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Understanding the effect of salinity tolerance on cyanobacteria associated with a harmful algal bloom in Lake Okeechobee, Florida

July 31, 2018

In an effort to simulate the survival of cyanobacteria as
they are transported from Lake Okeechobee to the estuarine
habitats that receive waters from the lake, a bioassay
encompassing a range of salinities was performed. An overall
decline in cyanobacteria health in salinity treatments greater
than 18 practical salinity units (psu) was indicated by loss of
cell membrane integrity based on SYTOX® Green staining,
but this loss varied by the kind of cyanobacteria present.
Microcystis aeruginosa was tolerant of salinities up to 18 psu;
however, higher salinities caused leaking of microcystin from
the cells. Dolichospermum circinale, another common bloomformer
in this system, did not tolerate salinities greater than
7.5 psu. Stimulation of mucilage production was observed and
is likely a mechanism used by both species to protect organism
viability. At 7.5 psu, microcystin increased relative to
chlorophyll-a, providing some evidence of biosynthesis when
M. aeruginosa is exposed to this salinity. This study indicates
that as freshwater cyanobacteria are transported to brackish
and marine waters, there will be a loss of membrane integrity
which will lead to the release of cellular microcystin into the
surrounding waterbody. Additional research would be needed
to determine the exact effect of salinity on this relationship.