Coral Bioerosion at Enewetak: Agents and Dynamics

Significant differences were found in the extent to which massive coral species at Enewetak are excavated by boring organisms: Goniastrea retiformis, 7.9%; Porites lutea, 2.5%; and Favia pallida, 1.2%. While polychaetes constituted the most abundant and diverse group of coral associates, clionid sponges accounted for approximately 70–80% of skeletal damage. Clionid boring rates are initially very high but burrowing ceases when a particular burrow size (˜0.6 cm) or distance from the surface (≦2 cm) is reached. Most coral skeletal excavation occurs within 2 cm of a dead surface. Therefore, bioerosional damage to corals depends primarily on the amount of skeletal surface not covered by live coral tissue. Damage to skeletons is inversely correlated with colony size but is not correlated with coral growth rates or water depth. Massive corals have a potential escape in size from catastrophic bioerosion. Models relating 1) coral growth forms to skeletal density and stability in currents, 2) resistance of coral skeletons to breakage by water movement and suspended rubble, and 3) dead surface area on coral heads to bioerosional damage and consequent probability of detachment from the substrate, are proposed.     

The reef coral Goniastrea aspera: a ‘winner’ becomes a ‘loser’ during a severe bleaching event in Thailand

The reef coral Goniastrea aspera is regarded as one of the most environmentally tolerant species on Indo-Pacific reefs. Its demise, following a severe bleaching event in the Andaman Sea in the north-eastern Indian Ocean in 2010, was surprising in view of the rapid recovery of co-existing species such as Porites lutea. Demographic studies of G. aspera at this site showed the population was mainly composed of large individuals, which recruited in the early 1990s. These results, and size-specific mortality observed in G. aspera, post-bleaching, suggest that factors, related to size and age, may have contributed to the coral’s marked decline.     

Interseasonal and interspecies diversities of <Emphasis Type="Italic">Symbiodinium</Emphasis> density and effective photochemical efficiency in five dominant reef coral species from Luhuitou fringing reef,northern South China Sea

Although it is well established that different coral species have different susceptibilities to thermal stress, the reasons behind this variation are still unclear. In this study, 384 samples across five dominant coral species were collected seasonally between September 2013 and August 2014 at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea, and their algal symbiont density and effective photochemical efficiency (Φ _PSII) were measured. The results indicated that both the Symbiodinium density and Φ _PSII of corals were subject to significant interspecies and seasonal variations. Stress-tolerant coral species, including massive Porites lutea and plating Pavona decussata, had higher symbiont densities but lower Φ _PSII compared to the vulnerable branching species of Acropora over the course of all four seasons. Seasonally, coral symbiont densities were the lowest during winter, while during the same period, Φ _PSII of corals was at the highest point. Further analysis suggested that dissolved inorganic nutrients and upwelling in the reef area were probably responsible for the observed seasonal variations in symbiont density. The fact that Porites lutea has the lowest Φ _PSII during all four seasons is likely related to their symbionts’ lower capacity to provide required photosynthates for calcification. These results suggest that a coral’s thermal tolerance is primarily and positively dependent on its symbiont density and is less related to its effective photochemical efficiency.     

Interaction between benthic algae (Lyngbya bouillonii, Dictyota dichotoma) and scleractinian coral Porites lutea in direct contact

Competition between the massive scleractinian coral Porites lutea and two benthic algal species, thin-filamentous blue-green Lyngbya bouillonii (Cyanophyta) commonly observed growing as mats and fleshy brown Dictyota dichotoma (Phaeophyta), was investigated. Experiments were designed to expose coral fragments to different treatments to test the role of abrasion, shading and allelopathy by Lyngbya and Dictyota on coral growth and physiology in direct physical contact. The growth rates of coral fragments were significantly lower in both the algal/coral and the net control (only plastic net touched the corals) treatments than in the manipulation control (contact with algae and plastic net was prevented), demonstrating the importance of abrasion in Porites-Lyngbya and Porites-Dictyota interactions. Furthermore, coral fragments exposed to Lyngbya grew significantly slowly than net controls, but this effect was not statistically significant for P. lutea maintained in contact with Dictyota. Light levels were reduced equally in the algal/coral and shading mimic (plastic net touched the corals shaded with neutral-density filters) treatments. However, there were no significant differences in the growth rates between the shading mimic and the net control treatments, suggesting that shading had no measurable effect on coral growth. Thus, the growth of P. lutea in contact with Dictyota was reduced by abrasion whereas in direct contact with L. bouillonii, abrasion was supplemented by additional factors unique to Lyngbya in mediating coral-algal competition. Physical contact with L. bouillonii induced a significant reduction in photochemical efficiency (F_v / F_m) of PSII and chlorophyll concentration of in hospite zooxanthellae of P. lutea fragments, as well as a decrease of the symbiotic dinoflagellate density. Analysis of the growth rate and F_v / F_m of the investigated algae revealed a significant reduction in both parameters for D. dichotoma but not for L. bouillonii when in direct contact with P. lutea fragments. Thus, the competitive inhibition by the coral P. lutea and the brown alga D. dichotoma was mutual, while L. bouillonii acted as a one-sided inhibitor for scleractinian corals inducing bleaching and severe damage of live coral tissue. The fact that mats-forming blue-green alga L. bouillonii acts as a poison for scleractinian corals and is able to kill live coral tissue is reported for the first time. Allelochemical mechanism of the effect on live coral tissue by this alga is suggested. Possible mechanisms of competitive interactions for substrate between the coral polyps of scleractinians and algal species investigated are discussed.     

Extension growth rates in two coral species from high-latitude reefs of Bermuda

Mean annual growth rates (skeletal linear extension) in the hermatypic coralsPorites astreoides Lamarck andDiploria labyrinthiformis (L.) were investigated mainly by X-radiography from a variety of localities at various depths on the high-latitude coral reefs of Bermuda. Growth rates of both species show an inverse curvilinear relationship with depth, with highest growth rates in the shallow inshore waters of Castle Harbour and lowest at the edge of the Bermuda platform and on the adjacent fore-reef slope. Annual density bands form seasonal couplets, with narrow, high density bands appearing to form in the spring-summer months and wider, low density bands over the rest of the year in both species. Comparison of the growth rates ofP. astreoides from Bermuda with those from lower latitude West Indian localities, particularly Jamaica, indicates an inverse relationship with latitude and a similar inverse curvilinear relationship with depth at both geographic locations. Growth rate-locality differences in Bermuda for both species are suggested to be controlled mainly by local differences in wave energy and food supply and possibly seasonal water temperature fluctuations; growth rate-depth differences by decreasing illumination with depth; and growth rate-latitudinal differences by reduction in winter water temperatures and light levels with increasing latitude.     

Regeneration of artificial injuries on scleractinian corals and coral/algal competition for newly formed substrate

Porites cylindrica and Porites lutea fragments of colonies were inflicted with five different injury types: chisel, file, Water Pik, osmotic and cement injuries. The fragments were maintained in outdoor aquaria for a period of 240 days under light intensities varying from 2-5% to 70-90% of incident surface photosynthetic active radiation (PAR₀). During the exposure, changes in weight of the fragments, the rates of regeneration of the injuries, abundance of algae and animals settled onto injured areas were monitored. The regeneration rate of the injuries depended on interspecific differences in corals, injury types, number and composition of algae and animals settled onto the lesions, and light and temperature conditions. Competitive interactions between polyps and settlers occurred after colonizers settled onto the damaged surface or the live tissue. It is noteworthy that recovered coral tissue generally overgrew about 100 algal species with or without inhibition of coral growth by algae. In the summer period, the cyanobacterium Lyngbya majuscula covered some lesions (osmotic and cement) by 100%, thus reducing dramatically the regeneration rate of the inflicted injuries and also caused coral bleaching when in direct contact.     

Tomodensimétrie et mesures du rapport isotopique 18Q/16Q sur Porites lutea à Mururoa (Polynésie française) : une nouvelle approche pour appréhender l'influence du rayonnement sur la croissance corallienne annuelle

We have analysed samples of the scleractinian coral Porites lutea from Mururoa by computerized tomography, a method that appears more reliable than classic measurements of coral density. We correlate density measurements with oxygen isotopic composition, and then with climatologicalparameters (sea surface temperature and solar radiation). We demonstrate that at the Mururoa site, solar radiation is the major factor influencing the density pattern of the coral skeleton (i.e. calcification). However, the relationship between the density pattern and radiation is neither simple nor linear.     

Bacterial Communities Associated with Porites White Patch Syndrome (PWPS) on Three Western Indian Ocean (WIO) Coral Reefs

The scleractinian coral Porites lutea, an important reef-building coral on western Indian Ocean reefs (WIO), is affected by a newly-reported white syndrome (WS) the Porites white patch syndrome (PWPS). Histopathology and culture-independent molecular techniques were used to characterise the microbial communities associated with this emerging disease. Microscopy showed extensive tissue fragmentation generally associated with ovoid basophilic bodies resembling bacterial aggregates. Results of 16S rRNA sequence analysis revealed a high variability between bacterial communities associated with PWPS-infected and healthy tissues in P. lutea, a pattern previously reported in other coral diseases such as black band disease (BBD), white band disease (WBD) and white plague diseases (WPD). Furthermore, substantial variations in bacterial communities were observed at the different sampling locations, suggesting that there is no strong bacterial association in Porites lutea on WIO reefs. Several sequences affiliated with potential pathogens belonging to the Vibrionaceae and Rhodobacteraceae were identified, mainly in PWPS-infected coral tissues. Among them, only two ribotypes affiliated to Shimia marina (NR043300.1) and Vibrio hepatarius (NR025575.1) were consistently found in diseased tissues from the three geographically distant sampling localities. The role of these bacterial species in PWPS needs to be tested experimentally.     

Natural inducers for coral larval metamorphosis

 Coral gametes from Acropora millepora (Ehrenberg, 1834) and from multi-species spawning slicks provided larvae for use in metamorphosis assays with a selection of naturally occurring inducer chemicals. Four species of crustose coralline algae, one non-coralline crustose alga and two branching coralline algae induced larval metamorphosis. However, one additional species of branching coralline algae did not produce a larval response. Metamorphosis was also observed when larvae were exposed to skeleton from the massive coral Goniastrea retiformis (Lamarck, 1816) and to calcified reef rubble, demonstrating metamorphosis is possible in the absence of encrusting algae. Chemical extracts from these algae and the coral skeleton, obtained using either decalcification or simple methanol extraction procedures, also contained active inducers. These results extend the number of crustose algal species known to induce coral metamorphosis, suggest that some inducers may not necessarily be strongly associated with the calcified algal cell walls, and indicate that inducer sources in reef habitats may be more diverse than previously reported. Accepted: 21 May 1999     

Metabolic plasticity of the corals Porites lutea and Diploastrea heliopora exposed to large amplitude internal waves

The metabolic plasticity of the two mounding coral species Porites lutea (Milne-Edwards and Haime, 1860) and Diploastrea heliopora (Lamarck, 1816) was investigated in the Similan Islands (Thailand), an offshore Andaman Sea island group subjected to large amplitude internal waves (LAIW). Nutrient concentrations were highly correlated with LAIW intensity and contributed to 3- and 10-fold higher symbiont densities in P. lutea and D. heliopora, respectively, along with elevated pigment concentrations, protein content, host tissue, and symbiont biomass. The comparison of LAIW-exposed and LAIW-sheltered island faces, and LAIW-intense and LAIW-weak years suggests a species-specific metabolic plasticity to LAIW, where D. heliopora benefits more from increased nutrient and organic matter availability than P. lutea. The ubiquitous LAIW in Southeast Asia and beyond may provide so far unexplored clues to coral acclimatization to disturbances on various scales, and hence, a potential key to coral resilience to climate change.     

Large-amplitude internal waves sustain coral health during thermal stress

Ocean warming is a major threat for coral reefs causing widespread coral bleaching and mortality. Potential refugia are thus crucial for coral survival. Exposure to large-amplitude internal waves (LAIW) mitigated heat stress and ensured coral survival and recovery during and after an extreme heat anomaly. The physiological status of two common corals, Porites lutea and Pocillopora meandrina, was monitored in host and symbiont traits, in response to LAIW-exposure throughout the unprecedented 2010 heat anomaly in the Andaman Sea. LAIW-exposed corals of both species survived and recovered, while LAIW-sheltered corals suffered partial and total mortality in P. lutea and P. meandrina, respectively. LAIW are ubiquitous in the tropics and potentially generate coral refuge areas. As thermal stress to corals is expected to increase in a warming ocean, the mechanisms linking coral bleaching to ocean dynamics will be crucial to predict coral survival on a warming planet.     

Stress response of two coral species in the Kavaratti atoll of the Lakshadweep Archipelago, India

Frequent occurrences of coral bleaching and the ensuing damage to coral reefs have generated interest in documenting stress responses that precede bleaching. The objective of this study was to assess and compare physiological changes in healthy, semi-bleached and totally bleached colonies of two coral species, Porites lutea and Acropora formosa, during a natural bleaching event in the Lakshadweep Archipelago in the Arabian Sea to determine the traits that will be useful in the diagnosis of coral health. In April 2002, three “health conditions” were observed as “appearing healthy,” “semi-bleached” and “bleached” specimens for two dominant and co-occurring coral species in these islands. Changes in the pigment composition, zooxanthellae density (ZD), mitotic index (MI) of zooxanthellae, RNA/DNA ratios and protein profile in the two coral species showing different levels of bleaching in the field were compared to address the hypothesis of no difference in health condition between species and bleaching status. The loss in chlorophyll (chl) a, chl c and ZD in the transitional stage of semi-bleaching in the branched coral A. formosa was 80, 75 and 80%, respectively. The losses were much less in the massive coral P. lutea, being 20, 50 and 25%, respectively. The decrease in zooxanthellar density and chl a was accompanied by an increased MI of zooxanthellae and RNA/DNA ratios in both the species. There was an increase in accumulation of lipofuscin granules in partially bleached P. lutea tissue, which is an indication of cellular senescence. Multivariate statistical analyses showed that colonies of P. lutea ranked in different health conditions differed significantly in chl a, chl c, ZD, RNA/DNA ratios, and protein concentrations, whereas in A. formosa chl a, chl c, chl a/c, phaeopigments and MI contributed to the variance between health conditions.     

Fluorescent and skeletal density banding in Porites lutea from Papua New Guinea and Indonesia

Shallow water Porites lutea corals were collected along two transects normal to mainland shorelines, parallel to gradients in water quality: one, 7 km long, near Motupore Island in South Papua New Guinea, the other, 70 km long, from Jakarta Bay along the Pulau Seribu chain in the Java Sea. The corals were slabbed and studies were made of skeletal density bands as revealed by X-ray photography and fluorescent bands as revealed by ultraviolet light. Water quality measurements and rain-fall data were assembled for the two areas and related to skeletal banding patterns. For both areas, with increasing distance form mainland there is a decrease in overall brightness of fluorescence in corals and an increase in the contrast between bright and dull fluorescent bands. Fluorescence is bright, but seasonal banding is obscure in corals within about 2 km of stream mouths at Motopure and about 5 km of the coast in Jakarta Bay; this suggests that, despite low freshwater run-off during dry seasons, there are sufficient organic compounds which cause fluorescence in coral skeletons, to swamp seasonal effects. During the wet seasons, deluges of freshwater consequent on mainland rainfall of greater than about 150 mm/ month extend at least 7 km offshore in the Motupore area and perhaps tens of kilometres into Java Sea, giving distinctive bright and dull fluorescent banding in off-shore corals. The fluorescent banding pattern within corals on the Motupore reefs is similar in most corals along the transect and it correlates well with the Port Moresby monthly rainfall data. This relationship suggests that the same body (or bodies) of freshwater affect all reefs of the area during the wet season. The fluorescent banding in Java Sea corals does not show a precise correlation with either mainland or island monthly rainfall data; indeed the pattern of fluorescent banding on Pulau Seribu can only be matched in corals from reefs less than about 25 km apart. This suggests that in this area discrete water bodies carrying the relevant organic acids for coral fluorescence affect the fringing reefs on the chain of islands. Comparisons of fluorescent and density banding have revealed that for these areas, in general, periods of high freshwater run-off are times of deposition of less dense skeleton in Porites lutea corals.     

Highly Heterogeneous Bacterial Communities Associated with the South China Sea Reef Corals Porites lutea,Galaxea fascicularis and Acropora millepora

Coral harbor diverse and specific bacteria play significant roles in coral holobiont function. Bacteria associated with three of the common and phylogenetically divergent reef-building corals in the South China Sea, Porites lutea, Galaxea fascicularis and Acropora millepora, were investigated using 454 barcoded-pyrosequencing. Three colonies of each species were sampled, and 16S rRNA gene libraries were constructed individually. Analysis of pyrosequencing libraries showed that bacterial communities associated with the three coral species were more diverse than previous estimates based on corals from the Caribbean Sea, Indo-Pacific reefs and the Red Sea. Three candidate phyla, including BRC1, OD1 and SR1, were found for the first time in corals. Bacterial communities were separated into three groups: P. lutea and G. fascicular, A. millepora and seawater. P. lutea and G. fascicular displayed more similar bacterial communities, and bacterial communities associated with A. millepora differed from the other two coral species. The three coral species shared only 22 OTUs, which were distributed in Alphaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, Chloroflexi, Actinobacteria, Acidobacteria and an unclassified bacterial group. The composition of bacterial communities within each colony of each coral species also showed variation. The relatively small common and large specific bacterial communities in these corals implies that bacterial associations may be structured by multiple factors at different scales and that corals may associate with microbes in terms of similar function, rather than identical species.     

澄黄滨珊瑚、大管孔珊瑚和丛生盔形珊瑚排卵前后小穗生长特征

澄黄滨珊瑚、大管孔珊瑚和丛生盔形珊瑚排卵前后分别采集珊瑚小穗,在实验室条件下进行为期60 d的养殖,观察其生长特性,结果表明:3种珊瑚排卵前后骨骼密度变化在1.541—2.137 g/cm3之间,差异不显著。3种珊瑚小穗的生长率表现出相对一致的变化趋势,同一规格珊瑚小穗排卵前期生长率明显高于排卵后期;同一时期大规格珊瑚小穗生长率明显高于小规格珊瑚小穗,而且养殖中后期生长较快,养殖前期生长较慢,差异显著(P0.05)。澄黄滨珊瑚小穗边缘组织延伸度排卵后期大于排卵前期,大管孔珊瑚小穗边缘组织延伸度排卵前期大于排卵后期,以上两种珊瑚的小规格珊瑚小穗与大规格珊瑚小穗组织延伸度相当。随着养殖时间的持续,丛生盔形珊瑚小穗螅体增殖速率加快,各养殖阶段螅体数差异显著(P0.05),珊瑚小穗规格和养殖季节对其小穗螅体增殖数量没有显著影响。3种珊瑚小穗生长指标间多呈显著正相关,仅大管孔珊瑚小穗初始直径、初始重量与组织延伸度间,以及丛生盔形珊瑚小穗初始重量与初始螅体数量、生长率间相关性不明显。     

Age structure of massive Porites lutea corals at Luhuitou fringing reef (northern South China Sea) indicates recovery following severe anthropogenic disturbance

Luhuitou fringing reef at Hainan Island (northern South China Sea) has experienced severe anthropogenic disturbance, with live coral cover declining by > 80 % since the 1960 s. To assess the size structure of Porites lutea, we measured the sizes of 1,857 colonies from the reef flat (0 m) and slope (2–4 m depth). Both populations were positively skewed and leptokurtic in shape, indicating a high abundance of smaller colonies (averaging 21.4 ± 2.3 cm on the flat and 31.9 ± 2.8 cm on the slope). Age structure of populations was determined through growth rates extracted from X-rays of P. lutea cores. The majority of colonies (> 95 %) were < 50 yr old, with 55 % of P. lutea on the reef flat having recruited following the establishment of a marine reserve in 1990. The abundance of younger colonies indicates significant recovery of P. lutea following the removal of chronic anthropogenic disturbance.     

Coral Growth and Bioerosion of Porites lutea in Response to Large Amplitude Internal Waves

The Similan Islands (Thailand) in the Andaman Sea are exposed to large amplitude internal waves (LAIW), as evidenced by i.a. abrupt fluctuations in temperature of up to 10°C at supertidal frequencies. Although LAIW have been shown to affect coral composition and framework development in shallow waters, the role of LAIW on coral growth is so far unknown. We carried out a long-term transplant experiment with live nubbins and skeleton slabs of the dominating coral Porites lutea to assess the net growth and bioerosion in LAIW-exposed and LAIW-protected waters. Depth-related, seasonal and interannual differences in LAIW-intensities on the exposed western sides of the islands allowed us to separate the effect of LAIW from other possible factors (e.g. monsoon) affecting the corals. Coral growth and bioerosion were inversely related to LAIW intensity, and positively related to coral framework development. Accretion rates of calcareous fouling organisms on the slabs were negligible compared to bioerosion, reflecting the lack of a true carbonate framework on the exposed W faces of the Similan Islands. Our findings show that LAIW may play an important, yet so far overlooked, role in controlling coral growth in tropical waters.     

Genotypic diversity and distribution of Ostreobium quekettii within scleractinian corals

The green filamentous endolithic alga Ostreobium quekettii resides inside skeletons of scleractinian corals in close proximity with their tissue and plays a role in the viability of the coral and its associates. This study examined the distribution and diversity of O. quekettii within scleractinian corals from the Red Sea (Eilat, Gulf of Aqaba), using a molecular phylogenetic marker. The massive coral species Porites lutea and Goniastrea perisi were sampled from a depth range of 6–55 m, and ribulose 1,5-bisphosphate carboxylase large subunit gene (rbcL) DNA sequence of the alga was amplified and analyzed for diversity and distribution of ecological patterns. This work reveals that O. quekettii has at least seven different clades distributed along a depth gradient in the examined scleractinian corals. Among the seven identified clades, four were found only in P. lutea, while the other two clades are found in both P. lutea and G. perisi. Goniastrea perisi colonies at depth of 30 m had a distinct O. quekettii clade that was absent in P. lutea. It is obvious from this study that the green endolithic alga O. quekettii is not a single genotype as previously considered but a complex of genotypes and that this differentiation is of ecological significance.     

Passive colonization and asexual colony multiplication in the massive coral Porites lutea Milne Edwards & Haime

Heads of the reef-building coral Porites lutea Milne Edwards & Haime are occasionally separated or torn loose from the substratum by bioerosion or mechanical stresses. Detached heads may survive and colonize down-slope or down-stream soft bottoms, forming incipient reefs in habitats unsuitable for colonization by larval settlement. One important result of this process is reef consolidation and growth on the lagoonward edge of truncated, inter-island reef flats on atolls. In some cases, portions of the detached colonies remain attached at the original site; thus there is asexual colony multiplication.     

Responses of massive and branching coral species to the combined effects of water temperature and nitrate enrichment

The branching coral species Pocillopora damicornis (Linnaeus) and the massive coral species Porites lobata Dana were exposed for 30 days to different temperatures and nitrate concentrations to study the response of the coral-zooxanthella symbiosis. Results suggest that the effect of nitrate enrichment on the polyp-zooxanthella symbiosis varies according to the coral morphology. After the experimental period only 30% of P. damicornis colonies remained healthy, in contrast to 90% of P. lobata. The branching P. damicornis was significantly affected by the addition of nitrate, whereas P. lobata was significantly influenced by water temperature. The two species showed enhanced zooxanthella volume, and chlorophyll contents per cell under high nitrate concentrations. The reduced zooxanthellae density in both species indicated a detrimental influence of the interaction of high nitrate and high temperature. Tissue soluble proteins in P. lobata were significantly reduced by elevated temperature. Results showed that tissue soluble proteins and chlorophylls in P. lobata were from two- to three-fold higher than in P. damicornis. The number of zooxanthellae in P. lobata was double that of P. damicornis. Therefore, we suggest that the slow-growing species P. lobata is better able to cope with changing environmental conditions than the fast-growing coral P. damicornis.