Ocean Research Project explain microplastics to us.

What are microplastics? And how do they affect our oceans?

Microplastics affect both humans and marine species. The clearest example of this can be seen with sea birds. Many different bird species spend most of their lives at sea and only come to land to reproduce. It is on remote islands where sea birds reproduce that people have filmed them feeding their babies plastic, as well as countless other birds dead or dying from ingesting plastics.
It’s much more difficult to monitor the effects of micorplastics on fish, sea turtles, etc. If a fish dies because it has a belly full of microplastics, it will sink to the bottom of the ocean. The open ocean is on average between 12,000 and 16,000 feet deep. We know more about the surface of the moon than we do about the sea floor. It’s nearly impossible to gauge how many fish are dying due to eating microplastics. Not all fish that eat microplastics will die.
Plastics are full of nasty chemicals; the smaller fish eat the small pieces of plastic thinking it’s food. Their bodies absorb the chemicals during digestion. The larger fish eat many smaller fish, and we eat the larger fish. We end up eating our own nasty chemicals through this process.

The answer to reducing the amount of plastic trash in our ocean is not at sea; it is on land. We must reduce the usage of one-time use plastic items, increase recycling and promote the use of true biopolymers.
Over the next 70 days, I will be sailing with a scientist from California to Japan conducting the first ever continent-to-continent marine plastic survey. We will sail over 7,000 miles non-stop. During the next couple of months you will read about the adventure, our research and how you can make a difference.