BBC Wildlife Magazine - - Agenda - Jack El­liot Mar­ley

Get­ting rid of preda­tors such as crown-of-thorns starfish helps corals over­come bleach­ing.

Com­mu­nity ef­forts to re­move preda­tory starfish are help­ing two co­ral reefs in the Mal­dives off­set the worst im­pacts of bleach­ing, sci­en­tists say.

Steve Newman, head of con­ser­va­tion at eco­tourism oper­a­tor Banyan Tree, says that vol­un­teers have re­moved more than 6,000 crown-of-thorns starfish and just over 1,000 pin cush­ion seast­ars since 2008.

“Re­moval ef­forts con­ducted by staff and guests were crit­i­cal in main­tain­ing high co­ral cover on both [the is­lands of ] Ihuru and Vab­bin­faru,” Newman says.

Though both species are nat­u­ral in­hab­i­tants of reefs in the Mal­dives, when co­ral is weak­ened by bleach­ing caused by higher sea tem­per­a­tures, they ex­ploit its frag­ile state and can elim­i­nate it from an area.

The ‘reef res­cue’ ini­tia­tive be­gan back in 2001 fol­low­ing a se­ri­ous bleach­ing episode in 1998, and it con­tin­ues to­day as reg­u­lar, fort­nightly trips to Ihuru and Vab­bin­faru.

Banyan Tree says th­ese act as an early warn­ing sys­tem, help­ing con­ser­va­tion­ists to spot the on­set of out­breaks be­fore they over­whelm the co­ral.

Else­where in the Mal­dives the picture is much gloomier. On some sites where there has been no starfish re­moval, co­ral cover has been re­duced by as much as 95 per cent fol­low­ing out­breaks. Other op­er­a­tors need to fol­low Banyan Tree’s ap­proach, Newman says.

A sur­vey car­ried out in 2016 found that higher-than-usual sea tem­per­a­tures, ex­ac­er­bated by the phe­nom­e­non of El Niño, had led to more than 60 per cent of reefs in the Mal­dives be­ing hit by bleach­ing.

When tem­per­a­tures rise, corals ex­pel the al­gae with which they have a unique re­la­tion­ship, lead­ing to bleach­ing and in many cases, the death of the co­ral polyps.

Crown-of-thorns starfish ex­ploit co­ral that has al­ready been weak­ened by bleach­ing.

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