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

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


1
Land Forcing and Coral Reefs Terrestrial Runoff
as a Factor in Coral Reef Distribution
By Casey J. McLaughlin University of
Kansas And Casey C. Smith Swarthmore College
2
Introduction
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 basin scale through freshwater
discharge into the coastal zone. As a first
estimate of a reefto--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.
3
Objective
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
4
Defining the limits of coral reef
distribution Minimum Sea Surface
Temperature Salinity Light Penetration Aragonit
e Saturation Nutrient 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
5
Environmental variables used to investigate
sediment--reef relationships in the context
of distribution-limiting variables
Land Forcing Annual Basin Discharge (log)
Spatial Limitations
Latitude 30N to 30S Reefs Coastal focus
6600 records Grid Cell 0.5 degrees
System Interaction Wave Height, Tidal Range,
and Chlorophyll-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
6
Reefbase Reef Inventory
7
LOICZ and Hexacorallia database structure
1. Selection Criteria 2. Data Integration 3.
Hypothesis Testing
8
Analysis Methods
  • 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
9
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-correla
tion with reef distribution
10
Unsupervised
Statistical Analysis of reef occurrence in
relation to combined env. variables
Unsupervised clustering of 6 env. variables with
reef overlay
Runoff does not dominate distribution
11
Supervised
Statistical Analysis of reef occurrence in
relation to log basin runoff
Supervised by runoff clustering of 6 env.
variables with reef overlay
High runoff values show strong control of reef
distribution
12
Deviations
1. Selection Criteria 2. Data Integration 3.
Hypothesis Testing
13
The Americas-- visualizing results an example
14
Africa and Arabia
15
Austral-Asia
16
Buffering an alternative test of reef--runoff
relationships
If Log runoff gt 9.8, few reefs are within 80
km (ocean and coastal)
17
Conclusions
  • Terrigenous runoff does influence 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
18
Web References
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
19
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