Small-scale temporal and spatial variations in protistan community composition at the San Pedro Ocean Time-series station off the coast of southern California

Small-scale spatial and temporal variabiliy in protistan community composition was investigated at the USC San Pedro Ocean Time-series (SPOT) station and contrasted with a 10 yr (2000 to 2010) dataset of samples collected at approximately monthly intervals from the same station. Surface seawater samples were collected for 12 consecutive days at the SPOT station, and an additional 17 stations (16 within a grid surrounding the SPOT station and 1 outlying station; 2 to 21 km apart) were sampled during 1 of the 12 sampling days, to investigate the small-scale temporal and spatial variability, respectively. Terminal restriction fragment length polymorphism (T-RFLP) analysis of the 18S rRNA gene was used to generate DNA fingerprints of the protistan community, which were used for the calculation of pair-wise Bray-Curtis and Jaccard similarity values at different spatial and temporal scales. Temperature, salinity, pH, wind, and upwelling did not appear to have any significant effect on community composition, and distance had a weak correlation with the similarity indices generated from spatial samples. Communities separated by the smallest spatial scales (0 to 2 km) had significantly higher average similarity than communities separated by small temporal scales (1 to 9 d). Comparisons with a 10 yr dataset of monthly samples revealed significantly lower average similarity values among communities separated by time periods >= 1 mo (45 to 52 %) compared to communities separated by the smallest spatial (0 to 2 km; 67 to 71 %) and temporal (1 d; 64 %) scales. Our results indicate that small-scale spatial and day-to-day variability of protistan communities was overshadowed by monthly, seasonal, and interannual variabilities.