SEAGRASS BIODIVERSITY IN THE INDIAN-RIVER LAGOON

All six species of seagrasses known from the tropical western hemisphe re as well as Halophila johnsonii grow in the Indian River Lagoon (IRL ). Halodule wrightii is the most common species, but Syringodium filif orme may be locally more abundant. Thalassia testudinum is limited to the southern portion of the IRL. The three Halophila species, H. decip iens, H. englemannii, and H. johnsonii, form mixed or monotypic beds w ith the larger species, while Ruppia maritima is found in the most sha llow areas and is the least common. A pronounced seasonal growth patte rn is evident for all species with maximum growth in April-May and max imum biomass in June-July. Wide ranges in productivity have been repor ted for the three larger seagrasses with spring levels approaching tho se found in other coastal communities in Florida. The distribution and ecological importance of the three species of Halophila may be much g reater than previously thought as shown by their abundance in deeper w ater, high productivity, and rapid turnover. The seagrass communities of the Indian River Lagoon have been shown to support a diverse epiphy tic and drift macroalgal flora and function as a habitat, nursery and food source for epifauna, macrobenthos, and manatees. Given the ecolog ical importance of seagrasses, a high priority for management of the I ndian River Lagoon must include protection and enhancement of these co mmunities. Selection of beds for management should consider ecological function of the species, biodiversity of associated fauna, and the le vel of continued anthropogenic impacts.