Effects of ocean acidification on the dissolution rates of reef-coral skeletons

Ocean acidification threatens the foundation of tropical coral reefs. This study investigated three aspects of ocean acidification: (i) the rates at which perforate and imperforate coral-colony skeletons passively dissolve when pH is 7.8, which is predicted to occur globally by 2100, (ii) the rates of passive dissolution of corals with respect to coral-colony surface areas, and (iii) the comparative rates of a vertical reef-growth model, incorporating passive dissolution rates, and predicted sea-level rise. By 2100, when the ocean pH is expected to be 7.8, perforate Montipora coral skeletons will lose on average 15 kg CaCO3 m−2 y−1, which is approximately −10.5 mm of vertical reduction of reef framework per year. This rate of passive dissolution is higher than the average rate of reef growth over the last several millennia and suggests that reefs composed of perforate Montipora coral skeletons will have trouble keeping up with sea-level rise under ocean acidification. Reefs composed of primarily imperforate coral skeletons will not likely dissolve as rapidly, but our model shows they will also have trouble keeping up with sea-level rise by 2050

Some coral diseases track climate oscillations in the Caribbean

Disease outbreaks continue to reduce coral populations worldwide. Understanding coral diseases and their relationships with environmental drivers is necessary to forecast disease outbreaks, and to predict future changes in coral populations. Yet, the temporal dynamics of coral diseases are rarely reported. Here we evaluate trends and periodicities in the records of three common coral diseases (white-band disease, yellow-band disease, and dark-spot syndrome) that were surveyed between 1997 and 2014 at 2082 sites throughout the Caribbean. The relationship between the periodicities of disease prevalence and El Niño Southern Oscillation (ENSO) cycles was examined using cross-wavelet analyses and convergent cross mapping (CCM). The prevalence of the diseases peaked every two to four years, and matched periodicities in ENSO conditions. CCM models suggested that environmental conditions associated with recent ENSO cycles may have influenced the patterns in disease prevalence. We also found no increasing trends in disease prevalence through time. Instead, our work suggests that the prevalence of coral diseases is dynamic and complex. The gradual increase in sea-surface temperature, a consequence of increasing greenhouse gas emissions, progressively raises the modal temperature threshold of each ENSO cycle. These dynamic cycles and the increasing modal temperatures appear to influence the dynamics of coral diseases

Coral disease hotspots in the Caribbean

Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful sea‐surface temperatures (SSTs). Yet, ocean warming is spatially heterogeneous and therefore has the potential to lead to hotspots of disease activity. Here, we take an epidemiological approach to examine spatial differences in the risk of white‐band disease on Acropora spp. and yellow‐band disease on Orbicella spp. in the Caribbean. Our analysis involved examining the spatial patterns of disease prevalence, and creating a Bayesian‐risk model that tested for regional differences in disease risk. The spatial examination of disease prevalence showed several clusters of white‐band disease, including high prevalence in the Turks and Caicos, Jamaica, Puerto Rico, the Virgin Islands, and Belize, whereas yellow‐band disease seemed most prevalent along the Yucatan Peninsula. The Bayesian‐risk model showed regional clusters of white‐band disease near the southern Dominican Republic, Puerto Rico, the Virgin Islands, and the Lesser Antilles, whereas the risk of yellow‐band disease was highest in the southern Caribbean. The relative risk of both diseases increased with warmer SSTs. The Bayesian‐risk model allowed us to predict where we should expect future outbreaks of coral diseases at a regional scale, and suggests regions where the implementation of disease mitigation plans may be most urgent

Broadscale survey of impacts of Cyclone Ivor on coral reefs

A survey of reefs in the vicinity of the path of Cyclone Ivor (19th March 1990) was conducted in July 1990. Physical damage caused by the cyclone was recognised as far as 40 km to the North of the path and 100 km to the South. Impact was most severe over a 50 km section of the outer Great Barrier Reef between Jewell Reef and Ribbon Reef no. 10. All forms of damage were seen to a depth of 20 m, which was the greatest depth examined. The major forms of damage were coral breakage, coral dislodgement, and peeling of the superficial reef matrix to a thickness of up to 1.5 m. The severity of impact declined irregularly with increasing distance from the path. Damage was patchy on scales of 100s -1000s m2 associated partly with local shelter and topography, partly with matrix robustness, but more with coral community age and size structure than composition. Large denuded areas in the worst damaged area will be entirely dependent on larval recruitment for recolonisation by corals. Recovery of smaller and less severely damaged areas will in addition be by way of regeneration of remnant patches and growth of colonies on patch margins. Cyclones cross the central Great Barrier Reef at a frequency which suggests that, if the width of the swathe caused by Cyclone Ivor is any indication, few reefs would have escaped major modification by cyclones this century

Immediate impact of the January 1991 floods on the coral assemblages of the Keppel Islands

Flood waters from the Fitzroy River inundated the Keppel Islands in January 1991 resulting in considerable decreases in salinity, for a period of 19 days, at the surface (8 to 10 ppt) and at shallow depths (15 to 28 ppt at 3 m). Data from coral surveys undertaken in 1989 were used to assess the degree of damage. The shallow coral reefs on the leeward edge of the islands were substantially damaged by the flood waters. Approximately 85% of the coral was dead and overgrown by turf algae. Absolute mortality continued to -1.3 m Low Water Datum (LWD), below this demarcation a narrow band of bleached coral was evident (expelled zooxanthellae). Beyond this distinct band, corals remained alive - although the reef only extended a further 1.0 to 1.5 m onto sand. The exposed slopes of Great Keppel Island, Bald Rock and Barron Island were only marginally affected. In contrast to the leeward side, these reefs have only narrow reef flats. Approximately 5% of the established colonies appeared recently dead and overgrown with turf algae, approximately 10% of the corals were bleached

A pilot study of baseline levels of water quality around Green Island

A pilot study was undertaken at Green Island in June 1989 to assess the spatial and temporal variation of a range of water quality parameters. It was a precursor to the implementation of a proposed baseline study of water quality around Green Island to ensure the optimum allocation of sampling in a cost effective manner

Phenotypic Variance Predicts Symbiont Population Densities in Corals: A Modeling Approach

We test whether the phenotypic variance of symbionts (Symbiodinium) in corals is closely related with the capacity of corals to acclimatize to increasing seawater temperatures. Moreover, we assess whether more specialist symbionts will increase within coral hosts under ocean warming. The present study is only applicable to those corals that naturally have the capacity to support more than one type of Symbiodinium within the lifetime of a colony; for example, Montastraea annularis and Montastraea faveolata.The population dynamics of competing Symbiodinium symbiont populations were projected through time in coral hosts using a novel, discrete time optimal-resource model. Models were run for two Atlantic Ocean localities. Four symbiont populations, with different environmental optima and phenotypic variances, were modeled to grow, divide, and compete in the corals under seasonal fluctuations in solar insolation and seawater temperature. Elevated seawater temperatures were input into the model 1.5 degrees C above the seasonal summer average, and the symbiont population response was observed for each location. The models showed dynamic fluctuations in Symbiodinium populations densities within corals. Population density predictions for Lee Stocking Island, the Bahamas, where temperatures were relatively homogenous throughout the year, showed a dominance of both type 2, with high phenotypic variance, and type 1, a high-temperature and high-insolation specialist. Whereas the densities of Symbiodinium types 3 and 4, a high-temperature, low-insolation specialist, and a high-temperature, low-insolation generalist, remained consistently low. Predictions for Key Largo, Florida, where environmental conditions were more seasonally variable, showed the coexistence of generalists (types 2 and 4) and low densities of specialists (types 1 and 3). When elevated temperatures were input into the model, population densities in corals at Lee Stocking Island showed an emergence of high-temperature specialists. However, even under high temperatures, corals in the Florida Keys were dominated by generalists.Predictions at higher seawater temperatures showed endogenous shuffling and an emergence of the high-temperature Symbiodinium specialists, even though their phenotypic variance was low. The model shows that sustaining these "hidden" specialists becomes advantageous under thermal stress conditions, and shuffling symbionts may increase the corals' capacity to acclimatize but not adapt to climatechange-induced ocean warming

Sedimentation resulting from road development, Cape Tribulation Area

The aims of the study were: to quantify the amount of sediment being carried by the streams of the Cape Tribulation area under both natural conditions and in disturbed areas adjacent to the New Road; to quantity the amount of sediment in the water column adjacent to the reefs; and to put into context the amount of increased sedimentation directly due to road developmen

Predicting coral dynamics through climate change

Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determining the rates of coral recovery and their long-term responses to increasing sea-surface temperatures is challenging. To do so, we first estimated coral recovery rates following past disturbances on reefs in southern Japan and Western Australia. Recovery rates varied between regions, with the reefs in southern Japan showing more rapid recovery rates (intrinsic rate of increase, r = 0.38 year⁻¹) than reefs in Western Australia (r = 0.17 year⁻¹). Second, we input these recovery rates into a novel, nonlinear hybrid-stochastic-dynamical system to predict the responses of Indo-Pacific coral populations to complex inter-annual temperature cycles into the year 2100. The coral recovery rates were overlaid on background increases in global sea-surface temperatures, under three different climate-change scenarios. The models predicted rapid recovery at both localities with the infrequent and low-magnitude temperature anomalies expected under a conservative climate-change scenario, Representative Concentration Pathway (RCP) 4.5. With moderate increases in ocean temperatures (RCP 6.0) the coral populations showed a bimodal response, with model runs showing either recovery or collapse. Under a business-as-usual climate-change scenario (RCP 8.5), with frequent and intense temperature anomalies, coral recovery was unlikely