I remember finding rounded green pebbles on the beach, and being startled to find that they were the remains of Coke bottles, battered into relative smoothness. I suppose I should have expected that plastic would be similarly battered. Some of the particles of plastic are 20 microns wide (the smallest size the researchers could see with their apparatus). The researchers say that amphipods, lugworms, and barnacles all ate the bits of plastic, but they don't know yet what long-term effects there will be as critters swallow the stuff. Maybe it'll be poisonous, maybe it'll block their guts--or maybe some bacteria will mutate to eat them. Sooner or later I expect the bacteria to make an appearance.
I suppose the best case is if the bacteria live in the lugworm guts. If free-floating bacteria can eat plastic--we have a lot of structural plastic around. . . Of course we have a lot of plastic in dumps too.
I don't know the biochemistry well enough to guess which variety of plastic is going to be eaten first. I also don't know what the waste products will be. This could get interesting.