Framework Builders Research Articles

Fauna diversity in Madracis spp. coral patches in the Colombian Caribbean

Madracis spp. coral patches are the main deep–sea framework builder observed on the shelf–break scarp of the Colombian Caribbean, between 107 and 230 m depth. The Marine Protected Area, Corales de Profundidad National Natural Park, was established in 2013 to protect a site of high biodiversity associated with Madracis communities. Our research summarizes the advances in knowledge of its biodiversity as the result of four expeditions and offers insights into the state of its associated fauna. Madracis colonies occur in five areas of the park but corals thrive and build coral patches in only two of the five, both in the southwest area. Our surveys have resulted in the inventory of 337 species. Mollusca (116) dominated the fauna, followed by Bryozoa (70), Cnidaria (50), Echinodermata (39), Arthropoda (14), Annelida (13), Brachiopoda (3), and Chordata (32 fishes). Store voucher specimens at the Museo de Historia Natural Marina de Colombia–Makuriwa and metadata are available online in the SiBM database. Checklist published through GBIF (DOI: 10.15470/vqshir)

Cambrian Series 2 (Stage 4) calcimicrobial reefs in Shandong Province, North China: Calcimicrobial diversity and contribution to reef construction

Calcimicrobes together with archaeocyaths became significant in reef construction during the early Cambrian; however, purely calcimicrobial reefs have not been as well documented as archaeocyath-bearing reefs. Here we describe the age-specific features of calcimicrobial reefs of the Zhushadong Formation (Cambrian Series 2, Stage 4) at the Sunmayu and Jinhe sections in Shandong Province, North China. The calcimicrobial reefs of the Sunmayu section are constructed mainly by Epiphyton, Kordephyton, and tubiform microbes. The reefs are in some cases dominated by Amgaina, passing from a framework of Kordephyton, Epiphyton, and tubiform microbes to dendritic growth of Epiphyton, and finally to aggregations of Amgaina. Calcimicrobial reefs in the Jinhe section are likewise constructed mainly by Epiphyton, Kordephyton, and tubiform microbes, but with subordinate Tarthinia and Bija. Epiphyton and Kordephyton as well as Amgaina were thus the main framework builders in the Zhushadong calcimicrobial reefs. Tubiform microbes contributed as encrusters, enhancing the framework rigidity, whereas Tarthinia and Bija played subordinate roles as encrusters and consolidators. Interreef deposits of the Sunmayu reefs are of peloidal or ooidal grainstone; these reefs are inferred to have formed in a high-energy shoal setting. In contrast, interreef deposits of the Jinhe reefs are of peloidal and intraclastic wackestone or grainstone with bioclasts such as trilobites and hyoliths. Tubular cavities, possibly representing burrows, are common in the spaces among frameworks. These calcimicrobial reefs are interpreted to have formed in a subtidal setting, where the water energy was lower than that in the Sunmayu section. In North China, reefs of Cambrian Epoch 2 are limited, as development of the carbonate platform began only toward the end of that epoch. The reefs of the Zhushadong Formation are therefore among the earliest on the North China Platform. The calcimicrobial reefs contain various kinds of calcimicrobes, and the calcimicrobial assemblages are similar to or more diverse than those of coeval archaeocyath-bearing reefs during this period of archaeocyath decline. Calcimicrobes thus flourished at that time and contributed greatly to the construction of reefs. These purely calcimicrobial reefs provide further information on the spatial and temporal changes in calcimicrobial diversity and reef construction during the period before and after the extinction of archaeocyaths.

New insights on the Late Quaternary evolution of Abrolhos reefs, Eastern Brazilian Shelf

The Abrolhos shelf, in the eastern Brazilian margin, encompasses the largest reef province in the South Atlantic, characterised by low coral diversity and a high level of endemism. Knowledge gaps about how the Abrolhos coastal reefs evolved, during the post LGM and MIS 6/MIS 5, favoured a paradigm that is revisited in the light of new data. Here, new data from two new, long boreholes (20 and 50 m-long) are presented in order to investigate and provide new insights into the evolution of two shallow reefs on the Abrolhos Shelf during the late Pleistocene and Holocene epochs. Results show that Holocene and Pleistocene reefs grew on highly turbid waters with a significant terrigenous sediment input. Corals and CCA assemblages were identified as main framework builders of Abrolhos inner-shelf reefs since the Pleistocene. No clear shallowing upward sequence of reef builders was observed, which differs from other reef sequences all over the world. In terms of Holocene reef growth, Pedra Grande and Coroa Vermelha reefs turned on roughly coevally at different depths and with different coral assemblages. Pedra Grande reef started growing circa 6.8 kyr BP in a water depth approximately 10 m deeper than Coroa Vermelha, which started growing around 6.4 kyr BP, but Coroa Vermelha turned off at around 4 kyr BP, while Pedra Grande kept growing until around 1.2 kyr BP. This novel reef stratigraphy data provided a new insight on the evolution of the Abrolhos coastal reefs, showing that different environmental and topographic controls could have acted spatially in different ways. Coroa Vermelha reef seems to have started its growth as a result of a topographic high control. Pedra Grande reef seems to be connected to a broader submerged reef setting and started to grow in deeper water depths. The presence of three reef arcs in Abrolhos is proposed, including a submerged reef arc.

Benthic macrohabitat classification and Madracis spp. coral patch distribution in a deep-sea marine protected area of Colombia

Corales de Profundidad National Natural Park (CPNNP), at the central Colombian Caribbean margin, has an extension of 142.195 ha with depths ranging from 34 to 1,234 m. The CPNNP’s essential ecological value isMadracisspp. as potential structure-forming deep-water coral; this work represents the first footages of these unique habitats for the Colombian Caribbean. In 11 sectors, remote video surveys are conducted, based on a detailed digital elevation model. From these sectors, four cover mesophotic zones (46–169m depth), and seven cover aphotic zones (up to 354m depth). After still images’ description and interpretation, a guide was generated with nine types of macrohabitats surrounding the coral formations of the CPNNP: soft substrate (mud/sand), soft substrate/rubble/rock with solitary corals, coral and shell rubble, rock/ledges with attached fauna, rugged stones with attached fauna, hard substrate with attached fauna, sandstone with attached fauna, soft substrate with burrows, and pockmark with attached fauna. Video transect analysis confirms the occurrence ofMadracisspp., with coral patches as the main framework builder of the CPNNP. These patches comprise many clumped 50 to 80 cm high coral colonies that developed over slow slopes, with seafloor elevations between 107 and 233 m and textured soils of soft and not very compact ridges, associated with the macrohabitat sandstone with attached fauna. This information is being used for the management and monitoring of this unique protected area.

Living coralligenous as geo-historical structure built by coralline algae

The most important reef of the Mediterranean is the Coralligène (Coralligenous = C), including several types of calcareous algal-invertebrate build-ups growing in normal open marine conditions. We analyzed and compared two C samples from the Ligurian Sea developed in different environmental settings: 1) off Portofino on a rocky cliff, at a depth of about 40 m and 2) in front of Bogliasco, on a sub-horizontal substrate at a depth of 10 m. The maximum AMS radiocarbon dating provided an older age for Bogliasco (about 5 ka BP) than for Portofino (about 3.6 ka BP), and the mean accumulation rate of the Portofino build-up (about 80 µm y−1) was found to be higher than the one in Bogliasco (about 65 µm y−1). The different sides of each build-up showed a remarkable heterogeneity in the dominant cover by living organisms, and the comparison between the two build-ups highlighted an evident diversity in their taxonomic composition and structure, although crustose coralline algae (CCA) are the dominant framework builder and major autogenic ecosystem engineers at both localities, in the present as in the past millennia. Other major components of the structure are bryozoans and serpulids, and an important role is played by sediment filling. In Bogliasco, extreme climate events and major peaks of fine matrix and terrigenous grains are observed, lithologically related to the drainage basin of the Poggio creek and associated with charophyte occurrence and reduced CCA abundance. The occurrence of the rare Sporolithon ptychoides was observed both in Portofino at about 750 BCE and in Bogliasco. These Sporolithon phases are likely related to warm and humid spells punctuating the Holocene climate fluctuations in the Ligurian Sea. Because coralline algae are confirmed to be the most important habitat engineer of the Mediterranean reefs, they deserve more attention in the framework of any monitoring initiative aimed at C management and conservation.

Cheilostomatida (Bryozoa) from the Ionian Apulian coast (Italy) with the description of new species

The mesophotic zone is a relatively poorly studied area of the Mediterranean Sea, drawing great interest by the scientific community in the last years. This zone represents a connection between the shallow water and the deep-sea communities, in which photophilic framework builders (e.g. coralline red algae) are gradually replaced by heterotrophic ones, such as ahermatypic corals and the bivalve Neopycnodonte cochlear. In this habitat the framework-forming organisms produce a hard substrate with a high topographic complexity, hosting a great biodiversity of secondary structuring taxa like bryozoans. During a survey on coralligenous banks in the mesophotic zone in c. 60 m depth off Gallipoli (southern Apulia), epibiotic aggregations of N. cochlear were found on the fans of the hexacoral Savalia savaglia. In the present paper the diversity of cheilostomatid bryozoans hosted by these bivalve aggregations is described and compared with published information on similar nearby habitats. A total of 48 taxa were found, six of which are newly described: Crassimarginatella matildae sp. nov., Micropora biopesiula sp. nov., Haplopoma celeste sp. nov., Schizomavella (Schizomavella) cerranoi sp. nov., Schizomavella (Calvetomavella) biancae sp. nov., and Schizoporella adelaide sp. nov. The species richness known from the southern Apulian shelf at this depth (47 species) is hereby raised to 83 cheilostomatid bryozoans. Moreover, only 12 species are shared with the other localities studied previously, while 36 are restricted to Gallipoli, supporting the hypothesis of a high rate of exclusivity among Apulian sites in terms of species composition. The differences in faunal composition, and particularly the presence of several new species discovered at Gallipoli, show once more that our knowledge of the bryozoan fauna in certain Mediterranean habitats is still incomplete and warrants further studies. https://doi.org/urn:lsid:zoobank.org:pub:DDC82039-EF44-4169-8198-C67F60B14BA0

Reef-building corals act as long-term sink for microplastic.

The pollution of the marine environment with microplastics is pervasive. However, microplastic concentrations in the seawater are lower than the number of particles entering the oceans, suggesting that plastic particles accumulate in environmental sinks. Yet, the exact long-term sinks related to the "missing plastic" phenomenon are barely explored. Sediments in nearshore biogenic habitats are known to trap large amounts of microplastics, but also the three-dimensional structures of coral reefs might serve as unique, living long-term sinks. The main framework builders, reef-building corals, have been shown to ingest and overgrow microplastics, potentially leading to a deposition of particles in reef structures. However, little is known about the number of deposited particles and the underlying processes determining the permanent deposition in the coral skeletons. To test whether corals may act as living long-term sink for microplastic, we exposed four reef-building coral species to polyethylene microplastics (200 particlesL-1 ) in an 18-month laboratory experiment. We found microplastics in all treatment specimens, with low numbers of particles trapped in the coral tissue (up to 2 particles per cm2 ) and much higher numbers in the skeleton (up to 84 particles per cm3 ). The numbers of particles accumulated in the coral skeletons were mainly related to coral growth (i.e., skeletal growth in volume), suggesting that deposition is a regularly occurring stochastic process. We estimate that reef-building corals may remove 0.09%-2.82% of the bioavailable microplastics from tropical shallow-reef waters per year. Our study shows for the first time that microplastic particles accumulate permanently in a biological sink, helping to explain the "missing plastic" phenomenon. This highlights the importance of coral reefs for the ecological balance of the oceans and reinforces the need to protect them, not only to mitigate the effects of climate change but also to preserve their ecosystem services as long-term sink for microplastic.

Early Miocene carbonate ramp development in a warm ocean, North West Shelf, Australia

AbstractAlthough carbonate ramps are widely described from the geological record, there is still a debate on the relative influence of water temperature, trophic conditions and type of carbonate factories on their development. The ca 2400 km long Australian North West Shelf is among the largest Cenozoic carbonate provinces worldwide, and records a transition from an early Miocene ramp to a middle Miocene rimmed platform. This change is observable on publicly available seismic data, giving the opportunity to investigate environmental influences on platform evolution. This study combines macroscopic and petrographic descriptions of early Miocene strata cropping out in the Cape Range Anticline (North West Cape, southern end of the North West Shelf) and of time‐equivalent well cuttings from the adjacent, offshore Exmouth Sub‐basin. Particular emphasis is placed on the identification of larger benthic foraminifera at a broad generic level, because differing taxa have a limited range of habitable conditions that serve as environmental proxies. The results show that early Miocene strata are dominantly composed of larger benthic foraminifera with minor coralline algae in the proximal platform, grading to micropackstones in the more distal platform. A ramp margin is inferred from the lithological data on the basis of the lack of framework builders and the presence of open oceanic indicators. Facies shallow upward through individual outcrops, with a proximal to distal trend towards the north‐west. These trends along outcrops are consistent with the seismic interpretations. Identification of taxa with warm, oligotrophic water affinity suggests that the ramp was formed in an oligotrophic and warm ocean, despite the absence of coral reefs. Changes of carbonate facies with depth do not seem to be associated with changes in ramp morphology, and the latter may have been controlled by physical oceanic parameters, such as offshore currents and waves.

Microplastics as a sedimentary component in reef systems: A case study from the Java Sea

AbstractMicroplastic pollution has been reported from coral reef systems all over the tropics. Exposure to microplastics has several negative impacts on coral health, such as bleaching, tissue necrosis, or an impairment of the coral’s immune system. Despite this potential risk for reef systems, the controlling processes for microplastics dispersion and accumulation in reef sediments are still largely under‐studied. Presented here is a study of microplastics (125 µm to 5 mm) distribution in two tropic atoll reef platforms in Kepulauan Seribu, Indonesia. Sediment samples were collected in different facies zones within the reef platform. Microplastics were concentrated using density floatation and characterized by light and scanning electron microscopy. Some particles were identified as polypropylene using micro‐Fourier transform infrared spectroscopy. All recovered microplastics were classified as secondary microplastics, likely derived from marine and local sources, with fibres as the most abundant type. Microplastics are showing similar transport and accumulation behaviour as fine siliciclastic grains. The abundance of microplastic is controlled by the proximity to the source area of larger plastic debris and hydrodynamic processes. Microplastics are not only present in low energy environments but also high energy settings such as the reef crest. Processes that contribute to accumulation in reef sediments are biofouling, interlocking and the creation of compound grains. Microplastics are present in sediment close to the seafloor (0 to 3.5 cm) but also at depths between 3.5 cm and 7.0 cm. Microplastic particles from below 3.5 cm are unlikely to be remobilized under modal weather conditions in the studied equatorial reefs. Subtidal reef sediment therefore can be regarded as a permanent sink for microplastics. The study shows that microplastics in coral reef environments deserve careful consideration since microplastics pose an additional threat to corals and their ability as framework builders in reef systems.

Impacts of water quality on Acropora coral settlement: The relative importance of substrate quality and light.

Coral larval settlement patterns are influenced by a vast array of factors; however, the relative roles of individual factors are rarely tested in isolation, leading to confusion about which are most crucial for settlement. For example, direct effects of the light environment are often cited as a major factor influencing settlement patterns, yet this has not been demonstrated under environmentally realistic lighting regimes in the absence of confounding factors. Here we apply programmable multispectral lights to create realistic light spectra, while removing correlating (but not obvious) factors that are common in laboratory settlement experiments. Using two common species of Acropora - key framework builders of the Great Barrier Reef - we find little evidence that light intensity or changes in the spectral profile play a substantial role in larval settlement under most environmentally realistic settings but can under more extreme or artificial settings. We alternatively hypothesise and provide evidence that chronic light conditions and recent sediment exposures that impact benthic substrates (e.g., crustose coralline algae) have a greater impact on settlement success. Under these conditions, there was a decrease of up to 74% settlement success. Management of water quality conditions that impact the quality of benthic-settlement substrates therefore should present a priority area of focus for improving coral recruitment.

Mesophotic Ecosystems: The Link between Shallow and Deep-Sea Habitats

Mesophotic ecosystems (MEs) are characterized by the presence of light-dependent organisms, found at depths ranging from ~30 to 150 m in temperate, subtropical and tropical regions. These communities occasionally create massive reef structures with diverse but characteristic morphologies, which serve as the framework builders of those ecosystems. In many localities, MEs are physically linked with shallow and deep-sea habitats, and while taxa from both environments share this space, a unique and endemic biodiversity is also found. The main MEs studied to date are the mesophotic coral ecosystems (MCEs) and the temperate mesophotic ecosystems (TMEs), which have received increased attention during the last decade. As shallow coral reef ecosystems are among the most threatened habitats on Earth, the potential of MEs to act as refugia and contribute to the resilience of the whole ecosystem has been a subject of scrutiny. New technologies and methods have become more available to study these deeper parts of the reef ecosystems, yielding many new discoveries. However, basic gaps in knowledge remain in our scientific understanding of the global diversity of MEs, limiting our ability to recognize biogeographic patterns and to make educated decisions for the management and conservation of these ecosystems.

Microaerophilic Fe-oxidizing micro-organisms in Middle Jurassic ferruginous stromatolites and the paleoenvironmental context of their formation (Southern Carpathians, Romania).

Ferruginous stromatolites occur associated with Middle Jurassic condensed deposits in several Tethyan and peri-Tethyan areas. The studied ferruginous stromatolites occurring in the Middle Jurassic condensed deposits of Southern Carpathians (Romania) preserve morphological, geochemical, and mineralogical data that suggest microbial iron oxidation. Based on their macrofabrics and accretion patterns, we classified stromatolites: (1) Ferruginous microstromatolites associated with hardground surfaces and forming the cortex of the macro-oncoids and (2) Domical ferruginous stromatolites developed within the Ammonitico Rosso-type succession disposed above the ferruginous microstromatolites (type 1). Petrographic and scanning electron microscope (SEM) examinations reveal that different types of filamentous micro-organisms were the significant framework builders of the ferruginous stromatolitic laminae. The studied stromatolites yield a large range of δ56 Fe values, from -0.75‰ to +0.66‰ with predominantly positive values indicating the prevalence of partial ferrous iron oxidation. The lowest negative δ56 Fe values (up to -0.75‰) are present only in domical ferruginous stromatolites samples and point to initial iron mobilization where the Fe(II) was produced by dissimilatory Fe(III) reduction of ferric oxides by Fe(III)-reducing bacteria. Rare-earth elements and yttrium (REE+Y) are used to decipher the nature of the seawater during the formation of the ferruginous stromatolites. Cerium anomalies display moderate to small negative values for the ferruginous microstromatolites, indicating weakly oxygenated conditions compatible with slowly reducing environments, in contrast to the domical ferruginous stromatolites that show moderate positive Ce anomalies suggesting that they formed in deeper, anoxic-suboxic waters. The positive Eu anomalies from the studied samples suggest a diffuse hydrothermal input on the seawater during the Middle Jurassic on the sites of ferruginous stromatolite accretion. This study presents the first interpretation of REE+Y in the Middle Jurassic ferruginous stromatolites of Southern Carpathians, Romania.

Evidence for a local reef eclipse in a shallow marine carbonate environment following the regional extinction of archaeocyaths in Laurentia (Stage 4, Cambrian)

Archaeocyathan sponges were the dominant metazoan framework builders during Series 2 of the Cambrian. After their near extinction during the Toyonian stage (middle Stage 4), this important ecological role was eventually filled by robustly skeletonized lithistid sponges. However, the exact timing of ecological restructuring is not well understood and was likely not contemporaneous across different paleocontinents. For example, reefs from the Wuliuan of China appear to show rapid replacement of archaeocyaths with lithistid sponges, yet the earliest occurrence of lithistids in Laurentia is not until the early Furongian. In this study, we explore the Mule Spring Limestone of Nevada, which contains shallow water carbonate environments from the immediate aftermath of the regional archaeocyathan extinction, for signs of reef-building activity. Within this formation, we find evidence of sparse microbial-built leolites and some potentially poorly preserved metazoan organisms. However, the totality of our field observations and thin-section point counts suggest that there was no substantial reef-building activity by either microbial or metazoan organisms within our study locality. Our data suggest the occurrence of a local reef eclipse during this interval for the locality investigated. We also incorporate geochemical proxies to determine paleoredox conditions, which suggest well-oxygenated marine conditions through the period of interest. Lack of hardground substrate is proposed as the cause for this gap in the reef record. These results show that a temporary loss of framework-building activity occurred after the regional extinction of archaeocyaths and demonstrates the ecological impact of losing framework builders on a reef environment.

Red Sea corals under Artificial Light Pollution at Night (ALAN) undergo oxidative stress and photosynthetic impairment.

Coral reefs represent the most diverse marine ecosystem on the planet, yet they are undergoing an unprecedented decline due to a combination of increasing global and local stressors. Despite the wealth of research investigating these stressors, Artificial Light Pollution at Night (ALAN) or “ecological light pollution” represents an emerging threat that has received little attention in the context of coral reefs, despite the potential of disrupting the chronobiology, physiology, behavior, and other biological processes of coral reef organisms. Scleractinian corals, the framework builders of coral reefs, depend on lunar illumination cues to synchronize their biological rhythms such as behavior, reproduction and physiology. While, light pollution (POL) may mask and lead de‐synchronization of these biological rhythms process. To reveal if ALAN impacts coral physiology, we have studied two coral species, Acropora eurystoma and Pocillopora damicornis, from the Gulf of Eilat/Aqaba, Red Sea, which is undergoing urban development that has led to severe POL at night. Our two experimental design data revealed that corals exposed to ALAN face an oxidative stress condition, show lower photosynthesis performances measured by electron transport rate (ETR), as well as changes in chlorophyll and algae density parameters. Testing different lights such as Blue LED and White LED spectrum showed more extreme impact in comparison to Yellow LEDs on coral physiology. The finding of this work sheds light on the emerging threat of POL and the impacts on the biology and ecology of Scleractinian corals, and will help to formulate specific management implementations to mitigate its potentially harmful impacts.

Marine radiocarbon reservoir age of the coralline intertidal alga Lithophyllum byssoides in the Mediterranean

Abstract Coralline algae are the most significant framework builders outside the coral-reef belt. Among them, littoral rims built by the coralline rhodophyte Lithophyllum byssoides are a particularly precise archive of relative sea-level histories in the microtidal environment. Their potential has been underutilized due to the unresolved question of the size of the marine radiocarbon reservoir effect (MRE), which is needed for accurate calibration of dates obtained from marine-derived carbon samples. Because this intertidal alga is submerged during high tide and exposed to the atmosphere during low tide there are questions regarding the source of the carbon it uses and the level of MRE. Consequently, here we provide the first direct evidence regarding the L. byssoides MRE based on samples of known age from museum collections. A total of eight samples of pre-bomb L. byssoides from the Mediterranean revealed a mean reservoir age R(t) of 336 ± 47 14C yr and a ΔR value of −28 ± 41 14C yr for the carbonate fractions. The MRE values obtained from the alga revealed them to be more homogeneous and generally lower compared to the Mediterranean shell MREs for the same period. However, the mean values (mean Mediterranean shells MRE 437 ± 115 14C yr, ΔR 100 ± 99) are statistically indistinguishable as they overlap statistically at 1 sigma due to the great dispersion of mollusc shell values. In 6 out of 9 L. byssoides samples significant 14C age differences between algal carbonate and organic fractions have been observed. The organic fractions revealed higher MRE values. The δ13C of organic matter in marine macroalgae L. byssoides collected from the natural environment ranged from −13.4‰ to −18.7‰ VPDB. The δ13C values of organic samples of L. byssoides from the Mediterranean and Atlantic showed homogeneous values within the species with a mean of −15.4‰, although the alga belongs to the phylum Rhodophyta where the variability is the highest. These δ13C values do not provide unequivocal indications on the source of the inorganic carbon (Ci) used by the alga, but slightly lower reservoir ages (R(t)) of the L. byssoides carbonate fractions in relation to Mediterranean mean shells MRE could point to minor partial uptake of CO2 from the atmosphere during emersion (up to 20%). This could not be statistically confirmed. Homogeneous values of L. byssoides δ13C in the Mediterranean might be related to sharp environmental conditions in the intertidal zone in which the species grew.

Depauperate skeletonized reef-dwelling fauna of the early Cambrian: Insights from archaeocyathan reef ecosystems of western Mongolia

Reef-dwelling organisms in the early Cambrian include typical members of the Cambrian Fauna such as trilobites, chancelloriids, and hyoliths. However, in comparison to later Ordovician reefs, Cambrian reefs often do not appear as diverse. Here, we investigate early Cambrian microbial-archaeocyathan reefs of the Salaagol Formation in the Zavkhan Basin of Mongolia as well as perform a literature survey of 40 early Paleozoic reefs to understand the timing of reef biodiversity. By using point count analysis, we can quantify the carbonate contribution of framework builders and reef-dwelling organisms in these ecosystems. We find that Mongolian reefs contained several genera of framework building archaeocyaths (5.0% by volume) and associated microbial forms (5.4%), but are unevenly distributed through the formation. Archaeocyathan contribution increases are potentially concurrent with negative shifts in carbon isotopic composition, similar to other localities in Gondwana. However, reef-dwelling biota was minimal (0.3%) throughout the Salaagol Formation and did not correlate to changes in framework builders or geochemical proxies such as U, V, and carbon isotopes. A literature survey of Ediacaran through Ordovician reefs suggests that there is a trend of increasing reef-dweller abundance, functional richness, and skeletonization through time. The changes in abundance (17.9% to 28.8% considered “frequent”) and functional richness (3.7 to 6.0 functional groups) could be due to an increase in productivity in the oceans during the Cambrian, thereby expanding the base of the food web during the lead up to the Ordovician Radiation. The trend of increasing skeletonization could be due to the evolution of more robust skeletons among reef dwellers in order to protect themselves from increased predation in reef environments. These trends suggest that, at least during the early Paleozoic, increases in biological diversity are not necessarily concurrent with the establishment of a framework reef.

An integrated morpho-molecular approach to delineate species boundaries of Millepora from the Red Sea

Fire corals of the hydrocoral genus Millepora provide an important ecological role as framework builders of coral reefs in the Indo-Pacific and the Atlantic. Recent works have demonstrated the incongruence between molecular data and the traditional taxonomy of Millepora spp. based on overall skeleton growth form and pores. In an attempt to establish a reliable and standardized approach for defining species boundaries in Millepora, we focused on those from the Red Sea. In this region, three species are currently recognized: the fan-shaped branching M. dichotoma, the blade-like M. platyphylla, and the massive/encrusting M. exaesa. A total of 412 colonies were collected from six localities. Two mitochondrial marker genes (COI and 16S rDNA) were sequenced to obtain phylogeny reconstructions and haplotype networks. Eight morphological traits of pores and the nematocysts of both polyp and eumedusoid stages were measured to determine whether significant morphological differences occur among the three species. Both markers clearly resolved M. dichotoma, M. platyphylla, and M. exaesa as distinct, monophyletic lineages in the Red Sea. Nevertheless, they also revealed deep genetic breaks with Southwestern Indian Ocean populations of the three species. In the Red Sea, the three species were further distinguished based on their pore and nematocyst features. A discriminant analysis revealed dactylopore density, number of dactylopores per gastropore, dactylopore distance, and gastropore diameter as the most informative discriminative characters. The heteronemes, the large and small stenoteles of polyps, and the distribution of mastigophores of eumedusoids also showed significant interspecific differences. An integrated morpho-molecular approach proved to be decisive in defining species boundaries of Millepora supported by a combination of pore and nematocyst characters, which may be phylogenetically informative.

Microbialites in Last Glacial Maximum and deglacial reefs of the Great Barrier Reef (IODP Expedition 325, NE Australia)

Microbialites are volumetrically abundant components in Last Glacial Maximum and deglacial reefs in the Australian Great Barrier Reef sampled by IODP Expedition 325 in 34 holes from 17 sites (M0030–M0058), along four transects on the shelf edge. Detailed radiometric datings show that four distinct reef phases developed between 28and 10 ka, displaying offlapping and then backstepping patterns. The reef boundstone facies include coralgal, coralgal-microbialite and microbialite boundstone. The microbialite consists of combinations of micrite/microspar, bioclasts, siliciclastic grains (up to 14.5%), fenestrae and encrusting epibionts. The micrite/microspar is high-magnesian calcite commonly irregularly clotted, fenestral and peloidal. Mesoscale microbialite fabrics include laminated, structureless, digitate, intraskeletal and boring-filling, and coatings on debris. Intraskeletal and boring-filling is the first fabric to develop in skeletal voids and borings. It is usually followed by structureless and laminated microbialite, locally overlain by digitate fabric. Microbialite-coated debris can occur at any stage in this succession, including in bioclastic accumulations where the scarce in situ framework builders are mainly encrusting corals. Lipid biomarkers of intermediate to high specificity for sulfate-reducing bacteria, together with δ13C values of these lipids, indicate that microbialite formation was favored by sulfate-reducing bacteria in anoxic microenvironments, probably under high nutrient levels. The microbialite in fore-reef deposits accumulated in the photic zone in water depths of a few to several tens of meters, within small spaces generated by large bioclasts and encrusting corals in the topmost centimeters of the sediment. These crusts that formed on the illuminated surface constitute a previously unrecognized style of microbialite formation in Quaternary reefs. As with the cryptic crusts described from other reef locations, its greatest development occurred during the Last Glacial Maximum and early deglaciation. Microbial carbonate formation during this interval may reflect elevated seawater carbonate saturation corresponding with relatively low levels of atmospheric CO2.

Bryozoans are Major Modern Builders of South Atlantic Oddly Shaped Reefs

In major modern reef regions, either in the Indo-Pacific or the Caribbean, scleractinian corals are described as the main reef framework builders, often associated with crustose coralline algae. We used underwater cores to investigate Late Holocene reef growth and characterise the main framework builders in the Abrolhos Shelf, the largest and richest modern tropical reef complex in the South Western Atlantic, a scientifically underexplored reef province. Rather than a typical coralgal reef, our results show a complex framework building system dominated by bryozoans. Bryozoans were major components in all cores and age intervals (2,000 yrs BP), accounting for up to 44% of the reef framework, while crustose coralline algae and coral accounted for less than 28 and 23%, respectively. Reef accretion rates varied from 2.7 to 0.9 mm yr−1, which are similar to typical coralgal reefs. Bryozoan functional groups encompassed 20 taxa and Celleporaria atlantica (Busk, 1884) dominated the framework at all cores. While the prevalent mesotrophic conditions may have driven suspension-feeders’ dominance over photoautotrophs and mixotrophs, we propose that a combination of historical factors with the low storm-disturbance regime of the tropical South Atlantic also contributed to the region’s low diversity, and underlies the unique mushroom shape of the Abrolhos pinnacles.

Using ezRAD to reconstruct the complete mitochondrial genome of Porites fontanesii (Cnidaria: Scleractinia)

Corals in the genus Porites are among the major framework builders of reef structures worldwide, yet the genus has been challenging to study due to a lack of informative molecular markers. Here, we used ezRAD sequencing to reconstruct the complete mitochondrial genome of Porites fontanesii (GenBank accession number MG754069), a widespread coral species endemic to the Red Sea and Gulf of Aden. The gene arrangement of P. fontanesii did not differ from other Scleractinia and consisted of 18,658 bp, organized in 13 protein-coding genes, 2 rRNA genes, and 2 tRNA genes. This mitochondrial genome contributes essential data to work towards a better understanding of evolutionary relationships within Porites.