When the Rena grounding took place, many vessels from afar came at short notice to assist with the salvage operation.

And with the vessels, also came marine pests that lived on the hulls.

The support barge Seatow 60 heading out to the scene, after the Rena grounding.

A recent comprehensive report conducted by NIWA found none of the many pest species that came into Tauranga Harbour with the vessels spread.

Other areas around the harbour were also cleared, including near Motiti Island, Otaiti [Astrolabe Reef] and Mount Maunganui.

Vessels such as support barge Seatow 60 entered New Zealand waters under emergency measures - the vessel had been sitting idle for two years Port Curtis, Gladstone in Australia.

The Ministry for Primary Industries commissioned NIWA to carry out in-water inspections to assess and identify any risk species.

The sides and submerged surfaces of the barge had a range of algae, barnacles, encrusting bryozoans, oysters, mussels and other organisms - many of which were not current in NZ waters.

The notifiable organism red algae was also identified on the support tug, and divers were sent to destroy it, according to NIWA's report.

Other species from the tropics were considered less likely to establish populations in NZ, so were a lower risk to marine ecosystems and resources.

Eleven of the 19 species recorded from barge and support vessels were not known in New Zealand - mangrove crabs, red algae and bivalves were the main focus.

NIWA used dive and shoreline searches, baited and un-baited crab traps and a small sled on the seabed. None of the five marine pests of most concern were found in their sampling and all the native species were returned to the harbour alive.

Areas surveyed included the Tauranga Moana, Matua, Otumoetai, Fraser Cove, Welcome Bay, Motiti Island and Astrolabe Reef itself.

A half day workshop was held at the Sulphur Point Field Station to train people in marine pest identification to other groups involved in the Rena Long Term Recovery Plan.