Be­hind the im­age

When Justin suited up to pho­to­graph a kelp ex­per­i­ment off Tas­ma­nia, he came away with more than just sea­weed.

BBC Wildlife Magazine - - CONTENTS - By JUSTIN GIL­LI­GAN

Oc­to­pus and crabs

The Maori oc­to­pus was des­per­ately at­tempt­ing to blend in with the on­slaught of prey an­i­mals and hunt them at the same time.

It was a crisp, clear De­cem­ber day, and Justin was pre­par­ing for what he an­tic­i­pated would be a rel­a­tively straight­for­ward as­sign­ment – pho­tograph­ing a se­ries of minia­ture kelp forests in a shal­low stretch of wa­ter known as the Mer­cury Pas­sage, near Tas­ma­nia’s Maria Is­land. The sea­weed, which had been painstak­ingly trans­planted onto con­crete blocks in patches of vary­ing size and den­sity, was part of a study on thin­ning – a con­se­quence of habi­tat degra­da­tion that is im­pact­ing kelp ecosys­tems across Aus­tralia’s cool seas.

As he snapped away, Justin’s at­ten­tion was di­verted by the sud­den ap­pear­ance of a colony of gi­ant spi­der crabs, which pro­ceeded to stam­pede through the re­search area in a mob the size of a foot­ball field. Dur­ing the au­tumn-win­ter moult, these crus­taceans are known to gather in vast num­bers in Port Phillip Bay, Mel­bourne, hun­ker­ing out of sight be­neath wooden jet­ties while their new shells har­den, be­fore re­turn­ing to deeper wa­ter. How­ever, the species had never been doc­u­mented around Maria Is­land be­fore.

Seabed smor­gas­bord

The ar­rival of the crabs was as much a sur­prise for Justin as it was for a Maori oc­to­pus that was qui­etly pa­trolling the sand – an im­pres­sive cephalo­pod that boasts a ten­ta­cle-span of 2m, and that mer­ci­lessly am­bushes prey along the seabed. “The oc­to­pus was clearly ex­cited and started rapidly chang­ing colour, des­per­ately at­tempt­ing to blend in with the on­slaught of prey an­i­mals and hunt them at the same time,” re­calls Justin. “The un­ex­pected ap­pear­ance of the crabs re­in­forces just how lit­tle we still know about Aus­tralia’s tem­per­ate reef ecosys­tem, an im­por­tant, highly pro­duc­tive habi­tat that we need to ac­knowl­edge as much as we do our co­ral reefs.”

JUSTIN GIL­LI­GAN Hail­ing from Aus­tralia, Justin is a pho­to­jour­nal­ist and ma­rine sci­en­tist. See more of his work at justingill­i­

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