Control survivalwas good in all bioassays regardless of salin-
ity (100% in FW, 2.5 and 10 ppt and 85±11, 90±6, 86±10
and 95±5% in 5, 15, 22 ppt and SW, respectively) attesting
to the euryhalinity of this species.
For two (2.5 and 15 ppt) of
the seven bioassays, data did not allow for calculation of confi-
dence intervals.
For one test (10 ppt) sufficient mortality could
not be achieved within Cu solubility limits to estimate an LC50.
The maximal dissolved Cu concentration at 10 ppt was 973 g/l
and the highest mortality was 33±3%.
The data from this test
is presented as >973 g/l in Figs. 1 and 2.
Calculated LC50’s
and confidence intervals (when available) display a biphasic
pattern with increasing Cu tolerance from FW to 10 ppt and
reduced Cu tolerance with salinity increasing from15 ppt to SW
(Fig. 2A).
The concentration of DOC was constant across salinities, the
H+ concentration decreased with increasing salinity while all
other electrolytes increased (Table 1).
As salinity increased, so
did pH and total CO2, resulting in an increased fraction of Cu
in the form of Cu dicarbonate.
At 35 ppt, Cu carbonate and Cu
dicarbonate combined to 87% of the total Cu (Table 2).
The
two forms of Cu generally believed to be most toxic, Cu2+
and CuOH+, increased from FW to 2.5 ppt but then decreased
with increasing salinity resulting in the lowest fractions in SW
(Table 2).