Populations of unicellular, marine sedimentary protists are constrained by a variety of physical environmental factors, but influences of flow regime have rarely been studied. We compared community structure among 3 subtidal sites differing in flow strength and grain size in a coastal bay. We used denaturing gradient gel electrophoresis (DGGE) to assess eukaryotic diversity based on 18S rDNA, and quantitative Protargol staining (QPS) to examine ciliate communities by microscopy. Sedimentary 18S rDNA in mid-summer was dominated by diatoms. Analyses of gel bands by presence/ absence among sites, dendogram, and multidimensional scaling showed that eukaryotic community structure was related to grain size more strongly than to flow regime. Among bands identified as diatoms by recovery and sequence analysis, 4 taxa (40%) differed among sites in relation to flow strength, and 2 taxa (29%) differed in relation to grain size. No bands had sequences matching ciliates, but QPS showed that 6 ciliate species (20%) were distributed in relation to flow, and 10 species (33%), in relation to grain size. Ciliate species richness and community similarity were greatest for the 2 strong-flow sites, despite differences in mean grain size. The strong-flow, silty site had the highest concentrations of chlorophyll a, total ciliates, karyorelictids, and scuticociliates, and the lowest ciliate species diversity. DGGE was run again for this site 1 mo later and revealed a shift in the rDNA pool to dominance by metazoans. Flow regime and grain size may be important factors structuring subtidal communities of sedimentary protists.KEY WORDS: Ciliates · Diatoms · Benthic · Community structure · Flow · Grain size · DGGE
Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 48: 91-104, 2007, Fernandez-Leborans 2001. Most of this research has been done in intertidal habitats, whereas little work has addressed the physical factors influencing subtidal populations.Recent studies have revealed impacts of flow regime on benthic protozoa and microalgae. Flow strength affects feeding rates of subtidal ciliates (Shimeta et al. 2001) and the species structure of ciliate communities on sandy shores (Lucchesi & Santangelo 1997). Resuspension stimulates growth and trophic interactions of unicellular sedimentary protists (Garstecki & Wickham 2001, Garstecki et al. 2002, and the fact that benthic diatoms and ciliates each show species-specific resuspension dynamics (Lucas et al. 2001, Shimeta et al. 2002 also suggests that flow regime can influence populations differentially and possibly impact community structure. Furthermore, resuspension dynamics can differ between sites in ways suggesting an interaction between flow regime and grain size (Shimeta et al. 2003). Detailed analyses of community structure have not been conducted, however, in relation to flow regime at subtidal habitats.Here we assess community structure at subtidal sites (ca. 15 m depth) that differ in flow regime and grain size in a coastal e...