I worked for WDEA-AM years ago. One of their towers was mounted on concrete
out in the salt water. This was about 20 feet from the low tide shoreline.
They had 120 radials and there was some current change with tide shift. This
was not a lot, but noticeable. A lot of radials would be the way to go and
your antenna should work even better.
Elevated radials would be affected by the changing ground beneath it.
WDEA-AM was a 5 KW station. With the salt water antenna, they used to get QSL
cards from Europe.