Spatial distribution of calcification and photosynthesis in the scleractinian coral Galaxea fascicularis

The spatial heterogeneity of photosynthesis and calcification of single polyps of the coral Galaxea fascicularis was investigated. Photosynthesis was investigated with oxygen microsensors. The highest rates of gross photosynthesis (Pg) were found on the tissue covering the septa, the tentacles, and the tissues surrounding the mouth opening of the polyp. Lower rates were found on the tissues of the wall and the coenosarc. Calcification was investigated by radioactive tracers. The incorporation pattern of ⁴⁵Ca and ¹⁴C in the corallites was imaged with use of a Micro-Imager. The -images obtained showed that the incorporation of the radioactive tracers coincided with the Pg distribution pattern with the highest incorporation rates found in the corallite septa. Thus, the high growth rate of the septa is supported by the high rates of Pg by the symbiont in the adjacent tissues. The total incorporation rates were higher in light than in dark, however, the distribution pattern of the radioisotope incorporation was not affected by illumination. This further emphasizes the close relation between calcification and photosynthesis.     

Microstructural characteristics of the stony coral genus Acropora useful to coral reef paleoecology and modern conservation

Identification of fossil corals is often limited due to poor preservation of external skeleton morphology, especially in the genus Acropora which is widespread across the Indo‐Pacific. Based on skeleton characteristics from thin section, we here develop a link between the internal skeleton structure and external morphology. Ten characteristics were summarized to distinguish Acropora and five related genera, including the type and differentiation of corallites, the skeleton nature of corallites (septa, columellae, dissepiments, wall), and calcification centers within septa. Acropora is distinctive for its dimorphic corallites: axial and radial. Isopora is similar to Acropora but possess more than a single axial corallites. Montipora and Astreopora (family Acroporidae) have monomorphic corallites and a synapticular ring wall, with clustered calcification center in the former and medial lines in the latter. Pocillopora and Porties are classified by distinctive dissepiments, columellae and septa. These microstructural skeleton characteristics were effective in the genus identification of fossil corals from drilled cores in the South China Sea. Eighteen detailed characteristics (ten of axial corallites, four of radial corallites, and four of coenosteum) were used in the Acropora species classification. The axial corallites size and structure (including corallite diameter, synapticular rings, and septa), the septa of radial corallites, and the arrangement of coenosteum were critical indicators for species identification. This identification guide can help paleoenvironmental and paleoecological analyses and modern coral reef conservation and restoration.     

Skeletal response of <Emphasis Type="Italic">Lophelia pertusa</Emphasis> (Scleractinia) to bioeroding sponge infestation visualised with micro-computed tomography

The skeleton morphology of the azooxanthellate cold-water coral Lophelia pertusa can be strongly influenced by invasive boring sponges that infest corallites in the still living part of the colony. Atypically swollen corallites of live Lophelia pertusa from the Galway Mound (Belgica Carbonate Mound Province, Porcupine Seabight, NE Atlantic), heavily excavated by boring organisms, have been examined with a wide range of non-destructive and destructive methods: micro-computed tomography, macro- and microscopic observations of the outer coral skeleton, longitudinal and transversal thin sections and SEM analyses of coral skeleton casts. As a result, three excavating sponge species have been distinguished within the coral skeleton: Alectona millari, Spiroxya heteroclita and Aka infesta. Furthermore, four main coral/sponge growth stages have been recognised: (1) cylindrical juvenile corallite/no sponge cavities; (2) flared juvenile corallite/linear sponge cavities (if present); (3) slightly swollen adult corallites/chambered oval sponge cavities; (4) very swollen adult corallites/widespread cavities. The inferred correlation between corallite morphology and boring sponge infestation has been detected in micro-computed tomography (micro-CT) images and confirmed in sponge trace casts and peculiar features of coral skeleton microstructure. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Ostracodes swallowed by Palaeozoic corals?

Middle Devonian heliolitids and favositids from Central Bohemia, belonging to Heliolites 'intermedius' LeMaitre and Favosites goldfussi Orbigny , incorporated ostracode shells within their living corallite structures. The ostracode shells were sealed in by skeletal tissue that was septal in origin (Heliolites) or they were roofed over by tabulae (Favosites). The foreign shell was near the axis of the polyp when trapped within the coral skeleton. Only ostracodes, not other rounded shells or sedimentary particles, were trapped in this way. Approximately one in 30 favositid corallites and one in 70 heliolitid corallites display this peculiar condition, where the ostracode shells seem to have been swallowed by the polyps. A probable scenario involves the injury of the mouth area and the trapping of the ostracodes. A high probability that the basal part of the polyp experienced a controlled penetration is the most striking part of the process. □ Favositids, heliolitids, ostracodes, coral growth violence, behavior, Middle Devonian, Bohemia.     

Skeletal microstructure of Galaxea fascicularis exsert septa: a high-resolution SEM study

The deposition of four crystal types at the growth surface of the septa of several color morphs of the coral Galaxea fascicularis was investigated over a 24-h period. Results suggest that nanocrystals, on denticles at the apices of exsert septa, may be the surface manifestation of centers of calcification. These crystals were also found on the septa of the axial corallite of Acropora formosa. The deposition of nanocrystals appears to be independent of diurnal rhythms. Internally and proximal to the septal apices, distinct clusters of polycrystalline fibers originate from centers of calcification and form fanlike fascicles. Upon these fascicles, acicular crystals grow and extend to form the visible fasciculi at the skeletal surface. Deposition of aragonitic fusiform crystals in both G. fascicularis and A. formosa occurs without diurnal rhythm. Nucleation of fusiform crystals appears to be independent of centers of calcification and may occur by secondary nucleation. Formation of semi-solid masses by fusiform crystals suggests that the crystals may play a structural role in septal extension. Lamellar crystals, which have not been reported as a component of scleractinian coral skeletons before, possess distinct layers of polyhedral plates, although these layers also do not appear to be associated with daily growth increments. The relationship of lamellar crystals to other components of the scleractinian coral skeleton and their involvement in skeletal growth is unknown.     

Growth characteristics of Protoheliolites norvegicus (Tabulata; Upper Ordovician; Estonia)

Protoheliolites is an early heliolitine coral characterized by closely spaced corallites separated in places by sparse coenenchyme. Growth characteristics in the type species, P. norvegicus, are revealed by detailed analysis based on serial peels and thin sections of coralla from the uppermost Katian of north‐western Estonia. Colonies of this species had a strong ability to recover from damage and partial mortality, resulting in various forms of rejuvenation, regeneration, fusion and reorganization of corallites; in some cases, this involved relatively large areas of undifferentiated soft parts. The shells of commensal cornulitids became enclosed in host coralla during colony growth. Coralla of P. norvegicus exhibit distinctive growth cycles due to responses to seasonal changes. The production of new corallites by coenenchymal increase usually occurred in low‐density bands, in which corallites generally display round to subrounded transverse outlines. In high‐density bands, the corallites became crenulated, their wall thickness increased, septal development was more pronounced, and the amount of coenenchyme increased. In addition to these cyclomorphic changes, there were significant astogenetic changes during growth. Compared with the early stage of colony development, distinctive characteristics in the late astogenetic stage include a decrease in the growth rate of the colony, better coordination among corallites, maximum development of corallite crenulations and septa in high‐density bands, more numerous coenenchymal tubules and a greater proportion of corallum area occupied by coenenchyme. In general, the role of polyps in determining morphological characteristics of individual corallites, such as tabularium area, corallite crenulations and wall thickness, was subordinate to the astogeny of the colony. Growth characteristics including colony‐wide coordination of polyp behaviour and subjugation of individuals to restore the colony following damage suggest a strong astogenetic control and high level of colony integration. Protoheliolites probably arose from a heliolitine genus rather than from a nonheliolitine group as some authors have proposed.     

Regularity and polarity in budding of the colonial scleractinian Dendrophyllia ehrenbergiana: consequences of radio‐bilateral symmetry of the scleractinian body plan

Sentoku, A. & Ezaki, Y. 2012: Regularity and polarity in budding of the colonial scleractinian Dendrophyllia ehrenbergiana: consequences of radio‐bilateral symmetry of the scleractinian body plan. Lethaia, Vol. 45, pp. 586–593. Regularities and polarity in budding of the azooxanthellate scleractinian Dendrophyllia ehrenbergiana were examined with the aim of understanding the developmental constraints on the formation of colonies. Its mode of budding, in light of the orientations of directive septa of offsets and the inclination angle of budding, is consistent with that of other dendrophyllids; however, the offsets of D. ehrenbergiana only occur near the two primary septa on the convex side of individual corallites, showing a plane of bilateral symmetry with a distinct polarity. These regularities and polarity are seen in the axial and its derived corallites throughout growth. Of note, the polarity at individual corallites is clearly reflected in subsequent colony growth by the branching pattern and corallite number. These characteristics imply the presence of radio‐bilateral symmetrical constraints on the asexual reproduction of the Scleractinia and give us invaluable clues to the understanding of shape‐making mechanisms of marine modular organisms. □Asexual reproduction, azooxanthellate coral, budding, colony, Dendrophyllia ehrenbergiana, polarity.     

Regularity in budding mode and resultant growth morphology of the azooxanthellate colonial scleractinian Tubastraea coccinea

Scleractinia exhibit a variety of growth forms, whether zooxanthellate or azooxanthellate, according to factors that control asexual reproduction and ensuing coral growth. The azooxanthellate branching scleractinian Dendrophyllia arbuscula shows regular modes of budding in terms of the locations of budding sites, the orientations of directive septa, and the inclination angle of budding throughout colonial growth. This study reports that such regularities are also found in the apparently different growth form of the massive dendrophylliid Tubastraea coccinea, which shows the following growth features: (1) the offsets (lateral corallites) always occur near four primary septa, except the two directive primary septa, meaning that the lateral corallites do not appear in the sectors of the two directive septa; (2) the two directive septa in lateral corallites tend to be oriented subperpendicular to the growth direction of the parental corallites; (3) the lateral corallites grow approximately diagonally upwards; and (4) these regularities are seen in the axial and derived lateral corallites among all generations during colony growth. Large differences in growth form are found between the branching D. arbuscula and massive T. coccinea, irrespective of the presence of specific regularities. It is likely that subtle modifications of certain parameters (e.g., budding interval, branch length, corallite size, and inclination angle of lateral corallites) have a strong effect on the overall growth morphology. A precise understanding of such regularities, which occur regardless of generation or taxonomic position, would contribute to understanding the “shape-controlling mechanism” of corals, which are an archetypal modular organism.     

Life‐history strategies of Manipora amicarum Sinclair, 1955 (Tabulata; Upper Ordovician; southern Manitoba,Canada)

Based on detailed study of transverse serial sections, we recognize various modes of corallite increase in a multichain cateniform coral, Manipora amicarum from the Selkirk Member, Red River Formation, in Manitoba. One type of axial increase and four types of lateral increase involve normal, undamaged corallites, and one type of axial increase and one type of lateral increase occur during recovery processes of corallites damaged by sediment or bioclast influx. All but one of these types of increase are comparable to those in a single‐chain coral, Catenipora foerstei, which we previously documented from the same stratigraphic unit and locality. In M. amicarum, the formation of double ranks and agglutinated patches of corallites by normal corallites, and by recovery processes following corallite damage, is common and presumably genetically controlled. Agglutinated patches originate differently in C. foerstei, occurring sporadically or temporarily in only some coralla. Average annual vertical corallum growth in M. amicarum, as indicated by cyclic fluctuations of tabularial area, is higher than in C. foerstei, which has comparatively smaller corallites. In general, annual growth in M. amicarum is positively correlated with average tabularial area, negatively correlated with frequency of damaged corallites, and is not related to the frequency of corallite increase. In C. foerstei, however, there is a positive association between annual growth rate and the frequency of increase by damaged corallites, related to episodes of sediment or bioclast influx probably generated by storms. In comparison with C. foerstei, M. amicarum has a low frequency of corallite termination and extensive partial mortality is rare. It seems that the relatively rapid overall vertical corallum growth in M. amicarum was effective for protecting the coral from unfavourable situations, possibly by maintaining the growth surface higher above the substrate than in C. foerstei. Although these two species show many similarities in the types of corallite increase, their reactions and strategies in relation to physical disturbance were quite different.     

Echinophyllia tarae sp. n. (Cnidaria,Anthozoa, Scleractinia), a new reef coral species from the?Gambier Islands,French Polynesia

A new shallow water scleractinian coral species, Echinophyllia tarae sp. n., is described from the Gambier Islands, French Polynesia. It is characterized by an encrusting corallum, a few large and highly variable corallites with protruding walls, and distinctive costosepta. This coral was observed in muddy environments where several colonies showed partial mortality and re-growth. The new species has morphological affinities with both Echinophyllia echinata and with Echinomorpha nishihirai, from which it can be distinguished on the basis of the diameter and the protrusion of the largest corallite, the thickness of the septa, and the development of the size of the crown of paliform lobes.     

Seasonal growth bands in Famennian rugose coral Scruttonia kunthi and their environmental significance

Large colonies of rugose coral Scruttonia kunthi occurring in the upper Famennian of Sudetes (southern Poland) reveal distinct growth banding in their skeletons. They were investigated for internal structural characteristics and stable isotopic composition. The skeletal tissue consists of alternating light and dark bands which differ in thickness, density and morphology of structural elements, and in occurrence of corallite contraction and rejuvenescense. Darker parts with densely arranged thick skeletal elements are thin in comparison to lighter parts. In addition, they include frequently offsets and contraction of corallites. A couplet of dense and less dense bands is interpreted to represent most probably an annual cycle. The calculated growth rate for Scruttonia kunthi varied from 6 mm/yr to 12 mm/yr. Growth-band formation was influenced environmentally. Oxygen isotopic data provide an evidence that high-density bands were formed in the season of higher environmental stress, with relatively warmer temperatures and higher sedimentation rates. Carbon isotopic signatures are very uniform, and thus enigmatic. They indicate that at least growth rate of the skeleton and seawater temperature had no influence on the coral δ¹³C.     

The impact of seawater temperature on coral growth parameters of the colonial coral Cladocora caespitosa (Anthozoa, Scleractinia) in the eastern Adriatic Sea

The scleractinian coral Cladocora caespitosa deserves a special place among the major carbonate bioconstructors of the Mediterranean Sea. Annual coral skeleton growth, coral calcification, and skeleton density of the colonial coral C. caespitosa taken from 25 locations in the eastern Adriatic Sea were analyzed and compared with annual sea surface temperatures (SST). The growth rates of the coral C. caespitosa from the 25 stations in the Adriatic Sea ranged from 1.92 to 4.19?mm per year, with higher growth rates of the investigated corallites in the southern part of the Adriatic Sea. These growth rates are similar to those measured in other areas of the Mediterranean Sea. The correlation between coral growth and sea temperatures in the Adriatic Sea is seen as follows: An X-radiograph analysis of coral growth in C. caespitosa colonies that are over 60?years old showed that higher growth rates of this coral coincided with a warmer period in the Mediterranean Sea. A positive significant correlation exists between corallite growth rates and SST and coral calcification and SST. A negative correlation exists between coral density and SST. Coral growth rates also showed a correlation with higher eutrophication caused by nearby fish farms, along with a greater depth of the investigated colonies and high bottom currents.     

Variation in skeletal microstructure of the coral Galaxea fascicularis: effects of an aquarium environment and preparatory techniques

To compare the crystalline microstructure of exsert septa, polyps of the scleractinian coral Galaxea fascicularis were sampled from shallow reef flat colonies, from colonies living at a depth of 9 m, and from colonies kept in a closed-circuit aquarium. Septal crystal structure and orientation was markedly different between corals in the field and in aquaria. In samples collected from deep water, acicular crystals were composed of conglomerates of finer crystals, and skeletal filling was considerably reduced when compared with samples collected from shallow water. Comparisons were also made between septa prepared in sodium hypochlorite (commercial bleach), sodium hydroxide (NaOH), hydrogen peroxide (H(2)O(2)), and distilled water (dH(2)O). Commercial bleach was the most effective solvent for tissue dissolution in investigations of skeletal structure. Samples prepared in NaOH commonly displayed crystalline artefacts, while the use of dH(2)O and H(2)O(2) was labor intensive and often resulted in unclean preparations. Fusiform crystals were seen only on G. fascicularis septa prepared in bleach and on Acropora formosa axial corallites prepared in either bleach or dH(2)O. We suggest that the mechanical agitation and additional washing necessary for samples prepared in dH(2)O, NaOH, or H(2)O(2) resulted in the loss of fusiform crystals from these preparations.     

Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula

Sentoku, A. & Ezaki, Y. 2011: Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula. Lethaia, Vol. 45, pp. 62–70. Scleractinia display a variety of growth forms, whether zooxanthellate or azooxanthellate, as the consequence of the combined effects of both intrinsic and extrinsic factors. New modules arise in colonial corals through asexual reproduction, including budding and division. The azooxanthellate, branching dendrophylliid Dendrophyllia arbuscula van der Horst 1922 , is a good species to investigate intrinsic regularities in budding, because: (1) the lateral corallites always occur in the vicinity of four primary septa, excluding the two directive primary septa; (2) the two directive septa in lateral corallites tend to be oriented almost perpendicular to the growth orientation of parental corallites; (3) the lateral corallites grow more‐or‐less diagonally upwards; and (4) these regularities are retained from the axial to the derived lateral corallites during colony growth. Accordingly, a colony of apparently complex dendroid corals is formed according to certain universal rules that apply to successive generations of corallites. The presence of two opposite sectors in which budding do not occur seems to be common to other azooxanthellate scleractinian families. Regularities, other than the orientation of the directive septa, are also commonly found at least in other azooxanthellate dendrophylliid genera. These regularities suggest the presence of strict developmental constraints on the asexual reproduction of the Scleractinia, both extant and extinct. These regularities by azooxanthellate scleractinians, as one of the representative colonial metazoan groups, provide us with fundamental data with which we can understand how colonies are constructed. □Azooxanthellate coral, budding, colony, Dendrophyllia arbuscula, regularity.     

Large dwellers of the Silurian Halysites biostrome: rhizosessile life strategies of cystiphyllid rugose corals from the Llandovery of Gotland

An exceptionally well‐preserved, unusual biostrome composed of the framebuilding cateniform tabulate coral Halysites catenularius (Linnaeus, 1767) bears an assemblage of the relatively large solitary cystiphyllid rugosan Cystiphyllum visbyense Wedekind, 1927. The corallites of solitary cystiphyllids are embedded within the ranks of the halysitid colonies, which developed on a soft, muddy substrate and in relatively turbid water. The cystiphyllid larvae successively settled mostly on the ranks of halysitid colonies and on colonies of the tiny phaceloid rugose coral Nanophyllum ramosum Johannessen, 1995, whereas calice‐in‐calice recruitment was not successful for these cystiphyllid corals. Further growth of C. visbyense was supported by rhizoid structures, which were most frequently developed on the cardinal (convex) side of the corallite. The process of formation of the rhizoid structures is here discussed and explained in detail, showing that they were formed by the extension of the basal ectodermal tissue of the polyp. The cystiphyllids, which settled on the walls of living corallites of halysitid colonies, used sweeper tentacles to kill the smaller polyps of the colony to maintain the space around them and expand. Hence, they ultimately used the halysitid colonies only as a hard substrate to stabilize their position on the soft muddy sediment.     

Ontogeny of 'epithecal' and septal structures in scleractinian corals

The ontogenetic development of a solitary scleractinian coral, Flabellum distinctum Edwards & Haime, has been studied in serial thin section, with special attention being paid to epithecal nature in relation to septal growth. The term 'epitheca' has been confusingly used for two different skeletal structures: epitheca ( sensu stricto ) and marginotheca. The latter is here newly proposed. 'epitheca' is defined as a calcareous investment developed on the outside of other skeletal structures of a corallite. It can be distinguished from the marginotheca in section by lacking a dark line (calcification centre) and by being unrelated to the formation of septa. 'marginotheca' defines the outer margin of the main skeletal structures of a corallite. It has a dark line which functionally coincides with that of the eutheca. It is of primary origin, preceding formation of septa and provides the origin of the septa. The marginotheca is one of the more important and fundamental skeletal structures for coral classification.     

Monthly variations in calix growth, polyp tissue, and density banding of the Mediterranean scleractinian Cladocora caespitosa (L.)

Monthly skeletal growth of the scleractinian, temperate coral Cladocora caespitosa (L.) from the Ligurian Sea (NW Mediterranean) was analysed for a period of 1 year and compared with seawater parameters. Measurements on corallite sections and on X-ray images showed that the formation of the high-density (HD) band and two dissepiments are favoured by fall–winter conditions, characterised by high quantities of rain, rough seas, and cold seawater. In summer, when the low-density (LD) band is formed, the corallites stretch upward and form one new dissepiment and one deep calix, where the polyps recede almost completely in August. These findings confirmed the adaptation of the temperate coral to winter environmental conditions, characterised by low irradiance and high availability of nutrients and food particles resuspended from bottom sediments. On the contrary, the high seawater temperature, irradiance, and ammonia contents stressed the coral in August and, when they persist in September, may cause the onset of mortality events.     

Contrasting Light Spectra Constrain the Macro and Microstructures of Scleractinian Corals

The morphological plasticity of scleractinian corals can be influenced by numerous factors in their natural environment. However, it is difficult to identify in situ the relative influence of a single biotic or abiotic factor, due to potential interactions between them. Light is considered as a major factor affecting coral skeleton morphology, due to their symbiotic relation with photosynthetic zooxanthellae. Nonetheless, most studies addressing the importance of light on coral morphological plasticity have focused on photosynthetically active radiation (PAR) intensity, with the effect of light spectra remaining largely unknown. The present study evaluated how different light spectra affect the skeleton macro- and microstructures in two coral species (Acropora formosa sensu Veron (2000) and Stylophora pistillata) maintained under controlled laboratory conditions. We tested the effect of three light treatments with the same PAR but with a distinct spectral emission: 1) T5 fluorescent lamps with blue emission; 2) Light Emitting Diodes (LED) with predominantly blue emission; and 3) Light Emitting Plasma (LEP) with full spectra emission. To exclude potential bias generated by genetic variability, the experiment was performed with clonal fragments for both species. After 6 months of experiment, it was possible to detect in coral fragments of both species exposed to different light spectra significant differences in morphometry (e.g., distance among corallites, corallite diameter, and theca thickness), as well as in the organization of their skeleton microstructure. The variability found in the skeleton macro- and microstructures of clonal organisms points to the potential pitfalls associated with the exclusive use of morphometry on coral taxonomy. Moreover, the identification of a single factor influencing the morphology of coral skeletons is relevant for coral aquaculture and can allow the optimization of reef restoration efforts.     

Simultaneous extension of both basic microstructural components in scleractinian coral skeleton during night and daytime,visualized by in situ 86Sr pulse labeling

Using in situ (12 h) pulse-labeling of scleractinian coral aragonitic skeleton with stable ⁸⁶Sr isotope, the diel pattern of skeletal extension was investigated in the massive Porites lobata species, grown at 5 m depth in the Gulf of Eilat. Several microstructural aspects of coral biomineralization were elucidated, among which the most significant is simultaneous extension of the two basic microstructural components Rapid Accretion Deposits (RAD; also called Centers of Calcification) and Thickening Deposits (TD; also called fibers), both at night and during daytime. Increased thickness of the ⁸⁶Sr-labeled growth-front in the RADs compared to the adjacent TDs revealed that in this species RADs extend on average twice as fast as TDs. At the level of the individual corallite, skeletal extension is spatially highly heterogeneous, with sporadic slowing or cessation depending on growth directions and skeletal structure morphology. Daytime photosynthesis by symbiotic dinoflagellates is widely acknowledged to substantially increase calcification rates at the colony and the corallite level in reef-building corals. However, in our study, the average night-time extension rate (visualized in three successive 12 h pulses) was similar to the average daytime extension (visualized in the initial 12 h pulse), in all growth directions and skeletal structures. This research provides a platform for further investigations into the temporal calibration of coral skeletal extension via cyclic growth increment deposition, which is a hallmark of coral biomineralization.     

Favia camranensis sp. n. (Scleractinia: Faviidae), a new coral species from Southern Vietnam

A new species of coral, Favia camranensis sp. n., from the Hon Nai reef, Cam Ranh Bay, in southern Vietnam is described. This coral differs from all known faviids in that its corallites project one above another by more than 2 mm. The septa and septa-costae are heavily ornamented with complexly serrated trabecular spines. This coral can form monospecific aggregations of 5–20 colonies.