Weeds and pests

Northern Pacific seastars from the Derwent

Introduced weeds and marine pests pose a serious threat to the ecology of the Derwent estuary.

Introduced weeds and marine species flourish in the Derwent by taking advantage of disturbed or altered environments.

Species have been introduced through hull fouling, ballast water discharges, fishing and aquaculture activities. Shipping is likely to be responsible for a majority of the estuary's introductions.

Seventy introduced marine species have been identified in the estuary. The greatest concentration of species is around the Hobart docks.

The following species are considered to be having the greatest ecological impact on the estuary:

  • Northern Pacific seastar (Asterias amurensis)
  • Japanese seaweed (Undaria pinnatifida)
  • Toxic Dinoflagellate (Gymnodinium catenatum)
  • Pacific oyster (Crassostrea gigas)
  • New Zealand half crab (Petrolisthes elongatus)
  • New Zealand seastar (Patiriella regularis)
  • New Zealand screw shell (Maoricolpus roseus)

All these species have invaded natural as well as disturbed habitat. They are generally abundant and widespread.

The Derwent Estuary Program works closely with its partners to monitor and raise awareness about marine pests, and to initiate projects to manage existing pests including the weeds rice grass and karamu.

Seal pup

Restoring and promoting the Derwent estuary