Mother Jones has a nice article about radioactivity off Japan’s coast, with lots of helpful graphics.
The good news is that the powerhouse of the Kuroshio Current—a humongous western boundary current like the Gulf Stream—appears to be forming a kind of firewall keeping the contamination away from Tokyo’s coast and funneling it east.
In conclusion:
Whatever pathways the Fukushima poisons take, they will certainly alter the springtime blossoming of Japan’s ocean, starting with the phytoplankton and working up the foodweb.As for the effects on the rest of the world ocean, it’s a matter of how much, how far, and for how long Fukushima’s newborn radionuclides go sailing.
Truth and Traditions 
Current international law doesn’t allow one barrel of nuclear wastes to go into the oceans because those phytoplankton and thousands of other species will have their genes attacked and mutated, at what rates with what probabilities of creating eco-disasters down the line — who knows?
It’s like the big oil spill in the Gulf, only probably much worse, because of the multiple impacts of radiation on reproduction and evolution of ALL species in the Pacific.
Does radiation concentrate as it goes up the food chain? Like PCBs?
Seems like we ought to be asking lots of questions of the few remaining scientists (most have become salaried technicians) about how they are going to measure the impacts of the different kinds of radiation from now on.
Does radiation concentrate as it goes up the food chain? Like PCBs?
Radiation is emitted by atoms. And I would think that those atoms would move up the food chain like PCBs.