Coun­try Diary

Sand­send, North York­shire

The Guardian - - WEATHER - Amy-Jane Beer Fol­low Coun­try diary @gdncoun­try­di­ary

Close to dead calm on the York­shire hem of the North Sea to­day. The waves are barely 10cm high and the wa­ter is so clear that, stand­ing knee-deep be­tween each half-hearted surge, I can see sand grains shift­ing on the bot­tom.

There’s a com­mo­tion fur­ther out – cries of warn­ing, then cu­rios­ity. Some­thing is col­lected cau­tiously in a bucket and brought to me for iden­ti­fi­ca­tion. Even close up against the blue plas­tic, it’s dif­fi­cult to see clearly – an ovoid empti­ness where the sand swirling in the wa­ter does not go. Then sud­denly, its fringes light up pink, gold and green.

It’s not a jel­ly­fish, this glim­mer­ing blob, but a ctenophore or comb jelly, one of a group thought to be more than 500m years old and about as dif­fer­ent from other mo­bile mul­ti­cel­lu­lar an­i­mal life as it’s pos­si­ble to be. The fairy fire that flick­ers along its trans­par­ent body is an il­lu­sion worked by ranks of tiny cilia packed into rows, called combs.

The mi­crostruc­ture of the combs gives them the op­ti­cal prop­er­ties of a pho­tonic crys­tal – an opales­cent abil­ity to sep­a­rate and re­flect par­tic­u­lar wave­lengths of light. As the cilia move, the re­flected wave­length (and hence colour) changes. By day the trick works with bor­rowed sun­light, and in dark­ness it plays with the bi­o­lu­mi­nes­cence gen­er­ated by the an­i­mal’s own body.

Within min­utes they’re ev­ery­where, flick­er­ing be­tween pres­ence and ab­sence. Now we see them, now we don’t. They range in size from grape to ki­wifruit, and re­sem­ble balls of glass be­ing blown.

I lift one (they don’t sting) and glass be­comes flesh. For all its del­i­cacy, it has heft. In my hand it is flabby and help­less, but in open wa­ter it will com­mand sur­pris­ing mus­cu­lar con­trol. In fact, this species, Beroë cu­cumis, and its rel­a­tives are for­mi­da­ble preda­tors of other ctenophores. The mouth at one end can ex­pand well be­yond the cir­cum­fer­ence of the body, and the an­i­mal be­comes all gape, ca­pa­ble of en­gulf­ing prey its own size. The size dis­par­ity in this swarm makes me won­der if all but the largest are liv­ing dan­ger­ously.

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