Issues : Figure Sets


In this Issue, students examine published data that address the causes of coral and seagrass decline in Florida. Activities engage students in data analysis and hypothesis testing and will increase their understanding of the complexities of ecological phenomena.

Coral reefs are important ecological habitats because they provide food and shelter to many organisms, they are home to many species including endangered ones, and in many tropical areas they are reliable sources of food. However, coral reefs are in trouble in all parts of the globe. For example, the coral reefs in the Florida Keys, which are the only coral reefs in the continental United States, have been dramatically in decline since the late 1980's. Marine ecologists have recorded long term data showing increases and epidemics of coral diseases (http://ourworld.compuserve.com/homepages/mccarty_and_peters/coraldis.htm) and the loss of coral species diversity.

These problems are not restricted to coral. Seagrasses are also integral parts of marine ecosystems by helping to clarify water, stabilize the sea bottom, serve as food sources for marine life, and provide habitats and nursery areas for many types of organisms, including shrimp. Unfortunately, seagrasses are also being threatened. Seagrass beds formerly covered most of Florida Bay, but have been dramatically in decline in tandem with coral. In addition, data indicate concomitant population declines in shrimp (record low harvests of pink shrimp), spiny lobsters, 100% mortality of sponges in some places, as well as algal blooms, higher water turbidity, and many other indicators of degraded water quality.

The seagrass and coral diseases and die-offs may be related to human activity in the Florida Bay watershed where the Keys are located (see MAP).

Scientists hold different viewpoints as to the causes of water quality degradation, which is most likely to be the immediate ecological cause of coral and seagrass decline.

Some attribute the water quality decline to WATER DIVERSION to the north of the Everglades for agricultural use and accompanying increase in salinity in the Bay.

Others attribute the water quality decline to the increase in agricultural activity and suburban development from which FERTILIZER, PESTICIDES, AND HERBICIDES run-off into the Bay. Fertilizers in turn cause nitrogen and phosphorous loading (see ESA Issues in Ecology - http://www.esa.org/sbi/sbi_issues/) that can lead to eutrophication (http://www.rsmas.miami.edu/groups/jmc/fla-bay/FBayOverview1.html).

Still others suggest that water quality may in fact be affected by factors other than water diversion/salinity, or organic pollution/eutrophication; instead, in the case of Florida Bay, water degradation may have resulted from the suite of environmental impacts from the building and operation of the new FLORIDA EAST COAST RAILWAY.

Finally, increasing water temperature - as a result of rising carbon dioxide - appears to be another contributor to coral decline in the Florida Bay (http://www.publicaffairs.noaa.gov/iyorwk35.html). As water temperature rises, corals expel their zooxanthellae and become "bleached". Coral bleaching events are on the rise globally.

Researchers therefore are not sure about the main cause of coral reef and seagrass decline or if it is due to some combination of these and perhaps other factors.

Additional Resources