Seasonal microbial community dynamics correlate with phytoplankton-derived polysaccharides in surface coastal waters

Abstract

Phytoplankton produce large amounts of polysaccharide gel material known as transparent exopolymer particles (TEP). We investigated the potential links between phytoplankton-derived TEP and microbial community structure in the sea surface microlayer and underlying water at the English Channel time-series station L4 during a spring diatom bloom, and in two adjacent estuaries. Major changes in bacterioneuston and bacterioplankton community structure occurred after the peak of the spring bloom at L4, and coincided with the significant decline of microlayer and water column TEP. Increased abundance of Flavobacteriales and Rhodobacterales in bacterioneuston and bacterioplankton communities at L4 was significantly related to the TEP decline, indicating that both taxa could be responsible. The results suggest that TEP is an important factor in determining microbial diversity in coastal waters, and that TEP utilisation could be a niche occupied by Flavobacteriales and Rhodobacterales.

Figure 1

(a) Location of L4 station in the Western English Channel and estuarine sampling sites on the Tamar and Plym estuaries. (b) Principal coordinates analysis plot describing betadiversity using the unweighted UniFrac distance matrix generated from OTU (97% similarity) presence/absence. Fifteen surveys were conducted over 19 weeks between 9 February and 2 July 2012 (numbers indicate week surveyed). Microlayer-enriched samples were collected using a mesh screen (sampling depth ⩽400 μm; open shapes) and underlying water samples were collected from 2 m (closed shapes). Estuarine microlayers and underlying water were sampled twice during the study period; 25 April and 27 June Tamar high tide (orange squares) and Tamar low tide (orange triangles), and 26 April and 29 June Plym high tide (purple squares) and Plym low tide (purple triangles). (c) The same analysis as b except using a weighted UniFrac distance matrix generated from OTU relative abundance.

Figure 2

(a) Transparent exopolymer particle (TEP) concentration in the microlayer and underlying water at L4 station. Surveys were conducted over 19 weeks between 9 February and 2 July 2012. Phytoplankton biomass at L4 station was determined from chlorophyll-a concentration in underlying water samples. (b) Relationship between the increase in abundance of the orders Flavobacteriales and Rhodobacterales in both bacterioneuston and bacterioplankton communities and the decline of TEP in the microlayer and underlying water at L4 station.