The morphological adaptation of <Emphasis Type="Italic">Lithocodium aggregatum</Emphasis> Elliott (calcareous green alga) to cryptic microhabitats (Lower Aptian,Spain): an example of phenotypic plasticity

Lithocodium aggregatum Elliott is interpreted as a heterotrichale chlorophycean alga with a prostrate and erect system within a well-calcified tissue. Within Lower Aptian coral rubble of the western Maestrat Basin, Spain, it forms thick masses of juxtaposed crusts around the bioclasts. In achieving a rapid and complete encrustation of the available bioclasts, Lithocodium applied several strategies, e.g., filling voids of structured surfaces with a special fabric or forming erect extensions to bridge adjacent substrates. In these deposits, different types of poorly if ever illuminated cryptic microhabitats can be distinguished: (1) existing crypts such as empty shells or structural voids within bioclasts (2) crypts resulting from the complete encrustation of adjacent bioclasts by Lithocodium itself and (3) syndepositionally created crypts, e.g., boreholes produced by lithophagid bivalves. In these cases, Lithocodium developed a poorly calcified structure of large cells with thin microcrystalline walls indicating a high degree of variability (phenotypic plasticity). This cryptic growth stage is interpreted as an adaption to the poorly illuminated crypts (photoadaption) in order to maximize light capture for photosynthesis. The Lower Cretaceous Lithocodium is therefore not per se a cryptoendolithic microorganism, but may show adaptation to develop and survive also in these already existing or newly created niches.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

Fluorescence census techniques for the early detection of coral recruits

Many coral recruits are very small and often cryptic at settlement making them difficult to detect with normal census techniques. Here we show that fluorescence census techniques can increase the accuracy of juvenile coral counts in highly fluorescent taxa. Using fluorescent filters at night, counts of coral recruits were 20–50% higher than during the day. Acropora abundances were up to 300% higher, the difference being made up of cryptic individuals, and individuals that were too small to see during the day. Fluorescence techniques will be particularly useful in regions where fluorescent taxa are dominant, such as most Indo-Pacific reefs. The technique offers particular promise to determine the influence of early post-settlement mortality on the ecology of fluorescent taxa, because corals can be detected at the size at which they settle.     

Microatoll microbialites of Lake Clifton,Western Australia: Morphological analogues ofCryptozoön proliferum Hall,the first formally-named stromatolite

Summary The Linnaean nameCryptozo?n proliferum Hall was proposed in 1883 for a previously undescribed life-form preserved in spectacular exposures of Cambrian limestones in New York State, USA. It is now recognised that these are exposures of stromatolitic microbialites, laminated organosedimentary structures formed from interaction between a benthic microbial community (BMC) and the environment. Microbialites are neither fossil organisms nor trace fossils. These complex structures are the products of dissipative, self-organising systems involving a BMC, the external environment and the accreting microbialite. Functionally analogous BMCs of different species compositions may build similar structures in similar environments in quite separate periods. The type exposures ofCryptozo?n proliferum show objects composed of complex, concentric rings, up to a metre in diameter, that have grown laterally without any restriction other than that provided by neighbouring structures. They are not the relicts of domes truncated by penecontemporaneous erosion or Pleistocene glaciation, but depositional forms in which upward growth was restricted. Analogous modern structures occur on a reef platform along the north east shore of hyposaline Lake Clifton, Western Australia. These are tabular thrombolitic microbialites that vary lakeward across the reef platform from low, compound structures to discrete, concentric structures up to 50 cm high. The Lake Clifton forms are, in turn, morphological analogues of microatolls found on coral reef platforms. Coral microatolls are coral colonies with flat, dead tops and living perimeters in which upward growth is constrained by the sea surface. In shallow water they form circular rims of laterally growing coral around a dead centre. In deeper water they form coral heads that develop flat tops on reaching sea level. It is concluded that both the tabular microbialites of Lake Clifton and the type exposures ofCryptozo?n proliferum are analogous to coral microatolls in both form and origin-structures that have been able to grow laterally, but in which upward growth is restricted by subaerial exposure. Similar microatoll microbialites have been described from other modern environments, including Great Salt Lake, Utah, USA and Stocking Island, Exuma Cays, Bahamas. Ancient examples may include some of the “tufa” deposits of the Basal Purbeck Formation in Dorset, UK, as well as the coalesced domal bioherms of the Upper Cambrian Arrinthrunga Formation of the Georgina Basin, Central Australia, and the “washbowl” structures described from the B?tsfjord Formation of the Varanger Peninsula, north Norway. Progress towards a reliable interpretation of ancient microbialites depends on an understanding of modern environments in which analogous structures are forming. This study of microatolls has demonstrated that other sessile life forms may create colonial ecomorphs that, used cautiously, can serve as analogues for understanding the factors controlling the growth and form of microbialites. The surprising lack of pre-Pleistocene examples of microatolls recorded to date has simply been due to their lack of recognition in the geological record. They occur in sequences from the Proterozoic onwards, and provide powerful environmental indicators of ancient reef platforms on which biological growth was adjusted to contemporary sea level.     

Effects of delayed settlement on post-settlement growth and survival of scleractinian coral larvae

Demographic connectivity requires both the dispersal of individuals between sub-populations, and their subsequent contribution to population dynamics. For planktonic, non-feeding marine larvae, the capacity to delay settlement enables greater dispersal distances, but the energetic cost of delayed settlement has been shown to adversely impact post-settlement fitness in several taxa. Here, we assess whether delayed settlement influences mortality rates or growth rates for the first 6 weeks following settlement of the scleractinian coral, Acropora tenuis. Coral larvae that were settled at 2, 4, and 6 weeks after spawning, and then deployed in the field, showed negligible effects of delayed settlement on post-settlement survival and time to initial budding for colony formation. Between-cohort differences in budding rate appeared to be explained by temporal variation in the post-settlement acquisition of zooxanthellae. The potential for coral larvae to remain in the pelagic zone for increased periods of time with little to no effect on post-settlement survival and growth suggests that the capacity for delayed settlement is likely to have meaningful demographic consequences for broadcast-spawning reef-building corals, and that the predicted trade-off between delayed settlement and post-settlement fitness is less applicable to reef-building scleractinian corals than other taxa with non-feeding larvae.     

Density‐dependent effects on initial growth of a branching coral under restoration

Coral reef restoration aims to help threatened coral ecosystems recover from recent severe declines. Here we address whether coral fragments should be out‐planted individually or in larger aggregations. Theory suggests alternative possible outcomes: whereas out‐plants within aggregations might suffer from heightened negative interactions with neighbors (e.g. competition for space), they may alternatively benefit from positive interactions with neighbors (e.g. buffering wave disturbances). On a degraded reef in the Caribbean (St. Croix, USVI), using out‐plants of the critically endangered staghorn coral Acropora cervicornis, we experimentally tested how aggregation density (1–20 out‐planted coral fragments spaced at approximately 5 cm) influenced initial coral growth (over 3 months). Coral growth declined as a function of aggregation size, and out‐plants within larger aggregations had fewer and shorter secondary branches on average, indicative of horizontal competition for space. Our results therefore suggest that wide spacing of individuals will maximize the initial growth of out‐planted branching corals.     

Targeted census of lionfishes (Scorpaenidae) reveals high densities in their native range

Indo-Pacific lionfishes generally exhibit cryptic behaviours and so can be missed when conducting non-targeted surveys. Here, the authors report the results from targeted surveys of lionfish at Moorea, French Polynesia. Lionfish from three species (Pterois antennata, Pterois radiata, Dendrochirus biocellatus) were observed at a mean density of 267 individuals ha⁻¹. This is substantially higher than previous estimates from the same area (Moorea) and represents the highest reported density of lionfishes from their Pacific range. Overall, this study highlights the importance of targeted survey techniques for detecting cryptic species on coral reefs.     

First record of coralline demosponges in the Pleistocene: implications for reef ecology

We report the first discovery of coralline sponges from Pleistocene reef limestones of Vanuatu. Sponges of the genus Acanthochaetetes were identified from two reef terraces of Middle and Late Pleistocene age. As these sponges document cryptic habitats in modern coral reefs, they may be index fossils of cryptic habitats in the Pleistocene as well, thereby providing clues on growth conditions in fossil reefs. The small size of the discovered specimens may be attributed to the transient nature of their cryptic habitats, either due to reef growth or the occurrence of an unusual event.     

The effect of substratum on the growth of Terpios,an encrusting sponge which kills corals

The effects of substratum on the growth of Terpios was demonstrated using experimental and observational data at Guam, Mariana Islands. Terpios growth was measured on live coral, reef rock, and red calcareous algae in the field. In addition, Terpios was transplanted onto live coral, air-blasted (clean) coral, reef rock, and plexiglass plates, and subsequent growth measured. Terpios grows fastest on clean substrata followed by live coral, reef rock and red calcareous algae in decreasing order. Terpios is sometimes overgrown by Montipora, Porites and red calcareous algae. Since Terpios grows fastest when living coral tissue is removed, it is not likely that Terpios ingests coral tissue as previously suggested in the literature. Instead, Terpios is probably an efficient competitor of corals for space. Terpios overgrows most hard, stable reef substrata, and the growth rate on all sample substrata is substantial. Therefore Terpios has a great potential for covering a reef and may be one of the most important causes of disturbance on some coral reefs.Contribution no. 206 from the University of Guam Marine Laboratory     

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.     

Effects of temperature, light and heterotrophy on the growth rate and budding of the temperate coral Cladocora caespitosa

Recent investigations have shown the temperate scleractinian coral Cladocora caespitosa to be a new potential climate archive for the Mediterranean Sea. Whilst earlier studies have demonstrated a seasonal variation in growth rates, they were unable to distinguish which environmental parameter (light, temperature, or food) was influencing growth. In this study, the effect of these three factors on the coral physiology and calcification rate was characterized to aid the correct interpretation of skeletal trace element variations. Two temperatures (13 and 23°C), irradiances (50 and 120 μmol m⁻² s⁻¹), and feeding regimes (unfed and fed with nauplii of Artemia salina) were tested under controlled laboratory conditions on the growth, zooxanthellae density, chlorophyll (chl) content, and asexual reproduction (budding) of C. caespitosa during a 7-week factorial experiment. Unlike irradiance, which had no effect, high temperature and food supply increased the growth rates of C. caespitosa. The effect of feeding was however higher for corals maintained at low temperature, suggesting that heterotrophy is especially important during the cold season, and that temperature is the predominant factor affecting the coral’s growth. At low temperature, fed samples had higher zooxanthellae density and chl content, possibly for maximizing photosynthetic efficiency. Sexual reproduction investment of C. caespitosa was higher during favourable conditions characterised by high temperatures and zooplankton availability.     

Herbivory facilitates growth of a key reef‐building Caribbean coral

The decline of reef‐building corals in conjunction with shifts to short‐lived opportunistic species has prompted concerns that Caribbean reef framework‐building capacity has substantially diminished. Restoring herbivore populations may be a potential driver of coral recovery; however, the impact of herbivores on coral calcification has been little studied. We performed an exclusion experiment to evaluate the impact of herbivory on Orbicella faveolata coral growth over 14 months. The experiment consisted of three treatments: full exclusion cages; half cage procedural controls; and uncaged control plates, each with small O. faveolata colonies. We found that herbivorous fish exclusion had a substantial impact on both macroalgal cover and coral growth. Fleshy macroalgae reached 50% cover within some exclusion cages, but were almost absent from uncaged control plates. Critically, O. faveolata calcification rates were suppressed by almost half within exclusion cages, with monthly coral growth negatively related to overgrowth by fleshy macroalgae. These findings highlight the importance of herbivorous fishes for coral growth and the detrimental impact of macroalgal proliferation in the Caribbean. Policy makers and local managers should consider measures to protect herbivorous fishes and reduce macroalgal proliferation to enable coral communities to continue to grow and function.     

Microhabitat use and prey selection of the coral-feeding snail <Emphasis Type="Italic">Drupella cornus</Emphasis> in the northern Red Sea

Corallivorous gastropods of the genus Drupella are known for population outbreaks throughout the Indo-Pacific region. Despite their potential to destroy wide areas of coral reef, prey preferences have never been analyzed with respect to prey availability, and juvenile ecology and food selectivity remain largely unknown. Here, the influence of water depth, coral abundance, colony shape, prey species, and intraspecific attraction among snails on distribution patterns, prey selection, and microhabitat use of D. cornus was studied in the northern Red Sea. Special emphasis was put on ontogenetic differences. The snails were most abundant in the shallowest reef zone (1 m depth). Adults were associated with several substrates and coral growth forms, whereas juveniles were highly cryptic and restricted to live branching corals. The genus Acropora was significantly preferred over other acroporid and pocilloporid corals. As revealed by resource selection ratios, Acropora acuminata was preferred by juveniles, A. selago by adults. In aquarium experiments, intraspecific attraction was high among both life stages. Overall, significant differences in juvenile and adult microhabitat and prey use suggest that juveniles have more specific habitat requirements, and indicate ecological impacts on coral communities different from that of adults. Prey preferences seem to depend on both coral genus and colony shape. Acropora corals provide the best combination of food and shelter and therefore determine distribution patterns of D. cornus.     

Effects of nursery table slope orientation on coral survival and growth

Transplanting nursery-reared corals is among one of the most common approaches to assist the recovery of degraded reefs. The nursery phase is considered essential for providing a favourable environment for coral fragments to grow into suitable sizes before transplantation to natural reef substrates. Several types of coral nursery designs have been used, but the effect of nursery table slope orientation on survival and growth of coral fragments has not been fully evaluated. Survival and growth of coral fragments from four species (Pectinia paeonia, Podabacia crustacea, Pocillopora acuta, Merulina ampliata) on three inclinations of nursery table top (horizontal (0°), diagonal (45°) and vertical (90°)) were monitored over six months. The effects of slope orientation on survival and growth of fragments were not significant among species except P. acuta, for which survivorship and growth decreased significantly only on vertical nursery tables. The conditions required for coral propagation, such as slope orientation of nursery tables and the initial size of fragments, clearly differ among species due to their inherent attributes and restoration success will greatly benefit from empirical studies derived from a wider range of species.     

Comparative physiological studies on the growth of cryptic species of Bostrychia intricata (Rhodomelaceae,Rhodophyta) in various salinity and temperature conditions

Inter‐ and intra‐specific physiological variations of intertidal macroalgae have been well investigated. However, studies on physiological responses of cryptic algal species have been poorly documented. Bostrychia intricata is a widespread marine red alga in the Southern Hemisphere, and has many cryptic species. We investigated the effect of different salinities and temperatures on the specific growth rate of three cryptic species (N2, N4 and N5) of B. intricata from New Zealand. Our data indicated that all cryptic species grew at the full range of salinities and temperatures tested, but exhibited a significant difference in their specific growth rates. Cryptic species N4 had a higher growth rate than the other two cryptic species under all experimental conditions, whereas cryptic species N2 occasionally showed a higher growth rate than cryptic species N5 at high salinities and lower temperatures. The distinct physiological properties of these cryptic species may explain their distribution pattern (a wider distribution of cryptic species N4 than N2 and N5) in New Zealand. The physiological divergence between the cryptic species could be related to their levels of evolutionary divergence, with more similar physiology between cryptic species, which share a more recent common ancestor (N2 and N5). Our findings underline that morphologically indistinguishable cryptic algal species are different in many other aspects and are truly independent entities.     

Settlement and growth of Antipathes pennacea on a shipwreck

A large population of the black coral Antipathes pennacea (Pallas) was studied underwater on a 37 year old shipwreck in Jamaican waters. The occurrence of A. pennacea at depths of 30–32 m supports previous observations that the minimum depth for black corals is reduced in turbid waters. Specimens of A. pennacea were found only on the underside of overhangs and 96 were measured. This pattern of occurrence suggests that the angle of inclination of the substrate is assesed prior to larval settlement. A. pennacea morphology was density dependent; isolated individuals grew three dimentionally in the form of a bush, the major stem being circular in cross section. Crowded individuals however, were tall with thin, oval or hourglass shaped stems and had a vertically orientated fan shape. The largest crowded individuals averaged growth rates of 57 mm height/year while the largest isolated individuals averaged 0.92 mm stem diameter/year.     

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.     

Scleritome construction,biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome.     

Coral density and predation affect growth of a reef-building coral

The influence of predation on the growth of stony corals has gained increased attention, although the degree to which coral conspecific density can modify the effects of corallivores remains poorly studied. Here, a field experiment was used to quantify the independent and combined effects of coral colony density and coral predators on the skeletal growth of massive Porites. Predator exclusion increased coral growth by 20%. Increasing coral density increased growth by 30%. However, the effect of predators was independent of coral density. Possible alternative mechanisms for increased skeletal growth at higher colony density include changes in near-field flow, resulting in increases in photosynthetic activity, nutrient uptake, or the increased accessibility of coral mutualists.     

Mortality and growth of juvenile coral Pocillopora damicornis (Linnaeus)

Early mortality in cohortsof the coral Pocillopora damicornis (Linnaeus) was monitored under experimental conditions on a reef in order to evaluate effects of sedimentation, grazing, predation and competition. Corals that settled in dishes in the laboratory were placed on the reef flat about 3 days after metamorphosis. Six different conditions were tested in each series of experiments: orientation of dishes (upward, vertical and downward) by with and without protection against potential grazers by covering the dish with a net. Survival of juvenile corals on both protected and unprotected dishes facing upward was lower than in the vertical or downward direction. Under the vertical facing and protected conditions, algal growth was more intensive and algae trapped sediment; mortality of juvenile corals by algae and sedimentation increased gradually. In the uprotected and vertical conditions, algal growth on the surface was removed constantly by grazing invertebrates and fishes and the juvenile corals were removed or killed as well. On the downward facing dishes, survivorship of juveniles was relatively high in both protected and unprotected conditions. This habitat attracted many sessile animals that killed some juveniles by competition. Thus, juvenile corals survived better in experimentally manipulated microhabitats not affected by direct sedimentation, not exposed to direct grazing activity, and not occupied by rapidly growing filamentous algae.