Marine biologists say populations of invasive pests are increasing in New Zealand's harbours.
Scientists from the National Institute of Water and Atmospheric Research or NIWA have noticed the trend during twice-yearly surveys of 11 ports.
They say species like the Japanese paddlecrab and Mediterranean fanworm, which have arrived in the past 15 years, are growing in number in some harbours.
The surveys are commissioned by the Ministry for Primary Industries. The ministry's manager of surveillance and incursion investigation, Brendan Gould, says they serve two purposes: to monitor the spread of established pests and to ensure that new arrivals can be identified quickly and eradicated.