2005 STATE OF CORAL REEF REPORT.pdf - Mote Marine Laboratory

Threats
page
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The State of Coral Reef Ecosystems of the United States and Freely Associated States: 2005
Guam and
Southern
Islands of
CNMI
Main Hawaiian
Islands
American
Samoa
Southern
United States
Puerto Rico and the
U.S. Virgin Islands
Figure 3.5. Coastal population change between 1990 and 2000 and associated development pressure pose a significant threat to
coral reef ecosystems, particularly in island jurisdictions with limited land area. Maps not drawn to scale. Maps: K. Buja. Data: U.S.
Census, 1990, 2000; Secretariat of the Pacific Community, http://www.spc.org.nc/prism, Accessed 2/15/05.
sediments on corals can be exacerbated by wave action that repeatedly resuspends sediments into the water
column (Rogers, 1990). Increased turbidity in the water column, whether episodic or chronic, reduces light
availability for photosynthesis and growth. Increases in nearshore sediment loads have been shown to affect
morphology of corals and gorgonians as well as inhibit the development and recruitment of coral larvae (Rogers,
1990). Coral species react differently to this stressor, and coral reefs in waters experiencing increased
turbidity may exhibit a shift in community composition toward greater dominance of corals that are more tolerant
of lower light levels and better adapted to remove sediments.
Alteration of watersheds and associated changes in vegetative cover often decrease the ability of the land to
absorb rainfall, which flows through streams and channels, carrying sediments and pollutants into nearshore
areas. Generally, runoff from developed watersheds carries higher sediment loads than from undeveloped
areas, and this is more pronounced in areas where the topography is characterized by steep slopes. Removal
of mangrove forests that normally trap sediments may allow a greater proportion of terriginous sediments to
reach reef ares.
In addition to sediments, runoff from developed watersheds tends to have higher concentrations of waste
products. Increased freshwater inputs are actually considered pollutants as they can decrease the salinity
levels in some nearshore areas. Other contaminants derived from human use of nearshore areas include oil
leaking from vehicles, pesticides and lawn fertilizers applied to yards, parks and golf courses, chemicals in
asphalt that wash off roads, excrement from livestock and domesticated animals, and litter.