Life upon pumice, drifting to us from NZ trenches

Denis Riek

Pumice. You have probably seen some along the tide line at the beach, much of these little grey rocks that float in with the onshore wind were born underwater 1,500kms to the east.

The small amounts are mostly what is left of the enormous amount of pumice that was produced when, in July 2012, the Havre seamount exploded in what is reported as the largest deep ocean volcanic eruption to be recorded, one and a half times the magnitude of Mt St Helens.

The initial raft was estimated to be in the vicinity of 400 square kilometres and two and three metres thick. 

Havre is close to the Kermadec Islands, midway between New Zealand and Tonga, in a very active volcanic trench. With the prevailing current, it took about a year for most of the pumice to drift across to the Coral Sea and disperse down the east coast, first reaching here in large amounts in May 2013, and then slowly decreasing after that.

Smaller pieces tended to not have much marine life attached, but larger pieces up to 15-20 cm were often overgrown, especially if they had been bobbing around in the open ocean for a lot longer. Unfortunately, there is only a small window of opportunity to collect and photograph – an hour or two in the sun and wind kills any stranded marine life, so I quickly get several promising pieces into an aerated saltwater tank and wait to see what emerges. 

What looked like a lifeless slimy lump on the beach slowly transforms. Anemones open up, goose-neck barnacles begin straining food particles, worms, amphipods and other crustaceans move through the hydroids and bryozoans that cover parts of the surface.

Nudibranchs are sometimes found, as are small crabs, tube building polychaete worms, snails, flatworms and corals. Several hours can often be spent, sitting in front of a small tank, peering down a macro lens, waiting for a worm to stick its head out of a hole, or a pair of nudibranchs to do what comes naturally.

I have been able to photograph around 60 species and that excludes the really small species that are beyond the range of my macro gear and my eyesight.

So, if you’re in Bruns, you might see an old bloke down the beach with an arm full of slimy pumice, or a bucket full of kelp holdfasts, or more often wandering along the tide line trying to beat the gulls to the latest stranding. It’s just me and now you know what I’m up to.’

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