Lo­cal reefs given all-clear on wa­ter qual­ity

Port Douglas & Mossman Gazette - - NEWS -

CLEAN wa­ter helps co­ral reefs thrive, ac­cord­ing to the largest study even un­der­taken on the Great Bar­rier Reef to ex­am­ine the re­la­tion­ship be­tween wa­ter qual­ity and reef health.

The study found reefs in clean wa­ter had greater di­ver­sity and were more re­silient to tem­per­a­ture changes.

On the other hand, 22 per cent of reefs on the GBR do not meet wa­ter qual­ity guide­lines.

“While the amount of co­ral cover on a reef doesn’t ap­pear to suf­fer from poor wa­ter qual­ity, the bio-di­ver­sity of those reefs does,” co­ral reef ecol­o­gist Dr Katha­rina Fabricius said.

While tourists wouldn’t no­tice the dif­fer­ence, reefs can lose a lot of their most sen­si­tive corals in dirty wa­ter.

The study mea­sured wa­ter clar­ity and nutri­ent lev­els at more than 2000 sites across the Great Bar­rier Reef, and cross­ref­er­enced those with lev­els of co­ral cover and di­ver­sity on 150 reefs.

The team mea­sured two fac­tors to de­ter­mine how clean the wa­ter was - chloro­phyll lev­els, which are used to de­ter­mine nutri­ent loads, and clar­ity.

The study found reefs were at risk when vis­i­bil­ity dropped be­low 10m and chloro­phyll lev­els rose over 0.45 mi­cro­gram per litre.

Clean wa­ter not only re­sults in health­ier reefs, they are also more re­silient to shocks.

Dr Fabricius said un­pub­lished data showed reefs in clear wa­ter were bet­ter able to bounce back from dis­rup­tions such as bleach­ing events.

“Reefs with tur­bid wa­ter have five times more sea­weed than nearby reefs in clean wa­ter, and this ad­di­tional sea­weed can com­pro­mise the abil­ity of co­ral to set­tle and re­claim ar­eas of reef af­ter bleach­ing events,” she said.

Dr Fabricius said it was too early to the Reef Res­cue pro­gram to have had a no­tice­able im­pact on the health of the reef.

“The fact state and fed­eral gov­ern­ments have got to­gether to tackle the is­sue is good,” she said.

“River loads of nu­tri­ents and sed­i­ments are four to ten times higher than in pre-Euro­pean times.

“We should start to see a de­cline in pes­ti­cides and fer­tilis­ers, be­cause they have a short half-life.

“It won’t be mak­ing a mea­sur­able dif­fer­ence to wa­ter clar­ity in the short term, how­ever.

“We’ve still got a lot of sed­i­ment built up in the rivers so it will prob­a­bly be a decade or two be­fore we see a marked dif­fer­ence.”

Dr Fabricius said the study had not looked at al­gal blooms, which can smother corals on a reef.

“One thing we’re re­ally concerned about, which wasn’t cov­ered in the study, is blooms of fil­a­men­tous sea­weed which usu­ally only last for a cou­ple of weeks a year.

“Typ­i­cally, these are late win­ter blooms, they oc­cur in Au­gust and Septem­ber.

“I’ve seen it at Green Is­land, great car­pets of green slimy sludgy stuff up to a foot thick.

“They may only last for a few weeks be­fore they break down, but af­ter­wards the patch of reef where these car­pets had smoth­ered the corals look pretty sick.”

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