(...) the last level is like a dolphin assault on an alien foothold on the sea floor were you lead a bunch of dolphins in an attack on there new hive.(...)
No, no, no!
Don't be fooled by the credits, the game continues. After reverting the Vortex Queen into a larval state the game still continues.
You are then sent by the Asterist to go to Atlantis (City of Forever) to find the time machine before the Vortex Queen can and destroy it. However what happens is that the Vortex Queen uses the machine (if either after or before Ecco I have no idea, but given that you sort of beat the Vortex Queen to it, I assume after which is a bit confusing) to go back in time, but she "finds creatures she could not rule over" and integrates with the rest of life on the planet. Ecco however does not destroy the time machine as the Asterist told him and uses it and "dissappears into the tides of time".