heuristic for coral bleaching. This temperature range is quite close to the upper limit
that the coral normally experience (Coles and Jokiel 1976).
It is known that not all corals, even of the same species, will exhibit signs of coral
bleaching over their entire surface under the conditions of thermal stress described
above. In addition to temperature stress, increases in the duration and intensity of light
exposure beyond the range of photoacclimatization has shown a strong correlation with
the coral bleaching response (Shick et al. 1996, Hoegh-Guldberg 1999, Lesser and
Farrell 2004). It is believed that the combination of high temperature combined with
increased insolation in surface waters leads to coral bleaching, and that the areas of
corals of the same species and symbiotic (zooxanthellate) clade that do not bleach are
perhaps not exposed to equivalent amounts of sunlight. The intensity of light on the
surface could be limited locally by physical shading, as in the bottom surfaces of corals
as opposed to the tops, or due to UVR screening substances. These include
chromophoric dissolved organic matter (CDOM) in the water column or mycosporinelike amino acids within the coral itself (Lesser and Farrell 2004, Otis, et al. 2004).
In order to gain an understanding of the role of light in coral bleaching, it is
necessary to determine the spectra and intensity of light at the coral surface. Providing
individual light sensors at each coral in a study region is prohibitively expensive and
may disrupt the environment. Therefore, an approach taken by the CREWS research
team has been to calculate coral light exposure by extrapolating from CREWS station
irradiance data.
8.1.1 Remote verification of coral bleaching alerts and predictions
One method we have developed to verify our coral bleaching alerts and predictions
has been to install an underwater camera that can transmit images locally to a shorebased station and then to the Web. The underwater Coral Camera infrastructure at St.
Croix (Figure 3) is composed of two cameras (above and below water) and a Niagara™
streaming video computer server (which encodes the signal from analog to digital)
located on shore, and also at AOML. The above-water camera, located on shore and
pointing directly at the CREWS station, is connected to a video server inside a building.
This camera is a manual zoom camera mounted in an industrial-strength all-weather
housing within direct line-of-sight of the station. The second camera is located
underwater and tethered to the CREWS station in such a manner that a diver is able to
move the camera to different viewing locations around the CREWS station, to as far
away as approximately 150 m, and down to a depth of 20 m. The camera is powered by
the central station’s solar-powered batteries and is in communication with the onshore
video server via a microwave link, consisting of a transmitter on the station and a
receiver onshore. Once the video signal is processed and converted into Windows
Media™ by the encoder, the signal is then prepared for streaming over the Internet.
This is possible only via an Internet Virtual Private Network (VPN) link between St.
Croix and AOML, since security is of paramount concern for all federal installations.
When an Internet user wishes to view the video stream, a request is sent to the AOML
based server. The server in turn creates a link over the VPN to the video server in St.
Croix. The server then packages the video stream and provides it to the Internet
requestor. In this way, after CREWS initiates bleaching alerts for St. Croix, a user can
look to the underwater Coral Camera to see if, indeed, bleaching is taking place. Since
different species bleach before others, however, it is of course important to position the
camera to point at the species of interest.
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Meteorological and Oceanographic Instrument Array
that the coral normally experience (Coles and Jokiel 1976).
It is known that not all corals, even of the same species, will exhibit signs of coral
bleaching over their entire surface under the conditions of thermal stress described
above. In addition to temperature stress, increases in the duration and intensity of light
exposure beyond the range of photoacclimatization has shown a strong correlation with
the coral bleaching response (Shick et al. 1996, Hoegh-Guldberg 1999, Lesser and
Farrell 2004). It is believed that the combination of high temperature combined with
increased insolation in surface waters leads to coral bleaching, and that the areas of
corals of the same species and symbiotic (zooxanthellate) clade that do not bleach are
perhaps not exposed to equivalent amounts of sunlight. The intensity of light on the
surface could be limited locally by physical shading, as in the bottom surfaces of corals
as opposed to the tops, or due to UVR screening substances. These include
chromophoric dissolved organic matter (CDOM) in the water column or mycosporinelike amino acids within the coral itself (Lesser and Farrell 2004, Otis, et al. 2004).
In order to gain an understanding of the role of light in coral bleaching, it is
necessary to determine the spectra and intensity of light at the coral surface. Providing
individual light sensors at each coral in a study region is prohibitively expensive and
may disrupt the environment. Therefore, an approach taken by the CREWS research
team has been to calculate coral light exposure by extrapolating from CREWS station
irradiance data.
8.1.1 Remote verification of coral bleaching alerts and predictions
One method we have developed to verify our coral bleaching alerts and predictions
has been to install an underwater camera that can transmit images locally to a shorebased station and then to the Web. The underwater Coral Camera infrastructure at St.
Croix (Figure 3) is composed of two cameras (above and below water) and a Niagara™
streaming video computer server (which encodes the signal from analog to digital)
located on shore, and also at AOML. The above-water camera, located on shore and
pointing directly at the CREWS station, is connected to a video server inside a building.
This camera is a manual zoom camera mounted in an industrial-strength all-weather
housing within direct line-of-sight of the station. The second camera is located
underwater and tethered to the CREWS station in such a manner that a diver is able to
move the camera to different viewing locations around the CREWS station, to as far
away as approximately 150 m, and down to a depth of 20 m. The camera is powered by
the central station’s solar-powered batteries and is in communication with the onshore
video server via a microwave link, consisting of a transmitter on the station and a
receiver onshore. Once the video signal is processed and converted into Windows
Media™ by the encoder, the signal is then prepared for streaming over the Internet.
This is possible only via an Internet Virtual Private Network (VPN) link between St.
Croix and AOML, since security is of paramount concern for all federal installations.
When an Internet user wishes to view the video stream, a request is sent to the AOML
based server. The server in turn creates a link over the VPN to the video server in St.
Croix. The server then packages the video stream and provides it to the Internet
requestor. In this way, after CREWS initiates bleaching alerts for St. Croix, a user can
look to the underwater Coral Camera to see if, indeed, bleaching is taking place. Since
different species bleach before others, however, it is of course important to position the
camera to point at the species of interest.
147
Meteorological and Oceanographic Instrument Array