We humans have put a lot of radiocative material in the ocean over the last few decades. Here's a brief summary, thanks to Deep Blue Home
Once we learned how to make bombs and reactors, we played with them like unknowing toddlers, spewing waste and fallout all over the world's oceans. So we do have some idea how Japan's leaking reactors can affect our oceans. We can expect radioactive fish, etc. And radioactive spinach, and radioactive water, and radioactive.....
My personal link is eating salmon from the Columbia River during the period when releases from the Hanford Nuclear site were getting into the fish. Do I still have a bit in me? Who knows?
Does any of this matter? Only time will tell. So far, radioactivity levels are fairly low--only a thousand times normal in the sea near the reactor--but that may change.