The Ecology and Physiology of an important brown seaweed (Dictyota) on coral reefs in the Florida Keys. Principal Investigator: Kevin Beach, University of Tampa. Co-Principal Investigator: Linda Walters, University of Central Florida.

Over the past decade, a brown seaweed (genus Dictyota) has become an increasingly common part of the reef environment in the Florida Keys. It is not known, however, if the increase in abundance is caused by pollution or the result of natural processes in the ecosystem. It is also unknown how the increase in abundance affects other organisms living on the reef. Changes in coral reef environments from coral dominated to seaweed dominated habitats are now common throughout many tropical and subtropical coastal regions, especially in Florida and the Caribbean. Identifying the causes of these changes is a high priority for managers and reef scientists. To date, no single factor has been identified as the cause of seaweed dominance in the Florida Keys. Elevated nutrient concentrations resulting from coastal development (sewage and agriculture) are frequently suggested. However, there is tremendous uncertainty as to which nutrients (if any) are responsible for causing increased amounts of seaweeds on the reefs. This project investigates nutrients and seaweed growth using new technology to measure the physiology of seaweeds (in this case Dictyota) in their natural habitats.

Dictyota grows both as free-standing individuals and attached to a variety of important reef organisms, including hard corals, seas fans, sponges, fire coral, and a variety of other organisms. As Dictyota abundance continues to increase, more and more other organisms are likely to come into direct contact with the seaweed. Thus, it is important to understand how Dictyota grows and interacts with other reef organisms. The alga can cause damage by overgrowing other species, and the seaweed also contains novel chemicals that are known to deter fish grazing and reduce the growth rates of other algae found in close proximity. The specific questions to be addressed during this mission are:

1. How does naturally occurring nutrient and light gradients affect the growth and physiology of Dictyota?
2. How does Dictyota that attaches to other organisms affects their growth and fitness?
3. How does Dictyota affects organisms growing in close proximity to it on the reef?
4. Does elevated cover of Dictyota alter the foraging behavior of herbiverous fish?