How plankton can make food delicious – but deadly

“Often people say it’s the best thing they ever ate,” someone warned.

I dread washing my windows. Giving them a token once-over last February, I slipped off the gunwales of the boat where I live and straight into the canal, down to the mulchy bottom, mouth fixed open in consternation and sucking in gallons of the sort of water you’d really rather not. Instead of my whole life flashing before me, I thought specifically of the time I had dropped a set of keys off the pontoon in 2003 and used a sea magnet to fish around (basically a big magnet like you see in cartoons, on the end of a rope), eventually bringing up a couple of saucepans encrusted in weird-looking – yet living – mussels. I also thought of the weeks during the summer when the canal turns a violent, near-luminous green from an all-enveloping “algal bloom”, through which the moorhens stoically attempt to cut, like Shackleton on the Endurance. So, I’m generally in the market for a programme about plankton.

An edition of The Food Chain (13 February, 1.30am) marvellously described the “tiny plants and animals, bacteria and viruses” that necessarily live in all of our waters. “Oh my gosh!” startled the presenter, Emily Thomas, gazing at some magnified examples found near Plymouth. “This one has sabre-like jaws!” And a stomach like an “elongated barrel with a tail sticking out, and lots of legs”!

Yes, said a scientist in doting response: apparently each species is so distinct that he and his team play “plankton charades” at parties. Rather less cutely, a Floridian fisherman explained that any innocent hogfish on a reef carelessly ingesting pestilential plankton can end up tasting more delicious than a hogfish could ever reasonably hope to taste – yet deadly to human beings.

In fact, extreme deliciousness is a sure sign of any reef fish riddled with brutal neurotoxins. “Often people say it’s the best thing they ever ate,” someone warned. (Thankfully the canal I ate tasted not delicious.) Meanwhile, global warming is ruinously shifting where sea plankton gather. Certain types are moving ever northward, seeking cooler waters, and taking with them some species of fish, especially cod, once and for all. We’re going to have to learn to love red mullet, was the long and short of it.