Assessing the climate vulnerability of the world’s natural and cultural heritage

Climate change is the fastest-growing global threat to the world’s natural and cultural heritage. No systematic approach to assess climate vulnerability of protected areas and their associated communities has existed—until now. The Climate Vulnerability Index (CVI) is scientifically robust, transparent, and repeatable, and has now been applied to various World Heritage properties. The CVI builds upon an established Intergovernmental Panel on Climate Change (IPCC) framework to systematically assess vulnerability through a risk assessment approach that considers the key values of the World Heritage property in question and identifies key climate stressors. The CVI process is then used to assess the climate-related vulnerability of the community (including local residents, domestic visitors, and international tourists) associated with the World Heritage property considering economic, social, and cultural connections. Climate impacts are increasingly adding to a wide range of compounding pressures (e.g., increasing tourism, infrastructure development, changing land use practices) that are affecting places, people, customs, and values. Applications of the CVI to date have led to commitments to integrate outcomes into relevant management plans, and to periodically repeat the process, enabling responsive management to changing future circumstances. The CVI has also demonstrated its potential applicability for protected areas beyond World Heritage properties. The CVI process engages local community members in determining impacts, provides opportunities for identifying adaptation and impact mitigation within the community, and aids broader communication about key climate issues

Coastal ocean radars applied to coral reef science and management

Coastal ocean radars provide detailed surface current maps and wind directions; some types of High Frequency radar also provide maps of wave heights. Radar range is dependent upon the radar frequency, extending up to 150 km from the shore. In the case of the Great Barrier Reef, this includes the continental shelf and some open water beyond. Detailed knowledge of the dynamics of the surface water opens the way for understanding much about localised environmental conditions, connectivity between sites and the movement of nutrients and pollution in the coastal ocean. Lagrangian tracking of buoyant particles can be achieved in the Great Barrier Reef lagoon within an accuracy (error) approaching 1 km per day of drift. This is a significant capability for search and rescue operations as well as reef science and management. A sequence of surface current maps has been shown to be useful for identifying areas where the currents are high enough to induce spontaneous turbulence throughout the water column. These areas are less vulnerable to coral bleaching because the heat from insolation is distributed through the water column rather than remaining at the surface. Spatial scales (i.e., range, resolution) for ocean radars are adjustable and it is shown that mapping of surface currents on a high resolution grid is possible with radars operating in the Very High Frequency band

A new, high-resolution global mass coral bleaching database

Episodes of mass coral bleaching have been reported in recent decades and have raised concerns about the future of coral reefs on a warming planet. Despite the efforts to enhance and coordinate coral reef monitoring within and across countries, our knowledge of the geographic extent of mass coral bleaching over the past few decades is incomplete. Existing databases, like ReefBase, are limited by the voluntary nature of contributions, geographical biases in data collection, and the variations in the spatial scale of bleaching reports. In this study, we have developed the first-ever gridded, global-scale historical coral bleaching database. First, we conducted a targeted search for bleaching reports not included in ReefBase by personally contacting scientists and divers conducting monitoring in under-reported locations and by extracting data from the literature. This search increased the number of observed bleaching reports by 79%, from 4146 to 7429. Second, we employed spatial interpolation techniques to develop annual 0.04 degrees x 0.04 degrees latitude-longitude global maps of the probability that bleaching occurred for 1985 through 2010. Initial results indicate that the area of coral reefs with a more likely than not (> 50%) or likely (> 66%) probability of bleaching was eight times higher in the second half of the assessed time period, after the 1997/1998 El Nino. The results also indicate that annual maximum Degree Heating Weeks, a measure of thermal stress, for coral reefs with a high probability of bleaching increased over time. The database will help the scientific community more accurately assess the change in the frequency of mass coral bleaching events, validate methods of predicting mass coral bleaching, and test whether coral reefs are adjusting to rising ocean temperatures

Case-control design identifies ecological drivers of endemic coral diseases

Endemic disease transmission is an important ecological process that is challenging to study because of low occurrence rates. Here, we investigate the ecological drivers of two coral diseases-growth anomalies and tissue loss-affecting five coral species. We first show that a statistical framework called the case-control study design, commonly used in epidemiology but rarely applied to ecology, provided high predictive accuracy (67-82%) and disease detection rates (60-83%) compared with a traditional statistical approach that yielded high accuracy (98-100%) but low disease detection rates (0-17%). Using this framework, we found evidence that 1) larger corals have higher disease risk; 2) shallow reefs with low herbivorous fish abundance, limited water motion, and located adjacent to watersheds with high fertilizer and pesticide runoff promote low levels of growth anomalies, a chronic coral disease; and 3) wave exposure, stream exposure, depth, and low thermal stress are associated with tissue loss disease risk during interepidemic periods. Variation in risk factors across host-disease pairs suggests that either different pathogens cause the same gross lesions in different species or that the same disease may arise in different species under different ecological conditions

Marine heatwave hotspots in coral reef environments: physical drivers, ecophysiological outcomes and impact upon structural complexity

A changing climate is driving increasingly common and prolonged marine heatwaves (MHWs) and these extreme events have now been widely documented to severely impact marine ecosystems globally. However MHWs have rarely recently been considered when examining temperature-induced degradation of coral reef ecosystems. Here we consider extreme, localised thermal anomalies, nested within broader increases in sea surface temperature, which fulfil the definitive criteria for MHWs. These acute and intense events, referred to here as MHW hotspots, are not always well represented in the current framework used to describe coral bleaching, but do have distinct ecological outcomes, including widespread bleaching and rapid mass mortality of putatively thermally tolerant coral species. The physical drivers of these localised hotspots are discussed here, and in doing so we present a comprehensive theoretical framework that links the biological responses of the coral photo-endosymbiotic organism to extreme thermal stress and ecological changes on reefs associated after MHW hotspots. We describe how the rapid onset of high temperatures drives immediate heat-stress induced cellular damage, overwhelming mechanisms that would otherwise mitigate the impact of gradually accumulated thermal stress. The warm environment, and increased light penetration of the coral skeleton due to the loss of coral tissues, coupled with coral tissue decay support rapid microbial growth in the skeletal microenvironment, resulting in the widely unrecognised consequence of rapid decay and degeneration of the coral skeletons. This accelerated degeneration of the coral skeletonson a reef scale hinder the recovery of coral populations and increase the likelihood of phase shifts towards algal dominance. We suggest that MHW hotspots, through driving rapid heat-induced mortality, compromise reefs' structural frameworks to the detriment of long term recovery. We propose that MHW hotspots be considered as a distinct class of thermal stress events in coral reefs, and that the current framework used to describe coral bleaching and mass mortality be expanded to include these. We urge further research into how coral mortality affects bioerosion by coral endoliths

Variation in growth rates of branching corals along Australia's Great Barrier Reef

Coral growth is an important component of reef health and resilience. However, few studies have investigated temporal and/or spatial variation in growth of branching corals, which are important contributors to the structure and function of reef habitats. This study assessed growth (linear extension, density, and calcification) of three branching coral species (Acropora muricata, Pocillopora damicornis and Isopora palifera) at three distinct locations (Lizard Island, Davies/Trunk Reef, and Heron Island) along Australia’s Great Barrier Reef (GBR). Annual growth rates of all species were highest at Lizard Island and declined with increasing latitude, corresponding with differences in temperature. Within locations, however, seasonal variation in growth did not directly correlate with temperature. Between October 2012 and October 2014, the highest growth of A. muricata was in the 2013–14 summer at Lizard Island, which was unusually cool and ~0.5 °C less than the long-term summer average temperature. At locations where temperatures reached or exceeded the long-term summer maxima, coral growth during summer periods was equal to, if not lower than, winter periods. This study shows that temperature has a significant influence on spatiotemporal patterns of branching coral growth, and high summer temperatures in the northern GBR may already be constraining coral growth and reef resilience

Branching coral growth and visual health during bleaching and recovery on the central Great Barrier Reef

Coral reefs are under threat from cumulative impacts such as cyclones, crown-of-thorns starfish (COTS) outbreaks and climate-driven coral bleaching events. Branching corals are more severely impacted by these events than other coral morphologies due to their sensitivity to heat stress and weaker skeletons and COTS preferred prey. The central Great Barrier Reef experienced unprecedented back-to-back bleaching events in 2016 and 2017. This study commenced in 2017 at the peak of heat stress and examined the impact of the heatwave on the survival and recovery of corals by assessing the growth, health (based on the visual health index) and physiological parameters (chlorophyll a, zooxanthellae density, lipid and protein content) of two species, Acropora millepora and Pocillopora acuta (N = 60 colonies for each species). It was conducted across a gradient of turbidity at three reefs, Pandora, Orpheus and Rib, that experienced in April 2017, degree heating weeks (DHW) of 9, 8 and 7, respectively. Orpheus experienced the worst bleaching, based on visual health score, followed by Rib and Pandora. Rib experienced the greatest mortality (78% by Nov 2017); however, this was attributed to the presence of actively feeding crown-of-thorns starfish. Growth rates of A. millepora were almost twice the rate of P. acuta. Both species showed significant seasonal variation with growth of A. millepora and P. acuta 35–40% and 23–33% significantly greater in the summer, respectively. Differences in growth rates were best explained by indicators of energy acquisition. For example, the most important predictor variable in determining higher growth rates and visual health score in A. millepora was chlorophyll a content. For P. acuta, visual health score was the best predictor variable for higher growth rates. This study highlights the important role that chlorophyll a and associated symbionts play in growth and survival in these corals during and after a heat stress event

Coral disease time series highlight size-dependent risk and other drivers of white syndrome in a multi-species model

Coral diseases contribute to the decline of reef communities, but factors that lead to disease are difficult to detect. In the present study, we develop a multi-species model of colony-scale risk for the class of coral diseases referred to as White Syndromes, investigating the role of current or past conditions, including both environmental stressors and biological drivers at the colony and community scales. Investigating 7 years of coral survey data at five sites in Guam we identify multiple environmental and ecological associations with White Syndrome, including a negative relationship between short-term heat stress and White Syndrome occurrence, and strong evidence of increasing size-dependent White Syndrome risk across coral species. Our findings result in a generalized model used to predict colony-scale White Syndrome risk for multiple species, highlighting the value of long-term monitoring efforts to detect drivers of coral disease