Wouldn't they just dominate the seas? Being in the water would give them more real estate and would let them work with higher volumes, therefore growing/evolvi

Wouldn't they just dominate the seas? Being in the water would give them more real estate and would let them work with higher volumes, therefore growing/evolving faster. And since we are going there as result of 'out-teching' land people they would flood everything (by melting ice) and colonize land space.