Spatial and Temporal Variation in South Florida Heterotrophic Diatom Communities: Taxonomic Identification and Ecological Implications

• Main Author: Blackburn, Michele V.
• Format: Others
• Published: NSUWorks 2008
• Subjects: Marine Biology; Oceanography and Atmospheric Sciences and Meteorology
• Online Access: http://nsuworks.nova.edu/occ_stuetd/256; http://nsuworks.nova.edu/cgi/viewcontent.cgi?article=1140&context=occ_stuetd

During the period January to December 2004, monthly water and sand samples were collected from the mangrove salt marsh and intertidal beach, respectively, of John U. Lloyd State Park. This study is the first to report on spatial and temporal distributions of heterotrophic diatoms in a subtropical region. A total of six non-pigmented (colorless, lacking photosynthetic pigments), heterotrophic diatom morphotypes were isolated from the mangrove and beach sample sites. Colorless diatoms were numerically significant in mangrove neuston during the fall and winter months. Cell counts peaked to 174 × 103 cells l-1 in December. Heterotrophic diatoms were most prevalent from mangrove plankton in October when they averaged 55.5 × 103 cells l-1. At the beach sample sites, non-pigmented diatom numbers were highest in upper and lower intertidal sand in April, with 71.1 and 94.9 cells g-1, respectively. Valve morphology is described in detail for the six diatom morphotypes isolated from the mangrove sites (I, II, V and VI) and beach sites (III and IV). Growth responses to changes in salinity and irradiance were examined in the laboratory for the six types of coastal diatoms. Most morphotypes were euryhaline, tolerating salinities between 10 and 50 ‰. Maximum growth responses were achieved between 20 and 40 ‰. Growth responses were not significantly different for heterotrophic diatoms during light and dark treatments. Additional experiments were conducted to investigate growth of morphotype VI in axenic and monoxenic cultures and to look for clues as to why some strains were observed to burrow in agar plates. The presence of bacteria did not significantly affect the growth response for morphotype VI. Morphotype VI did not form visible burrow in axenic or polyxenic cultures (and in other experiments, only burrowed at 7.5 gl-1 agar concentrations). The ability of diatoms to burrow into different phycocolloid bases at different concentrations was tested. The data suggests that heterotrophic diatoms digest complex carbohydrates as a nutrient source allowing them to out-compete bacteria (since few bacteria are capable of digesting phycocolloids). If true, heterotrophic diatoms may be capable of digesting recalcitrant particulate carbon in situ. This is particularly true of the two marine morphotypes (III and IV) that were observed to develop numerous burrows and were the only morphotypes capable of burrowing through non-nutrient agar at twice the standard concentration (30 g agar l-1).