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•Multi-scale µCT and SEM analysis used to characterize biogenic calcareous nodules.•µCT and machine learning based image analysis coupled to compute volume fractions.•Taxa-specific ...volumetric quantification obtained for biogenic carbonate nodule.•CCA and Encrusting Foraminifers are key contributors to Red Sea carbonate budget.
Biogenic carbonate structures such as rhodoliths and foraminiferal-algal nodules are a significant part of marine carbonate production and are being increasingly used as paleoenvironmental indicators for predictive modeling of the global carbon cycle and ocean acidification research. However, traditional methods to characterize and quantify the carbonate production of biogenic nodules are typically limited to two-dimensional analysis using optical and electron microscopy. While micro-computed tomography (µCT) is an excellent tool for 3D analysis of inner structures of geomaterials, the trade-off between sample size and image resolution is often a limiting factor. In this study, we address these challenges by using a novel multi-scale µCT image analysis methodology combined with electron microscopy, to visualize and quantify the carbonate volumes in a biogenic calcareous nodule. We applied our methodology to a foraminiferal-algal nodule collected from the Red Sea along the coast of NEOM, Saudi Arabia. Integrated µCT and SEM image analyses revealed the main biogenic carbonate components of this nodule to be encrusting foraminifera (EF) and crustose coralline algae (CCA). We developed a multi-scale µCT analysis approach for this study, involving a hybrid thresholding and machine-learning based image segmentation. We utilized a high resolution µCT scan from the sample as a ground-truth to improve the segmentation of the lower resolution full volume µCT scan which provided reliable volumetric quantification of the EF and CCA layers. Together, the EF and CCA layers contribute to approximately 65.5 % of the studied FAN volume, corresponding to 69.01 cm3 and 73.32 cm3 respectively, and the rest is comprised of sediment infill, voids and other minor components. Moreover, volumetric quantification results in conjunction with CT density values, indicate that the CCA layers are associated with the highest amount of carbonate production within this foraminiferal-algal nodule. The methodology developed for this study is suitable for analyzing biogenic carbonate structures for a wide array of applications including quantification of carbonate production and studying the impact of ocean acidification on skeletal structures of marine calcifying organisms. In particular, the hybrid µCT image analysis we adopted in this study proved to be advantageous for the analysis of biogenic structures in which the textures and components of the internal layers are distinctly visible despite having an overlap in the range of CT density values.
A study investigated multispecies aggregations of mushroom corals in the Gambier Islands, French Polynesia The species compositions of juveniles and adult mushroom corals indicate that success of ...sexual reproduction in the assemblages is not necessarily species-dependent and that any effect of interspecific competition by overtopping is not apparent.
Recent investigations have shown the potential of red coralline algae as paleoclimatic archive. A previously unexplored subfamily of coralline algae, the Lithophylloideae, was investigated from the ...Gulf of Aden (Balhaf, Yemen). Seasonal changes in Mg/Ca, Li/Ca and Ba/Ca composition of Lithophyllum kotschyanum f. affine were investigated by Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). For the first time in coralline algae, the Li/Ca composition was analyzed and showed a highly significant and positive correlation with Mg/Ca and SST. Monthly algal Mg/Ca and Li/Ca variations indicate a positive correlation with sea surface temperature (SST), and sea surface salinity (SSS), although low growth rates decrease the resolution of the algal record. Albeit no or weak positive correlation between monthly algal Ba/Ca and local SST was found, fluctuations in Ba/Ca suggest the seasonal influence of nutrient-rich deep waters introduced by upwelling, and record an increase of sedimentation at the sampling site likely due to an intensified land use in the area. The Mg/Ca age model shows an average algal extension rate of 1.15mmyr−1, and reveals multiple intra-annual banding (previously unreported in the genus Lithophyllum) together with carposporangia formation in late February-early March, when temperature begins to increase. The concentration of MgCO3 in the thallus of L. kotschyanum f. affine is 20mol% (1SE), confirming that within the genus, the species sampled in warmer regions contain higher mol% MgCO3. The concentrations of LiCO3 and BaCO3 are 8μmol% (0.7SE) and 0.5μmol% (0.03SE), respectively. Despite the limitations from low-growth rate and species-specific vital effect, coralline algae confirm their utility in climate and oceanographic reconstruction.
A combined morphological and genetic study of the coral genus
Stylophora
investigated species boundaries in the Gulf of Aden, Yemen. Two mitochondrial regions, including the hypervariable IGS9 spacer ...and the control region, and a fragment of rDNA were used for phylogenetic analysis. Results were compared by multivariate analysis on the basis of branch morphology and corallite morphometry. Two species were clearly discriminated by both approaches. The first species was characterised by small corallites and a low morphological variability and was ascribed to a new geographical record of
Stylophora madagascarensis
on the basis of its phylogenetic distinction and its morphological similarity to the type material. The second species was characterised by larger corallite size and greater morphological variability and was ascribed to
Stylophora pistillata
. The analysis was extended to the intrageneric level for other
S.
pistillata
populations from the Red Sea and the Pacific Ocean. Strong internal divergence was evident in the genus
St
y
lophora
.
S. pistillata
populations were split into two highly divergent Red Sea/Gulf of Aden and western Pacific lineages with significant morphological overlap, which suggests they represent two distinct cryptic species. The combined use of morphological and molecular approaches, so far proved to be a powerful tool for the re-delineation of species boundaries in corals, provided novel evidence of cryptic divergence in this group of marine metazoans.
Coral communities in South Yemen, are dominated by large Porites colonies accounting for up to 47% of the total benthic cover and forming a high three-dimensional framework. A distinct orange-reddish ...band spreading over approximately 50% of the Porites lutea colonies was recently observed (Fig. 1a). As the band progressed over the coral it faded behind leaving the dead coral skeleton for other organisms to colonise (Fig. 1a). Although spreading like a coral disease, the band was actually an infestation of a sponge belonging to the genus Clathria (Microciona) forming encrustations less than 1 mm thick. The subsurface canals of the aquiferous system meandering from oscules are visible in Fig. 1b. Clathria (Microciona) insinuates within the first 12 mm of the coral skeleton (Fig. 1c) filling corallites (Fig. 1d) and leaving spicules (Fig. 1e). No signs of bioerosion were visible. Toxic substances production could explain the successful overgrowth of the coral. Coral tissue destruction was rapid; preliminary results indicate it grows at an average rate of 1 cm month1. Up to now Terpios hoshinota has been reported to threaten Pacific corals especially in polluted and stressed areas (Plucer-Rosario 1987; Rutzler and Muzik 1993) and Mycale grandis rapidly overgrows corals in Hawaii (Coles and Bolick 2007). Clathria (Microciona) sp., however, differs from these sponges in presenting an unusual growth strategy leaving the dead coral skeleton behind and being strongly species-specific for Porites lutea.
According to current experimental evidence, coral reefs could disappear within the century if CO.sub.2 emissions remain unabated. However, recent discoveries of diverse and high cover reefs that ...already live under extreme conditions suggest that some corals might thrive well under hot, high-pCO.sub.2, and deoxygenated seawater. Volcanic CO.sub.2 vents, semi-enclosed lagoons, and mangrove estuaries are unique study sites where one or more ecologically relevant parameters for life in the oceans are close to or even worse than currently projected for the year 2100. Although they do not perfectly mimic future conditions, these natural laboratories offer unique opportunities to explore the mechanisms that reef species could use to keep pace with climate change. To achieve this, it is essential to characterize their environment as a whole and accurately consider all possible environmental factors that may differ from what is expected in the future, possibly altering the ecosystem response.
We studied the sclerobiont community associated with organogenic and lithic cobbles from soft bottoms in the Khao Lak coastal area (Andaman Sea) that was damaged by the 2004 tsunami. The 15 cobbles ...examined originate from grab and hand sampling carried out in the years 2006 and 2007 in the depth range of 4.6–15.2 m. A rich endo- and epibenthos was identified, mainly consisting of algae, foraminifers, sponges, cnidarians, polychaetes, bryozoans and bivalves. Associations on each examined cobble show similarities in composition and structure being characterized by a few dominant groups. Differences were noted in the degree and pattern of colonization, distinguishing for each cobble an upward and a downward side at the time of sampling. The mean total coverage is 15.09% being higher on the upper sides (17.4%) compared to the lower sides (12.8%). Calcareous algae, bivalves and sponges prevail on upper sides, while bryozoans prevail on lower sides. The sclerobionts distribution allowed to infer the orientation of cobbles on the seafloor during colonization. Major colonization values, exceeding 30% coverage, were observed on organogenic cobbles located in the proximity of reefs or collected from below 12 m of water depth. Conversely, cobbles from the shallowest stations result poorly colonized, independently of their composition. The water turbidity and wave motion as a possible cause of the observed distributions were discussed. The Khao Lak cobble community seems to be largely unaffected by the tsunami event, as suggested by the estimated biodiversity, abundance and coverage of sclerobionts.
Specimen collection: An essential tool Rocha, L. A.; Aleixo, A.; Allen, G. ...
Science (American Association for the Advancement of Science),
05/2014, Letnik:
344, Številka:
6186
Journal Article
Coral communities were investigated in the northwestern Gulf of Aden, Yemen, for their composition, structure, and bioconstruction potential. Although no true reef was encountered, high cover coral ...carpets were found where hard substrate was available. Seven different types of coral communities were differentiated, and both non-framework and framework coral communities were found. Monotypy or oligotypy seem to be consistent characteristics of framework-building coral communities in the study area. Apart from substrate availability, proximity to the upwelling area and exposure were found to be the most important environmental factors influencing coral communities' structure, composition, and bioconstruction potential.
The scleractinian species Psammocora explanulata and Coscinaraea wellsi were originally classified in the family Siderastreidae, but in a recent morpho-molecular study it appeared that they are more ...closely related to each other and to the Fungiidae than to any siderastreid taxon. A subsequent morpho-molecular study of the Fungiidae provided new insights regarding the phylogenetic relationships within that family. In the present study existing molecular data sets of both families were analyzed jointly with those of new specimens and sequences of P. explanulata and C. wellsi. The results indicate that both species actually belong to the Cycloseris clade within the family Fungiidae. A reappraisal of their morphologic characters based on museum specimens and recently collected material substantiate the molecular results. Consequently, they are renamed Cycloseris explanulata and C. wellsi. They are polystomatous and encrusting like C. mokai, another species recently added to the genus, whereas all Cycloseris species were initially thought to be monostomatous and free-living. In the light of the new findings, the taxonomy and distribution data of C. explanulata and C. wellsi have been updated and revised. Finally, the ecological implications of the evolutionary history of the three encrusting polystomatous Cycloseris species and their free-living monostomatous congeners are discussed.
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