Calcification by Reef-Building Sclerobionts

It is widely accepted that deteriorating water quality associated with increased sediment stress has reduced calcification rates on coral reefs. However, there is limited information regarding the growth and development of reef building organisms, aside from the corals themselves. This study investigated encruster calcification on five fore-reefs in Tobago subjected to a range of sedimentation rates (1.2 to 15.9 mg cm⁻² d⁻¹). Experimental substrates were used to assess rates of calcification in sclerobionts (e.g. crustose coralline algae, bryozoans and barnacles) across key reef microhabitats: cryptic (low-light), exposed (open-horizontal) and vertical topographic settings. Sedimentation negatively impacted calcification by photosynthesising crustose coralline algae in exposed microhabitats and encrusting foram cover (%) in exposed and cryptic substrates. Heterotrophs were not affected by sedimentation. Fore-reef, turbid water encruster assemblages calcified at a mean rate of 757 (SD ±317) g m⁻² y⁻¹. Different microhabitats were characterised by distinct calcareous encruster assemblages with different rates of calcification. Taxa with rapid lateral growth dominated areal cover but were not responsible for the majority of CaCO₃ production. Cryptobiont assemblages were composed of a suite of calcifying taxa which included sciaphilic cheilostome bryozoans and suspension feeding barnacles. These calcified at mean rates of 20.1 (SD ±27) and 4.0 (SD ±3.6) g m⁻² y⁻¹ respectively. Encruster cover (%) on exposed and vertical substrates was dominated by crustose coralline algae which calcified at rates of 105.3 (SD ±67.7) g m⁻² y⁻¹ and 56.3 (SD ±8.3) g m⁻² y⁻¹ respectively. Globally, encrusting organisms contribute significant amounts of carbonate to the reef framework. These results provide experimental evidence that calcification rates, and the importance of different encrusting organisms, vary significantly according to topography and sediment impacts. These findings also highlight the need for caution when modelling reef framework accretion and interpreting results which extrapolate information from limited data.     

The cyanophyte Wetheredella in Ordovician reefs and off-reef sediments

Wetheredella tumulus n.sp. was an important constituent, both binder and frame builder, in reef and off-reef sediments of the Ashgillian Ellis Bay Formation of Anticosti Island in eastern Canada. In individual small, stromatolite-like mounds, it built a skeletal platform for attachment of associated serpulid worm tubes, bryozoans, crinoids and small brachiopods. In larger bioherms, Wetheredella was an encruster, binding waveswept reef tops of halysitid and heliolitid corals. Wetheredella is interpreted as a blue-green alga related to Silurian Rothpletzella from Gotland and the genus Girvanella.     

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.     

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.     

Carbonate production of an emergent reef platform, Warraber Island, Torres Strait, Australia

Complex relationships exist between tropical reef ecology, carbonate (CaCO₃) production and carbonate sinks. This paper investigated census-based techniques for determining the distribution and carbonate production of reef organisms on an emergent platform in central Torres Strait, Australia, and compared the contemporary budget with geological findings to infer shifts in reef productivity over the late Holocene. Results indicate that contemporary carbonate production varies by several orders of magnitude between and within the different reef-flat sub-environments depending on cover type and extent. Average estimated reef-flat production was 1.66 ± 1.78 kg m⁻² year⁻¹ (mean ± SD) although only 23% of the area was covered by carbonate producers. Collectively, these organisms produce 17,399 ± 18,618 t CaCO₃ year⁻¹, with production dominated by coral (73%) and subordinate contributions by encrusting coralline algae (18%) articulated coralline algae, molluscs, foraminifera and Halimeda (<4%). Comparisons between the production of these organisms across the different reef-flat zones, surface sediment composition and accumulation rates calculated from cores indicate that it is necessary to understand the spatial distribution, density and production of each major organism when considering the types and amounts of carbonate available for storage in the various reef carbonate sinks. These findings raise questions as to the reliability of using modal production rates in global models independent of ecosystem investigation, in particular, indicating that current models may overestimate reef productivity in emergent settings. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Competitive dominance by tabular corals: an experimental analysis of recruitment and survival of understorey assemblages

Tabular and staghorn corals of the genus Acropora often form low-diversity stands on shallow coral reefs, presumably due to their rapid growth rate and ability to outcompete understorey assemblages. Coral cover underneath the abundant Indo-Pacific tabular coral, Acropora hyacinthus, was four times lower than on the adjacent substratum on the reef crest at Lizard Island on the northern Great Barrier Reef. We investigated the effect of A. hyacinthus on patterns of recruitment and mortality by placing experimental panels and coral fragments underneath large colonies of A. hyacinthus. After 8 weeks, recruitment of corals, filamentous algae and crustose coralline algae (CCA) underneath A. hyacinthus was 96, 85 and 50% lower, respectively, compared to panels placed in the open. In contrast, recruitment by bivalves and polychaetes was uniform among treatments, while bryozoans recruited four times more abundantly under A. hyacinthus than in the open. Consequently, the low rate of recruitment by corals beneath A. hyacinthus does not appear to be due to a reduction in the delivery of larvae underneath tables. Instead, the disparity between phototrophic and heterotrophic taxa suggests that diminished light levels under A. hyacinthus are partially responsible for the divergence in recruit assemblages. To test the effect of A. hyacinthus on early mortality and growth of established organisms, recruitment panels were placed on the open for 9 weeks then transplanted underneath A. hyacinthus for a further 8 weeks. The survivorship of juvenile corals underneath tables was less than half that of those on control panels on the unshaded reef crest. Furthermore, the abundance of algal turfs and CCA was sharply lower on transplanted panels. In contrast, heterotrophic organisms increased in cover, regardless of treatment. Experimental branch fragments of Acropora intermedia and Pocillopora damicornis also survived poorly following transplantation underneath A. hyacinthus, compared to adjacent, unshaded controls. We conclude that A. hyacinthus is a formidable competitor which can kill neighbouring corals by overgrowing them, and pre-empt future competition by reducing coral recruitment.     

Effects of herbivory,nutrients, and reef protection on algal proliferation and coral growth on a tropical reef

Maintaining coral reef resilience against increasing anthropogenic disturbance is critical for effective reef management. Resilience is partially determined by how processes, such as herbivory and nutrient supply, affect coral recovery versus macroalgal proliferation following disturbances. However, the relative effects of herbivory versus nutrient enrichment on algal proliferation remain debated. Here, we manipulated herbivory and nutrients on a coral-dominated reef protected from fishing, and on an adjacent macroalgal-dominated reef subject to fishing and riverine discharge, over 152 days. On both reefs, herbivore exclusion increased total and upright macroalgal cover by 9-46 times, upright macroalgal biomass by 23-84 times, and cyanobacteria cover by 0-27 times, but decreased cover of encrusting coralline algae by 46-100% and short turf algae by 14-39%. In contrast, nutrient enrichment had no effect on algal proliferation, but suppressed cover of total macroalgae (by 33-42%) and cyanobacteria (by 71% on the protected reef) when herbivores were excluded. Herbivore exclusion, but not nutrient enrichment, also increased sediment accumulation, suggesting a strong link between herbivory, macroalgal growth, and sediment retention. Growth rates of the corals Porites cylindrica and Acropora millepora were 30-35% greater on the protected versus fished reef, but nutrient and herbivore manipulations within a site did not affect coral growth. Cumulatively, these data suggest that herbivory rather than eutrophication plays the dominant role in mediating macroalgal proliferation, that macroalgae trap sediments that may further suppress herbivory and enhance macroalgal dominance, and that corals are relatively resistant to damage from some macroalgae but are significantly impacted by ambient reef condition.     

Wave exposure shapes reef community composition and recovery trajectories at a remote coral atoll

In a time of unprecedented ecological change, understanding natural biophysical relationships between reef resilience and physical drivers is of increasing importance. This study evaluates how wave forcing structures coral reef benthic community composition and recovery trajectories after the major 2015/2016 bleaching event in the remote Chagos Archipelago, Indian Ocean. Benthic cover and substrate rugosity were quantified from digital imagery at 23 fore reef sites around a small coral atoll (Salomon) in 2020 and compared to data from a similar survey in 2006 and opportunistic surveys in intermediate years. Cluster analysis and principal component analysis show strong separation of community composition between exposed (modelled wave exposure > 1000 J m⁻³) and sheltered sites (< 1000 J m⁻³) in 2020. This difference is driven by relatively high cover of Porites sp., other massive corals, encrusting corals, soft corals, rubble and dead table corals at sheltered sites versus high cover of pavement and sponges at exposed sites. Total coral cover and rugosity were also higher at sheltered sites. Adding data from previous years shows benthic community shifts from distinct exposure-driven assemblages and high live coral cover in 2006 towards bare pavement, dead Acropora tables and rubble after the 2015/2016 bleaching event. The subsequent recovery trajectories at sheltered and exposed sites are surprisingly parallel and lead communities towards their respective pre-bleaching communities. These results demonstrate that in the absence of human stressors, community patterns on fore reefs are strongly controlled by wave exposure, even during and after widespread coral loss from bleaching events.

     

Ecology of cryptic coral reef communities. III. Abundance and aggregation of encrusting organisms with particular reference to cheilostome bryozoa

The distribution and abundance of encrusting cheilostome bryozoans under foliaceous reef corals was studied at two depths at Rio Bueno, Jamaica. 46 species of cheilostomes were found, but most of these are rare. Only three species occupy, on average, > 5 % of the space available, and each of these is distributed differently. Steginoporella sp. nov. is most abundant at ? 10 m depth where it occasionally overgrows the entire edge zone (marginal 5 cm) of individual corals. Stylopoma spongites (Pallas) is most abundant at ? 21 m where it may also dominate coral edges. Abundance of both these species drops off sharply with distance from coral edges. The third species, Reptadeonella “plagiopora”, is more abundant at ? 10 m than ?21 m depth, but shows no significant variation in cover away from coral edges.Distributions of major groups of encrusting organisms and cheilostome species under corals are predictable enough for definition of spatially distinct assemblages by discriminant function analysis. Particularly distinct is the edge-zone community at ? 10 m where cheilostomes predominate. Nevertheless, variances in organism abundances are extremely high, especially for Steginoporella sp. nov. and Stylopoma spongites the great abundance of which results from relatively few, larger-than-average size colonies, rather than many smaller colonies. Edge-zone communities from replicate m² quadrats at the same depth were significantly different. The same was true within individual quadrats. Transects only 10 to 20 cm apart routinely differed as much as those 50 to 100 m apart. Edge-zone communities also varied significantly with coral size.Increase of Steginoporella sp. nov. and Stylopoma spongites abundance with increasing coral size and age suggests that larval recruitment and juvenile survival by these species is extremely slow and patchy. But once they have reached some critical size, colonies of these species may persist indefinitely by continued clonal growth onto newly grown coral undersurface as it becomes available. Communities under individual corals may develop largely independently, influenced by their unique histories (priority effects) and interactions between their particular inhabitants.     

Regional‐scale dominance of non‐framework building corals on Caribbean reefs affects carbonate production and future reef growth

Coral cover on Caribbean reefs has declined rapidly since the early 1980's. Diseases have been a major driver, decimating communities of framework building Acropora and Orbicella coral species, and reportedly leading to the emergence of novel coral assemblages often dominated by domed and plating species of the genera Agaricia, Porites and Siderastrea. These corals were not historically important Caribbean framework builders, and typically have much smaller stature and lower calcification rates, fuelling concerns over reef carbonate production and growth potential. Using data from 75 reefs from across the Caribbean we quantify: (i) the magnitude of non‐framework building coral dominance throughout the region and (ii) the contribution of these corals to contemporary carbonate production. Our data show that live coral cover averages 18.2% across our sites and coral carbonate production 4.1 kg CaCO₃ m^?2 yr^?1. However, non‐framework building coral species dominate and are major carbonate producers at a high proportion of sites; they are more abundant than Acropora and Orbicella at 73% of sites; contribute an average 68% of the carbonate produced; and produce more than half the carbonate at 79% of sites. Coral cover and carbonate production rate are strongly correlated but, as relative abundance of non‐framework building corals increases, average carbonate production rates decline. Consequently, the use of coral cover as a predictor of carbonate budget status, without species level production rate data, needs to be treated with caution. Our findings provide compelling evidence for the Caribbean‐wide dominance of non‐framework building coral taxa, and that these species are now major regional carbonate producers. However, because these species typically have lower calcification rates, continued transitions to states dominated by non‐framework building coral species will further reduce carbonate production rates below ‘predecline’ levels, resulting in shifts towards negative carbonate budget states and reducing reef growth potential.     

Storm-induced coral rubble deposition: Pleistocene records of natural reef disturbance and community response.

Shallow-water Pleistocene coral reef facies in Barbados (dominated by Acropora palmata rubble) record evidence of deposition under contrasting non-catastrophic - (fair-weather?) and storm-induced conditions. Depositional styles are interpreted on the basis of coral rubble fabrics and calcareous encruster successions. Terrace exposures on the west of the island comprise uniform (3-4 m thick) depositional sequences. Individual coral samples exhibit similarities in encruster community composition and thickness, and a transition from photophilic to sciaphilic encrusting forms. These are indicative of colonization during gradual burial in an accumulating rubble pile. By contrast, NE coast sites comprise repetitive sequences of discrete (0.4-1 m thick) depositional units. Rubble colonization within each unit is characterized by a vertical succession from thin (1-2 mm), sciaphilic encruster-dominated sequences at the base, to progressively thicker (up to 20 mm), photophilic encruster-dominated sequences at the top. These are interpreted as multiple storm deposits, with upper surfaces colonized by opportunist coral species (primarily Agaricia agaricites). In contrast to many modern hurricane-impacted reef systems, however, there is no evidence of long-term shifts in coral community composition following physical disturbance. Colony sizes of opportunist corals at the tops of storm units are consistent with growth over timescales of <10 years. These are overlain on each occasion by a new A. palmata rubble pile, indicating successful recovery over successive physical disturbance cycles.     

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.     

Ecology of cryptic coral reef communities. IV. Community development and life histories of encrusting cheilostome bryozoa

Life histories of encrusting cheilostome species from the cryptic reef community at Rio Bueno, Jamaica, were studied on fouling panels over 3 yr. Recruitment and growth were generally slow compared with those reported for temperate cheilostomes. Most species that became abundant and persisted throughout the study did so through relatively rapid growth to a large size by a few successful colonies, rather than by accumulating great numbers of small colonies. This pattern, which reflects a striking increase in maximum survival with increasing colony size, is the basis for the extremely patchy distributions of bryozoans under corals. Reproduction in these species is delayed, and only a few long-lived, large colonies ever reproduce. Only one species, Drepanophora tuberculatum (Osburn), approached the characteristic opportunistic pattern of high recruitment, small colony size, and early reproduction.Grazing and nesting activities of one yellowtail damselfish greatly affected distributions of major taxa and cheilostome species on one set of panels. Species more abundant on grazed panels are more heavily calcified and showed other protective features, compared with species more abundant elsewhere. Despite intensive grazing by the fish, overgrowth interactions occurred frequently on both sets of panels. The fish affected what organisms were present, but did not obviously reduce the amount of overgrowth.     

Linking Demographic Processes of Juvenile Corals to Benthic Recovery Trajectories in Two Common Reef Habitats

Tropical reefs are dynamic ecosystems that host diverse coral assemblages with different life-history strategies. Here, we quantified how juvenile (<50 mm) coral demographics influenced benthic coral structure in reef flat and reef slope habitats on the southern Great Barrier Reef, Australia. Permanent plots and settlement tiles were monitored every six months for three years in each habitat. These environments exhibited profound differences: the reef slope was characterised by 95% less macroalgal cover, and twice the amount of available settlement substrata and rates of coral settlement than the reef flat. Consequently, post-settlement coral survival in the reef slope was substantially higher than that of the reef flat, and resulted in a rapid increase in coral cover from 7 to 31% in 2.5 years. In contrast, coral cover on the reef flat remained low (~10%), whereas macroalgal cover increased from 23 to 45%. A positive stock-recruitment relationship was found in brooding corals in both habitats; however, brooding corals were not directly responsible for the observed changes in coral cover. Rather, the rapid increase on the reef slope resulted from high abundances of broadcast spawning Acropora recruits. Incorporating our results into transition matrix models demonstrated that most corals escape mortality once they exceed 50 mm, but for smaller corals mortality in brooders was double those of spawners (i.e. acroporids and massive corals). For corals on the reef flat, sensitivity analysis demonstrated that growth and mortality of larger juveniles (21–50 mm) highly influenced population dynamics; whereas the recruitment, growth and mortality of smaller corals (<20 mm) had the highest influence on reef slope population dynamics. Our results provide insight into the population dynamics and recovery trajectories in disparate reef habitats, and highlight the importance of acroporid recruitment in driving rapid increases in coral cover following large-scale perturbation in reef slope environments.     

Ocean acidification and calcifying reef organisms: a mesocosm investigation

A long-term (10 months) controlled experiment was conducted to test the impact of increased partial pressure of carbon dioxide (pCO₂) on common calcifying coral reef organisms. The experiment was conducted in replicate continuous flow coral reef mesocosms flushed with unfiltered sea water from Kaneohe Bay, Oahu, Hawaii. Mesocosms were located in full sunlight and experienced diurnal and seasonal fluctuations in temperature and sea water chemistry characteristic of the adjacent reef flat. Treatment mesocosms were manipulated to simulate an increase in pCO₂ to levels expected in this century [midday pCO₂ levels exceeding control mesocosms by 365 ± 130 μatm (mean ± sd)]. Acidification had a profound impact on the development and growth of crustose coralline algae (CCA) populations. During the experiment, CCA developed 25% cover in the control mesocosms and only 4% in the acidified mesocosms, representing an 86% relative reduction. Free-living associations of CCA known as rhodoliths living in the control mesocosms grew at a rate of 0.6 g buoyant weight year⁻¹ while those in the acidified experimental treatment decreased in weight at a rate of 0.9 g buoyant weight year⁻¹, representing a 250% difference. CCA play an important role in the growth and stabilization of carbonate reefs, so future changes of this magnitude could greatly impact coral reefs throughout the world. Coral calcification decreased between 15% and 20% under acidified conditions. Linear extension decreased by 14% under acidified conditions in one experiment. Larvae of the coral Pocillopora damicornis were able to recruit under the acidified conditions. In addition, there was no significant difference in production of gametes by the coral Montipora capitata after 6 months of exposure to the treatments.     

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).     

Indirect consequences of fishing: reduction of coralline algae suppresses juvenile coral abundance

Removing predatory fishes has effects that cascade through ecosystems via interactions between species and functional groups. In Kenyan reef lagoons, fishing-induced trophic cascades produce sea urchin-dominated grazing communities that greatly reduce the overall cover of crustose coralline algae (CCA). Certain species of CCA enhance coral recruitment by chemically inducing coral settlement. If sea urchin grazing reduces cover of settlement-inducing CCA, coral recruitment and hence juvenile coral abundance may also decline on fished reefs. To determine whether fishing-induced changes in CCA influence coral recruitment and abundance, we compared (1) CCA taxonomic compositions and (2) taxon-specific associations between CCA and juvenile corals under three fisheries management systems: closed, gear-restricted, and open-access. On fished reefs (gear-restricted and open-access), abundances of two species of settlement-inducing CCA, Hydrolithon reinboldii and H. onkodes, were half those on closed reefs. On both closed and fished reefs, juveniles of four common coral families (Poritidae, Pocilloporidae, Agariciidae, and Faviidae) were more abundant on Hydrolithon than on any other settlement substrate. Coral densities were positively correlated with Hydrolithon spp. cover and were significantly lower on fished than on closed reefs, suggesting that fishing indirectly reduces coral recruitment or juvenile success over large spatial scales via reduction in settlement-inducing CCA. Therefore, managing reefs for higher cover of settlement-inducing CCA may enhance coral recruitment or juvenile survival and help to maintain the ecological and structural stability of reefs.     

Coral microbialite environment in a Middle Miocene reef of Hungary

The presence of microbial crusts (microbialites) is reported here for the first time from a Middle Miocene (Badenian) coral reef in Hungary. The succession of initiation and development of the microbial crusts is described in relation to the reef architecture. The main features of the palaeoenvironment are discussed, with focus on the associated invertebrate faunas, mostly corals, molluscs, bryozoans, and crabs. We conclude that the microbial crusts developed under normal marine conditions and were a significant contributor to reef framework development, including its strengthening through calcification of the microbial organisms. Microbialites are anticipated in other Early and Middle Miocene coral reef occurrences of the Mediterranean–Paratethys realm, and to date may have simply escaped positive recognition.     

A geospatial assessment of the relationship between reef flat community calcium carbonate production and wave energy

The ability of benthic communities inhabiting coral reefs to produce calcium carbonate underpins the development of reef platforms and associated sedimentary landforms, as well as the fixation of inorganic carbon and buffering of diurnal pH fluctuations in ocean surface waters. Quantification of the relationship between reef flat community calcium carbonate production and wave energy provides an empirical basis for understanding and managing this functionally important process. This study employs geospatial techniques across the reef platform at Lizard Island, Great Barrier Reef, to (1) map the distribution and estimate the total magnitude of reef community carbonate production and (2) empirically ascertain the influence of wave energy on community carbonate production. A World-View-2 satellite image and a field data set of 364 ground referencing points are employed, along with data on physical reef characteristics (e.g. bathymetry, rugosity) to map and validate the spatial distribution of the four major community carbonate producers (live coral, carbonate sand, green calcareous macroalgae and encrusting calcified algae) across the reef platform. Carbonate production is estimated for the complete reef platform from the composition of these community components. A synoptic model of wave energy is developed using the Simulating WAves Nearshore (SWAN) two-dimensional model for the entire reef platform. The relationship between locally derived measures of carbonate production and wave energy is evaluated at both the global scale and local scale along spatial gradients of wave energy traversing the reef platform. A wave energy threshold is identified, below which carbonate production levels appear to increase with wave energy and above which mechanical forcing reduces community production. This implies an optimal set of hydrodynamic conditions characterized by wave energy levels of approximately 300 J m^?2, providing an empirical basis for management of potential changes in community carbonate production associated with climate change-driven increases in wave energy.     

Recruitment Variability of Coral Reef Sessile Communities of the Far North Great Barrier Reef

One of the key components in assessing marine sessile organism demography is determining recruitment patterns to benthic habitats. An analysis of serially deployed recruitment tiles across depth (6 and 12 m), seasons (summer and winter) and space (meters to kilometres) was used to quantify recruitment assemblage structure (abundance and percent cover) of corals, sponges, ascidians, algae and other sessile organisms from the northern sector of the Great Barrier Reef (GBR). Polychaetes were most abundant on recruitment titles, reaching almost 50% of total recruitment, yet covered <5% of each tile. In contrast, mean abundances of sponges, ascidians, algae, and bryozoans combined was generally less than 20% of total recruitment, with percentage cover ranging between 15–30% per tile. Coral recruitment was very low, with <1 recruit per tile identified. A hierarchal analysis of variation over a range of spatial and temporal scales showed significant spatio-temporal variation in recruitment patterns, but the highest variability occurred at the lowest spatial scale examined (1 m—among tiles). Temporal variability in recruitment of both numbers of taxa and percentage cover was also evident across both summer and winter. Recruitment across depth varied for some taxonomic groups like algae, sponges and ascidians, with greatest differences in summer. This study presents some of the first data on benthic recruitment within the northern GBR and provides a greater understanding of population ecology for coral reefs.