As far as power... the break down seems to be as follows: https://steemd.com/distribution

Newbie (0.01 - 0.09m), User (0.1 - 0.99m), Super User (1 - 9.99m), Hero (10 - 99.99m), SuperHero (100 - 999.99m), Legend (1000m+)

So if we translate that to the ocean we should have a lot more levels than minnow, dolphin, whale.

Whale would obviously be the Legend.
Dolphin I usually thought was the Super Hero level...

Though there are a lot of missing levels so perhaps Dolphin could span several of those ranks.

It'd be cool to actually break this into many levels and have badges and such. :)

EDIT: Plankton, Minnow, Fish, Dolphin, Whale, Kraken :P