are there any aquatic plants (seaweeds) growing in the Dead Sea, or is the
salt concentration too high for them?

As far as I know, nothing grows in the Dead Sea except perhaps some bacteria.
It seems to be a saturated solution and produces interesting formations of rock
salt crystals.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)