LUMEN BE­INGS LIGHT­ING THE DEPTHS

Cosmos - - Contents -

Be­neath the waves await daz­zling light shows. JAMES

MITCHELL CROW takes a peek.

1 COMB JEL­LIES

Lights play­ing across the sur­face of the sea at night may seem oth­er­worldly. They’re not: they are the work of sin­gle-celled or­gan­isms.

In fact, more than three-quar­ters of marine species emit light – far more than any­body sus­pected, ac­cord­ing to a study pub­lished in April by Séver­ine Mar­tini and Steve Had­dock from the Mon­terey Bay Aquar­ium Re­search In­sti­tute in Cal­i­for­nia. For 17 years the re­searchers have plumbed the depths to watch the light show us­ing re­motely-op­er­ated subs fit­ted with high-def­i­ni­tion video.

At depths down to 100 me­tres, comb jel­lies steal the show. (See page 23.)

2 LION’S MANE JEL­LY­FISH

Be­guil­ingly beau­ti­ful though it may be, the Lion’s Mane jel­ly­fish is not a species you want to en­counter on a night swim. The big­gest jel­ly­fish in the sea, its ‘mane’ of sting­ing ten­ta­cles can reach 30 me­tres in length. Like the comb jelly, the Lion’s mane is a near-sur­face swim­mer, but 500 to 1500 me­tres be­low its jel­ly­fish rel­a­tives still dom­i­nate the light show. Why do they glow? We can’t be sure. The­o­ries in­clude to at­tract prey, star­tle a preda­tor or to cam­ou­flage them­selves against a moon­lit sky from preda­tors be­low.

Deep-sea sub­mersibles equipped with highly sen­si­tive video cam­eras cap­ture a daz­zling light show be­neath the waves.

WORDS BY JAMES MITCHELL CROW

3 GHOSTLY SEADEVIL

The deeper they sent their sub­mersibles, the less bi­o­lu­mi­nes­cence Mar­tini and Had­dock saw. But that’s be­cause there are sim­ply fewer crea­tures at these food-sparse depths. The pro­por­tion of all marine species that can bi­o­lu­mi­nesce re­mains a vir­tu­ally con­stant 75% at all depths, the re­searchers re­port.

Among fish, the new sur­vey found that al­most 55% of deep sea species can light up. The ghostly seadevil, found at depths of about 2,250 me­tres, is ac­tu­ally a pale species of an­gler­fish – fa­mous for its built-in bi­o­lu­mi­nes­cent fish­ing rods. In the case of the seadevil – also called the soft left­vent an­gler – the fish­ing rod is re­duced to a small skin flap held in front of the mouth.

4 LARVACEANS

Be­low 2,250 me­tres, small tad­pole-like crea­tures called larvaceans are the most com­mon glow­ing crea­tures cap­tured in Mar­tini and Had­dock’s high-sen­si­tiv­ity footage. About a cen­time­tre in length, they are ac­tu­ally tu­ni­cates that never moved on from their lar­val stage.

At depths where no light pen­e­trates from the sur­face, crea­tures don’t have to glow very brightly to light up their sur­round­ings. Un­der the bright lights of a deep sea sub­mersible, their bi­o­lu­mi­nes­cence can be drowned out. The new study was the first de­tailed sur­vey to use video cam­eras sen­si­tive enough to pick out this low-level bi­o­lu­mi­nes­cence. The re­sults are il­lu­mi­nat­ing, show­ing the ocean is a much brighter place than we ever imag­ined.

CREDIT: ALEXAN­DER SEMENOV / GETTY IMAGES CREDIT: ALEXAN­DER SEMENOV / GETTY IMAGES

Comb jelly ( Beroe cu­cumis). Lion’s mane jel­ly­fish ( Cyanea capil­lata).

PETER DAVID / GETTY IMAGES CREDIT: WIM VAN EG­MOND / SCI­ENCE PHOTO LI­BRARY

Ghostly Seadevil ( Haplophryne mol­lis). A lar­vacean of the genus Oiko­pleura.

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