The ecological significance of growth and reproduction by an important sediment producing green seaweed. C. Smith (University of Hawaii)

This Aquarius mission represents the second year of a two year program to study the ecology of seaweeds at Conch Reef. Year two research expands on activities previously conducted, and provides an opportunity to obtain additional measurements on ecological process that are typically quite variable - so multiple years are needed to better understand results.

Rationale for this mission remains unchanged. There is great concern that seaweeds may be overgrowing and killing corals in some reef environments, possibly due to changes in water quality that enhance the growth rates of seaweed, yet few studies exist that have looked at the ecology of seaweeds in Florida. Research using the Aquarius underwater laboratory will investigate the growth dynamics of important algal species at Conch Reef.

Green calcareous seaweeds of the genus Halimeda are important in their roles as benthic primary producers and as biological stabilizers, where they help to consolidate coral reefs in shallow and mid-depth habitats. For example, Halimeda contributes more to reef sediments than either corals or corraline algae; producing over a meter of carbonate accretion every 500 years. Considering that Halimeda is so abundant in reef environments it is remarkable that so little is known about how the seaweed grows, its population structure, and physiology. This project, continuing work started in 1994, has a main objective to determine how the ecology of Halimeda varies in different reef environments, from shallow water to depths at which reef growth stops in the Key Largo area (about 35 meters). The project will specifically address: 1) the effects of light intensity on growth and overall size; 2) how the seaweeds reproduce; and 3) how different reproductive processes effect the population genetics of the seaweed. Light is likely the most influential physical factor that drives growth and reproduction, directly affecting the distribution and abundance of the genus. Reproduction in the genus includes sex, or the plants can simply fragment with separate pieces growing into new adults. These different modes of reproduction have important affects on the overall genetic structure of populations, which provides important information about factors affecting the success of the seaweed in coral reef environments.