Diatoms epiphytic on the emergent grass Spartina alterniflora in a Louisiana salt marsh

Vertical distribution of diatoms epiphytic on Spartina alterniflora from shoreline and inland sites was studied in a Louisiana salt marsh during a 13-month period. Seasonally, the diatom density at higher elevations on S. alterniflora showed a monomodal cycle with a peak that coincided with the annual demise of the above-ground portions of the marsh grass, seasonality of tidal ranges, and dissolved nitrogen. Diatom community density decreased with increased elevation on the culm and with the collecting site respective to shoreline. Taxa per sample ranged from 10-67 with a grand mean of 39. Species diversity (H′) ranged from 0.99-5.05 with a grand mean of 3.20. While shoreline samples had the greater density, species diversity (H') was greater inland. Similarity indices (SIMI) indicated that the community structure for most comparisons was near unity. However, this skewing toward unity was caused by the abundance of a single taxon (Denticula subtilis).