This project emanates from a discussion and explicit requests for actions from MISTRA and FRN during the workshop "Coral Bleaching — and death" in Stockholm, November 1998.
Swedish scientists have been working in tropical seas and with coral research for many years. Detailed studies of coral reef biology has been performed by Olle Lindén and his group at Stockholm University for many years most intensely in the Indian Ocean. Investigations of reef biology have also been performed at Stockholm University by Nils Kautsky.
The Centre for Image Analysis (CBA) has been working in the Caribbean for about 10 years with different types of remote sensing projects on sea bottoms, currents and deposits (Lindell & Bertholdsson, 1992, Lindell, 1996, Morel & Lindell, 1998). One of the last performed tasks has been the Planning and Management of the coastal zone of Jamaica including mapping of all bottoms around the island, including mapping of the coral reefs (Norrman et al, 1998).
Swedish experience and knowledge on aquatic remote sensing has a long history and has substantially increased during the past 10 years due to the EU-funded SALMON project, the MISTRA RESE project and the work in Jamaica by T. Lindell. Scientific problems related to coral bleaching and ocean colour imagery are of the same basic structure and character as we have approached in the above mentioned projects. What is needed for a meaningful approach on the operational monitoring of reefs is the experience from hyperspectral sensors, from modelling of optical properties of the water, understanding the spectral behaviour of the bottom strata, and handling of the atmospheric correction of hyperspectral data.
2. Introduction
Coral reefs are perhaps the most biologically diverse and ecologically complex of all marine sea bed communities. They are unique in that they are entirely created through biological activity. The reefs are the result of the deposition of calcium carbonate over eons of geological time. They are among the oldest of all marine environments with a geological history that stretches back more than 500 million years in time.
Corals are invertebrate marine organisms in the Anthozoa class (phylum Cnidaria) that have a skeleton - external or internal - of a stony, leathery or horny consistency. The term coral is also used for the
skeleton of these animals, particularly the stony corals. Stony or hard corals include approximately 1,000 species. Common types of hard corals are brain, mushroom and staghorn corals. Atolls and coral reefs consist of stony corals. Most living stony corals are yellowish or brownish in colour, or olive coloured depending on the colour of the algae that live on the coral. The skeleton, however, is always white and consists almost entirely of calcium carbonate. This is deposited in a body-like shape surrounding the polyp inside it. Growth rate varies depending on age, food supply, water temperature and species. Atolls and coral reefs grow at an average rate of 0.5-2.8 cm per year.
A sensitive symbiosis, giving the corals its colours, is characterising the co-existence between the coral and the algae. If the coral is exposed to some kind of stress (e.g. an increase in ocean temperature, solar radiation, exposure to air, or pollution) the algae could leave the coral. When the algae is leaving, the coral is bleaching.
Since the 1980's, cases of coral bleaching have been observed. Bleaching caused extensive devastation among coral reefs in the eastern Pacific Ocean at the beginning of the 1980's and in the Caribbean during the mid to end 1980s. From mid 1997 to the end of 1998, bleaching of hard and soft corals has occurred that is without precedent. Most researchers claim that bleaching has been more frequent and more extensive during recent years.
3. Project Plans
This introductory pilot project of Swedish activities focuses on observations of coral bleaching from remote sensors. We are confident, however, that meaningful contributions in this field should include tools for the operational monitoring of reefs. An isolated pilot or demo project is not our primary objective. This pilot project therefore includes suggestions for a more constructive approach for the future research, in order to allow meaningful monitoring and quantification of the reef observations. Such a continuation of the project should be in close co-operation with international research groups.
The pilot project contains the following tasks:
1. The creation of a network of contacts for discussions and exchange of field and remote sensing data and as a basis for future integrated co-operation.
2. Demonstrating the ability of the satellites to provide a tool for detection of bleached corals.
The demo project is intended only to demonstrate that mapping of bleached coral reefs is possible from remote sensors. The intention is to use the present knowledge of the bleaching for selecting areas for the remote sensing. To get reference data for comparisons either a well mapped area, including the extension of the reef, is needed or data from the area of investigation from an earlier satellite image. The survey could be performed using Landsat, SPOT or IRS data. The result could be displayed as "difference images" or maps and in diagrams /tables of spectral differences.
The following work has been performed within this project
Summeries of our papers could be found at Papers