Beach flotsam 'horrible' but harmless

Folk who can't tell their aplysia from their nudibranch can rest assured the sea slugs washing up on Whangarei beaches are the former, and are not toxic.
Sea hares, from the aplysia family, started turning up in numbers around the Waipu River mouth over the past few weeks, and more recently on Parua Bay and Whangarei Heads beaches.
They are a type of sea slug and not the nudibranch sea squirts responsible for poisoning dogs on Auckland beaches last year, Department of Conservation marine biologist Vince Kerr said. Several people had brought specimens into the conservancy office fearing they might be toxic, he said.
Parua Bay resident Pat Parker said she was at the Wharf Rd beach at the weekend with her grandchildren when she saw the slugs for the first time.
They had been washed up to the high-tide line and appeared to be dead or dying. Most were about the size of a child's palm but Mr Kerr said sea hare commonly grew to twice that size. They had a typical sluglike feel on the outside, a soft internal shell, and a sucker foot underneath.
Ms Parker said some people at the beach thought they might have been jellyfish. "They were excreting purple liquid, and they looked pretty horrible," she said. "I wondered if they were poisonous because even the seagulls weren't interested in them." Most had flattened as they dried on the sand but those that were alive immediately puffed into a rounder shape when back in the water.
Mr Kerr said no one knew why they were dying and washing up.
A reduction in snapper or other fish that fed on sea hares could lead to an overpopulation that could not sustain itself, he said.
Sea hares browse on kelp on the seabed and their bodies are camouflaged by taking on the colour of their food. The ink, which might be reddish or purple depending on that food, was squirted out to deter predators. It is thought the ink also interferes with the smell senses of predators.
Sea hares live in temperate and tropical waters worldwide, and there are eight kinds in New Zealand waters.