Repercussions of salinity changes and osmotic stress in marine phytoplankton species

• Marine phytoplankton tolerates short-term exposures to salinities in the range 5–35.
• Short-term low salinity does not stop the survival upstream of toxic marine microalgae.
• Low salinity equally alters photosynthesis and cell growth in Tetraselmis suecica.
• Harmful algae exposed to low salinity show different Pg and ΦPSII activity response.
• In low salinity conditions, O2 production-consumption ratio varies depending to specie.

The short-term effect of low salinity was studied using laboratory protocols on some coastal phytoplankton species such as chlorophycea Tetraselmis suecica, among diatom the strain Nitzschia N1c1 and dinoflagellates Alexandrium minutum and Prorocentrum lima. All of cultures were exposed to low salinities, and cell growth rate, photosynthetic quantum yield (ΦPSII), and gross photosynthesis (Pg) were analyzed. Growth rate inhibition was similar in all species, and all of them also tolerate short-term exposures to salinities in the range 5–35. There were no significant differences between ΦPSII and Pg endpoints from Tetraselmis suecica and Nitzschia sp., while Alexandrium minutum and Prorocentrum lima displayed a higher affectation rate on Pg than on ΦPSII activity. The influence of low salinity was higher on respiration in T. suecica, while both dinoflagellates had higher net photosynthesis. Nitzschia sp. exhibited similar involvement of the two photosynthetic parameters. Therefore, although the four phytoplankton monocultures studied are able to survive in internal areas of estuaries under low salinity conditions, the photosynthetic activity is more affected than the growth rate in all phytoplankton communities studied except in chlorophycea T. suecica, which has increased tolerance for this salinity decrease.

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