Physiology and taxonomy of scleractinian corals: a case study in the genus Stylophora

The morphology and skeletal characteristics of colonies of the coral genus Stylophora living on the reef edge at 1 m depth on the Jordanian coast of the Gulf of Aqaba (Red Sea) are those of S. mordax (Dana 1846) which has not been reported previously from that area. These colonies were considered earlier as ecomorphs of S. pistillata (Esper 1797) which lives down to at least 67 m on the reef slopes. Growth, organic content and metabolism were compared in colonies living at different depths (1,5,10 and 30 m). The trends of twelve parameters between 1 and 5 m were different from the variation observed between 5 and 30 m. Colonies living at 1 m have a higher chlorophyll content but a lower metabolic activity and growth rate than colonies living at 5 m. Most of these pecularities cannot be explained by the influence of environmental factors. It is therefore suggested that S. mordax is a valid taxon.     

Consequences of fission in the coral <Emphasis Type="Italic">Siderastrea siderea</Emphasis>: growth rates of small colonies and clonal input to population structure

Colony age and size can be poorly related in scleractinian corals if colonies undergo fission to form smaller independent patches of living tissue (i.e., ramets), but the implications of this life-history characteristic are unclear. This study explored the ecological consequences of the potential discrepancy between size and age for a massive scleractinian, first by testing the effect of colony origin on the growth of small colonies, and second by quantifying the contribution of ramets to population structure. Using Siderastrea siderea in St. John (US Virgin Islands) as an experimental system, the analyses demonstrated that the growth of small colonies derived from sexual reproduction was 2.5-fold greater than that of small ramets which were estimated to be ≈100 years older based on the age of the parent colonies from which they split. Although fission can generate discrete colonies, which in the case of the study reef accounted for 42% of all colonies, it may depress colony success and reef accretion through lowered colony growth rates.     

Patterns of resistance and resilience of the stress-tolerant coral Siderastrea radians (Pallas) to sub-optimal salinity and sediment burial

The coastal lagoons of south Florida, U.S., experience fluctuating levels of sedimentation and salinity and contain only a subset of the coral species found at the adjacent reefs of the Florida Reef Tract. The dominant species within these habitats is Siderastrea radians, which can reach densities of up to 68 colonies m^- 2 and is commonly exposed to salinity extremes (< 10 psu to > 37 psu) and chronic sediment burial. In this study, we document the patterns of resistance and resilience of S. radians to sub-optimal salinity levels and sediment burial in a series of short-term, long-term, acute, chronic, single-stressor, and sequential-stressor experiments.S. radians displayed remarkable patterns of resistance and resilience and mortality was documented only under prolonged (≥ 48 h) continuous exposure to salinity extremes (15 and 45 psu) and chronic sediment burial. A reduction in photosynthetic rates was documented for all salinity exposures and the decrease in photosynthesis was linearly related to exposure time. Negative impacts on photosynthetic rates were more severe under low salinity (15 psu) than under high salinity (45 psu). Corals exposed to intermediate, low-salinity levels (25 psu), exhibited initial declines in photosynthesis that were followed by temporary increases that may represent transient acclimatization patterns. The impacts of sediment burial were influenced by the duration of the burial period and ranged from a temporary reduction in photosynthesis to significant reductions in growth and tissue mortality. The maintenance of P/R ratios > 1 and the rapid (< 24 h) recovery of photosynthetic rates after burial periods of 2-24 h indicates that S. radians is able to resist short-term burial periods with minor physiological consequences. However, as burial periods increase and colonies become covered at multiple chronic intervals, sediment burial resulted in extended photosynthetic recovery periods, reduced growth, and mortality. Under normal conditions (i.e., no salinity stress), S. radians was very effective at clearing sediments, and > 50% of the colonies' surface area was cleared within 1 h. However, clearing rates were influenced by physiological status, and prior exposure to sub-optimal salinity significantly reduced the clearing rates of stressed colonies.The response of S. radians to disturbance documented in this study characterizes this species as highly stress-tolerant and provides an explanation for its present high abundance in both reef and marginal environments. Moreover, the key life-history attributes of S. radians, such as brooding reproductive strategy, small colony size, high stress-tolerance, and high recruitment rates, suggest the potential for this species to replace reef-building taxa under increased disturbance scenarios in Florida and elsewhere in the region.     

The effects of elevated temperature on the photosynthetic efficiency of zooxanthellae in hospite from four different species of reef coral: a novel approach

Bleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are known as zooxanthellae, and/or loss of algal pigments. The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, Agaricia lamarki, Agaricia agaricites and Siderastrea radians was examined by pulse-amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (30–36°C). Zooxanthellae within M. annularis and A. lamarki were found to be more sensitive to elevated temperature, virtually complete disruption of photosynthesis being noted during exposure to temperatures of 32 and 34°C. The photosynthetic efficiency of zooxanthellae within S. radians and A. agaricites decreased to a lesser extent. Differences in the loss of algal cells on an aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the non-invasive PAM technique with whole-cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbionts within different species of coral. Zooxanthellae within M. annularis appear to be more susceptible to heat-induced damage at or near the reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non-photochemical pathways, thereby protecting the photosystem from damage during heat exposure.     

Differential survival of nursery‐reared Acropora cervicornis outplants along the Florida reef tract

In recent decades, the Florida reef tract has lost over 95% of its coral cover. Although isolated coral assemblages persist, coral restoration programs are attempting to recover local coral populations. Listed as threatened under the Endangered Species Act, Acropora cervicornis is the most widely targeted coral species for restoration in Florida. Yet strategies are still maturing to enhance the survival of nursery‐reared outplants of A. cervicornis colonies on natural reefs. This study examined the survival of 22,634 A. cervicornis colonies raised in nurseries along the Florida reef tract and outplanted to six reef habitats in seven geographical subregions between 2012 and 2018. A Cox proportional hazards regression was used within a Bayesian framework to examine the effects of seven variables: (1) coral‐colony size at outplanting, (2) coral‐colony attachment method, (3) genotypic diversity of outplanted A. cervicornis clusters, (4) reef habitat, (5) geographical subregion, (6) latitude, and (7) the year of monitoring. The best models included coral‐colony size at outplanting, reef habitat, geographical subregion, and the year of monitoring. Survival was highest when colonies were larger than 15 cm (total linear extension), when outplanted to back‐reef and fore‐reef habitats, and when outplanted in Biscayne Bay and Broward–Miami subregions, in the higher latitudes of the Florida reef tract. This study points to several variables that influence the survival of outplanted A. cervicornis colonies and highlights a need to refine restoration strategies to help restore their population along the Florida reef tract.     

Spatial and size-frequency distribution of <Emphasis Type="Italic">Acropora</Emphasis> (Cnidaria: Scleractinia) species in Chinchorro Bank,Mexican Caribbean: implications for management

The Mexican Government decreed Chinchorro Bank reef as a Biosphere Reserve in 1996. The aim of this study was to evaluate the spatial and size-frequency distribution of Acropora spp. in order to provide further knowledge and tools to enhance management. A field survey was conducted, within six regions, to locate and measure Acropora patches in the reef lagoon. Density, colony size and living tissue cover of Acropora colonies were evaluated using the line-intercept transect technique, combining direct observations and video transects. The results showed that Acropora spp. was preferentially distributed in the southern regions; where cover and density were high. Based on these results and considering that Acropora spp. produces landscape heterogeneity, which in turn generates shelter for other species, including some of considerable economic importance, then at least the South East region should be considered as a key area for Acropora species conservation, and should be included in the Chinchorro Bank management plan.     

The aftermath of coral bleaching on a Maldivian reef—a quantitative study

Since the bleaching event of 1998, the development of the reef flat and upper reef slope on a Maldivian reef (the Komandoo house reef; Komandoo Island, Lhaviyani atoll or Fadiffolu atoll) is under detailed observation. We quantitatively recorded specific losses, re-colonisation by coral larvae on transects on the reef flat and on dead Acropora tables at the reef slope and regeneration of partly damaged large Porites and Diploastrea—colonies over the period from 1999 to 2004. The detrimental effects on the reef structure by bioerosion and hydrodynamics, as well as the overall status of the reef community were qualitatively assessed. Recruitment soon after the bleaching was more pronounced than in the following years, Pavona varians being a main constituent. The temporal re-colonisation pattern points at an emergency spawning of local Scleractinia just prior to the bleaching, whereas a sharp decrease of young settlers in 2001 and 2002 confirms a reduction of fertile colonies. The dominant species in the coral community shifted from acroporids and pocilloporids to agariciids. The skeletal deposition of recovering Diploastrea heliopora was equivalent to that before the bleaching, but much less than that of neighbouring Porites lobata colonies. The slow and scattered formation of new reef substance, which would structurally strengthen the reef, is however outweighed by the collapse of dead protruding and spacious colonies (e.g., Acropora tables). Six years after the bleaching, the formerly three-dimensional structure of the reef flat and upper reef slope presents as a levelled field of rubble, only partly consolidated by incrusting corals. Considering the recurrence of bleaching events (1987, 1998) and the results of the present study, one may assume a cascading deterioration of the status of the reef for the future.     

Extent and effect of Black Band Disease on a Caribbean reef

The effect of Black Band Disease (BBD) among colonies ofMontastrea annularis, M. cavernosa, Diploria strigosa, D. labryinthiformis, S. siderea andColpophyllia natans was determined at 7 shallow locations in the Virgin Islands. Between September 1988 and November 1988, 0.2% of 9204 colonies of these species were infected with BBD in 6908 m² of reef at 22 randomly chosen areas. Infected colonies were not clumped suggesting that the disease is not highly infectious between colonies. BBD infection rates in areas surveyed 4 times between August 1988 and September 1989 in Greater Lameshur Bay, St. John, USVI, were significantly lower in winter compared to summer. BBDs were found on 5.5% of the colonies ofD. strigosa in Fall 1988, and 7 out of 12 infected colonies lost >75% of their tissue in 6 months. Low level, chronic BBD infections could convert 3.9% of the living cover ofD.strigosa to free space per year, thereby creating substrata for successional processes.     

Calcifying coral abundance near low-pH springs: implications for future ocean acidification

Rising atmospheric CO₂ and its equilibration with surface ocean seawater is lowering both the pH and carbonate saturation state (Ω) of the oceans. Numerous calcifying organisms, including reef-building corals, may be severely impacted by declining aragonite and calcite saturation, but the fate of coral reef ecosystems in response to ocean acidification remains largely unexplored. Naturally low saturation (Ω ~ 0.5) low pH (6.70–7.30) groundwater has been discharging for millennia at localized submarine springs (called “ojos”) at Puerto Morelos, México near the Mesoamerican Reef. This ecosystem provides insights into potential long term responses of coral ecosystems to low saturation conditions. In-situ chemical and biological data indicate that both coral species richness and coral colony size decline with increasing proximity to low-saturation, low-pH waters at the ojo centers. Only three scleractinian coral species (Porites astreoides, Porites divaricata, and Siderastrea radians) occur in undersaturated waters at all ojos examined. Because these three species are rarely major contributors to Caribbean reef framework, these data may indicate that today’s more complex frame-building species may be replaced by smaller, possibly patchy, colonies of only a few species along the Mesoamerican Barrier Reef. The growth of these scleractinian coral species at undersaturated conditions illustrates that the response to ocean acidification is likely to vary across species and environments; thus, our data emphasize the need to better understand the mechanisms of calcification to more accurately predict future impacts of ocean acidification.     

A late Devonian (Frasnian) coral-bafflestone reef at Houshan in Guilin, South China

Summary Givetian to early Carboniferous sediments of South China are characterized by carbonates. Middle and Late Devonian strata are best developed in the Guilin area. Reefs and organic shoals are recorded by various lithofacies types indicating the existence of an extended carbonate platform and a change of the composition of reef communities in time. Starting in the late Devonian, stromatoporoids and corals were replaced by algae that subsequently played an important role together with stromatoporoids, receptaculitids and fasciculate rugose corals in reef communities. In Houshan, 5 km west of Guilin, a coral-bafflestone reef occurs in the Frasnian strata, situated near an offshore algal-stromatoporoid reef. The coral reef was formed in a back-reef area adjacent to the inner platform margin. The coral-bafflestone reef is unique among the late Devonian reefs of South China with regard to the biotic composition. The reef is composed of fasciculate colonies ofSmithiphyllum guilinense n. sp. embedded within in packstones and wackestones. The height of colonies reaches 1 m. The community is low-diverse. The species ofSmithiphyllum occurring in the Frasnian reef complexes of Guilin exhibit a distinct facies control:Smithiphyllum guilinense occurs in or near to margin facies and formed bafflestone, constituting a coral reef whereasSmithiphyllum occidentale Sorauf, 1972 andSmithiphyllum sp.—characterized by small colonies with thin corallites—are restricted to the back-reef and marginal slope facies. The bush-like coral colonies baffled sediments. Algae and stromatoporoids (mainlyStachyodes) are other reef biota. Reef-dwelling organisms are dominated by brachiopods. The reefs are composed from base to top of five lithofacies types: 1) cryptalgal micrite, 2) peloidal packstone, 3) stromatactis limestone, 4) coral-bafflestone, and 5) pseudopeloidal packstone. The reef complex can be subdivided into back-reef subfacies, reef flat and marginal subfacies, and marginal fore-slope subfacies. The Houshan coral-bafflestone reef is not a barrier reef but a coral patch reef located near the inner margin of a carbonate platform.     

Differentiation betweenPhaeocystis pouchetii (Har.) Lagerheim andPhaeocystis globosa Scherffel

An Arctic clone ofPhaeocystis pouchetii LAGERHEIM was compared toPhaeocystis globosa SCHERFFEL isolated from the southern North Sea with regard to temperature tolerance and colony shapes. Already youngP.pouchetii colonies (<100 m) show the typical distribution of the cells in groups, separated from each other by wide zones of cell-free mucilage; the maximum colony size is ca 2 mm in diameter.P.pouchetii colonies form clouds with bubble-like vesicles, spherical colony-shapes are seldom found.P.globosa colonies are spherical up to a size of 2 mm; the cells are distributed homogeneously over the periphery of the colonies. A pouchetii-like distribution of cells never occurs either in the spherical young colonies or in the pear-shaped old colonies (size up to 8 mm). A development from the colony shape of the globosa-type to the pouchetii-type or vice versa was never found. Therefore the colony shape has to be considered a constant distinctive character. Single cells ofP.pouchetii andP.globosa cannot be separated from each other by using the light microscope; this also holds for the flagellates and the non-motile cells.P.pouchetii grows well between 0°C and 14°C,P.globosa between 4°C and 22°C, respectively. Because of the distinctive differences in the morphology of the colonies and the differences in temperature tolerances we propose thatPhaeocystis globosa should no longer be considered conspecific withPhaeocystis pouchetii.     

Sediment retention in encrusting Palythoa spp.—a biological twist to a geological process

 Carpet sea anemones of the genus Palythoa are common inhabitants of reef crest environments in the Florida Keys reef tract. Through a unique assimilation mechanism, Palythoa spp. entomb carbonate sediment within their tissues. The amount of sediment assimilated is significant, averaging almost 45% of wet tissue weight. Palythoa spp. assimilate all available minerals on the reef. Aragonite, magnesium calcite, calcite and minor quantities of siliciclastic components are all assimilated in proportions comparable to their content in adjacent sediment sinks. There is also no preference in terms of skeletal composition; coral grit, coralline red algae, Halimeda and other allochems are all equally assimilated into Palythoa spp. tissue. The only preference is particle size. Sediment extracted from tissue samples is generally ?125 μm in size, far finer than ambient sediment found adjacent to Palythoa spp. colonies (predominantly >500 μm). Much of the finest sediment extracted from Palythoa spp. tissue is composed of elongated crystal aggregates of aragonite. These particles appear to have been produced in situ through biologically influenced mineralization. Aggregates nucleated on exogenous sediment and attained their elongated form as assimilation proceeded. When Palythoa spp. colonies die, the assimilated sediment and the crystal aggregates are released back into the reef environment. The eventual fate of this material has yet to be determined. Accepted: 5 July 1996     

Growth of Mediterranean reef of<Emphasis Type="Italic"> Cladocora caespitosa</Emphasis> (L.) in the Late Quaternary and climate inferences

A sclerochronological analysis was performed on Cladocora caespitosa corals from Late Pleistocene terraces near Taranto (Apulia, Italy) to reconstruct the main palaeoenvironmental conditions at the time of their growth. The fossil corallites were sampled in the Santa Teresiola uplifted bank or ‘open frame reef’ attributed to the Last Interglacial Period. The typical, annual growth pattern of the temperate coral with two alternate high- and low-density bands allowed the reconstruction of two multidecadal growth curves of 61 and 95 years. Trend analysis showed oscillations in annual growth rates similar to those observed in recent, living colonies sampled along a north–south latitudinal transect around the Italian and Croatian coasts as far as Tunisia. The mean growth rate of the fossil reef (4.2 ± 2 mm year⁻¹) is comparable to those measured on colonies living in the coldest part of the Mediterranean Sea. The comparison with data from living Croatian banks shows how fossil C. caespitosa lived in a semi-enclosed environment characterized by seasonal inputs of fresh, cold water. The greatest variations in decadal growth rates of the fossil colonies support the hypothesis of larger amplitude of the seasonal cycles in the past. The death of the fossil bank was probably due to a sudden alluvial input that suffocated the reef with a great amount of mud. Another possible cause of the death of the bank was a prolonged increase in summer temperatures that caused colony mortality and enhanced algal colonization.     

Experimental fragmentation reduces sexual reproductive output by the reef-building coral Pocillopora damicornis

Natural and anthropogenic disturbances may fragment stony reef corals, but few quantitative data exist on the impacts of skeletal fragmentation on sexual reproduction in corals. We experimentally fragmented colonies of the branching coral Pocillopora damicornis and determined the number and size of planula larvae released during one lunar reproductive cycle. Partially fragmented colonies significantly delayed both the onset and peak period of planula release compared with intact control colonies. Most fragments removed from the corals died within 11–18 days, and released few planulae. The total number of planulae released per coral colony varied exponentially with remaining tissue volume, and was significantly lower in damaged versus undamaged colonies. However, the number of planulae produced per unit tissue volume, and planula size, did not vary with damage treatment. We conclude that even partial fragmentation of P. damicornis colonies (<25% of tissue removed) decreases their larval output by reducing reproductive tissue volume. Repeated breakage of corals, such as caused by intensive diving tourism or frequent storms, may lead to substantially reduced sexual reproduction. Therefore, reef management should limit human activities that fracture stony corals and lead to decreases in colony size and reproductive output. Accepted: 2 February 2000     

Relocating bleached Platygyra sinensis facilitates recovery from thermal stress during a minor bleaching event

The recovery of bleached corals is crucial in ensuring the persistence of the coral reef ecosystem function. This study investigated whether relocating bleached Platygyra sinensis colonies was a viable measure to accelerate their recovery. During a mild bleaching event in 2014, eight bleached colonies of P. sinensis were relocated from an affected reef at Sultan Shoal, Singapore, to a reef at Kusu that was less impacted. Another eight colonies at Sultan Shoal were tagged as controls. After five months, 88% of relocated bleached colonies at Kusu showed full recovery whereas only 25% of the control bleached colonies at Sultan Shoal had recovered. The differential coral recovery among the two sites was most likely due to lower seawater temperatures and faster water flow at Kusu, which helped to mitigate the effects of thermal stress on the bleached corals. This relocation study demonstrated that relocating bleached P. sinensis to sites with more favourable environmental conditions is a viable approach to reduce bleaching impacts for this species.     

Boring by Macro-organisms in the Coral Montastrea annularis on Barbados Reefs

The fauna boring into Montastrea annularis includes sponges, bivalves, sipunculid and polychaete worms and barnacles. Sponges are most important in hard tissue destruction and account for more than 90% of the total boring in most heads. Bivalves and barnacles are locally important. Sipunculids and sabellids account for less than 4% of the total boring. The volume removed from coral samples by boring ranged from 3–60% and samples from a deeper bank reef were more highly bored than fringing reef samples. An average of 20% of the volume of bank reef corals, and 5% of the volume of fringing reef corals, was removed by boring. The distribution of individual borers is not a function of depth. The density and variety of borers and the extent of boring in coral heads is greater in older heads. The ratio of living coral surface to dead encrusted areas on colonies also influences borer density and the extent of boring.     

Linear extension rate is independent of colony size in the coral Pocillopora damicornis

Measurements of the skeletal extension rate of branches of the reef coral Pocillopora damicornis showed that the linear extension rate is independent of colony size for colonies from 1.9 to 19 cm in diameter. Analysis of existing data from Western Australia, Samoa, the Great Barrier Reef and Hawaii supports the finding that linear extension is not related to colony size in this species.     

A unique coral reef formation discovered on the Great Astrolabe Reef, Fiji

 A spectacular mound-like reef formation (126 m in circumference, 10 m high) dominated by highly arched and record-size colonies of the unattached mushroom coral Halomitra pileus, along with 17 other species of the family Fungiidae, occurs in 31 m of water on the sedimentary lagoon floor of the Great Astrolabe Reef, Fiji. Core samples show radiocarbon dates which indicate that the formation hypothetically began building ∼4500 y ago, with a calculated mean accretion rate of 2.2 mm ⋅ y^-1. The majority of fossil and living material is contributed by H. pileus colonies between 40–70 cm mean diameter, with some individuals up to 1.5 m in diameter. The size, fungiid diversity, and geological history of the bioherm is unprecedented and represents the first example of a coral reef constructed almost entirely by Fungiidae. Accepted: 29 July 1996     

Fragmentation in Montipora ramosa: the genet and ramet concept applied to a reef coral

The fates of Montipora ramosa fragments have been followed and related to physical factors on the reef. The degree of genetic homogeneity between colonies of M. ramosa was assessed by reciprocal grafting techniques, and the cross reef cline interpreted in terms of the degree of fragmentation. Two botanical terms, genet and ramet, referring to individuals derived from sexual (planula settlement) and asexual (fragmentation of colonies) processes respectively have been introduced to the coral literature.     

Holocene growth history of an eastern Pacific fringing reef,Punta Islotes,Costa Rica

Rock and sediment cores reveal that a well-developed fringing reef in Golfo Dulce, Pacific Costa Rica, up to 9 m thick was established on Cretaceous basalt about 5500 y BP. It is presently being smothered with fine sediments and is almost completely dead. This reef is made up of three main facies that are represented by comparable extant reef zones: reef-flat branching coral, fore-reef slope massive coral, and fore-reef talus sediment facies. Reef growth began with the establishment of small patch reefs dominantly formed by the branching coral Pocillopora damicornis. P. damicornis spread across the basalt bench and massive colonies of Porites lobata grew on the outer slopes, eventually blocking the seaward transport of Pocillopora fragments to the fore-reef talus sediments. The reef flourished until 500 years ago. Lower accumulation rates during the past 500 years may be due to deteriorating environmental conditions rather than slower growth after the reef reached sea level. Present-day reef communities are severely degraded with less than 2% living coral cover. The increased turbidity associated with the final stage of degradation of this reef is probably related to human activity on the adjacent shores, including deforestation, mining, and road construction.