Where is that yummy smell coming from?

A. Is it the krill below?

B. The algae the krill are eating?

C. Or the plastic the algae cling to, on the ocean's surface?

The correct answer is B. When krill start to munch on algae, the latter emit a chemical as a kind of SOS. Birds smell this chemical and (sort of) come to the algae's rescue -- by eating the krill. 

Unfortunately, much of the algae on the ocean's surface coats plastic debris, so seabirds are getting a 2-for-1 that might be tasty, but is also toxic. 

And it doesn't stop there. Plastic in the ocean, which absorbs other chemicals that come from oil, pesticides, and other pollutants, is often consumed by fish and other marine species. This affects not only them, but also organisms that eat those fish (like us).