RS Monitoring of Coral Reefs in Belize

Measure Distance

Measure Area

Query Layers

Please enter the longitude and latitude for a location within the region of interest (longitude: 88.4 to 87.0°W, latitude: 16.2 to 20.2°N) to query all layers present at that location.

Help

Data layers can be displayed by ticking the check box to the left of their name in the layer tree in the left hand panel of the maps tab. The selection of multiple layers is allowed and if more than one layer is selected, that which is nearest the top of the layer tree will be displayed above the others. Although queries return information on all layers present, multiple raster layers (e.g., those displaying habitats, temperature and wave exposure) can not be viewed simultaneously. Only the coastline, area of interest and base layers can be viewed with other layers without loss of visual information.

In addition to making the website full-screen size using keyboard key F11, the layer tree and legend panels may be minimised by clicking the arrows to the right of their titles.

Navigation and querying of the map can be achieved either using the tools described below or in some cases using the keyboard. Keyboard arrow keys may be used to scroll the map in the north, east, south and west directions.The Home and End keys also scroll the map left and right. Page Up and Page Down scroll the map up and down. Plus and minus keys zoom in and out of the map respectively.

The query tools can be used to return information about a specific location selected by the user. Query results are returned in the panel at the bottom left of the screen.

	Zoom to Previous Extent	Return to previous extent.
	Zoom to Next Extent	Zoom to next extent.
	Zoom to Original Extent	Return to the original extent.
	Pan	Pan the map with a drag of the mouse.
	Zoom Box	The Zoom Box control enables zooming directly to a given extent, by drawing a box on the map.
	Zoom In	Zoom in at a selected location.
	Zoom Out	Zoom out at a selected location.
	Query Layers	Query all layers at location selected by mouse.
	Query Layers	Query all layers at position specified by user.
	Measure	Measures the length of a line drawn between two points on the map.
	Measure Area	Measures the area of a polygon drawn on the map.

Monitoring coral reefs in Belize using remote sensing was a five-month Earth Observation (EO) demonstration carried out by the Marine Spatial Ecology Laboratory at the University of Exeter (UK) within the framework of the European Space Agency Earth Observation Market Development programme, in support of the World Bank, which was interested in ascertaining the potential of EO data for monitoring the health of, and stressors acting upon, coral reefs off the coast of Belize. The project provides state-of-the-art EO based information tools with a solid scientific base that might support environmental monitoring and the management of coral reefs in the area.

Figure 1. Study area: northern Mesoamerican barrier reef system (16.2-20.2°N 87.0-88.4°W).

General Project Context

The European Space Agency programme on Earth Observation Market Development funded a project entitled “Exploitation of Earth Observations services in support of Environmental Impact Assessment and Monitoring”. The objective of the project is to investigate and define services and products for better exploitation of EO data in support of Environmental Impact Assessment and related environmental monitoring and to enlarge the EO user community.

This particular service trial was developed in support of the World Bank, specifically in the context of the “Regional project on adaptation to climate impacts in coastal zones in the Caribbean”, currently being conducted through the Caribbean Community Climate Change Center. As part of this project, a pilot research activity has been included to promote the restoration of coral populations affected by increased sea surface temperatures and lower sea pH. The information generated by this service will foster the use of EO data within the World Bank and its relevant departments, and feed into their research activities.

Details of the Service

The objectives of this project are threefold:

1. To review how state-of-the-art remote sensing capabilities can help support the monitoring of coral reefs, assess their health and quantify possible stress, and provide recommendations for the development of a robust early warning system of stress in reef areas.
2. To deliver high-resolution maps of sea-state parameters that can help reef managers to quantify possible stress on Belize’s reefs, making maximum use of existing data sets and ESA projects.
3. To deliver reef habitat maps for selected locations based on appropriate EO data from various missions in combination with ancillary data.

The area of interest includes the Northern Mesoamerican Barrier Reef System (NMBRS), shown in Figure 1. This area constitutes a number of off-shore atolls, patch, fringing and barrier reefs. The NMBRS provides ecosystem services including coastal protection and nursery habitats, and is fundamental for the livelihood of the inhabitants of Belize, principally through the tourism and fishing industries.

Coral reefs in the NMBRS face a number of threats; chief amongst these are coral bleaching, which occurs during periods of exceptionally warm sea temperature, and overfishing of herbivorous fishes, which up to April 2009 were the most frequently-caught fish group in Belize; however all herbivores are now under protection. To date, there is a lack of knowledge regarding spatial variability in oceanographic patterns at reefs in Belize that could aid in the categorisation of reef environments, likely to influence reef function and resistance and resilience to disturbance events. In this project we reviewed how state-of-the-art remote sensing capabilities can help support the monitoring of coral reefs, assess their health and quantify possible stress, mapped reef habitats at selected locations in the NMBRS, and explored extrinsic factors that can improve reef resistance and resilience to disturbances by mapping (1) sea surface temperature patterns, (2) vulnerability of reefs to coral bleaching, (3) vulnerability of reefs to experiencing a phase shift, changing from a coral-dominated to a macroalgae-dominated state, if herbivores are absent and (4) coral connectivity among reefs: four important factors influencing the establishment of monitoring and management priorities in the region.

Sea Surface Temperature (SST) Patterns

All-day SST data were obtained from the Along-Track Scanning Radiometer and the Advanced Along-Track Scanning Radiometer (collectively called (A)ATSR) instruments on board of the European Remote Sensing and ENVISAT satellites. We used the Gridded Surface Temperature full resolution product (1 km).

The SST climate (1991-2008) in the study area was characterised using five data layers: (1) average temperature, (2) standard deviation, (3) minimum and (4) maximum monthly mean, proxies for local tolerance thresholds, and (5) the probability of occurrence of warm anomalies (hot spots greater than 1°C: Strong et al. 1997).

The thermal regime of an area determines the environmental setting of the communities and influences variability in bleaching response and post-bleaching mortality. In the NMBRS, shallow waters at the Bays (Ascension, Espiritu Santo and Chetumal), atoll lagoons and the barrier reef lagoon experience colder average SSTs, colder winters and broader variation. Warmer waters and more frequent thermal anomalies are experienced in areas of slow water flow, as in the Gulf of Honduras, and in shallow and sheltered regions on the internal side of the bays and atoll lagoons.

Thermal Regimes Experienced by Corals

Figure 1. Acute and chronic
thermal stress categories.

The approach for classifying reefs by thermal regime was developed by the Remote Sensing Working Group of the World Bank / GEF Coral Reef Targeted Research Project. Due to the limited temporal resolution of the (A)ATSR dataset (=35 days), the 4 km NOAA AVHRR pathfinder product was used for the generation of this data layer. The filtered 4 km weekly mapped product used (1985-2005) was provided by Scott Heron, William Skirving and Mark Eakin of Coral Reef Watch, NOAA.

The response of corals to thermal stress depends on the temperatures that they are acclimated to (chronic stress) and the prolonged, elevated temperatures that they experience during disturbance events (acute stress). We used the maximum of monthly mean temperatures experienced over the entire 21 year dataset as a measure of chronic stress. The frequency of degree heating weeks during the mass bleaching event in 1998 was used as a measure of acute stress. Reefs can be classified according to their past temperature patterns into the following categories: (A) high chronic (thus acclimated) and low acute stress, expected to cope best with rising temperatures, (B) high chronic and high acute stress, where the selection for more thermally-tolerant genotypes would be greatest, (C) low chronic and low acute stress, not acclimated to any thermal stress and expected to be fair badly if subjected to unusual warming, and (D) low chronic and high acute stress, likely to be the worst-affected by climate change (Figure 1).

Areas that are predicted to fare better under future climate change (from a thermal perspective, A) are rare and scattered across the study area, mainly in the barrier reef and the atolls. Areas with high selection pressure (B) are located in shallow sheltered areas with slow water flow, such as at the Gulf of Honduras or on the leeward side of the barrier lagoon, while areas that are expected to fair worst under a climate change scenario are distributed mainly in the north of the study area.

Vulnerability of Reefs to Phase Shifts

Figure 2. (a) Exposure map for the study area (16.2-20.2°N 87.0-88.4°W). Land and reef crest are black. Relative exposure measures ranges from 0 to 0.3 J/m³ (b) detailed region showing shading effects.

Wave exposure, a proxy for estimating the vulnerability of reefs to phase shifts, was calculated using the method described by Ekebom et al. (2003) and Harborne et al. (2006), where the exposure of a location is a function of the shape of the basin, and the routine wind speed and direction. The original method was improved (1) by including spatial variability in wind fields using scatterometer wind data, due to the large size of the study area and the variable wind distribution over the NMBRS and (2) by assessing the wave exposure along the coastline and additionally along reef-crest areas. This last addition is particularly important in the NMBRS where reefs are not always located at the land-ocean boundary.

Wind speed and direction for the period 2004-2008 were obtained from the Active Microwave Instrument (AM) on board of the ERS-2. The product used was the wind scatterometer fast delivery product, with a spatial resolution of 25 km. Landsat imagery (25 m) was used to identify coastline and reef-crest areas.

Areas with high wave exposure and faster algal growth are more prone to an increase in macroalgae abundance if grazers are absent. Regional variations in wave exposure within the NMBRS are characterised by higher values at the north of the barrier reef, between Ambergris Cay and Belize City, where the winds are strongest. At a local scale, the seaward side of the atolls and the barrier reef (unless shadowed by a reef structure to the east) experience higher exposures and are thus the most vulnerable to algal blooms if their reefs are depleted of herbivorous fishes (Figure 2).

Connectivity

Larval connectivity data was provided by Dr. Claire Paris. The model was parameterised using oceanographic data for August 2003.

Coral reef persistence and recovery following disturbance events depend not only on coral growth, but also upon the arrival of larvae to reseed the population. Larval transport is driven by the general pattern of currents in the area and coincides with previous wide-scale assessments for the Caribbean (Cowen et al. 2006). Reefs at the extremes of the study area exhibit some isolation. Offshore atolls serve mainly as sources of larvae, while reefs in the barrier reef have the highest number of connections.

Habitat mapping

Mumby and Harborne (1999) produced a reef habitat classification for Belize and this scheme was used to map reefs in two sections of the NMBRS. The first map covers the southern extreme of the barrier reef (16.16-16.70°N, 87.83-88.41°W) and the second covers the central section of the barrier reef, the Turneffe Islands and Lighthouse reef (17.04-17.82°N, 87.07-88.18°W). The existing maps created from 1997 Landsat imagery were updated using the most recent Quickbird and Landsat imagery. The maps were produced using water column correction, supervised classification and contextual editing. In the NMBRS, shallow areas are covered mainly by seagrass and sand. Coral reefs are located on the seaward side of the barrier reef, around the atolls and rhomboid reefs. Within the Barrier, reefs are rare in the south, in the Gulf of Honduras. Reefs are also scarce around the deep shipping channel south of Belize City, an area characterised by low water quality.

	Marine Spatial Ecology Lab (MSEL) This service project was carried out by MSEL. The Marine Spatial Ecology Laboratory is part of the School of Biosciences at the University of Exeter, UK. MSEL currently comprises thirteen researchers working on various projects in coral reef ecology and remote sensing. A unique aspect of MSEL research is that remotely-sensed data are used to drive spatial models of coral reef ecosystem dynamics and provide explicit advice for reef management, including the design of marine reserves. MSEL research includes the design of networks of marine reserves in Belize and the Bahamas, and has led to changes in the management policies of the World Bank and new conservation legislation to protect parrotfish in Belize and Bonaire. Project leader: Peter J Mumby Project manager: Iliana Chollett Researchers: Ian Elliott, John Hedley
	The European Space Agency (ESA) This service project was funded by the ESA. The European Space Agency is Europe’s gateway to space. Its mission is to shape the development of Europe’s space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world. ESA's programmes are designed to find out more about the Earth, its immediate space environment, our Solar System and the Universe, as well as to develop satellite-based technologies and services, and to promote European industries. ESA is an international organisation with 18 Member States, but its headquarters are in Paris, France, where policies and programmes are all decided.
	The Luxembourg System Integrator for Aerospace and Defense Systems (LuxSpace) This service project was managed by LuxSpace. The Luxembourg system integrator for aerospace and defense systems (LuxSpace) is a space-technology company established by OHB technology AG at Betzdorf, Luxembourg. LuxSpace is responsible for offering space-technology and defense systems and services in the global commercial and institutional market. Its main focus is on small satellites for research, communications, navigation and earth observation.
	abcGIS This website (including the web based mapping server) was constructed by Helen Edwards of abcGIS. abcGIS consulting provides high quality, state of the art, web GIS applications using the latest emerging open source technologies, specialising in the development of applications for marine environments.

Acknowledgements

The European Space Agency provided the (A)ATSR sea surface temperature and wind scatterometer data.

The approach for classifying reefs by thermal regime was developed by the Remote Sensing Working Group of the World Bank / GEF Coral Reef Targeted Research Project.

Claire Paris at the Rosenstiel School of Marine and Atmospheric Science/ Division of Applied Marine Physics (RSMAS/AMP), University of Miami, USA, provided the larval connectivity matrix used in this project.

Scott Heron, William Skirving and Mark Eakin, from Coral Reef Watch, National Oceanic and Atmospheric Administration (NOAA) provided the weekly AVHRR Pathfinder product used for the SST analyses for reserve design.

Renata Ferrari (MSEL, University of Exeter) took all the photographs included in this website. Renata has spent the last year at Glover’s atoll, living, diving and researching Belizean reefs.