Seagrass biodiversity in the Indian River Lagoon

All six species of seagrasses known from the tropical western hemisphere as well as Halophila johnsonii grow in the Indian River Lagoon (IRL). Halodule wrightii is the most common species, but Syringodium filiforme may be locally more abundant. Thalassia testudinum is limited to the southern portion of the IRL. The three Halophila species, H. decipiens, H. englemannii, and H. johnsonii, form mixed or monotypic beds with the larger species, while Ruppia maritima is found in the most shallow areas and is the least common. A pronounced seasonal growth pattern is evident for all species with maximum growth in April-May and maximum biomass in June-July. Wide ranges in productivity have been reported for the three larger seagrasses with spring levels approaching those found in other coastal communities in Florida. The distribution and ecological importance of the three species of Halophila may be much greater than previously thought as shown by their abundance in deeper water, high productivity, and rapid turnover. The seagrass communities of the Indian River Lagoon have been shown to support a diverse epiphytic and drift macroalgal flora and function as a habitat, nursery and food source for epifauna, macrobenthos, and manatees. Given the ecological importance of seagrasses, a high priority for management of the Indian River Lagoon must include protection and enhancement of these communities. Selection of beds for management should consider ecological function of the species, biodiversity of associated fauna, and the level of continued anthropogenic impacts.