Green tur­tle

This month, the con­ser­va­tion spot­light falls on a mega­her­bi­vore and its diet.

BBC Wildlife Magazine - - Wild News -

Where does it live?

The Green Tur­tle ( Ch­elo­nia my­das) is a sea tur­tle that lives in the wa­ters of the Caribbean. Its name comes from the colour of its body fat, re­sult­ing from the adults’ diet of sea­grass and al­gae.

What’s the prob­lem?

A sea­grass from the Red Sea, in­tro­duced to the east­ern Caribbean in 2002, has al­ready spread halfway across the re­gion. Halophila stip­u­lacea is re­plac­ing the na­tive sea­grass, which pro­vides food and shel­ter for many other or­gan­isms. Be­tween 2011 and 2017, Halophila spread from six to 20 per cent of our mon­i­tor­ing sites on Bon­aire Is­land, while na­tive sea­grass de­clined by 33 per cent.

Why is that bad news for tur­tles?

Halophila is far less nu­tri­tious than the na­tive sea­grasses, and is largely ig­nored by graz­ing green tur­tles. They’ll only eat it if there’s noth­ing else avail­able, and then they have to put more ef­fort into graz­ing to meet their nu­tri­tional needs. This leads to slower growth rates and de­layed sex­ual ma­tu­rity, which is sig­nif­i­cant in this slowde­vel­op­ing species.

Tur­tles are mak­ing mat­ters worse?

Yes. By pref­er­en­tially graz­ing on the na­tive sea­grasses, the tur­tles are giv­ing Halophila a com­pet­i­tive edge and help­ing it spread to new ar­eas. The in­va­sion is hap­pen­ing faster in grazed re­gions.

Can it be stopped?

Halophila is mainly a prob­lem in trop­i­cal wa­ters. In the Mediter­ranean, it can­not com­pete with the na­tive sea­grasses adapted to cooler con­di­tions. We can’t do much to stop it spread­ing. But we can cre­ate con­di­tions in which the na­tive sea­grasses flour­ish by ad­dress­ing lo­cal en­vi­ron­men­tal prob­lems such as pol­lu­tion, dredg­ing and wa­ter clar­ity.

Can the tur­tles adapt?

The tur­tles may be able to switch di­ets from sea­grass to al­gae, al­though that’s not straight­for­ward be­cause they carry a spe­cial­ist cast of gut mi­crobes that help them digest sea­grass in par­tic­u­lar. Our con­cern is that this in­va­sion is hap­pen­ing faster than they can adapt. S Black­man


is as­sis­tant pro­fes­sor at Wa­genin­gen Univer­sity in the Nether­lands.


Jour­nal of Ecol­ogy: https://besjour­nals.on­lineli­brary.wi­ley. com/doi/10.1111/1365-2745.13021

The green tur­tle’s na­tive sea­grass diet has given a non-na­tive sea­grass a com­pet­i­tive edge.

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