Find­ing Nemo? We may be los­ing him, says cli­mate study

The Guardian Australia - - The Guardian View / Environment -

The clown­fish, the colour­ful swim­mer pro­pelled to fame by the 2003 film Find­ing Nemo, is un­der threat from warm­ing ocean waters wreak­ing havoc with sea anemones, the struc­tures that serve as its home, a study has found.

Closely re­lated to corals, sea anemones are in­ver­te­brate marine crea­tures that live in sym­bio­sis with al­gae, which pro­vide them with food, oxy­gen and colour.

Clown­fish, also known as anemone­fish, in turn use the struc­tures as shel­ter to lay their eggs and raise their young – keep­ing the anemones clean in re­turn.

For the study, pub­lished in the jour­nal Na­ture Com­mu­ni­ca­tions, a re­search team mon­i­tored 13 pairs of orange-fin anemone­fish liv­ing among the coral reefs of Moorea Is­land in the South Pa­cific.

They were mon­i­tored be­fore, dur­ing and af­ter the El Niño weather event that in 2016 caused ma­jor coral bleach­ing as the Pa­cific Ocean warmed.

Half of the anemones in the study “bleached”, ex­pelling the al­gae that live on them and turn­ing bone white, the team found. This hap­pens in re­sponse to en­vi­ron­men­tal stress, such as ocean warm­ing or pol­lu­tion.

“Among the clown­fish liv­ing in the bleached anemones, the sci­en­tists ob­served a dras­tic fall (-73%) in the num­ber of vi­able eggs,” said a state­ment from France’s CNRS re­search in­sti­tute. “These fish were lay­ing eggs less fre­quently and they were also lay­ing fewer and less vi­able eggs.”

No changes were ob­served among fish with un­bleached abodes.

Blood sam­ples showed a sharp in­crease in lev­els of the stress hor­mone cor­ti­sol in the af­fected fish, and a “sig­nif­i­cant drop” in sex hor­mones that de­ter­mine fer­til­ity, the team re­ported.

The health of the anemones and the fish im­proved three to four months af­ter the end of the warm­ing event.

Fur­ther re­search is needed, the team said, to ex­am­ine the ef­fects of a longer, or more in­tense, warm­ing pe­riod, and whether af­fected fish would deal bet­ter or worse with a new bleach­ing episode.

Ex­cep­tional ocean warm­ing events are pre­dicted to be­come more fre­quent as the av­er­age global tem­per­a­ture rises. Nearly 200 na­tions agreed un­der the 2015 Paris agree­ment to limit warm­ing to two de­grees Cel­sius (3.6 de­grees Fahren­heit) over in­dus­trial lev­els.

A level of about 1C has al­ready been reached and sci­en­tists fear the ceil­ing will be shat­tered, with po­ten­tially dis­as­trous con­se­quences for the Earth’s cli­mate.

In June last year, a study said many of the real-life Ne­mos swim­ming in chil­dren’s fish tanks around the world were caught us­ing cyanide – another threat to the species.

Find­ing Nemo, the movie about the quest of a young fish sep­a­rated from its fam­ily, re­sulted in more than a mil­lion clown­fish be­ing har­vested from trop­i­cal reefs as pets.

The clown­fish is un­der threat from warm­ing ocean waters that are dam­ag­ing its anemone home. Pho­to­graph: Rein­hard Dirscherl/Getty Im­ages/WaterFrame RM

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