Global Forecasting of Coral Bleaching Events
In July 2008, NOAA Coral Reef Watch launched a new seasonal prediction tool for coral bleaching conditions to
augment its real-time satellite monitoring. A model of thermal stress from two to 16 weeks in the future was
developed through collaboration with the Physical Sciences Division of the NOAA Earth System Research
Laboratory, to forecast the risk of coral bleaching well in advance. The system is built on sea surface
temperature forecasts provided by NOAA's Linear Inverse Model (LIM) that has successfully produced
predictions of tropical Pacific and Atlantic SST anomalies. This presentation will outline this product, and
compare the forecast with satellite observations of actual thermal stress. Such forecasting tools provide
critical and timely decision support for coral reef managers and scientists worldwide.
Seasonal Dynamical Prediction of Coral Bleaching in the Great Barrier Reef, Australia
Sea surface temperature (SST) is now recognised as the primary cause of mass coral bleaching events. Coral bleaching occurs during times of stress, particularly when SSTs exceed the coral colony's tolerance level. Global warming is potentially a serious threat to the future of the world's reef systems with predictions by the international community that bleaching will increase in both frequency and severity. Advance warning of anomalous sea surface temperatures, and thus potential bleaching events, would allow for the implementation of management strategies to minimise reef damage. Seasonal SST forecasts from the coupled ocean-atmosphere model POAMA (Bureau of Meteorology) have skill in the Great Barrier Reef (Australia) several months into the future. We will present model forecasts and probabilistic products for use in reef management, and assess model skill in the region. These products will revolutionise the way in which coral bleaching events are monitored and assessed in the Great Barrier Reef and Australian region.
Coping with commitment: Projecting future thermal stress on coral reefs worldwide and the potential importance of the Central Equatorial Pacific
Sea surface temperatures of only 1-2°C greater than the usual summer maximum can cause mass coral bleaching, a paling of the reef-building animals caused by a breakdown of the symbiosis with the colourful dinoflagellates Symbiodinium. A range of recent studies have concluded that anthropogenic climate change may rapidly increase the frequency of mass coral bleaching events, leading to declines in coral cover, shifts in the composition of corals and other reef-dwelling organisms, and stress on the human populations that depend on coral reef ecosystems for food, income and shoreline protection. Recent analysis with AVHRR observed sea surface temperatures and the results of two global climate models (GFDL CM2.0 and CM2.1) shows physical warming commitment from current accumulation of greenhouse gases in the atmosphere will cause over half of the world's coral reefs to experience harmfully frequent (p > 0.2 year-1) severe thermal stress events (DHM > 2°C/month) by 2080. An additional "societal" warming commitment, caused by the time required to shift from a "business-as-usual" emissions trajectory to a 550 ppm CO2 stabilization trajectory, may cause over 80 percent of the world's coral reefs to experience harmfully frequent events by 2030. Thermal adaptation or acclimation of 1.5°C - whether accomplished via biological mechanisms, coral community shifts and/or management interventions - would postpone the forecast by 50-80 years, possibly providing time for the world to shift from the business-as-usual emissions trajectory to a stabilization trajectory which could protect the majority of reefs from harmfully frequent thermal stress events. Sensitivity analysis using historical sea surface temperatures, bleaching reports and coral cover observations indicates that coral reefs in regions which experience high year-to-year SST variability, in particular the atolls of the central equatorial Pacific, may possess higher thermal stress thresholds and greater resistance to projected ocean warming. These coral reefs are critical areas for further monitoring, research and conservation, as they may serve as a natural model for understanding the response of coral reef ecosystems to projected increase in the frequency of thermal stress events.
Ocean Acidification: A Major Driver of Coral Bleaching in the 21st Century?
Heat stress long been known to drive patterns of coral bleaching. Recently, however, it was discovered that ocean acidification can drive coral bleaching independently of temperature. This raises the question: how important will acidification be in driving coral bleaching under climate change? Here, we develop and apply a model that accounts for both thermal stress and ocean acidification in the coral bleaching response. Our analyses, which combine experimental bleaching data under manipulated ocean chemistry and warming with projections of CO2 and SST based on global circulation models, show that ocean acidification will become a key driver of future mass bleaching events within a few decades. Our findings, based on highly conservative assumptions, reveal that coral bleaching alert systems based on warming alone could underestimate coral bleaching by up to 50% during the 21st century. This is a striking result that will affect coral reef management strategies worldwide and has policy implications relating to global efforts to reduce greenhouse gas emissions.
Regional Monitoring of Ocean Acidification in Coral Reef Environments
The surface oceans serve as an important natural sink for increasing atmospheric carbon dioxide (CO2)
concentrations. As this CO2 reacts with seawater it reduces pH (acidification) and redistributes inorganic
carbon species. A growing number of experimental studies now document adverse effects on a range of coral
and related species as a consequence of ocean acidification. Mapping and monitoring the distribution of such
changes in ocean chemistry provides an important context for understanding the potential impacts and
identifying the most susceptible regions. NOAA Coral Reef Watch (CRW) and the AOML Ocean Chemistry
Division now offer an experimental Ocean Acidification Product Suite that provides a synthesis of satellite and
modeled environmental datasets to derive a synoptic estimate of sea surface carbonate chemistry in regions
occupied by prominent coral reef ecosystems. This tool compliments on-going geochemical surveys and
monitoring efforts in the region by providing estimates of changing ocean chemistry on a broader spatial and
temporal scale than shipboard observations alone can permit. The data are web accessible providing monthly
regional maps of a variety of relevant parameters including sea surface aragonite saturation state, pCO2(sw),
total alkalinity, carbonate ion, and bicarbonate ion and are available in multiple of formats including .gif and
Google Earth and HDF. We will discuss recent advances in algorithm refinements and progress of expanding
such efforts beyond the Greater Caribbean Region.
The Role of Observation Systems in Coral Reef Monitoring and Management
The Great Barrier Reef (GBR) located along north eastern Australia consists of some 3,500 individual reefs along 2,500km of coast. At over 315,000 square kilometres in area it represents a large dynamic system, is complex at all scales, sparsely monitored and relatively poorly understood. Managing such a complex system, including the impact of threats such as Climate Change and terrestrial run-off, requires a detailed understanding of the forces that drive the system and the resulting observed biological responses such as productivity, coral bleaching and coral disease. The Great Barrier Reef Ocean Observing System (GBROOS), a geographic node of the Australian Integrated Marine Observing System (IMOS), has deployed a range of observing infrastructure at a number of sites along the GBR. The project looks to measure and monitor the impact of oceanic water from the Coral Sea on the continental shelf reef systems an in particular the role of upwelling and intrusions. In the southern region there is a concentration of observing infrastructure around Heron and One Tree Islands including deep water moorings, ocean surface radar, satellite remote sensing (SST and Ocean Colour), on- reef meteorological stations and wireless sensor networks. This area therefore provides an opportunity to gain an understanding of how the oceanic waters impact and force shallower reef systems and in particular how the thermal environment within the reef lagoons is influenced by oceanic and other processes. The data from all of these systems will be integrated to form a picture of the thermal events occurring in this region during the 2008-09 summer period. Initial analysis of the real-time sensor network data shows the lagoons of Heron and One Tree Islands heating slowly over a number of weeks followed often by sharp cooling periods where the lagoon temperature can drop five degrees Celsius in a day or two. The presentation will look to link the within lagoon data with the deep water data, tidal information and meteorological observations. Understanding the linkages between processes occurring at the oceanic level around the reefs and those occurring within the reef is a critical part of understanding the overall impacts of thermal and other events affecting reef well-being. To manage these real-time data is critical as it allows for adaptive responses such as focused biological and other sampling to better capture how the corals respond to particular events. Both Heron and One Tree Islands have permanently manned research stations allowing responsive sampling to be undertaken during events of interest. The observations are valuable in developing better models of these systems by identifying overall patterns of thermal events and the ability to predict periods that may have high bleaching potential. Observation systems, linked into modelling and visualisation tools, can therefore provide monitoring of events as they occur, indications of potential future scenarios and help facilitate timely management outcomes.
Predicting the risk of coral disease outbreak using satellite SST.
Several environmental parameters have been linked to outbreaks of coral disease. Here we describe the influence of remotely-sensed summer and winter temperatures, as well as local observations of coral cover, to predict the risk of White Syndrome disease outbreaks on the Great Barrier Reef, Australia. Coral disease is an emerging risk to coral reef ecosystems that is likely to escalate with ocean warming due to climate change. The aim of this work is to provide reef managers with an expert system for predicting disease risk on coral reefs as far as six months in advance of summer outbreaks.