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 <i>Navicula</i> aff. <i>erifuga, Karayevia amoena</i>, <i>Tryblionella apiculata</i>, <i>Planothidium delicatulum</i>, <i>Melosira moniliformis</i> var. <i>octogona,</i> and <i>Entomoneis japonica.</i> 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, <i>T. apiculata</i> and <i>K. amoena</i>, were essentially euryhaline, while the other four showed various constraints on their salinity response. Two species, <i>P. delicatulum</i> and <i>M. moniliformis</i> var. <i>octogona</i>, showed optimal growth outside the range of the salinities normally occurring in the environment from which they were isolated.