Faunal variation on pelagic Sargassum

Pelagic Sargassum was collected in late summer, late winter, and early and late spring from inshore waters, the Gulf Stream and the Sargasso Sea of the Western North Atlantic Ocean. The noncolonial macrofauna was picked from the weed samples. The 34 samples contained 67 species and 11,234 individuals. The Shannon-Wiener index of diversity had a mean value of 2.419±0.177 (t.₀₅s _x ^– ) and a statistical range between 1.401 and 3.437 (t.₀₅ s). Mean diversity values were not significantly different among the various sampling series, and diversity did not vary with raft volume. High diversity values were related to an equitable distribution of species resulting from a stable environment and an area low in productivity. Species composition of the Sargassum organisms varied seasonally and geographically. Animals were more abundant in the spring than in the fall samples. Samples collected on a transect in the Gulf Stream and Sargasso Sea maintained a similar faunal composition.Contribution No. 351 from the Virginia Institute of Marine Science, Gloucester Point, Virginia, USA.From a thesis submitted to the faculty of the School of Marine Science, The College of William and Mary, in partial fulfillment of the requirements for the degree of Master of Arts in Marine Science.