The Food Chain

You've swallowed many of them throughout your life without realising, and some look like aliens: we look at plankton, the sea's smallest living creatures that have a big global impact. At the centre of the food web, and responsible for most of the air we breathe, these microscopic plants and animals are eaten by fish in our seas, which are eaten by bigger creatures, and eventually eaten by humans. But what happens when new problems hit these ancient critters, which have existed for millions of years? And how does it affect our health - and our plates?We speak to Jeff Herman in the US, whose skin was left crawling and in sweats after he got Ciguatera food poisoning from eating a hogfish. He tells us how his nightmarish symptoms were linked to toxins created by plankton.We share a voyage with the crew in charge of the world's oldest plankton recorder in Plymouth, England. They have been monitoring the world's seas since the 1930s to check on the health of these tiny creatures so vital to our food chain. Plankt