Salinity responses of benthic diatoms inhabiting tidal flats

We performed culture experiments using intertidal benthic diatoms collected from a river mouth tidal flat (Fujimae Tidal Flats, Nagoya, Japan) to study their responses to salinity. The six species examined were Navicula aff. erifuga, Karayevia amoena, Tryblionella apiculata, Planothidium delicatulum, Melosira moniliformis var. octogona, and Entomoneis japonica. Clones were grown at ten salinity levels from 0 to 50 psu. Three species were unable to grow at low salinities (0 and 0.1 psu), but all were able to grow, though at a reduced rate, in hypersaline conditions (50 psu). All species had wider tolerance ranges than the salinity range of their original habitat (4–16 psu). Two species, T. apiculata and K. amoena, were essentially euryhaline, while the other four showed various constraints on their salinity response. Two species, P. delicatulum and M. moniliformis var. octogona, showed optimal growth outside the range of the salinities normally occurring in the environment from which they were isolated.