Niwa hunting down unwanted aliens
Exotic invaders hitching a ride into Bluff’s colourful waters are being hunted.
A team of four Niwa specialists has been sweeping the harbour for biosecurity threats this week.
Project manager Don Morrisey, biosecurity technician Caroline Williams and research diver Pete Notman showed off their work yesterday.
Dr Morrisey said the team aimed the sweep at high-risk species known to pose a threat.
Invasive species commonly arrive in New Zealand ports on boat hulls or inside ship ballast water.
Despite international regulations which meant ballast water had to be emptied in the open sea, some organisms would always slip through, he said.
The team laid crab traps in different locations, as well as making diving inspections and dredging for sediment.
Among the undesirables they were looking for were European shore crabs, an aggressive predator which would decimate native species, and the Chinese mitten crab, which burrowed into river banks and caused erosion and instability.
There was also the Japanese skeleton shrimp, which was first found in the harbour in August last year. However, Dr Morrisey said it appeared not to have yet spread beyond where it was first found.
When diving, the team were looking for a type of clam from Asia which bred in large numbers, and the shore-sweeps along beaches enabled them to spot pests on the foreshore or hiding under rocks.
The team was also searching for the North Pacific seastar which fed on bivalve molluscs in large numbers.
An infestation in Bluff would threaten the famous oyster beds, paua, toheroa and mussels.
Dr Morrisey said the starfish started life as planktonic larvae, which were impossible to spot in the water.
Probes were being developed which could spot the larvae, but were still some years off, he said.
Demonstrating a dredge of the sea floor, he found a starfish, fortunately a native rather than the dreaded North Pacific.
While the team went out in all conditions, they were enjoying the summer trip to Bluff, and hoped to complete the sweep in four days.
Mr Notman said underwater Bluff was the prettiest harbour in the country, with sea sponges growing in banks of yellow, red, orange, purple, blue and green around the wharves, and the waters teemed with life.
Dr Morrisey said Niwa performed the sweeps under contract from the Ministry of Agriculture and Forestry.