[syhprum (OP)]

There  has been much concern of late over the amount of plastic rubbish going into the oceans, I feel that it is probably unnecessary to worry as new forms of bacteria will evolve that will consume this abundant food supply.

[Bored chemist]

I guess it depends on the time scale you are talking about.
Given long enough it's quite likely.
On the other hand we might manage to kill ourselves by choking the oceans before that happens. Life doesn't need to worry- but we might.

The big problem is that biology is essentially the study of dirty water (for example, we are typically about 40 Kg of water and 30 Kg of other stuff) and the plastics are often completely insoluble in water so, at best, only their surface can be attacked by  biology.

[evan_au]

There are a number of species of bacteria which snack on oil spills. But in places like the Gulf of Mexico there are natural oil seeps which give them a natural habitat.

http://www.scientificamerican.com/slideshow/gulf-oil-eating-microbes-slide-show/

Oil is a liquid, so I guess it is relatively easy for anaerobic bacteria to live inside a blob of oil. Hard plastics are more difficult.