Small Corallites Research Articles

Responses of urban reef corals during the 2016 mass bleaching event

Predicting the bleaching responses of corals is crucial in light of frequent heat stress events to manage further losses of biodiversity and ecosystem functioning, especially for reefs impacted by urbanisation. We examined if the coral cover and community at various Singapore sites changed during the 2016 global coral bleaching event. Bleaching prevalence varied widely among sites in June 2016, and was best explained by site and coral species. While some sites were minimally impacted, others registered significant decreases in coral cover and community changes persisting till March 2017, when normal colouration was mostly regained by corals. Bleaching susceptibility was associated with larger corallites in hermaphrodites and smaller corallites in gonochores (probably due to the cost of maintaining dual sexual functions in hermaphrodites), and with increasing proximity between polyps (likely because thermal damage would be less contained among polyps with greater physiological integration). However, bleaching resilience—the capacity to regain baseline pigmentation—was poorly explained by the traits studied. Our findings suggest that the interplay between local conditions and species composition strongly affects bleaching outcomes on urbanised reefs, and underscore the utility of coral traits for predicting bleaching responses to help in formulating appropriate management strategies.

Cionodendron and related lithostrotionid genera from the Mississippian of eastern Australia: systematics, stratigraphy and evolution

Denayer, J. & Webb, G.E., 26.2.2015. Cionodendron and related lithostrotionid genera from the Mississippian of eastern Australia: systematics, stratigraphy and evolution. Alcheringa 39, xxx–xxx. ISSN 0311-5518.The Mississippian colonial rugose corals of eastern Australia are taxonomically reviewed and assigned to formal genera. Their homeomorphy with the Eurasian genera Siphonodendron and Lithostrotion but also Heterostrotion resulted from parallel evolution within the Lithostrotionidae. Fasciculate species are reassigned to Cionodendron, as they share a robust columella, septotheca and two series of tabellae. Based on common characters, three species groups are recognized: the C. columen Group (characterized by the occurrence of parricidal and non-parricidal increase), the C. hallense Group (development of second-order lonsdaleoid dissepiments) and the C. arundineum Group (lacking the previous characters). Fourteen species are recognized, one being new (C. smithi sp. nov.) and two documented for the first time in the area. The oldest species are late Tournaisian in age, but the genus is most diverse in the middle–late Visean. Several morphological lineages are recognized within the three groups. The massive species are classified in the newly erected genus Australastraea that likely evolved from one of the early species of Cionodendron in the early Visean. Eleven species were identified, two being newly described (A. arcifera, sp. nov., A. carinata sp. nov.) and two others documented for the first time. Australastraea is characterized by a septotheca that is commonly discontinuous, conferring a pseudo-cerioid or astreoid habit. Two morphological groups are identified: the A. wilkinsoni Group (small corallites with simple narrow dissepimentarium) and the A. columnare Group (large corallites with complex dissepimentarium). The small fasciculate species previously referred to Lithostrotion williamsi are here reassigned to the new genus Pickettodendron, which differs from Cionodendron by the lack of minor septa and presence of a complete tabularium but is, nevertheless, relatively closely related to that genus. Pickettodendron is represented by three species, one being new (P. nudum sp. nov.), and is restricted to the early (–‘middle’) Tournaisian. A polyphyletic origin of the Cionodendroninae is considered, with Cionodendron and Australastraea originated in a first species of Amygdalophyllum and Pickettodendron originated in a second one. The biostratigraphic value of the Cionodendroninae is currently limited owing to the poor stratigraphic coverage of appropriate facies but correlations were made possible by the identification of A. columellaris and C. consanguineum in the early Visean of New South Wales and Queensland, and A. columnare and A. sp. in the middle–late Visean of both states. The Cionodendroninae assemblages of eastern Australia are strongly endemic and possibly represent one of the scarce remains of the Panthalassa Province.Julien Denayer [julien.denayer@ulg.ac.be], Evolution and Diversity Dynamics Lab, Geology Department, University of Liège, B18, Allée du Six-Août, Sart Tilman, B-4000 Liège, Belgium; Gregory E. Webb [g.webb@uq.edu.au], Integrated Palaeoenvironmental Research Group, School of Earth Sciences, University of Queensland, QLD 4072, St-Lucia, Australia.

An identification guide to some major Quaternary fossil reef‐building coral genera (Acropora, Isopora, Montipora, and Porites)

AbstractFossil coral identification is essential for paleoenvironment and sea level reconstructions and in paleoecological and evolutionary studies. It follows the taxonomy of their modern analogues and therefore is based on the external skeleton macromorphology. However, for geologists examining outcrops or drill cores, identification largely relies on cross sections. The coral surface is usually obscured by encrusters or by sediments, or because corals are broken or eroded. It is therefore important to understand the relationship between the internal structure of corals and their surface morphology. We provide a comprehensive description of the internal structure of four common coral genera (Acropora, Isopora, Montipora, and Porites). This identification guide is addressed to reef geologists who wish to identify Quaternary reef corals at the generic level based on cross sections. The massive basal part of Acropora is composed of an interbranch space filled with a highly regular mesh‐like network of skeletal elements parallel and perpendicular to growth direction. Corallites have conspicuous dissepiments with a ladder‐like appearance in longitudinal section. Corallites of Isopora are structurally similar but they do not show the same differentiation into axial and radial corallites. Corallites are generally sinuous and the coenosteum is less regular. Montipora has smaller corallites which appear as tubes lined with spiny septa. The coenosteum is characterized by long rod‐like skeletal elements parallel to growth direction projecting upward at the colony surface to form spinules or larger ornementations. These vertical rods are connected laterally by short bar‐like skeletal elements. In Porites, the size of corallites is similar to Montipora but they are juxtaposed and completely filled with skeletal elements. Longitudinal cross sections display a dense network of corallites' skeletal components parallel and perpendicular to growth direction. This new taxonomic guide provides a useful reference material for those who attempt to identify reef‐building corals in the fossil record.

Euphyllia baliensis sp. nov. (Cnidaria: Anthozoa: Scleractinia: Euphylliidae): a new species of reef coral from Indonesia

Euphyllia baliensis sp. nov. (Hexacorallia: Scleractinia: Euphylliidae) is described from 10 specimens from Bali, Indone-sia. This species forms phaceloid colonies, and is distinguished morphologically from others in its genus by its compara-tively very small corallites (averaging 3 mm diameter) and much shorter, thinner, lightly calcified branches. It also exhibitsan unusual pattern for Hexacorallia in having four or eight primary and secondary septa. Living corals typically havefleshy polyps extended during the day. Tentacles are ‘anchor’, ‘kidney’ or ‘hammer’ shaped at their tips, occasionally withadditional smaller bulbous protuberances, the latter resembling ‘mittens’ or ‘gloves’. Tentacles are dull to dark reddish-brown with lime green bases and cream tips, becoming bluish on retraction. Type specimens were collected from 27-37 m depth off the central eastern coast of Bali, Indonesia. To date the species has not been reported from any other locality.

Extreme morphological plasticity enables a free mode of life in Favia gravida at Ascension Island (South Atlantic)

Samples of free-living corals of Favia gravida (Scleractinia: Faviidae) have been studied. They were collected from an intertidal rock pool on Ascension Island, southern Atlantic Ocean. They consist of phaceloid clusters of corallites that appear to be able to easily break apart from each other by the formation of slits inbetween them, which indicates the occurrence of asexual reproduction by fragmentation. The base of the fragments is usually tapering or conical and covered by an epitheca. Small corallites on the base of some specimens suggest that the corals also reproduce by budding. By not depending on a solid substratum for reproduction, the corals appear to be utterly adapted to a free mode of life. These traits have not been reported before from Favia, which normally consists of massive corals. The variable shape of the corals at hand indicate that they have adopted a plastic free-living growth form that appears to be confined to a rock pool habitat.

Comparison of morphological and genetic analyses reveals cryptic divergence and morphological plasticity in Stylophora (Cnidaria, Scleractinia)

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 Stylophora. 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.

Relating coral species traits to environmental conditions in the Jakarta Bay/Pulau Seribu reef system, Indonesia

A key question in ecology is how biological traits of species determine their locations within an ecosystem. Identifying associations between species traits and environmental variables can help us to understand the causes of disturbance and predict whether species with given traits will persist under changing environmental conditions. To this end corals and environmental variables were sampled in 20 patch reefs of Pulau Seribu, located to the northwest of Jakarta, Indonesia. RLQ analysis, a multivariate ordination approach was subsequently used to relate species traits (colony shape, colony form, corallite size, reproductive mode and adaptive strategy) to environmental variables (e.g., heavy metal concentration in seawater and sediment, salinity, dissolved oxygen, and the cover of sand, dead coral, algae, sponges and soft corals). Using RLQ analysis, we identified environmental gradients associated with significant variation in species traits. Stress tolerant species with a massive morphology, meandroid shape and large corallites were associated with sites with a high abundance of algae and a relatively high concentration of potentially toxic heavy metals in seawater including Cu and Cd, whereas ruderal species and species with a branching morphology and very small corallites were linked to midshore sites. Competitively dominant species with a laminar or free-living morphology, phaceloid shape, very large corallites and brooding reproductive mode were linked to offshore sites with abundant Ca and Sr in the sediment and a high cover of Halimeda algae and sponges. Results of this study indicate that disturbance has differentially affected the marine environment of the Pulau Seribu system, which in turn interacts with coral species traits to determine local species composition.

Psammocora albopicta sp. nov., a new species of Scleractinian Coral from the Indo-West Pacific (Scleractinia; Siderastreidae)

A new scleractinian coral species, Psammocora albopicta, is described. The species forms encrusting colonies which can attain large sizes and has very small corallites with a styliform columella. Calice and columella diameter, colline shape and corallite density on the skeleton surface are the morphological characters that separate the species from the other species in the genus. A high degree of variation in septa shape and ornamentation, as well as collines development can be found within the same specimen. Living colonies are dark brown to dark green and present white patterns on all, or part, of the surface. Type material was collected in the Arabian Gulf, additional specimens were collected in the Gulf of Aden, and the study of museum collections allows extension of the species distribution to the western Indo-Pacific.

Reef development on a deepening platform: two Early Cretaceous coralgal patch reefs (Catí, Llàcova Formation, eastern Spain) compared

Two coralgal patch reefs of the Hauterivian Llàcova Formation (Maestrat Basin, eastern Spain), exposed at two consecutive stratigraphic levels within a single section, have been studied to document taxonomic implications of a changing environment. These two reefal palaeocommunities differ substantially in coral taxonomic composition, microbialite formation pattern and in abundance and composition of encrusters and bioeroders. Of a total of 14 coral species, just one ( Stylina parvistella) occurs in both reefs, yet is abundant in the (lower) reef A and rare, occurring near the reef base, in the reef B assemblage. Reef A is dominated by a phototrophic fauna and coral species with small corallites and imperforate septa (a stylinid-thamnasteriid-heterocoeniid-actinastreid association), along with an encruster association dominated by Bacinella and Lithocodium. Reef B is characterised by a balanced phototrophic-heterotrophic fauna that gradually passes into a heterotrophic-dominated assemblage. During this latest growth stage, microsolenid corals dominated the assemblage. The encruster fauna is characterised by sponges, polychaetes and bryozoans. Moderate deepening during a transgressive systems tract (TST) depositional sequence and elevated nutrient supply are interpreted to represent the driving environmental parameters that caused faunal compositions to differ between these two reefal palaeocommunities. Nine coral taxa, previously known only from younger (Barremian–Cenomanian) strata, have been identified, namely Dimorphocoenia? rudis, Eocomoseris raueni, Eocomoseris sp., Holocoenia jaccardi, Latusastrea irregularis, Mesomorpha sp., Microsolena kugleri, Polyphylloseris mammillata and Polyphylloseris sp. This observation emphasises the importance of the Hauterivian Stage as a period of evolutionary transition in Late Jurassic–Cretaceous coral faunas.

Corallite size and spacing as an aspect of niche‐partitioning in tabulate corals of Silurian reefs, Racine Formation, North America

Tabulate corals are common in reefs of the Silurian (Wenlockian) Racine Formation in Wisconsin and Illinois, North America. Variation in size and spacing of corallites in this fauna represents an aspect of niche-partitioning that is probably related to feeding. Corallite morphospace, represented by a plot of corallite diameter versus number of corallites per square cm, is characteristically partitioned among favositines, alveolitines, halysitines, syringoporids, and heliolitines, usually with minimal overlap between these major taxonomic groups. Within all groups except alveolitines, morphospace occupied by each major taxon is partitioned further between forms with small corallites and forms with larger corallites. This is probably related to differences in feeding, with ­larger corallite forms specializing in tentacular capture of larger prey, and smaller ­corallite forms specializing in smaller prey involving capture by cilia-directed sheets of mucus as well as by tentacles. Feeding-based differences among tabulates augmented niche-partitioning effected by colony form and relation to substrate. Cerioid, cateniform, coenenchymal, and fasciculate colony types in the Racine fauna were primarily adapted to a soft substrate. Ragged edges of colonies indicate growth during episodic sedimentation, and colonies were partially buried during life. Most tabulates are ­scattered through wackestone and packstone and were not major contributors to reef growth.

A new tetradiid coral from the Late Ordovician of Manitoba

Tetradiids are common Ordovician fossils in many parts of the world. Their occurrence in the western interior of North America has been noted, but they have never previously been described from this region. Rhabdotetradium garsonense n.sp. occurs in the Selkirk Member of the Red River Formation at Garson, Manitoba (Late Ordovician, Maysvillian). This species is characterized by small corallites with diameters commonly 0.6–1.1 mm; in transverse sections these are separated from one another or occur in clumps or chains. The variability of corallite arrangement within single coralla of this species illustrates the difficulty of discriminating tetradiid genera. The diagnosis of Rhabdotetradium is revised to more clearly delineate the boundary between it and Paratetradium, which has corallites arranged contiguously in elongate chains.

Early Middle Ordovician Corals from Western Utah

Two species from western Utah are among the oldest known corals from North America. The older of the two, Lichenaria simplex (?) (Bassler) is cerioid with small corallites that lack both septae and, tabulae. It is described from two small specimens from the Lehman Formation of the Ibex area where it occurs in the Whiterockian Pseudoolenoides acicauda trilobite zone (Zone N). The younger species, Eofletcheria utahia n. sp. ranges from cerioid and phaceloid to dendroid, lacks septae, but has well defined complete tabulae. It seems likely that E. utahia has been identified in faunal listings from western U.S. Middle Ordovician occurrences both as Lichenaria and as Eofletcheria depending on the portion of the colony that was examined. Eofletcheria utahia is the most common fossil in the Crystal Peak Dolomite in western Utah. It occurs there with the brachiopods Kirkina millardensis Salmon and Orthambonites perplexus Ross in Zone 0 of Hintze. Conodonts from zone o indicate that it is Chazyan

Correlation of Density Banding in Reef Coral Skeletons With Environmental Parameters: The Basis for Interpretation of Chronological Records Preserved in the Coralla of Corals

Many species of scleractinian reef corals deposit aragonite skeletons with cyclic bands of higher and lower density whose periodicity is annual. As these growth bands are frequently preserved in fossil corals, attention has been focused on their possible use as environmental indicators in as much as density variations may reflect changes in water temperature and/or light intensity. Relationships between skeletal growth banding and environmental parameters have been investigated by X-radiographic examination of 1488 specimens of modern reef corals representing 31 reef localities widely distributed over the Indo-Pacific and Caribbean regions. Average monthly seawater temperature and solar radiation data are available for each locality, and the date of collection is known for each sample. Of the 47 genera and subgenera included in the study, density variations were most pronounced in skeletons of Astreopora, Coscinarea, Cyphastrea, Favia (especially species with small corallites such as F. stelligera), Goniastrea, Hydnophora (massive forms only, e.g. M. microconos), Leptoria, Montastrea (especially M. annularis, with small corallites), Pavona, Polyastra, and Plesiastrea. Less useful are Diploastrea, Diploria, and Favites (which tend to have large corallite diameters), and Goniopora, Alveopora, Porites, Siderastrea, and Stephanaria (which frequently exhibit numerous secondary density variations within the annual cycle). Despite considerable variability among different individual corals from the same population, the average thickness of the skeletal growth bands is positively correlated with mean annual water temperature. By comparing characteristics of the outermost growth increment and the date of collection with monthly records of water temperature and solar radiation, it appears that maximum skeletal density is associated with those periods of the year when seawater temperature is above average.

Species of Tetradium in the Cincinnati Series

T. fibratum, the genotype, was described by Safford from rocks of Trenton age. It possesses four-sided corallites with prominent septa. T. minus Safford is small and has small corallites. T. approximatum, listed by Ulrich with no description, has only Bassler's (U. S. Nat, Mus., Bull. 92, 2:1264-1265, 1915) indirect definition in which he cites several references under the synonymy of this name. These citations include at least two different species, and the name approximatum is here restricted to Tetradium minus Foerste not Safford (Bull. Sci. Lab. Denison Univ., 14:311, pl. 10, figs, la-lb, 1909).