New life on the Kaiko¯ura seabed

Kaikoura Star - - OUT & ABOUT -

Deep sea life in the Kaiko¯ura Canyon is re­cov­er­ing faster than ex­pected from last Novem­ber’s mas­sive earthquake but it’s too early to say whether the re­bound will con­tinue at the same pace.

The 7.8 mag­ni­tude Kaiko¯ura Earthquake caused huge changes to the ge­ol­ogy of the canyon. Some places where the vol­ume of or­gan­isms liv­ing in the mud had been among the high­est in the world, were left de­void of life.

Changes caused by the quake were ‘‘a cat­a­strophic event for the ecol­ogy of the canyon’’, Niwa marine ecol­o­gist Dr Dave Bow­den said ear­lier this year.

But the lat­est re­search trip to the canyon, which fin­ished on Sun­day, has found some hope­ful signs.

Sci­en­tists sam­pled the seafloor scoured or buried in the earthquake to be­gin to work out the po­ten­tial for re­cov­ery of the deep sea ecosys­tem. The re­search is also high­light­ing how vi­o­lent the un­der­sea dis­tur­bance was.

Niwa ecol­o­gist Dr Daniel Le­duc said there was ev­i­dence that ju­ve­niles of an­i­mals that once dom­i­nated the head of the canyon have be­gun colonis­ing the seafloor.

‘‘The deep sea com­mu­ni­ties might be re­cov­er­ing faster than we orig­i­nally thought, with high den­si­ties of small or­gan­isms such as urchins and sea cu­cum­bers in some ar­eas of the canyon, as well as large num­bers of rat­tail fishes swim­ming im­me­di­ately above the seabed.’’

Niwa Kaiko¯ura deep sea project leader Dr Ash­ley Row­den said ev­i­dence from else­where in the world had sug­gested smaller or­gan­isms were likely to re­spond rel­a­tively rapidly af­ter the sub­ma­rine mud­slides.

But it had been thought larger or­gan­isms such as the urchins and sea cu­cum­bers could take many years to re­cover, and may never re­cover to their pre­vi­ous com­po­si­tion.

‘‘So to come back af­ter 10 months and be­gin to see some of the ju­ve­niles of those species was some­what of a sur­prise to us,’’ Row­den said. Essen­tially those species so far only had one po­ten­tial re­cruit­ment pe­riod, in spring and sum­mer, fol­low­ing the quake.

‘‘It’s very early days. It’s pos­i­tive in the sense there are in­di­ca­tions it’s faster than we might have ex­pected, but at the same time what the on­go­ing tra­jec­tory is, is still un­known.’’

It might be the an­i­mals ini­tially had enough food to grow to a cer­tain size, but not enough con­tin­u­ous food sup­ply be­yond that. It was also pos­si­ble there could be fur­ther, al­though smaller, sub­ma­rine land­slides.

The edge of the Kaiko¯ura Canyon is at a depth of about 150 me­tres, and drops down to around 3000m. The head of the canyon comes within a few hun­dred me­tres of the coast­line just south of Kaiko¯ura.

Row­den said the Niwa sci­en­tists had some in­for­ma­tion from the edge of the canyon but most of it was from the floor at the base of the canyon, at depths of hun­dreds to thou­sands of me­tres.

As well as signs of re­cov­ery, re­searchers had also found ar­eas within the canyon that did not ap­pear to have been af­fected at all by land­slides.

‘‘That’s im­por­tant in the sense that the func­tion­ing in those ar­eas can carry on,’’ Row­den said.

‘‘Pop­u­la­tions of or­gan­isms that live there can sup­ply new re­cruits for dis­turbed ar­eas.’’

Ge­ol­o­gists have also been able to con­firm the earthquake caused a sig­nif­i­cant loss of ma­te­rial from high up in the canyon.

The col­lapse and loss of ma­te­rial at the canyon head trig­gered a vi­o­lent and vig­or­ous cur­rent mov­ing a dense, mud-laden cloud, Niwa ge­ol­o­gist and voy­age leader Dr Alan Or­pin said.

‘‘We’ve had an event that has passed through the canyon at sig­nif­i­cant speed - many tens of kilo­me­tres an hour. That’s been of suf­fi­cient speed and vigour that it’s re-shaped the seabed.’’

Much of the ma­te­rial passed out into the deep ocean, while ev­i­dence of the power of the cur­rent could be seen in the way gravel waves on the floor of the canyon had been re­shaped.

‘‘It’s pretty stag­ger­ing stuff. This is big ge­ol­ogy,’’ Or­pin said.

The gravel waves on the floor of the canyon were a few me­tres high and hun­dreds of me­tres long. It was thought the gravel may have been de­liv­ered to the base of the canyon thou­sands of years ago when sea lev­els were lower.

‘‘What the move­ment of these gravel waves shows is that the big dense cloud of ma­te­rial that moved down through the canyon, moved at a suf­fi­cient speed and was suf­fi­ciently vi­o­lent that it was mov­ing gravel, just like a river in flood,’’ Or­pin said.

‘‘The vi­o­lence of it was suf­fi­cient that the fine grain mud couldn’t set­tle. It couldn’t fall to the seabed be­cause the cur­rent’s too strong. A good pro­por­tion of that fine grain mud then would have moved be­yond the canyon.’’

A dense mud cloud at least 200m high then passed along the Hiku­rangi Chan­nel, with ev­i­dence show­ing it trav­elled along the chan­nel at least as far north as off­shore Gis­borne.

It was thought that in some parts of the canyon me­tres of sed­i­ment had been re­moved, while in some ar­eas ma­te­rial was de­posited.

On top of the ar­eas of eroded seabed and of the gravel waves a blan­ket of soft, soupy mud 5-15cm deep had formed, Or­pin said.

He was rea­son­ably con­fi­dent that layer was no older than the earthquake.

It would have been formed from the tail end of the sed­i­ment cloud caused by the earthquake, and by nor­mal back­ground sed­i­men­ta­tion since the quake.

PHOTO: NIWA

Ju­ve­nile sea urchins found in Kaiko¯ura Canyon this month.

PHOTO: NIWA

A multi-cor­ing de­vice used to take seabed sam­ples in Kaiko¯ura Canyon is brought back aboard NIWA re­search ves­sel Tan­garoa.

PHOTO: NIWA

Life re­turns to ar­eas of the Kaiko¯ura Canyon. This photo shows a rat­tail fish and a dense bed of forams.

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