Survival Of Coral Reefs Research Articles

Hyposalinity stress compromises the fertilization of gametes more than the survival of coral larvae

The life cycle of coral is affected by natural and anthropogenic perturbations occurring in the marine environment. In the context of global changes, it is likely that rainfall events will be more intense and that coastal reefs will be exposed to sudden drops in salinity. Therefore, a better understanding of how corals—especially during the pelagic life stages—are able to deal with declines in salinity is crucial. To fill this knowledge gap, this work investigated how gametes and larva stages of two species of Acropora (Acropora cytherea and Acropora pulchra) from French Polynesia cope with drops in salinity. An analysis of collected results highlights that both Acropora coral gametes displayed the same resistance to salinity changes, with 4h30-ES50 (effective salinity that decrease by 50% the fertilization success after 4h30 exposure) of 26.6 ± 0.1 and 27.5 ± 0.3‰ for A. cytherea and A. pulchra, respectively. This study also revealed that coral gametes were more sensitive to decreases in salinity than larvae, for which significant changes are only observed at 26‰ for A. cytherea after 14 d of exposure. Although rising seawater temperatures and ocean acidification are often perceived as the main threat for the survival of coral reefs, our work indicates that 70% of the gametes could be killed during a single night of spawning by a rainfall event that decreases salinity to 26‰. This suggests that changes in the frequency and intensity of rainfall events associated with climate changes should be taken seriously in efforts to both preserve coral gametes and ensure the persistence and renewal of coral populations.

Variation in black and white band disease progression in corals of the Gulf of Mannar and Palk Bay, Southeastern India.

Information on the progression of coral diseases and transmission to live corals is scarce despite the fact that coral disease poses one of the most lethal threats to the survival of coral reefs. In this study, in situ progression rates of lesions similar to black band disease (BBD) and white band disease (WBD) were measured in different species of corals from the Gulf of Mannar (GoM) and Palk Bay, southeastern India, during the period between January and December of 2009. Maximum progression rates of 3 and 1.6 cm mo-1 for BBD and WBD, respectively, were observed during May, when the temperature exceeded 30°C. The annual progression rate was 10.9 and 4.9 cm yr-1 for BBD at GoM and Palk Bay, respectively. Significant variation in the progression rate (p < 0.001) was observed between months in all the examined species. Significant correlation between temperature and disease progression rates for BBD (R2 = 0.875, p ≤ 0.001) and WBD (R2 = 0.776, p ≤ 0.001) was recorded. Rates of disease progression were higher in Palk Bay than in GoM. This could be attributed to the higher temperature coupled with higher anthropogenic activities in Palk Bay. Severe mortality was observed due to both BBD and WBD. No sign of recovery was noticed in the disease-affected colonies at either study site. Anthropogenic activities should be checked, and further research on both the transmission and progression rate and role of the diseases in reef dynamics should be carried out to understand the causal factors in reef degradation and generate a plan to manage the reef properly.

Doors are closing on early development in corals facing climate change.

Marine invertebrates are particularly vulnerable to climatic anomalies in early life history stages because of the time spent in the water column. Studies have focused on the effect of seawater temperature on fertilization, development, and larval stages in corals; however, none of them show comparative results along an environmental gradient. In this study, we show that temperatures in the range of 15–33°C have strong effects on fertilization rates and embryonic stages of two coral species, Acropora muricata in the subtropical environment and Acropora hyacinthus in subtropical and temperate environments. Deformations after the first cleavage stages were observed at low (15°C) and high (33°C) temperatures. Development was delayed by 6–7 h in the slightly non-optimal temperature of 20°C. We found significant differences in fertilization rates and responses of embryos from different latitudes, with temperate corals being more sensitive to extremely hot temperatures and vice versa. We hypothesize that the coral development is restricted to a narrow temperature range and deviation outside this window could inhibit a species' continuance and ecological success. Thus, it would have significant negative effects on adult populations and communities, playing a role in future of coral reef survival.

Impacts of temperature increase and acidification on thickness of the surface mucopolysaccharide layer of the Caribbean coral Diploria spp.

Coral mechanisms of resilience and resistance to stressors such as increasing sea surface temperature and ocean acidification must first be understood in order to facilitate the survival of coral reefs as we know them. One such mechanism is production of the protective surface mucopolysaccharide layer (SML). In this study, we investigated changes in the thickness of the SML in response to increasing temperature and acidification for the three Caribbean scleractinian coral species of the genus Diploria, which have been shown to exhibit differential resilience to disease and bleaching. Among the three species, Diploria strigosa is known to have a higher susceptibility to disease, Diploria labyrinthiformis is known to bleach more quickly, and Diploria clivosa is relatively unstudied. When temperature was increased from 25 to 31 °C over a 1- or 6-week period, the overall thickness of the SML decreased from 33 to 55 % for all three species. Average SML thickness at 25 °C for all three species ranged from 106 to 156 μm, while average thickness at 31 °C ranged from 64 to 86 μm. SML thickness was significantly different among species at 25 °C, but not at 31 °C. D. labyrinthiformis demonstrated lower fragment mortality due to thermal stress when compared to the other Diploria species. Acidification from pH 8.2 to 7.7 over 5 weeks had no effect on SML thickness for any species. The observed decrease in SML thickness in response to increased temperature might be attributed to a decrease in the production of mucus or an increase in the viscosity of the SML. These findings may help to explain the increased prevalence of coral disease during the warmer months, since increased temperature compromises an important aspect of coral innate immunity, as well as differences in disease and bleaching susceptibilities between Diploria species.

Do Clouds Save the Great Barrier Reef? Satellite Imagery Elucidates the Cloud-SST Relationship at the Local Scale

Evidence of global climate change and rising sea surface temperatures (SSTs) is now well documented in the scientific literature. With corals already living close to their thermal maxima, increases in SSTs are of great concern for the survival of coral reefs. Cloud feedback processes may have the potential to constrain SSTs, serving to enforce an “ocean thermostat” and promoting the survival of coral reefs. In this study, it was hypothesized that cloud cover can affect summer SSTs in the tropics. Detailed direct and lagged relationships between cloud cover and SST across the central Great Barrier Reef (GBR) shelf were investigated using data from satellite imagery and in situ temperature and light loggers during two relatively hot summers (2005 and 2006) and two relatively cool summers (2007 and 2008). Across all study summers and shelf positions, SSTs exhibited distinct drops during periods of high cloud cover, and conversely, SST increases during periods of low cloud cover, with a three-day temporal lag between a change in cloud cover and a subsequent change in SST. Cloud cover alone was responsible for up to 32.1% of the variation in SSTs three days later. The relationship was strongest in both El Niño (2005) and La Niña (2008) study summers and at the inner-shelf position in those summers. SST effects on subsequent cloud cover were weaker and more variable among study summers, with rising SSTs explaining up to 21.6% of the increase in cloud cover three days later. This work quantifies the often observed cloud cooling effect on coral reefs. It highlights the importance of incorporating local-scale processes into bleaching forecasting models, and encourages the use of remote sensing imagery to value-add to coral bleaching field studies and to more accurately predict risks to coral reefs.

Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Wave-resistant algal rims—chiefly composed of carbonate from crustose coralline algae—form critical structures for the survival of many shallow coral reefs, raising concerns about the susceptibility of these protective structures to ocean acidification. Research now shows that dolomite-rich frameworks—common in shallow coral reefs globally—are likely to persist as carbon dioxide increases. Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum1,2, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons3. However, the recent discovery4 of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate5, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6–10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 (∼ 700 ppm) and control (∼ 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.

Nutrient enrichment can increase the susceptibility of reef corals to bleaching

Mass coral bleaching, resulting from the breakdown of coral-algal symbiosis has been identified as the most severe threat to coral reef survival on a global scale. Regionally, nutrient enrichment of reef waters is often associated with a significant loss of coral cover and diversity. Recently, increased dissolved inorganic nitrogen concentrations have been linked to a reduction of the temperature threshold of coral bleaching, a phenomenon for which no mechanistic explanation is available. Here we show that increased levels of dissolved inorganic nitrogen in combination with limited phosphate concentrations result in an increased susceptibility of corals to temperature-and light-induced bleaching. Mass spectrometric analyses of the algal lipidome revealed a marked accumulation of sulpholipids under these conditions. Together with increased phosphatase activities, this change indicates that the imbalanced supply of dissolved inorganic nitrogen results in phosphate starvation of the symbiotic algae. Based on these findings we introduce a conceptual model that links unfavourable ratios of dissolved inorganic nutrients in the water column with established mechanisms of coral bleaching. Notably, this model improves the understanding of the detrimental effects of coastal nutrient enrichment on coral reefs, which is urgently required to support knowledge-based management strategies to mitigate the effects of climate change. © 2013 Macmillan Publishers Limited. All rights reserved.

Human Pathogen Shown to Cause Disease in the Threatened Eklhorn Coral Acropora palmata

Coral reefs are in severe decline. Infections by the human pathogen Serratia marcescens have contributed to precipitous losses in the common Caribbean elkhorn coral, Acropora palmata, culminating in its listing under the United States Endangered Species Act. During a 2003 outbreak of this coral disease, called acroporid serratiosis (APS), a unique strain of the pathogen, Serratia marcescens strain PDR60, was identified from diseased A. palmata, human wastewater, the non-host coral Siderastrea siderea and the corallivorous snail Coralliophila abbreviata. In order to examine humans as a source and other marine invertebrates as vectors and/or reservoirs of the APS pathogen, challenge experiments were conducted with A. palmata maintained in closed aquaria to determine infectivity of strain PDR60 from reef and wastewater sources. Strain PDR60 from wastewater and diseased A. palmata caused disease signs in elkhorn coral in as little as four and five days, respectively, demonstrating that wastewater is a definitive source of APS and identifying human strain PDR60 as a coral pathogen through fulfillment of Koch's postulates. A. palmata inoculated with strain PDR60 from C. abbreviata showed limited virulence, with one of three inoculated fragments developing APS signs within 13 days. Strain PDR60 from non-host coral S. siderea showed a delayed pathogenic effect, with disease signs developing within an average of 20 days. These results suggest that C. abbreviata and non-host corals may function as reservoirs or vectors of the APS pathogen. Our results provide the first example of a marine “reverse zoonosis” involving the transmission of a human pathogen (S. marcescens) to a marine invertebrate (A. palmata). These findings underscore the interaction between public health practices and environmental health indices such as coral reef survival.

The presence of multiple phenoloxidases in Caribbean reef-building corals

The melanin-synthesis pathways, phenoloxidase (PO) and laccases, are staple components of invertebrate immunity and have been shown to be vital in disease resistance. The importance of this pathway in immunity is a consequence of the release of oxygen radicals with cytotoxic effects and the production of insoluble melanin, which aids in the encapsulation of pathogens and parasites. Recently, melanization has been demonstrated as a critical immune response in several coral systems, although the biochemical components have not been thoroughly investigated. Coral diseases are posing a serious threat to coral reef survival, necessitating a full understanding of resistance mechanisms. In this study, we take a comparative approach to probe potential pathway components of melanin-synthesis in seven species from four different families of healthy Caribbean reef-building corals. Using different quinone substrates, we tested for the activity of the POs catecholase and cresolase, as well as laccase activity in each coral species. Since many invertebrate POs demonstrate some dependence on cations such as copper, calcium and magnesium, we treated the coral extracts with the chelators EDTA and EGTA to test the reliance of coral catecholase on these cations. The activity of the antioxidants peroxidase, superoxide dismutase and catalase was also tested in each coral and correlated to PO activity. All corals had demonstrable catecholase, cresolase and laccase activities, but only catecholase and cresolase activities varied significantly among species. Catecholase activity in each coral species was reduced by treatment with EDTA and EGTA, although some coral species were less affected than the others. Overall, these data show remarkable heterogeneity among the seven coral species of boulder-like reef building Caribbean coral. These differences may originate from the level of investment of each coral species into immunity and may explain disease ecology on the reef.

Assessment of Survival, Mortality and Recovery of Coral Reefs of East Kish Island, Persian Gulf

Coral reefs are specialized communities that develop clear, well-lit tropical and subtropical water; they provide shelter and canopy for great variety of organisms, living in mean temperature of 20 degrees C. Coral Bleaching and mortality have been associated with elevated seawater temperature. The aim of the study was to investigate coral bleaching and evaluate health condition of the corals. Distribution of coral reefs around Kish Island was determined by the Timed Swim (TS) technique. This survey carried out in 2 times (May and October, 2009) in 2 depths of 3-5 m and 6-10 m. Two Divers swam in constant speed for a set amount of time in three dive sites. The timed swim survey around the Kish Island showed that the most healthy live hard coral assemblages were found in the site called Persian Gulf seaport, whereas the greatest percentage of bleached corals were located in Jurassic Park station, located at the southeast of the Island. Branching corals (Acropora sp.) were bleached among all 3 stations and no sign of recovery could be detected. In Big coral site suitable substrate for accumulation of living organisms including Echinometra mathaie (sea urchin) existed due to presence of great amount of algae on dead corals and rocks. Based on the observation, it seems that the cause of reef destruction in Kish Island fall in to two categories, natural and human impacts.

Introduction to the theme section “coral reefs in a changing environment”

This theme section, ‘‘Coral reefs in a changing environment’’, stems from the ASLO Aquatic Sciences Meeting 2009 in Nice, France (January 25–30), where session # 28 (Coral reefs and coral communities in a changing environment) was chaired by Cornelia Maier, Bernhard Riegl and Christian Wild. This session included 12 oral and 9 poster contributions covering a broad range of topics, and attracted a large number of visitors. That the upcoming 2010 European ISRS meeting in Wageningen, the Netherlands, has a similar motto, ‘‘Reefs in a changing environment’’, appears to emphasize the importance and timeliness of the question: How do corals and coral reefs respond to rapid environmental change? Clearly, anthropogenically-induced climate change and pollution alter the chemistry and temperature of seawater at an unprecedented and rapid rate, and constitute a major threat to the survival of tropical, temperate and cold-water coral reefs and coral communities. CO2-induced ocean acidification and warming, along with terrestrial runoff and pollution, negatively affect health, growth and calcification of corals. However, the extent to which these indirect and direct anthropogenic stresses interact and impact corals and coral-generated reef ecosystems needs to be addressed in more detail. The following six contributions to the theme section reflect a high diversity with respect to the scientific contents on both the species and the community level. The manuscripts address the effects of the two groups of parameters linked to global climate change: firstly, indirectly anthropogenically caused effects such as surface temperature (Heyward and Negri 2010; Thompson and Dolman 2010; Naumann et al. 2010) and pH (Ries et al. 2010); and, secondly, directly anthropogenically caused effects such as inorganic nutrient concentrations (Naumann et al. 2010; Tanaka et al. 2010) or natural regular disturbances (Browne et al. 2010) on coral metabolism (Naumann et al. 2010; Tanaka et al. 2010; Ries et al. 2010), coral development (Heyward and Negri 2010) and coral reef community structure and cover (Browne et al. 2010; Thompson and Dolman 2010). In this context, the goals were to identify the relative influence of one or more of the factors related to environmental change. The articles in the theme section focusing on the factor temperature reveal that, below the bleaching threshold, it positively correlates with particulate organic matter (POM) release by scleractinian corals (Naumann et al. 2010), but may also negatively effect the development and distribution of their larvae (Heyward and Negri 2010). Thompson and Dolman (2010) highlight that temperature-induced coral bleaching events, even if they only occur in the frequency and severity of those in the recent past, may lead to a reduction of fast-growing staghorn coral cover in nearshore reefs of the Great Barrier Reef (GBR). This was supported by the finding that mass coral bleaching, in contrast to other stress events such as crown-of-thorns starfish outbreaks and cyclones, resulted in significant changes of benthic community composition and hard coral Communicated by Editor in Chief Prof. Rolf Bak

Resilience of Coral-Associated Bacterial Communities Exposed to Fish Farm Effluent

BackgroundThe coral holobiont includes the coral animal, algal symbionts, and associated microbial community. These microbes help maintain the holobiont homeostasis; thus, sustaining robust mutualistic microbial communities is a fundamental part of long-term coral reef survival. Coastal pollution is one major threat to reefs, and intensive fish farming is a rapidly growing source of this pollution.Methodology & Principal FindingsWe investigated the susceptibility and resilience of the bacterial communities associated with a common reef-building coral, Porites cylindrica, to coastal pollution by performing a clonally replicated transplantation experiment in Bolinao, Philippines adjacent to intensive fish farming. Ten fragments from each of four colonies (total of 40 fragments) were followed for 22 days across five sites: a well-flushed reference site (the original fragment source); two sites with low exposure to milkfish (Chanos chanos) aquaculture effluent; and two sites with high exposure. Elevated levels of dissolved organic carbon (DOC), chlorophyll a, total heterotrophic and autotrophic bacteria abundance, virus like particle (VLP) abundances, and culturable Vibrio abundance characterized the high effluent sites. Based on 16S rRNA clone libraries and denaturing gradient gel electrophoresis (DGGE) analysis, we observed rapid, dramatic changes in the coral-associated bacterial communities within five days of high effluent exposure. The community composition on fragments at these high effluent sites shifted towards known human and coral pathogens (i.e. Arcobacter, Fusobacterium, and Desulfovibrio) without the host corals showing signs of disease. The communities shifted back towards their original composition by day 22 without reduction in effluent levels.SignificanceThis study reveals fish farms as a likely source of pathogens with the potential to proliferate on corals and an unexpected short-term resilience of coral-associated bacterial communities to eutrophication pressure. These data highlight a need for improved aquaculture practices that can achieve both sustainable industry goals and long-term coral reef survival.

Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.

10th Anniversary Review: a changing climate for coral reefs

Tropical coral reefs are charismatic ecosystems that house a significant proportion of the world's marine biodiversity. Their valuable goods and services are fundamental to the livelihood of large coastal populations in the tropics. The health of many of the world's coral reefs, and the goods and services they provide, have already been severely compromised, largely due to over-exploitation by a range of human activities. These local-scale impacts, with the appropriate government instruments, support and management actions, can potentially be controlled and even ameliorated. Unfortunately, other human actions (largely in countries outside of the tropics), by changing global climate, have added additional global-scale threats to the continued survival of present-day coral reefs. Moderate warming of the tropical oceans has already resulted in an increase in mass coral bleaching events, affecting nearly all of the world's coral reef regions. The frequency of these events will only increase as global temperatures continue to rise. Weakening of coral reef structures will be a more insidious effect of changing ocean chemistry, as the oceans absorb part of the excess atmospheric carbon dioxide. More intense tropical cyclones, changed atmospheric and ocean circulation patterns will all affect coral reef ecosystems and the many associated plants and animals. Coral reefs will not disappear but their appearance, structure and community make-up will radically change. Drastic greenhouse gas mitigation strategies are necessary to prevent the full consequences of human activities causing such alterations to coral reef ecosystems.

Metagenomic analysis of the microbial community associated with the coral Porites astreoides

The coral holobiont is a dynamic assemblage of the coral animal, zooxanthellae, endolithic algae and fungi, Bacteria,Archaea and viruses. Zooxanthellae and some Bacteria form relatively stable and species-specific associations with corals. Other associations are less specific; coral-associated Archaea differ from those in the water column, but the same archaeal species may be found on different coral species. It has been hypothesized that the coral animal can adapt to differing ecological niches by 'switching' its microbial associates. In the case of corals and zooxanthellae, this has been termed adaptive bleaching and it has important implications for carbon cycling within the coral holobiont and ultimately the survival of coral reefs. However, the roles of other components of the coral holobiont are essentially unknown. To better understand these other coral associates, a fractionation procedure was used to separate the microbes, mitochondria and viruses from the coral animal cells and zooxanthellae. The resulting metagenomic DNA was sequenced using pyrosequencing. Fungi, Bacteria and phage were the most commonly identified organisms in the metagenome. Three of the four fungal phyla were represented, including a wide diversity of fungal genes involved in carbon and nitrogen metabolism, suggesting that the endolithic community is more important than previously appreciated. In particular, the data suggested that endolithic fungi could be converting nitrate and nitrite to ammonia, which would enable fixed nitrogen to cycle within the coral holobiont. The most prominent bacterial groups were Proteobacteria (68%), Firmicutes (10%), Cyanobacteria (7%) and Actinobacteria (6%). Functionally, the bacterial community was primarily heterotrophic and included a number of pathways for the degradation of aromatic compounds, the most abundant being the homogentisate pathway. The most abundant phage family was the ssDNA Microphage and most of the eukaryotic viruses were most closely related to those known to infect aquatic organisms. This study provides a metabolic and taxonomic snapshot of microbes associated with the reef-building coral Porites astreoides and presents a basis for understanding how coral-microbial interactions structure the holobiont and coral reefs.

Juvenile coral population dynamics track rising seawater temperature on a Caribbean reef

There is now widespread consensus that climate change-related increases in seawater temperature have become a leading cause of coral mortality by bleaching. However, despite widely reported and geographically extensive coral-bleaching episodes, little is known about the less con- spicuous demographic consequences of elevated temperature for coral populations. Here, I use 12 yr of daily temperature records and 8 yr of annual surveys of juvenile corals (≤40 mm diameter, a size range that includes recruits) from the US Virgin Islands to demonstrate the subtle effects of an unusu- ally rapid increase in seawater temperature (0.06°C per year since 1989) on coral community struc- ture in shallow water (5 to 9 m depth). The analysis reveals that the density of juvenile corals is cor- related positively with mean seawater temperature, but concurrently, in warm years, juvenile corals tend to grow slowly and appear to die faster, in a pattern leading to changes in relative generic abun- dance. Although perturbations such as these appear minor against the backdrop of widespread reef degradation, summation of these subtle effects could result in major changes, with far-reaching eco- logical consequences for the survival of coral reefs.

Effects of chemically dispersed oil on the brain coral, Diploria strigosa

The frequency of oil spills in tropical seas may threaten coral reef survival and some of the past research has indicated that oil alone as well as oil dispersed with chemical dispersants is toxic to corals. These experiments were probably realistic of intertidal reef zones and sheltered shallow reef areas. However, few experiments have incorporated analytical chemistry necessary to relate reported biological effects to actual oil spill concentrations and exposure times. This paper outlines some new results with emphasis on a 3 year programme carried out in Bermuda using a flow-through laboratory dosing system, comparative laboratory and field experiments, real time measurements of oil concentrations, and non-destructive bioassays to allow repetitive data collection from the same specimens. Suggestions for future research programmes are given in light of these results. In addition to research on the effects of oil and chemically dispersed oil on other coral species and associated organisms in the coral reef, the relative sensitivity of the various ecosystems comprising the tropical coastal zone (mangroves, seagrasses and reef) must also be addressed. It is hoped that such advances will ensure that overall oil spill clean-up decisions will give due consideration to the individual physical and biological characteristics of each of these tropical environments.

The effects of oil spills and dispersant use on corals: A review and multidisciplinary experimental approach

Coral reefs are environmentally and economically important ecosystems. The present frequency of oil spills in tropical seas may threaten coral reef survival. Some of the research to date suggests oil and dispersed oil is toxic to corals, but few experiments have tested realistic spill concentrations and exposure times. This paper outlines an experimental design which includes a flow-through laboratory dosing and seawater system, comparative laboratory and field experiments, real-time measurements of water accommodated fraction (WAF) of oil in seawater and coral tissue, and non-destructive bioassays to allow repetitive data collection from the same specimens. A major emphasis is long-term effects on growth and histology. Short-term bioassays reveal temporary effects followed by recovery generally within one week. Although no long-term effects on coral growth are detectable at this stage, histology and growth studies are not yet complete.