- Characterization of the organisms that make up the reef via spectral classification of hyperspectral imagery, with a particular focus on the discrimination of different species of scleractinian corals that dominate the benthic zone, and of other invertebrates and algae.
- Comparisons of the spectral signatures with oceanographic and water quality data to look for biological indicators of environmental stress in the spectral response. In particular, we are trying to characterize spectrally the physiological response of corals to salinity, temperature, dissolved oxygen, PAR, as well as varying concentrations of major nutrient elements and Chlorophyll a
- Comparisons of high-resolution in situ (underwater) readings with a hand-held GER spectroradiometer to the spectra extracted from the overhead imagery, to quantify the change in the spectral response due to the intervening water column. The spectrometer is equipped with a 10-meter fiber optic underwater cable fitted with a cosine receptor possessing a hemispherical field-of -view (FOV)
- Characterization via spectral classification of non-native benthic species that have invaded the reef and pose a threat to the health of the ecosystem
- Spectral discrimination of healthy vs. bleached corals due to the change in spectral response caused by the loss of photosynthetic pigments. This approach appears to be one of the most promising means of remote detection of coral health.
Hawai'i
View of our study site,
Kaneohe Bay, with Coconut Island in the background, the home of the Hawaiian
Institute of Marine Biology (HIMB)
Because of the sensitivity of coral reef ecosystems to natural and anthropogenic
stress and because of the rapidity with which observed changes occur, methods
that provide immediate baseline and subsequent monitoring data over large areas
are necessary to focus restoration and conservation efforts, and produce results on
time scales that permit adaptive management. We are applying techniques in
hyperspectral remote sensing to shallow coral reef ecosystems to address these
issues.
The specific goals of this project are:
The study area is Kaneohe Bay, an estuarine and coral reef ecosystem on the windward NE coast of Oahu and the largest embayment in the Hawaiian archipelago. Often referred to as one of the most intensively studied coral reef systems in the world, it is protected from the tradewind swell by a barrier reef. This protection allows extensive coral reef development within the Bay, with 60 patch and fringing reefs that provide habitat and shelter to a variety of reef fishes, sea turtles, invertebrates and algae.
A view of the North end of Kaneohe Bay, with several shallow patch reefs visible in the foreground
Both natural processes and anthropogenic activity have historically impacted
Kaneohe Bay to the point it has been cited as one of the best examples of the
resiliency of natural ecosystems to environmental offense. Nine perennial
streams and their associated estuarine components discharge in the Bay, for a
total stream discharge of approximately 214,000 m3/day. Annual rainfall in this area averages 140-240 cm/year. However periodic intense storms may
greatly increase these values.
Central Kaneohe Bay, where the increasing urbanization pressure poses additional threats to the health of the reef communities
Besides large freshwater inputs and the
deposition of land-derived sediments from natural processes, additional impacts
to the reef communities result from anthropogenic activities, namely
agriculture, grazing and the ever increasing urbanization pressure. Increased
urbanization causes increased sedimentation from runoff, dredging, reef erosion,
freshwater kills (exacerbated by stream channelization), and the well documented
effects of sewage and eutrophication. Currently, the watersheds around the
southern and central sectors of the Bay are largely urbanized, while most of the
northern bay bears rural and agricultural areas.
The three dominant species of scleractinian corals in the Bay are:
Porites compressa, shown below
Montipora capitata, shown below
Pocillopora damicornis, shown below
Increased nutrient inputs also support the luxuriant growth of the "green bubble
algae", Dictyosphaeria cavernosa. This alga outgrows living coral
colonies, particularly in the central sectors of the Bay
D. cavernosa smothering a Porites compressa head and moving on to a Montipora capitata colony
D. cavernosa is one of the key species we are trying to characterize spectrally
to monitor its abundance and distribution with overhead imagery since it has
historically been the best indicator of the eutrophication levels in the Bay and
of the overall health of this ecosystem
D. capitata is common especially in the central and southern sectors of the Bay, where nutrient inputs are higher, and usually occurs below 7-8 ft of water where most of the coral heads are partially or completely smothered. The above picture is a typical sighting of the southern/central reefs of the Bay
