Trichodesmium sp. clade distributions in the western north atlantic ocean

Abstract

To better understand the factors determining Trichodesmium clade (Clade III vs. Clade I) distribution, a quantitative polymerase chain reaction method was developed and applied to a sample set from the western North Atlantic. Clade distributions were compared with a suite of physicochemical parameters on a cruise transect from Woods Hole, Massachusetts, to Barbados during the spring of 2011. Clade I comprised. 90% of the total Trichodesmium spp. population. Depth distributions of both clades were similar in waters where there was a shallow (, 20 m) mixed-layer depth (MLD), but segregated in the water column where the MLD was deep (. 80 m). Surface abundances of both clades were higher when the MLD was, 20 m. Temperature and salinity were correlated with both clades in the data set as a whole. However, when stations influenced by a freshwater salinity anomaly were removed, dissolved inorganic phosphorus and total dissolved phosphorus correlated with Clade I cell density only. These correlations underscore the influence of phosphorus in driving Trichodesmium sp. dynamics in this region and are suggestive of niche partitioning between the two clades.