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Land Forcing and Coral Reefs: Terrestrial Runoff as a Factor in Coral Reef Distribution

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By:

Casey J. McLaughlin

University of Kansas

And

Casey C. Smith

Swarthmore College

Coastal ecosystems such as coral reefs are increasingly in danger from non-local anthropogenic effects such as deforestation, land use, and pollution in inland river basins. These non-local pressures are channeled from a potentially large basinscale through freshwater discharge into the coastal zone. As a first estimate of a reef—to--runoff relationship, I examined global reef distributions as a function of total runoff within the same 30’ grid cell. The resulting correlation suggested that runoff inhibited reef occurrence when runoff was greater than 1010 m3/yr. Combining basin runoff and five additional variables (average sea surface temperature, minimum salinity, wave height, tidal range, Chlorphyll-A) selected to proxy the effect of runoff, increased predictive capabilities. The use of statistical representation of spatial and temporal variability allowed useful analytical comparisons of the environmental variables. Spatial and temporal statistics (standard deviations minimum/maximum months, ranges) were summarized for each variable into a standard 30’ spatial grid cell, providing a common framework for K-means clustering routine. Further classification of runoff-related stresses can then be made, for example, by adding modeled sediment discharge to refine the prediction of areas of reef stress from human activities. This information is important to understanding both paleo-environmental forcing of reefs and the potential effects of present and future human alterations to the hydrologic cycle.

www.epa.gov/Oceans and Coastal Protection Coral Reefs and Your Coastal Watershed.htm

- Investigate the relationship between terrigenous runoff and coral reef distribution

- Integrate land and ocean based data sets to test coral reef distribution relative to fresh water discharge

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

Craig Quirolo

http://www.reefrelief.org

Defining the limits of coral reef distribution:

Minimum Sea Surface TemperatureSalinityLight PenetrationAragonite SaturationNutrient Loads

Conceptual tie-in:

We consider sediment loads

in addition to proxies for the other variables

Scale:

1 degree grid system

1,000 reef locations

1-100 year time scale

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

Environmental Limits to Coral Reef

Development, Where Do We Draw the Line?

Kleypas, Joan, McManus, John, and Meñez, Lambert

American Zoologist, Vol. 39, No. 1 February 1999

Environmental variables used to investigate

sediment--reef relationships in the context of

distribution-limiting variables

Spatial Limitations:

Land Forcing:

Annual Basin Discharge (log)

Latitude: 30N to 30S

Reefs: Coastal focus ~6600 records

Grid Cell: 0.5 degrees

System Interaction:

Wave Height, Tidal Range, andChlorophyll-A

Ocean Influence:

Average Sea Surface Temperature

Minimum Salinity

Location:

ReefBase reef location inventory~10,000 total records

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

Reefbase Reef Inventory

LOICZ and Hexacorallia

database structure

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

- K-means clustering (LOICZVIEW) of runoff, reef occurrence
- and environmental variables
- Visualization
- Buffering and spatial querying using ArcView GIS

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

Statistical Analysis of reef occurrence in relation to log basin runoff

Runoff

Unsupervised

runoff clustering

with reef overlay

Considered alone,

runoff has a strong

anti-correlation

with reef

distribution

Statistical Analysis of reef occurrence in relation to combined env. variables

Unsupervised

Unsupervised

clustering of

6 env. variables

with reef overlay

Runoff does not

dominate

distribution

Statistical Analysis of reef occurrence in relation to log basin runoff

Supervised

Supervised by

runoff: clustering of 6

env. variables

with reef overlay

High runoff values

show strong control

of reef distribution

Deviations

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

The Americas--

visualizing results:

an example

Africa and Arabia

Austral-Asia

If Log runoff > 9.8, few reefs are within ~80 km (ocean and coastal)

- Terrigenous runoff doesinfluence reef distribution --occurrence threshold roughly 9.6x106 meters3/year/0.5 degree coastal cell
- Integration of data is both possible and useful
- Spatial and temporal resolution are always problems --hypothesis to be tested must match the scale of the data and vice versa

1. Selection Criteria

2. Data Integration

3. Hypothesis Testing

http://www.reefbase.org/

http://www.kgs.ukans.edu/Hexacoral/index.html

http://www.reefbase.org

http://www.nioz.nl/loicz/

http://www.palantir.swarthmore.edu/~maxwell/loicz/

Support:

NSF OCE-00-03970, ‘Biogeoinformatics of the Hexacorallia’; IGBP-LOICZ; UNEP-GEF