CURIOUSCITY
What lurks in Wellington Harbour?
‘Ithink people would be very shocked if they realised what was under the sea. It looks so pristine and green from the surface and sparkly and lovely. But, in actual fact, it’s a real tip under the water at times,’’ National Institute of Water and Atmospheric Research (Niwa) marine biologist Serena Wilkens says.
She specialises in biosecurity, monitoring marine pests that travel in the ‘‘biofouling’’ on ships’ hulls and in ballast water – the growths of seaweed, barnacles, sea squirts, mussels and sponges that accumulate over long journeys.
Her team keeps an eye on invasive marine species arriving into the country’s waters – and on locals they don’t want to spread further – performing a twice annual survey nationally.
They may look pretty, but one particular species of starfish – the Northern Pacific sea star – is one such unwelcome visitor in Wellington. Scientists use traps to catch the starfish, and also crabs on the sea floor to see if they are guests that could be a threat to the local ecosystem.
‘‘Wellington, fortunately, hasn’t had too many,’’ Wilkens says.
They are trying to keep newcomers at bay like the mediterranean sandworm, and the ‘‘feisty’’ paddle crab – both of which have taken up residence in Auckland.
But sometimes its the harbour’s human visitors that foul the seabed.
On Saturday, volunteers mucking in for Wellington Harbour Spring Clean went diving to fish out the rubbish that ends up in the harbour.
Some of Niwa’s marine experts join the cleanup, along with volunteers from the Department of Conservation, the Ministry for Primary Industries, Victoria University, Wellington City Council, Sustainable Coastlines, and members of the public in kayaks and dive gear.
The cleanup, which has been running since 2009, has brought kilograms of rubbish ashore – ranging from shopping trolleys and road cones to tin cans, sunglasses, tyres, bikes, scooters, cellphones, and tablets.
Divers have even found pairs of shoes, Wilkens says. ‘‘Sometimes you wonder how people have ended up losing both shoes at the same time. You name it and people throw it over the side, unfortunately.’’
The accidental junk – ships and car wrecks – can prove a boon for marine life. Although, Wilkens wouldn’t like to see any more wrecks added to the harbour’s collection, which includes a vehicle submerged in Mahanga Bay.
‘‘That’s actually become an amazing artificial reef and it’s full of baby crayfish and it’s teeming with fish life.’’
Niwa marine geologist Dr Scott Nodder is interested in a different sort of seabed ‘‘lurker’’. He was part of team that found and mapped the Aotea Faultline, which was discovered in 2014. They got funding to map its extent and fault characteristics and found it traced a path of about two kilometres from popular swimming spot Oriental Bay to out past Aotea Wharf.
‘‘[It] looks like the seabed has been moved by about a metre on this fault,’’ Nodder says.
‘‘And, over the last 10,000 years, we think this fault has moved maybe three or four times, from what we can tell from our data.’’
The scientists estimated the fault could trigger a magnitude 6 to 7 shake, although a tsunami was ‘‘unlikely’’.
‘‘So a little bit less than the recent Kaikoura earthquake [on November 14] but a significant feature nonetheless.’’
Their data suggested the fault was up to 30km in length, reaching inland: ‘‘Which would mean that it would basically go from Oriental Bay through Te Aro and possibly out on the south coast.’’
Historic seismic activity is responsible for much of the uplift that created flat land for the city to be built, Nodder says.
So the shakes are frightening, but they’re also responsible for giving our waterfront its charm: ‘‘You’ve got masses of hills and a beautiful harbour and I think all of that has been generated by millions of years of tectonic activity.’’ See video at dompost.co.nz