Effects of temperature on photosynthesis and respiration in hermatypic corals

Photosynthesis and respiration rates of the reef corals Pocillopora damicornis (Linn.), Montipora verrucosa (Lamarck), Porites compressa Dana and Fungia scutaria Lamarck were measured under controlled temperatures. Results indicate that coral metabolism is closely adapted to ambient temperature conditions. Tropical corals measured at Enewetak, Marshall Islands, showed greater primary production compared to maintenance requirements at elevated temperatures than did subtropical varieties of the same species in Hawaii. Photosynthesis: respiration (P:R) ratios were significantly and negatively related with temperature between 18° and 31°C for all Hawaiian corals, whereas at Enewetak this ratio generally showed a curvilinear relationship for this temperature range. Extrapolations of P:R regressions on temperatures to a value of 2.0 (estimated as a minimum required for long-term functional autotrophy) coincide for Hawaiian specimens with published upper lethal temperatures. Extrapolation of P:R regressions for Enewetak specimens at temperatures above 25°C suggests lethal temperatures for these corals to be 2 to 5 C° higher than for Hawaiian corals, in good agreement with recent experimental findings. Interspecific differences in P:R temperature regressions for Hawaiian corals correlating with upper lethal temperature tolerances are described.Contribution No. 505 of the Hawaii Institute of Marine Biology.     

Indirect effects of a key ecosystem engineer alter survival and growth of foundation coral species

Stegastes nigricans, a "farmerfish" that cultivates algal turf and defends territories from grazers and other intruders, can affect coral indirectly due to increased competition with farmed algal turf and/or reduced predation resulting from territorial aggression directed at corallivores. To investigate the indirect effects of this key ecosystem engineer on coral mortality and growth, we transplanted caged and exposed fragments of four coral species to patch reefs in French Polynesia on which we manipulated the presence of S. nigricans and turf, and to reefs naturally devoid of S. nigricans. Reef access was two to four times higher for herbivorous fishes, and two times higher for corallivorous fishes, when S. nigricans was removed, indicating that reef access is reduced for two important guilds of fishes when S. nigricans is present. Stegastes' territoriality indirectly benefited delicate acroporids (Montipora floweri and Acropora striata), yielding a twofold to fivefold reduction in skeletal loss due to lower predation frequencies in the presence of S. nigricans. Three corals, A. striata, M. floweri, and especially Porites australiensis, suffered mortality due to overgrowth significantly more frequently in the presence of farmed turf, but Pocillopora verrucosa did not. Algal abundance predicted the frequency of overgrowth for only A. striata and P. australiensis. M. floweri were more likely to be overgrown when exposed (uncaged) in the presence of S. nigricans, suggesting an interaction modification, in this case that initial predation increased susceptibility to competition with turf. In this community, the presence of S. nigricans may increase algal overgrowth of massive Porites by facilitating its turf competitors and simultaneously reduce predation of branching corals through territorial exclusion of corallivores. These indirect interactions may underlie previously documented community transitions from disturbance-resistant massive coral to recovering branching corals within S. nigricans territories.     

High genetic diversity of the symbiotic dinoflagellates in the coral Pocillopora meandrina from the South Pacific

Symbioses between dinoflagellates in the genus Symbiodinium (commonly referred to as zooxanthellae) and scleractinian corals are an essential feature for the maintenance of coral reefs. The fine-scale diversity and population structure of the zooxanthellae inhabiting the coral Pocillopora meandrina, a major reef building species in Polynesia, was examined. We used two polymorphic microsatellites to study seven populations from the South Pacific, whose host structuring has been previously investigated. The symbionts of P. meandrina showed high levels of diversity, with more than one zooxanthella genotype being identified in most of the host individuals. Genetic differentiation between symbiont populations was detected at a large scale (2,000 km) between the Tonga and the Society Archipelagos. Within the Society Archipelago, the two most remote populations (Tahiti and Bora-Bora; 200 km apart) were only weakly differentiated from each other. Statistical tests demonstrated that the symbiont genetic structure was not correlated with that of its host, suggesting that dispersal of the symbionts, whether they are transported within a host larva or free in the water, depends mainly on distance and water currents. In addition, the data suggests that hosts may acquire new symbionts after maternal transmission, possibly following a disturbance event. Lastly, the weak differentiation between symbiont populations of P. verrucosa and P. meandrina, both from Moorea, indicated that there was some host-symbiont fine-scale specificity detectable at the genetic resolution offered by microsatellites.     

Influence of corallivory, competition, and habitat structure on coral community shifts

The species composition of coral communities has shifted in many areas worldwide through the relative loss of important ecosystem engineers such as highly branched corals, which are integral in maintaining reef biodiversity. We assessed the degree to which the performance of recently recruited branching corals was influenced by corallivory, competition, sedimentation, and the interactions between these factors. We also explored whether the species-specific influence of these biotic and abiotic constraints helps to explain recent shifts in the coral community in lagoons of Moorea, French Polynesia. Population surveys revealed evidence of a community shift away from a historically acroporid-dominated community to a pocilloporid- and poritid-dominated community, but also showed that the distribution and abundance of coral taxa varied predictably with location in the lagoon. At the microhabitat scale, branching corals grew mainly on dead or partially dead massive Porites ("bommies"), promontories with enhanced current velocities and reduced sedimentation. A demographic study revealed that growth and survival of juvenile Pocillopora verrucosa and Acropora retusa, the two most common branching species of each taxon, were affected by predation and competition with vermetid gastropods. By 24 months of age, 20-60% of juvenile corals suffered partial predation by corallivorous fishes, and injured corals experienced reduced growth and survival. A field experiment confirmed that partial predation by corallivorous fishes is an important, but habitat-modulated, constraint for branching corals. Competition with vermetid gastropods reduced growth of both branching species but unexpectedly also provided an associational defense against corallivory. Overall, the impact of abiotic constraints was habitat-specific and similar for Acropora and Pocillopora, but biotic interactions, especially corallivory, had a greater negative effect on Acropora than Pocillopora, which may explain the local shift in coral community composition.     

The effects of an abnormal decrease in temperature on the Eastern Pacific reef-building coral Pocillopora verrucosa

Coral bleaching events are associated with abnormal increases in temperature, such as those produced during El Niño. Recently, a breakdown in the coral–dinoflagellate (genus Symbiodinium) endosymbiosis has been documented in corals exposed to anomalously cold-water temperatures associated with La Niña events. Given the ecological significance of such events, as well as the threat of global climate change, surprisingly little is known about the physiological response of corals to cold stress. This study evaluated some physiological effects of continuous temperature decline in colonies of the eastern Pacific reef-building coral Pocillopora verrucosa. Twenty days of incubation at 18.5–19.0 °C resulted in a substantial decrease in holobiont lipid and Chla content, as well as an increase in Symbiodinium density. These observations suggest a combination of symbiont acclimation due to the temperature decline and reallocation of carbon toward algal growth as opposed to translocation to the host coral. With a decreased availability of symbiont-derived carbon, the coral likely catabolized storage lipids in order to survive the stress event. Despite this stress and some tissue necrosis, no mortality was noted and corals recovered quickly when returned to the ambient temperature. As these results are in marked contrast to similar studies investigating elevated temperature on this coral from this same location, Pocillopora in the Mexican Central Pacific may be more prone to long-term damage and mortality during periods of ocean warming as opposed to ocean cooling.     

Synergistic effects of temperature,salinity and light on the hermatypic coral Montipora verrucosa

Temperature tolerance in the reef coral Montipora verrucosa (Lamarck) is affected by salinity and light. Low salinity reduces ability of the coral to survive shortterm exposure to elevated temperature. High natural light intensity aggravates damage sustained by corals at high temperature. In long-term growth experiments, high light intensity caused substantial loss of zooxanthellar pigment, higher mortality rates, reduced carbon fixation and lowered growth rate at both upper and lower sublethal temperatures Effects of light at optimal temperature were less dramatic. Interactions between physical environmental factors appear to be most important near the limits of tolerance for a given factor. Acclimation capability was indicated, and was influenced by both thermal history and pigmentation state of stressed corals.Contribution No. 543 of the Hawaii Institute of Marine Biology.     

Dynamics of a coral reef community after mass mortality of branching <Emphasis Type="Italic">Acropora</Emphasis> corals and an outbreak of anemones

Dynamics of a coral reef community at Tiao-Shi Reef, southern Taiwan were studied using permanent transects to examine coral recovery and successive cascades to collapse stage resulting from chronic anthropogenic impacts and typhoons. Three distinct zones were recognized within a relatively small study area (250 m across) formerly dominated by large stands of branching Acropora corals. The first zone still retains the dominance of branching Acropora corals, although they show a significant decreasing tendency. The second zone exhibits recovery with a significant increase in branching Montipora stellata, which is recruited and grows faster than branching Acropora corals. The third zone is occupied by anemone, Condylactis sp., and demonstrates a stable phase of coral deterioration without recovery. Such differences in coral reef community dynamics within a small spatial scale illustrate mosaic dynamics which have resulted from degradation of the water quality, patchy mortality of large branching Acropora thickets caused by typhoons, the rapid asexual fragmentation and growth of M. stellata making it a successful colonizer, and occupation by anemone, Condylactis sp., together with unstable remnants of dead Acropora rubbles have not allowed coral recruits to survive.     

Asynchronous deposition of dense skeletal bands in Porites lutea

Alternate dense and less-dense skeletal bands in massive corals have been used for many years to record the history of growth in species such as Porites lutea and Montastrea annularis, based on the assumption that one dense band and one less-dense band is equivalent to a year's growth. This report demonstrates that specimens of Porites lutea Edwards and Haime (collected from the same neighbourhood in Phuket, Thailand, from November 1983 through November 1984) produce skeletal bands asynchronously and that one year's growth in corals from certain sites may regularly consist of four bands of varying density. The annual banding pattern observed at all sites includes the deposition of a dense band in response to high sedimentation loads and, probably, reduced light levels.     

Effects of temperature on the mortality and growth of Hawaiian reef corals

Three common species of Hawaiian reef corals, Pocillopora damicornis (L.), Montipora verrucosa (Lamarck) and Fungia scutaria Lamarck, were grown in a temperature-regulated, continuous-flow sea water system. The skeletal growth optimum occurred near 26°C, coinciding with the natural summer ambient temperature in Hawaii, and was lowest at 21° to 22°C, representing Hawaiian winter ambient. Levels of approximately 32°C produced mortality within days. Prolonged exposure to temperatures of approximately 30°C eventually caused loss of photosynthetic pigment, increased mortality, and reduced calcification. Corals lived only 1 to 2 weeks at 18°C. The corals showed greater initial resistance at the lower lethal limit, but ultimately low temperature was more deleterious than high temperature. Results suggest that a decrease in the natural water temperature of Hawaiian reefs would be more harmful to corals than a temperature increase of the same magnitude.Contribution No. 504 of the Hawaii Institute of Marine Biology.     

Variability of stable isotopes and maximum linear extension in reef-coral skeletons at Kaneohe Bay, Hawaii

Stable-isotope and growth records of coral skeletons are often used to reconstruct tropical paleoclimate, yet few surveys have systematically examined the natural variability in coral skeletal ¹³C, ¹⁸O and maximum linear skeletal extension (MLSE) across depth. Here, interspecific, intraspecific, and geographical variations in coral skeletal ¹³C, ¹⁸O, and MLSE were examined in the corals Porites compressa, P. lobata, and Montipora verrucosa grown at 1.7, 5.0, and 8.3 m depth from August 1996 to March 1997 at The Point Reef and Patch Reef #41 field sites in Kaneohe Bay, Hawaii. Coral skeletal ¹³C values significantly decreased with depth and differed between species, but did not vary between field sites. ¹⁸O values were not significantly different across depth within a species, but did differ among species and field sites. High-resolution analysis of the intra-annual variation in skeletal ¹³C and ¹⁸O in P. compressa at 2.0 m depth confirms that these isotopes reflect changes in solar irradiance and temperature, respectively. Changes in MLSE across depth were consistent within, but highly variable among, species. Peak MLSE occurred at 1.7, 5.0, and 8.3 m for P. lobata, P. compressa, and M. verrucosa, respectively. Such interspecific variation in MLSE patterns may be attributable to one or more of the following: increases in zooplankton in the diet, changes in metabolic processes, or changes in growth form with depth. Overall, these results imply that natural inter- and intraspecific variability in coral skeletal ¹³C, ¹⁸O, and MLSE should be considered when interpreting and comparing coral-based tropical paleoclimate data from various coral species, depths, and field sites. Received: 6 October 1998 / Accepted: 8 July 1999     

Short-term growth measurements of corals using an accurate buoyant weighing technique

An accurate method for determining the growth rates of the skeleton of isolated branch tips (nubbins) of corals over intervals of less than 24 h is described. The skeletal weight of the coral was estimated from its buoyant weight in seawater whose density had been accurately determined. The coral tissues accounted for between 1 and 5% of the total buoyant weight in Pocillopora verrucosa and Acropora humilis with differing relative tissue biomass. After correcting for tissue buoyant weight, predictions of skeletal weight were accurate to within 1%. The method was used to estimate the growth of sample nubbins of Porites porites of similar diameter, in 2 m of water at Discovery Bay, Jamaica. Since growth of these branch tips is apical, growth rate could be expressed without correction for the size. The mean 24 h skeletal growth rate ranged between 40 and 47 mg. Differences could be measured between day-time and night-time growth, the day: night ratio being 3.7. The method also showed that P. porites virtually ceases calcification during the 4 to 5 d periods that it becomes enclosed in a mucus tunic. Nubbins of P. porites attached to the reef at different locations showed clear differences in growth rate with depth, and between clear and turbid water sites. The growth rate of nubbins was compared with that of branch tips of whole corals by measuring the linear extension after staining with Alizarin Red S. After 3 1/2 mo, the mean linear extension was 4.1 mm in each case, indicating that the growth rate of nubbins is the same as that of branch tips of the whole colony. It is suggested that this buoyant weighing technique will find applications in laboratory experiments with calcification mechanisms and as a bioassay on reefs exposed to environmental stress.Contribution No. 464 of the Discovery Bay Marine Laboratory     

Ingestion and assimilation of nitrogen from benthic sediments by three species of coral

We quantified the nitrogen and enzyme hydrolyzable amino acid (EHAA) concentrations of sediments prior to and after corals sloughed, ingested, and egested sediments layered onto their surfaces, for the three coral species Siderastrea siderea, Agaricia agaricites, and Porites astreoides in Jamaica. The percent nitrogen of the sediments egested by all three species was lower than in the sediments available to the corals. Additionally, the sediments sloughed (not ingested) by A. agaricites and P. astreoides were lower in percent nitrogen, while the sediments sloughed by S. siderea had the same percent nitrogen as that of the available sediments. The percent nitrogen of the sediments sloughed and egested by P. astreoides showed significant negative and positive relationships, respectively, to increasing sediment loads, while the percent nitrogen of the sediments sloughed and egested by both S. siderea and A. agaricites showed no relationship to sediment load. EHAA concentrations were not significantly different between the sloughed and available sediments but were significantly lower in the sediments egested by S. siderea and A. agaricites (EHAA concentrations were not measured for P. astreodies sediment fractions). Comparisons of the nitrogen and EHAA concentrations in the sloughed and egested sediments to what was available prior to coral processing show that maximum ingestion was between 0.1 and 0.2 µg N µg^–1 coral N cm^–2 and between 0.5 and 0.6 µg EHAA·cm^–2. Maximum assimilation efficiencies were estimated to be 30–60% of the available nitrogen. The data show that corals ingest and alter the nitrogen concentration of particles that land on their surfaces. The corals abilities to process these sediments, and the sediments possible contributions to coral nutrition, are discussed based on these results.Communicated by O. Kinne, Oldendorf/Luhe     

Sexual reproduction of three coral species from the Mexican South Pacific

Our understanding of the reproductive biology of corals from the Mexican southeastern Pacific is limited, and consequently, the role of reproduction in structuring coral communities is unclear. As a first attempt to understand the importance of sexual reproduction in structuring and maintaining of the coral communities from this region, we documented the reproductive cycles over 2 years (2003–2004) in three main reef-building corals species in the region. Pocillopora damicornis was shown to be hermaphroditic with asynchronous gamete development observed only in 2004; P. gigantea was characterized as both gonochoric and cosexually hermaphroditic. Absence of mature gametes was documented in both species, and an observation may be attributed to the 2003 El Niño Southern Oscillation event, which may have inhibited reproductive maturation via thermal stress. Porites panamensis was gonochoric with asynchronous development, and planulae were generally brooded. The presence of mature gametes and planulae in P. panamensis polyps suggests that this species is an important contributor to local and, likely, regional recruitment of this species. Further research should seek to identify important source populations for these coral recruits and document the exchange of larvae between coral populations of the Mexican Pacific.     

Preparation of high molecular weight DNA from hermatypic corals and its use for DNA hybridization and cloning

Previous attempts to extract high molecular weight DNA from hermatypic corals have failed because the starting material was mature tissue. The following paper describes the isolation of DNA from coral sperm which is of high molecular weight, and is suitable for DNA hybridization, digestion with restriction endonucleases and cloning. Gross DNA hybridization and hybridization with cloned repetitive DNA was used to investigate relatedness amongst members of the scleractinian coral family Acroporidae. Acropora formosa and A. pulchra were found to share a common (highly homologous) DNA sequence repeat; a related but less homologous sequence was present in A. latistella, and no homologous sequence was detected in Montipora digitata. These results imply a close taxonomic relationship between A. formosa and A. pulchra, and suggest that molecular criteria of this sort will be extremely useful in coral taxonomy.     

Stimulation of fat-body production in the polyps of the coralPocillopora damicornis by the presence of mutualistic crabs of the genusTrapezia

A mutualism exists between the xanthid crabs of the genusTrapezia and their host corals,Pocillopora damicornis. It has previously been established that these obligate coral residents benefit the coral hosts by defending them against echinoderm predators and by increasing the survival of polyps located deep between the coral branches. In turn, the corals apparently benefit the crabs by producing lipid-filled structures on which the trapezid crabs feed; these fat bodies may contain some of the lipid which in previous studies of coral metabolism has been termed excess. It was determined by experiments conducted at the Hawaii Institute of Marine Biology that the presence of crabs in colonies ofP. damicornis stimulates the polyps to produce the lipid-filled fat bodies; removal of crabs causes corals to cease producing fat bodies. A structure very similar to the fat bodies ofP. damicornis has been reported inAcropora durvillei. Both of these coral genera ordinarily possess xanthid-crab mutualists. This association between branching corals and crustaceans may have evolved because corals of these genera provide shelter among their branches and because these shallow-water corals are evidently capable of releasing lipid which is excess to the corals' metabolic needs, but which can be utilized by the crabs.     

Lipids and stable carbon isotopes in two species of Hawaiian corals,<Emphasis Type="Italic"> Porites compressa</Emphasis> and<Emphasis Type="Italic"> Montipora verrucosa</Emphasis>, following a bleaching event

Mass coral bleaching events have occurred on a global scale throughout the worlds tropical oceans and can result in large-scale coral mortality and degradation of coral reef communities. Coral bleaching has often been attributed to periods of above normal seawater temperatures and/or calm conditions with high levels of ultraviolet radiation. Unusually high shallow-water temperature (>29°C) in Kaneohe Bay, Hawaii, USA, in late summer (20 August–9 September) and fall (1–7 October) of 1996 produced visible bleaching of two dominant corals, Porites compressa Dana, 1864 and Montipora verrucosa Dana, 1864. The present study examined chlorophyll a (chl a), total lipid concentrations, and lipid class composition in corals of both species in which the entire colony was non-bleached, moderately bleached, or bleached. Skeletal, host tissue, and algal symbiont ¹³C values were also measured in non-bleached and bleached colonies. In additional unevenly bleached colonies, paired samples were collected from bleached upper surfaces and non-bleached sides. Samples were collected on 20 November 1996 during the coral recovery phase, a time when seawater temperatures had been back to normal for over a month. Chl a levels were significantly lower in bleached colonies of both species compared with non-bleached specimens, and in bleached areas of unevenly bleached single colonies. Total lipid concentrations were significantly lower in bleached P. compressa compared with non-bleached colonies, whereas total lipid concentrations were the same in bleached and non-bleached M. verrucosa colonies. The proportion of triacylglycerols and wax esters was lower in bleached colonies of both species. Both bleached and non-bleached M. verrucosa had from ~17% to 35% of their lipids in the form of diacylglycerol, while this class was absent in P. compressa. ¹³C was not significantly different in the host tissue and algal symbiont fractions in non-bleached and bleached samples of either species. This suggests that the ratio of carbon acquired heterotrophically versus photosynthetically was the same regardless of condition. Skeletal ¹³C was significantly lower in bleached than in non-bleached corals. This is consistent with previous findings that lower rates of photosynthesis during bleaching results in lower skeletal ¹³C values. The two species in this study displayed different lipid class compositions and total lipid depletions following bleaching, suggesting that there is a difference in their metabolism of lipid reserves and/or in their temporal responses to bleaching and recovery.Communicated by J.P. Grassle, New Brunswick     

Do corals select zooxanthellae by alternative discharge?

Loss of zooxanthellae (dinoflagellate Symbiodinium) from corals will sometimes lead to mass mortality of corals. To detect and quantify Symbiodinium released from corals, we developed a zooxanthellae “trap” and a quantitative PCR (qPCR) system with Symbiodinium clades A–F-specific primer sets. The trap was attached to a branch or the surface of several wild stony corals, and the water samples within the traps, including released Symbiodinium, were subjected to qPCR. All tested corals released clade C Symbiodinium at estimates of ~5,900 cells h⁻¹ cm⁻² of coral surface. Although all tested Pocillopora eydouxi harboured both clades C and D, some of these colonies released only clade C or released a lesser amount of clade D than that in the tissues. Our Symbiodinium quantification system revealed that wild hermatypic corals constantly release Symbiodinium to the environment. Our result suggests that some corals may discharge certain clades of Symbiodinium alternatively.     

Lipids of some Caribbean and Red Sea corals: total lipid,wax esters,triglycerides and fatty acids

The Caribbean reef-building corals Porites porites (Pallas) and Montastrea annularis (Ellis and Solander) and the Red Sea corals Pocillopora verrucosa (Ellis and Solander), Stylophora pistillata (Esper) and Goniastrea retiformis (Lamark) were analysed for total lipid, wax ester and triglyceride content, and fatty acid composition. M. annularis contained about 32% of dry weight as total lipid, whereas much lower values of between 11 and 17% were recorded for the other four species. It is concluded that there is greater variation in coral total lipid than hitherto thought. The total lipid contained a substantial proportion of wax ester (22 to 49%) and triglyceride (18 to 37%). The storage lipids (wax esters and triglycerides) accounted for between 6 and 20% of the dry weight and between 46 and 73% of the total lipid. Variation in lipid content between species could not be attributed to geographical location, but the low values for total lipid in Red Sea corals may in part be due to environmental factors as these samples were collected in winter. All corals analysed contained high levels of saturated fatty acids, the most abundant fatty acids being 16:0, 18:0 and 18:1n-9. Marked differences were observed in polyunsaturated fatty acid (PUFA) content between species, with comparatively low levels of 10 and 11% of fatty acids being recorded in M. annularis and G. retiformis, respectively. The values for the other species ranged between 21 and 37%. Fatty acid composition may vary according to the proportions of fatty acids obtained from diet, algal photosynthesis and synthesis by the animal tissues.     

Genetic diversity,clonality and connectivity in the scleractinian coral Pocillopora damicornis: a multi-scale analysis in an insular,fragmented reef system

Clonality and genetic structure of the coral Pocillopora damicornis sensu lato were assessed using five microsatellites in 12 populations from four islands of the Society Archipelago (French Polynesia) sampled in June 2008. The 427 analysed specimens fell into 132 multilocus genotypes (MLGs), suggesting that asexual reproduction plays an important role in the maintenance of these populations. A haploweb analysis of ITS2 sequences of each MLG was consistent with all of them being conspecific. Genetic differentiation was detected both between and within islands, but when a single sample per MLG was included in the analyses, the populations turned out to be nearly panmictic. These observations provide further evidence of the marked variability in reproductive strategies and genetic structure of P. damicornis throughout its geographic range; comparison with results previously obtained for the congeneric species Pocillopora meandrina underlines the importance of life history traits in shaping the genetic structure of coral populations.     

Experimental tests of suspension feeding in Atlantic reef corals

The ability of 15 species of Atlantic reef corals to act as suspension feeders was demonstrated by their removal of suspended particles from sea water in culture vessels. Mean clearance rates varied from 16.6 to 145.5 ml water cleared/h/cm² of live coral tissue. The lowest rates was found in Porites porites which is primarily a tentacle feeder, and the highest in Diploria clivosa which acts as both a tentacle feeder and suspension feeder. Rates of particle clearance in Agaricia agaricites, which is primarily a suspension feeder, were influenced by current velocity and type of food.