16 Remote Sensing of Coral Reefs and Their Environments . . .
319
These different configurations create significant contrasts in terms of exposure
of coastal habitats and their benthic and pelagic living communities to physical
factors (e.g. temperature, circulation, wave climate, cloud cover, sedimentation) and
create a large diversity of ecological and functional niches. Among the main coastal
habitats, coral reefs, seagrass meadows, and mangroves are of high importance given
their daily use by human populations. The amount of ecosystem services (fishery
and aquaculture, shoreline protection, nutrient recycling and so forth) provided by
this trio of coastal habitats is essential to the livelihood of islanders and coastal
continental populations (Gullstroem et al. 2002). Increasing human populations and
climate change threaten ecosystem resilience and the sustainability of these services
in the long term (Hughes et al. 2003). Conservation projects at various scales intend
to mitigate these impacts by implementing a range of management actions, some
purely local at the scale of villages, others at national and trans-boundary scales
(Wells et al. 2007).
This extremely brief panorama of the Red Sea and Western Indian Ocean context
identifies the potential use of remote sensing for coastal research and management.
First, the large ocean-scale domain and the variety of configurations naturally call for
the use of synoptic low to moderate resolution (50 km down to 1 km) observations of
the atmosphere, ocean and land dynamics along the coast and near the reefs. Second,
the ecological and economical importance of coral reefs, seagrass meadows and mangroves call for high to very high resolution (30 to 1 m) observations in order to map
the distribution of these habitats and monitor their changes. Third, climate changeinduced threats promote the combined use of low resolution and high resolution data
in synergy to observe (and predict) the trajectories of habitats under the observed (or
forecasted) physical forcing. Fourth, management and conservation activities need
accurate habitat and physical stress maps to design adequate conservation plans and
assess the amount and sustainability of services provided by habitats at a variety of
scales, from transboundary to local, from the entire region to few tens of kilometre
square.
This review compiles representative remote sensing studies to illustrate these different applications in the region of interest. The review is not necessarily completely
exhaustive and does not cite all existing papers in peer reviewed, conference proceedings and grey literature, but it points to gaps and perspectives. When interesting
remote sensing applications have not yet been conducted in the Red Sea and Indian
Ocean, pilot studies from other regions are cited. Also, this author assumes that the
reader is familiar with basic remote sensing principles and vocabulary and with the
most commonly used remote sensing sensors to date. The following chapters do
not enter methodological details but rather emphasize the applications. Finally the
main focus is on coral reef ecosystems, but seagrass and mangroves studies are also
frequently cited. In agreement with the terminology used by Andréfouët and Riegl
(2004), direct remote sensing refers to the use of remote sensing to study the habitats
themselves, while indirect remote sensing implies that the ocean and the atmosphere
surrounding the habitats are studied.
319
These different configurations create significant contrasts in terms of exposure
of coastal habitats and their benthic and pelagic living communities to physical
factors (e.g. temperature, circulation, wave climate, cloud cover, sedimentation) and
create a large diversity of ecological and functional niches. Among the main coastal
habitats, coral reefs, seagrass meadows, and mangroves are of high importance given
their daily use by human populations. The amount of ecosystem services (fishery
and aquaculture, shoreline protection, nutrient recycling and so forth) provided by
this trio of coastal habitats is essential to the livelihood of islanders and coastal
continental populations (Gullstroem et al. 2002). Increasing human populations and
climate change threaten ecosystem resilience and the sustainability of these services
in the long term (Hughes et al. 2003). Conservation projects at various scales intend
to mitigate these impacts by implementing a range of management actions, some
purely local at the scale of villages, others at national and trans-boundary scales
(Wells et al. 2007).
This extremely brief panorama of the Red Sea and Western Indian Ocean context
identifies the potential use of remote sensing for coastal research and management.
First, the large ocean-scale domain and the variety of configurations naturally call for
the use of synoptic low to moderate resolution (50 km down to 1 km) observations of
the atmosphere, ocean and land dynamics along the coast and near the reefs. Second,
the ecological and economical importance of coral reefs, seagrass meadows and mangroves call for high to very high resolution (30 to 1 m) observations in order to map
the distribution of these habitats and monitor their changes. Third, climate changeinduced threats promote the combined use of low resolution and high resolution data
in synergy to observe (and predict) the trajectories of habitats under the observed (or
forecasted) physical forcing. Fourth, management and conservation activities need
accurate habitat and physical stress maps to design adequate conservation plans and
assess the amount and sustainability of services provided by habitats at a variety of
scales, from transboundary to local, from the entire region to few tens of kilometre
square.
This review compiles representative remote sensing studies to illustrate these different applications in the region of interest. The review is not necessarily completely
exhaustive and does not cite all existing papers in peer reviewed, conference proceedings and grey literature, but it points to gaps and perspectives. When interesting
remote sensing applications have not yet been conducted in the Red Sea and Indian
Ocean, pilot studies from other regions are cited. Also, this author assumes that the
reader is familiar with basic remote sensing principles and vocabulary and with the
most commonly used remote sensing sensors to date. The following chapters do
not enter methodological details but rather emphasize the applications. Finally the
main focus is on coral reef ecosystems, but seagrass and mangroves studies are also
frequently cited. In agreement with the terminology used by Andréfouët and Riegl
(2004), direct remote sensing refers to the use of remote sensing to study the habitats
themselves, while indirect remote sensing implies that the ocean and the atmosphere
surrounding the habitats are studied.