Problems of Scale in Coral Reef Ecology

Ecological phenomena occur on a variety of scales ranging from angstroms to kilometers. Below, we offer case studies illustrating that imagery generated at almost any scale can be analyzed using image processing tools combined with GIS techniques.

1. An individual coral colony.

Digital processing of underwater video. Underwater video provides a closer look at an individual coral colony. Multispectral classification allows for a GIS interpretation of the coral's condition. This Agaricia lamarcki is suffering from a tissue loss disease termed "white plague." The coral tissue dies, leaving a bare white skeleton which is quickly colonized by an algal turf community. The non-invasive, non-destructive aspects of underwater video imaging enable us to closely follow the fate of individual coral colonies, or collect data on the abundance and distribution of coral communities.

GIS Analysis of Coral Tissue Coverage:

Category...............Percent Cover

Coral Tissue.................37.89

Algal Turf......................46.47

Bare Skeleton...............15.36

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Totals............................99.72

2. An individual reef.

Aerial photography. While satellite imagery can be used to determine reef from non-reef, aerial photographs can provide a much finer scale but without the spectral resolution and measure of absolute radiance. Aerial photographs can be converted to RGB digital imagery with digital scanning. Multispectral cluster analysis then transforms the image into the GIS (Geographical Information System) domain; with appropriate ground truthing and georeferencing, the coverage of classes can be calculated. We have done this with 1:40,000 air photographs to a resolution of approximately 5 meters and with handheld 35 mm photographs of selected patch reefs with resulting spatial resolution of less than 25 cm. Biomass estimates from these photographic images compares favorably with line transects and underwater quadrat mapping.

Habitat Coverage on Key Largo Dry Rocks

(Classification from 35 mm slide):

 

Class..................................Percent Cover

Acropora palmata.....................9.70

Millepora / Sea Fan Zone..........10.62

Montastrea annularis.................6.28

Fore Reef Corals..........................7.22

Reef Flat Zone............................12.06

Shallow Sand................................3.47

Sand Pocket..................................2.33

Thalassia Seagrass......................40.94

White Caps, Wave Glitter..............2.87

Breaking Waves.............................1.02

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Totals..........................................99.73

3. A reef tract.

Satellite imagery. This classified SPOT

 image of the Key Largo National Marine

Sanctuary with a pixel resolution of 20 m makes it possible to distinguish reefs from grassbeds, sand, and hardbottom communities.

 

Habitat Coverage Estimates

Key Largo National Marine Sanctuary

 

Habitat...................% Cover..      Sq. Meters

Coral Reef....................6.20.......22,146,400

Rubble..........................0.83........ 2,967,200

Sand...........................22.73.......81,353,200

Sand Island...................0.03..............91,600

Seagrasses..................15.72.......56,248,800

Seagrass/hardbottom....0.21.............738,400

Seagrass/mud...............0.13.............471,200

Ocean.........................45.11.....161,423,200

Clouds (no data)...........4.37.......15,654,000

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Totals.......................100.02.......357,870,800

4. Coral Atolls Influence Oceanic Productivity.

This false color CZCS image shows that coral reefs may influence the productivity of neighboring waters. This image shows the Alphonse Atoll Group, Seychelle Islands, and its associated island mass effect chlorophyll plume. Oceanic current movement is from east to west (right to left). The plume trails off approximately 100 km to the west of the atoll. Highest chlorophyll values (red) are close to the island and the upcurrent patch of freshly upwelled (low chlorophyll, blue) water can be seen close to the eastern edge of the islands. The forked main axis of the plume and the swirling at its farthest fringes suggest that atoll-induced upwellings may spawn mesoscale eddies into the Indian Ocean. (Data from CZCS image 7930808222.N17)

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