Sparkling seas ex­plained

Australian Geographic - - Wild Australia -

A sin­is­ter truth lies be­hind the rise of beau­ti­ful night-time blooms of bi­o­lu­mi­nes­cent plank­ton.

IT’S A phe­nom­e­non that’s be­come so pop­u­lar to see and pho­to­graph it has its own Face­book group – Bi­o­lu­mi­nes­cence Aus­tralia – with about 9000 mem­bers.

This fo­rum al­lows users to alert oth­ers to sight­ings of bi­o­lu­mi­nes­cent plank­ton blooms, and swap spec­tac­u­lar im­ages, videos and sto­ries of their ex­pe­ri­ences.

Through this group in Au­gust, pho­tog­ra­pher and am­a­teur as­tronomer David Fin­lay was first alerted to a re­mark­able bloom along the beaches of Vin­cen­tia, Jervis Bay, on the New South Wales south coast (at right).

Sixty peo­ple gath­ered that evening to see plank­tonic or­gan­ism Noc­tiluca scin­til­lans glow­ing by the buck­et­ful along the tide­line.

The light­show grew brighter and lasted 4–5 hours as the tide came in. “It was hard to be­lieve,” David told ABC Ra­dio. His cap­ti­vat­ing im­ages were sub­se­quently splashed across the Aus­tralian me­dia.

David is one of many to re­cently take im­ages and video of this kind of bi­o­lu­mi­nes­cent bloom. A few days ear­lier, the Port of Napier, in New Zealand, was aglow with Noc­tiluca. Sim­i­lar blooms were filmed at Jervis Bay in 2013 and 2015. Port Lin­coln in South Aus­tralia and Laud­erdale, near Ho­bart in Tas­ma­nia, are now other com­mon places to wit­ness bi­o­lu­mi­nes­cence, and strik­ing im­ages of the phe­nom­e­non have fea­tured in the Aus­tralian Geo­graphic Na­ture Pho­tog­ra­pher of the Year com­pe­ti­tion.

Noc­tiluca – also known as ‘sea sparkle’ – is nei­ther plant nor an­i­mal, but a sin­gle-celled plank­tonic or­gan­ism called a di­noflag­el­late, which in­gests other plank­ton.With di­am­e­ters typ­i­cally of about 0.5mm, di­noflag­el­lates are hard to see with the naked eye.

But when they bloom en masse – of­ten due to ex­cess nu­tri­ents in the wa­ter – they can form a red slime.

At night, how­ever, when these tiny or­gan­isms are dis­turbed by move­ment, such as foot­steps or pound­ing surf, they emit a bril­liant blue glow.

Light is pro­duced by the com­pound lu­ciferin, which in di­noflag­el­lates is de­rived from chloro­phyll, the chem­i­cal plants use to turn light into food.

Ac­cord­ing to Scripps In­sti­tu­tion of Oceanog­ra­phy in Cal­i­for­nia, the light flashes from in­di­vid­ual di­noflag­el­lates (which to­gether form the over­all glow we see) star­tle their main preda­tors, also tiny or­gan­isms.These also act as a ‘bur­glar alarm’ at­tract­ing even larger preda­tors to pick off Noc­tiluca’s pri­mary preda­tors, cope­pods (small crus­taceans).

But is the in­creas­ing in­ci­dence of this bi­o­lu­mi­nes­cence show ac­tu­ally shin­ing a light on the en­vi­ron­men­tal dam­age we are do­ing? Bi­o­lu­mi­nes­cent blooms are linked to two en­vi­ron­men­tal prob­lems: they of­ten oc­cur around bays with river mouths, and they’re also more fre­quent af­ter heavy rain­fall. Both sug­gest pol­lu­tion and agri­cul­tural run-off are lead­ing to a con­cen­tra­tion of nu­tri­ents such as phos­pho­rus and ni­tro­gen in the wa­ter caus­ing pop­u­la­tions to ex­plode.

The spread of sea sparkle is also linked to cli­mate change. Be­fore 1994 they’d rarely been seen around Tas­ma­nia. But as wa­ters have warmed, this has be­come one of the most com­mon places in Aus­tralia to see them.

Rare bi­o­lu­mi­nes­cent blooms in Mum­bai, In­dia, in May this year, and along the beaches and bays of China and Hong Kong in 2015, have wor­ried au­thor­i­ties there. Noc­tiluca blooms can kill fish by com­pet­ing with them for re­sources and ex­cret­ing toxic quan­ti­ties of am­mo­nia into the wa­ter. This year, sci­en­tists at the US Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion and In­dian Na­tional Cen­tre for Ocean In­for­ma­tion Ser­vices blamed the in­tense blooms in Mum­bai on cli­mate change.

So, while there’s no ques­tion these ma­rine equiv­a­lents of the au­rora aus­tralis – also ob­served at night in Aus­tralia’s south-east – are beau­ti­ful to be­hold, there’s a more com­pli­cated and wor­ri­some story be­hind their grow­ing preva­lence.

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