By CATHERINE MASTERS
Big sea slugs linked to excess sewage at a North Shore beach are packing a powerful environmental message.
Their presence in huge numbers sliming along part of the southern end of Long Bay are a sure sign that something is not quite right, says Torbay resident and scientist Professor John Buckeridge.
He said that while the North Shore City Council was upgrading its sewage systems, it still needed to take a long, hard look at the impact of high-density housing - and the associated sewage load - on the area's once-pristine beaches.
The creatures - known as sea hares, but related to sea slugs - are not dangerous in themselves.
However, the algae they fed on indicated bacteria in the water and Professor Buckeridge warned people not to swim at the south end of the beach, or in nearby Awaruku Stream.
The sea hares, which range in size from a few centimetres to as large as a man's hand, spurt out an inky, purplish fluid when squashed and are opportunists that feed on nutrients created by sewage.
Professor Buckeridge is the associate dean of the faculty of science and engineering at the Auckland University of Technology and heads the Earth and Oceanic Sciences research centre at the department.
"It may not be solely sewage - it probably is sewage - but it would also come from increased nutrient levels, perhaps from fertilisers, runoff and that sort of thing."
Sometimes the stench was horrendous and even the seagulls would not go near the slugs.
"The numbers we've got now are far, far in excess of anything I've ever seen before in all the 20 years I've been living here."
The council had a tendency to be reactive, rather than proactive, in dealing with environmental matters, said Professor Buckeridge.
Council representatives could not be reached last night.
Hugh Leersnyder, the Auckland Regional Council's coastal resources manager, said he knew little about sea hares.
However, there had been an unusual amount of seaweed containing cyanobacteria (on which sea hares feed) on eastern beaches.
But that was a natural phenomenon caused by La Nina's warm weather patterns.
Mr Leersnyder said algae specialists had advised the council that the bacteria was not related to human causes.
Said Professor Buckeridge: "What I'm worried about is that there are new developments, sort of Coronation Street style, around Albany and areas that are going up very, very dense.
"The council says they were a mistake but they're still in the process of being developed."
Each of the flats in the tenement blocks produced the same amount of sewage as homes on traditional quarter-acre sections that were once common on the North Shore.
"That's an issue and we've got to face up to the fact that if you're going to do that you've got to, I think, build better sewage-disposal systems in advance."
The slugs were an environmental indicator, he said.
"What happens is we get very, very low biodiversity but large numbers of a few species.
"When that happens that's what I'd call an indication that something's not quite right."
Sea slug invasion a sign of environment woes: expert
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