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

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

Diversity Partitioning of Stony Corals Across Multiple Spatial Scales Around Zanzibar Island, Tanzania

The coral reefs of Zanzibar Island (Unguja, Tanzania) encompass a considerable proportion of the global coral-reef diversity and are representative of the western Indian Ocean region. Unfortunately, these reefs have been recently subjected to local and regional disturbances. The objectives of this study were to determine whether there are potentially non-random processes forcing the observed coral diversity patterns, and highlight where and at which spatial scales these processes might be most influential.A hierarchical (nested) sampling design was employed across three spatial scales, ranging from transects (<or=20 m), stations (<100 m), to sites (<1000 m), to examine coral diversity patterns. Two of the four sites, Chumbe and Mnemba, were located within Marine Protected Areas (MPAs), while the other two sites, Changuu and Bawe, were not protected. Additive partitioning of coral diversity was used to separate regional (total) diversity (gamma) into local alpha diversity and among-sample beta diversity components. Individual-based null models were used to identify deviations from random distribution across the three spatial scales. We found that Chumbe and Mnemba had similar diversity components to those predicted by the null models. However, the diversity at Changuu and Bawe was lower than expected at all three spatial scales tested. Consequently, the relative contribution of the among-site diversity component was significantly greater than expected. Applying partitioning analysis for each site separately revealed that the within-transect diversity component in Changuu was significantly lower than the null expectation.The non-random outcome of the partitioning analyses helped to identify the among-sites scale (i.e., 10's of kilometers) and the within-transects scale (i.e., a few meters; especially at Changuu) as spatial boundaries within which to examine the processes that may interact and disproportionately differentiate coral diversity. In light of coral community compositions and diversity patterns we strongly recommend that Bawe be declared a MPA

Development and Validation of Computational Fluid Dynamics Models for Prediction of Heat Transfer and Thermal Microenvironments of Corals

We present Computational Fluid Dynamics (CFD) models of the coupled dynamics of water flow, heat transfer and irradiance in and around corals to predict temperatures experienced by corals. These models were validated against controlled laboratory experiments, under constant and transient irradiance, for hemispherical and branching corals. Our CFD models agree very well with experimental studies. A linear relationship between irradiance and coral surface warming was evident in both the simulation and experimental result agreeing with heat transfer theory. However, CFD models for the steady state simulation produced a better fit to the linear relationship than the experimental data, likely due to experimental error in the empirical measurements. The consistency of our modelling results with experimental observations demonstrates the applicability of CFD simulations, such as the models developed here, to coral bleaching studies. A study of the influence of coral skeletal porosity and skeletal bulk density on surface warming was also undertaken, demonstrating boundary layer behaviour, and interstitial flow magnitude and temperature profiles in coral cross sections. Our models compliment recent studies showing systematic changes in these parameters in some coral colonies and have utility in the prediction of coral bleaching