Floristic composition of diatoms (Bacillariophyta) epiphytic on two species <I>Bostrychia</I> Montagne (Rhodophyta)

Abstract

It was collected 42 samples of diatoms (Bacillariophyceae) epiphytic on the macroalgae Bostrychia radicans and Bostrychia calliptera in two periods of the seasonal cycle: dry (October 1996) and rainy (April 1997), in the Parna Açu mangrove, located at the Island of São Luís, State of Maranhão, Brazil. There were recognized 67 infrageneric taxa, distributed in 16 orders, 22 families, 30 genera, 49 species, 16 varieties and two forms. The better represented family was Bacillariaceae with 11 taxa, followed by the Naviculaceae with 8 species and Pleurosigmataceae with 6. The genera with larger number of species were Nitzschia with 10 taxa, Navicula with 7 taxa and Gyrosigma with 5 taxa. The species Amphora exigua, Cocconeis distans, Denticula subtilis, Melosira moniliformis, Navicula contenta, Nitzschia fasciculata, Terpsinoe americana and Terpsinoe musica occurred in more than 75% of the samples analyzed, being considered very frequent in the dry period as well as in the rainy one. Of the total of the taxa 36 are marine, 21 estuarine and 10 freshwater. In agreement with treir tolerance to salinity, 73% are mesohalobe, 7% euhalobe and 20% polihalobe. Regarding the form of life, 69% are epiphytic, 13% are planktonic and 18% were not fciund in the literature.