类：在退化生物礁区投放造礁生物逐渐成礁,投放人工礁体补充造礁生物逐渐成礁。针对海洋生物礁保护和修复的需要,提出下一步应加强海洋造礁生物生态特征、海洋造礁生物种群丧失因素和海洋生物礁保护与...     

Competition between corals and algal turfs along a gradient of terrestrial influence in the nearshore central Great Barrier Reef

Competition between benthic algae and corals is a key process in the community ecology of reefs, especially during reef degradation. However, there have been very few experimental tests for competition between corals and benthic algae, despite widespread assumptions that algae are generally superior competitors, especially in eutrophic conditions. This study tested for competition for space between the massive coral Porites lobata and algal filamentous turfs on three reefs along a cross-shelf gradient of terrestrial influence, by experimentally removing or damaging either corals or algae. The corals and algae were competing for space, but, significantly, the algae appeared to have little effect on coral growth. In contrast, corals significantly inhibited algal growth, suggesting Porites was the competitive superior. Importantly, coral growth was generally positive, even on the reef with the greatest terrestrial influence. Competitive outcomes did not support the argument that algae are more successful competitors in more eutrophic conditions.     

Paleoecology of Pennsylvanian phylloid algal buildups in south Guizhou,China

Pennsylvanian phylloid algal reefs are widespread and well exposed in south Guizhou, China. Here we report on reefs ranging from 2 to 8 m thickness and 30–50 m lateral extension. Algae, the main components, display a wide spectrum of growth forms, but are commonly cyathiform (cup-shaped) and leaf-like (undulate plates). The algal reef facies is dominated by boundstone. Algal thalli form a dense carpet whose framework pores are filled with marine cement and peloidal micrite. The peloidal matrix is dense, partly laminated or clotted with irregular surfaces and often gravity defying. Algal reefs in Guizhou differ from examples reported to date by the high biodiversity of organisms other than phylloids: e.g., the intergrowth of algae with corals (some of which are twice the size of algal thalli) and numerous large brachiopods. This contrasts to previous views that phylloid algal “meadows” dominated the actual seafloor, excluding other biota. Also, the pervasive marine cements (up to 50%) including botryoidal cement are noteworthy. Algal reefs developed at platform margins, a depositional environment similar to that of modern Halimeda mounds in Java, Australia and off Bahamas, and to that of time-equivalent examples reported from the Canadian Arctic Archipelago. Whereas nutrients appear decisive in the growth of Halimeda reefs, algal reefs reported herein seemingly grew under conditions of low nutrient levels. Overall, algal reefs in Guizhou challenge previous views on growth forms, diversity patterns, and depositional environments and add to the spectrum of these partly puzzling biogenic structures.