Differences in silica content between marine and freshwater diatoms

Marine diatoms are shown to have on average one order of magnitude less silica per unit of biovolume than freshwater species. Silica content (pmol cell −1 ) increases linearly with biovolume ( µ m 3 ) in both marine (1og 10 [silica content] = 0.91 log 10 [biovolume] — 3.16; r = 0.92; P < 0.0001; N = 44) and freshwater diatoms (log 10 [silica content] = 1.03 1og 10 [biovolume] — 2.45; r = 0.91; P < 0.0001; N = 62). Therefore, a first#x2010;order estimate of the amount of silica utilized by diatom production can be made from diatom biovolumes. Si: C molar ratios for marine diatoms and for freshwater diatoms also are different and demonstrate that appropriate molar ratios must be used for marine and freshwaters in estimating biogenic silica production from primary production. Among possible reasons for the disparity are differences in sinking strategy, the adaptation of marine diatom species to a low dissolved silica environment, and differences in salinity between the two environments.