Differential Impact of Monsoon and Large Amplitude Internal Waves on Coral Reef Development in the Andaman Sea

The Andaman Sea and other macrotidal semi-enclosed tropical seas feature large amplitude internal waves (LAIW). Although LAIW induce strong fluctuations i.e. of temperature, pH, and nutrients, their influence on reef development is so far unknown. A better-known source of disturbance is the monsoon affecting corals due to turbulent mixing and sedimentation. Because in the Andaman Sea both, LAIW and monsoon, act from the same westerly direction their relative contribution to reef development is difficult to discern. Here, we explore the framework development in a number of offshore island locations subjected to differential LAIW- and SW-monsoon impact to address this open question. Cumulative negative temperature anomalies – a proxy for LAIW impact – explained a higher percentage of the variability in coral reef framework height, than sedimentation rates which resulted mainly from the monsoon. Temperature anomalies and sediment grain size provided the best correlation with framework height suggesting that so far neglected subsurface processes (LAIW) play a significant role in shaping coral reefs.     

Benthic Reef Primary Production in Response to Large Amplitude Internal Waves at the Similan Islands (Andaman Sea,Thailand)

Coral reefs are facing rapidly changing environments, but implications for reef ecosystem functioning and important services, such as productivity, are difficult to predict. Comparative investigations on coral reefs that are naturally exposed to differing environmental settings can provide essential information in this context. One prevalent phenomenon regularly introducing alterations in water chemistry into coral reefs are internal waves. This study therefore investigates the effect of large amplitude internal waves (LAIW) on primary productivity in coral reefs at the Similan Islands (Andaman Sea, Thailand). The LAIW-exposed west sides of the islands are subjected to sudden drops in water temperature accompanied by enhanced inorganic nutrient concentrations compared to the sheltered east. At the central island, Ko Miang, east and west reefs are only few hundred meters apart, but feature pronounced differences. On the west lower live coral cover (-38 %) coincides with higher turf algae cover (+64 %) and growth (+54 %) compared to the east side. Turf algae and the reef sand-associated microphytobenthos displayed similar chlorophyll a contents on both island sides, but under LAIW exposure, turf algae exhibited higher net photosynthesis (+23 %), whereas the microphytobenthos displayed reduced net and gross photosynthesis (-19 % and -26 %, respectively) accompanied by lower respiration (-42 %). In contrast, the predominant coral Porites lutea showed higher chlorophyll a tissues contents (+42 %) on the LAIW-exposed west in response to lower light availability and higher inorganic nutrient concentrations, but net photosynthesis was comparable for both sides. Turf algae were the major primary producers on the west side, whereas microphytobenthos dominated on the east. The overall primary production rate (comprising all main benthic primary producers) was similar on both island sides, which indicates high primary production variability under different environmental conditions.     

Macroalgae Decrease Growth and Alter Microbial Community Structure of the Reef-Building Coral, Porites astreoides

With the continued and unprecedented decline of coral reefs worldwide, evaluating the factors that contribute to coral demise is of critical importance. As coral cover declines, macroalgae are becoming more common on tropical reefs. Interactions between these macroalgae and corals may alter the coral microbiome, which is thought to play an important role in colony health and survival. Together, such changes in benthic macroalgae and in the coral microbiome may result in a feedback mechanism that contributes to additional coral cover loss. To determine if macroalgae alter the coral microbiome, we conducted a field-based experiment in which the coral Porites astreoides was placed in competition with five species of macroalgae. Macroalgal contact increased variance in the coral-associated microbial community, and two algal species significantly altered microbial community composition. All macroalgae caused the disappearance of a γ-proteobacterium previously hypothesized to be an important mutualist of P. astreoides. Macroalgal contact also triggered: 1) increases or 2) decreases in microbial taxa already present in corals, 3) establishment of new taxa to the coral microbiome, and 4) vectoring and growth of microbial taxa from the macroalgae to the coral. Furthermore, macroalgal competition decreased coral growth rates by an average of 36.8%. Overall, this study found that competition between corals and certain species of macroalgae leads to an altered coral microbiome, providing a potential mechanism by which macroalgae-coral interactions reduce coral health and lead to coral loss on impacted reefs.     

Depth-Independent Reproduction in the Reef Coral Porites astreoides from Shallow to Mesophotic Zones

Mesophotic coral ecosystems between 30–150 m may be important refugia habitat for coral reefs and associated benthic communities from climate change and coastal development. However, reduced light at mesophotic depths may present an energetic challenge to the successful reproduction of light-dependent coral organisms, and limit this refugia potential. Here, the relationship of depth and fecundity was investigated in a brooding depth-generalist scleractinian coral, Porites astreoides from 5–37 m in the U.S. Virgin Islands (USVI) using paraffin tissue histology. Despite a trend of increasing planulae production with depth, no significant differences were found in mean peak planulae density between shallow, mid-depth and mesophotic sites. Differential planulae production over depth is thus controlled by P. astreoides coral cover, which peaks at 10 m and ~35 m in the USVI. These results suggest that mesophotic ecosystems are reproductive refuge for P. astreoides in the USVI, and may behave as refugia for P. astreoides metapopulations providing that vertical larval exchanges are viable.     

澄黄滨珊瑚和丛生盔型珊瑚非培养放线菌多样性

【目的】研究澄黄滨珊瑚(Porites lutea)和丛生盔型珊瑚(Galaxea fascicularis)联合放线菌物种多样性。【方法】实验提取两种珊瑚的总DNA,利用放线菌特异性引物对样品总DNA进行扩增,通过构建16S rRNA基因克隆文库和系统发育分析,对三亚鹿回头岸礁区优势物种澄黄滨珊瑚和丛生盔型珊瑚联合放线菌的多样性和群落结构进行研究。【结果】118个从澄黄滨珊瑚克隆文库中随机挑选的阳性克隆子归为58个OTUs,主要分布于酸微菌亚目、棒状杆菌亚目、微球菌亚目、丙酸杆菌亚目和未知类群。丛生盔型珊瑚克隆文库共获得96个序列,归为31个OTUs,主要分布于酸微菌亚目和未知的放线菌类群。多样性指数和稀疏度曲线分析结果显示澄黄滨珊瑚联合放线菌物种多样性比丛生盔型珊瑚更高。【结论】澄黄滨珊瑚和丛生盔型珊瑚拥有较高水平的放线菌物种多样性和复杂的群落结构,并隐藏着大量的高等级放线菌新分类单元。     

Fungi in Porites lutea: association with healthy and diseased corals.

Healthy and diseased scleractinian corals have been reported to harbour fungi. However, the species of fungi occurring in them and their prevalence in terms of biomass have not been determined and their role in coral diseases is not clear. We have found fungi to occur regularly in healthy, partially dead, bleached and pink-line syndrome (PLS)-affected scleractinian coral, Porites lutea, in the reefs of Lakshadweep Islands in the Arabian Sea. Mostly terrestrial species of fungi were isolated in culture from these corals. Hyaline and dark, non-sporulating fungi were the most dominant forms. Fungal hyphae extended up to 3 cm within the corals. Immunofluorescence detection using polyclonal immunological probes for a dark, initially non-sporulating isolate (isolate # 98-N28) and for a hyaline, non-sporulating fungus (isolate # 98-N18) revealed high frequencies of these in PLS-affected, dead and healthy colonies of P. lutea. Total fungal biomass accounted for 0.04 to 0.05% of the weight of corals in bleached corals and was higher than in PLS-affected and healthy colonies. Scanning electron microscopy revealed the presence of fungi within the carbonate skeleton and around polyps. Fungi appear to be a regular component of healthy, partially dead and diseased coral skeleton.     

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.     

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.     

Patterns and possible environmental controls of skeletogenesis of Porites lutea,South Thailand

Eleven fringing reef sites were investigated over a distance of about 50 km in the Phuket Region. There is a wide range in exposure to wave energy, and also water turbidity across the area. Annual increments of growth of shallow-water reef-front colonies of Porites lutea were calculated for the period November 1984 November 1986 using seasonal fluorescent banding (revealed with ultraviolet light) and Alizarin staining. Measurement of linear extension rate, skeletal bulk density, calcification rate, polyp numbers per unit area and colony surface morphology were made and compared. Linear extension rate and skeletal bulk density are inversely related within and between reef sites. Linear extension rate decreases and bulk density increases along a gradient of increasing hydraulic energy of the setting. Calcification (the product of linear extension rate and bulk density), although varying slightly from site to site, does not appear to relate to any obvious environmental inshore-offshore gradient. Skeletal bulk density is the most sensitive discriminator between reef sites, and we suggest that hydraulic energy of the setting is the main control on these spatial variations in skeletogenesis.     

Genetic diversity and large-scale connectivity of the scleractinian coral Porites lutea in the South China Sea

Coral Reefs - In light of recent declines in scleractinian communities worldwide, research on the genetic structure of and connectivity among coral populations has assumed importance. However, the...     

Metamorphosis of a Scleractinian Coral in Response to Microbial Biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.     

Differential Response of Fish Assemblages to Coral Reef-Based Seaweed Farming

As the global demand for seaweed-derived products drives the expansion of seaweed farming onto shallow coral ecosystems, the effects of farms on fish assemblages remain largely unexplored. Shallow coral reefs provide food and shelter for highly diverse fish assemblages but are increasingly modified by anthropogenic activities. We hypothesized that the introduction of seaweed farms into degraded shallow coral reefs had potential to generate ecological benefits for fish by adding structural complexity and a possible food source. We conducted 210 transects at 14 locations, with sampling stratified across seaweed farms and sites adjacent to and distant from farms. At a seascape scale, locations were classified by their level of exposure to human disturbance. We compared sites where (1) marine protected areas (MPAs) were established, (2) neither MPAs nor blast fishing was present (hence “unprotected”), and (3) blast fishing occurred. We observed 80,186 fish representing 148 species from 38 families. The negative effects of seaweed farms on fish assemblages appeared stronger in the absence of blast fishing and were strongest when MPAs were present, likely reflecting the positive influence of the MPAs on fish within them. Species differentiating fish assemblages with respect to seaweed farming and disturbance were typically small but also included two key target species. The propensity for seaweed farms to increase fish diversity, abundance, and biomass is limited and may reduce MPA benefits. We suggest that careful consideration be given to the placement of seaweed farms relative to MPAs.     

The Biology and Economics of Coral Growth

To protect natural coral reefs, it is of utmost importance to understand how the growth of the main reef-building organisms—the zooxanthellate scleractinian corals—is controlled. Understanding coral growth is also relevant for coral aquaculture, which is a rapidly developing business. This review paper provides a comprehensive overview of factors that can influence the growth of zooxanthellate scleractinian corals, with particular emphasis on interactions between these factors. Furthermore, the kinetic principles underlying coral growth are discussed. The reviewed information is put into an economic perspective by making an estimation of the costs of coral aquaculture.     

Response of Pleistocene Coral Reefs to Environmental Change Over Long Temporal Scales

SYNOPSIS. TWO studies from the Pleistocene coral reef fossilrecord demonstrate the sensitivity of reef communities to bothlocal environmental parameters and habitat reduction. In thefirst study, Pleistocene reef coral assemblages from Papua NewGuinea show pronounced constancy in taxonomic composition andspecies diversity between 125 and 30 ka (thousand years). Spatialdifferences in reef coral community composition during successivehigh stands of sea level were greater among sites of the sameage than among reefs of different ages, even though global changesin sea level, atmospheric CO₂ concentration, tropical benthichabitat area, and temperature varied at each high sea levelstand. Thus, local environmental variation associated with runofffrom the land had greater influence on reef coral communitycomposition than variation in global climate and sea level.Proportional sampling from a regional species pool does notexplain the temporal persistence and local factors likely playeda major role. Examination of coral reef response to global changeshould not only involve regional diversity patterns but alsolocal ecological factors, and the interactive effects of localand global environmental change. In the second study, Pleistocene extinction of two widespread,strictly insular species of Caribbean reef corals, Pocilloporacf. palmata (Geister, 1975) and an organ-pipe growth form ofthe Montastraea "annularis" species complex, was natural anddid not involve gradual decrease in range and abundance, butwas sudden (thousands of years) throughout the entire range.One explanation is that sea level drop at the Last Glacial Maximum(LGM—18 ka) resulted in a threshold of habitat reduction,and caused disruption of coral metapopulation structure. Thresholdeffects predicted by metapopulation dynamics may also explainthe apparent paradox of the large amount of degraded modernreef habitat without any known modern-day reef coral extinctions.The rapid extinction of widespread Pleistocene species emphasizesthe vulnerability of reef corals in the face of present rapidenvironmental and climatic change.     

The dynamics of the restoration of mechanical damage to colonies of the scleractinian coral Porites lutea under conditions of competition with algal settlers for substratum

Natural and anthropogenic catastrophes in the last decades of the 20th century and at the beginning of the new century have evoked significant changes in the biological diversity of coral reefs, viz., the mortality of hermatypic scleractinian corals that are replaced by communities of marine algae and seaweeds. In this connection, the study of the dynamics of algal colonization of a newly formed substratum and competition for the substratum between hermatypic corals and algae is of topical interest. This paper describes the results of investigations conducted in 2003 at the Sesoko Marine Biological Station of Ryukyu University (Okinawa, Japan). Colonies of the massive scleractinian coral Porites lutea were sampled from a fringing reef of Sesoko Island. Damages were inflicted on the upper portions of the colonies, the damaged coral fragments were placed in aquaria and maintained for six months under different light intensities in the absence of herbivorous and corallivorous animals. The experiments showed that under bright (70–90% of incident photosynthetically active radiation, PAR₀) and under moderate light (20–30% of PAR₀), the damaged parts of colonies of about 25 cm² were overgrown by newly formed polyps within six months. Under dim light (2–5% of PAR₀), this period was not sufficient for recovery from lesions. During the first month, the recovery rate of colonies was the highest and depended on the physiological state of the corals and light intensity: in bright and moderate light it was two times and more higher than under low light. During the subsequent months, the recovery rate was significantly lower and depended mainly on the degree of overgrowth of dead portions with algae and on their species composition. Under bright and moderate light, algal colonization of damaged colonies started with the settling of colonial and filamentous diatoms, cyanobacteria and green algae, followed by the formation of the algal turf community. Communities of red calcareous crusts and fleshy algae were mainly formed on damaged corals under low light. A comparison of experimental results showed that damaged colonies maintained in aquaria in the absence of herbivorous and corallivorous animals recovered 1.5 times faster than in the sea. We hypothesize that herbivorous fish have a negative rather than positive influence on the recovery of damaged colonies.     

Response of Coral Assemblages to the Interaction between Natural Temperature Variation and Rare Warm-Water Events

We examined changes in coral assemblages in four back-reef locations across the warm 1998 E1 Niño–Southern Oscillation (ENSO) event based on annually collected line-transect data from 3 years before and after this event. The physical locations of the reefs differed such that there was a 120%–275% warm-season range in the SDs of seawater temperatures but only minor differences in mean temperatures, based on 2 non-ENSO years. We tested the predictions that (a) rare warm-water events would produce fewer changes in eurythermal than stenothermal coral assemblages; and (b) after the disturbance, the stenothermal assemblages would more closely resemble the eurythermal ones. The 1998 event produced fewer changes in coral cover and community similarity among the assemblages in the reefs with high variation in temperature than in those with low variation in temperature. Despite the initially lower taxonomic richness in the eurythermal assemblage, there was an additional loss of taxonomic richness in the high and none in the stenothermal reefs. There was some evidence for taxonomic convergence, of the stenothermal towards the eurythermal reefs and a general loss of some of the branching taxa, such as branching Porites, Pavona, and Stylophora, and a relative increase in massive Porites and Favia. There was, however, moderate site specificity that did not produce true convergence. The eurythermal assemblages maintained the basic community structure but lost taxonomic richness, whereas the opposite was true for the stenothermal assemblages.     

Impact of recent coastal development and human activities on Nha Trang Bay, Vietnam: evidence from a Porites lutea geochemical record

Nha Trang Bay (NTB) is located on the Central Vietnam coast, western South China Sea. Recent coastal development of Nha Trang City has raised public concern over an increasing level of pollution within the bay and degradation of nearby coral reefs. In this study, multiple proxies (e.g., trace metals, rare earth elements (REEs), and Y/Ho) recorded in a massive Porites lutea coral colony were used to reconstruct changes in seawater conditions in the NTB from 1995 to 2009. A 14-year record of REEs and other trace metals revealed that the concentrations of terrestrial trace metals have increased dramatically in response to an increase in coastal development projects such as road, port, and resort constructions, port and river dredging, and dumping activities since 2000. The effects of such developmental processes are also evident in changes in REE patterns and Y/Ho ratios through time, suggesting that both parameters are critical proxies for marine pollution.