Caulerpa is an alga but it's not like pond scum. It grows leafy fronds (up to 15cm tall) from runners that will cover the sea floor. This plant can form dense meadows, in waters 1m to 35m deep.
It grows on many surfaces, including sandy sea floors, rocky outcroppings, mud, and human structures, like jetties, buoys, and ship ropes.
Why this is a problem for New Zealand
It can reduce the nursery habitat for fish, by crowding out native marine plant species. This can reduce population sizes of recreationally and commercially important fish stocks.
The dense clumps can block fish from feeding on bottom-dwelling invertebrates – small animals like crabs, clams, and worms.
Caulerpa contains a toxin to prevent animals from eating it. Some fish species can still eat caulerpa safely, but the toxin stays in their flesh. Humans can be made sick if they eat fish with caulerpa toxin.
How it could get here
It's a popular species for aquariums overseas. It looks a lot like other harmless aquarium algae. The aquarium trade is one way for caulerpa to get to New Zealand. MPI has strict measures in place to limit the chances of unwanted pests, like caulerpa, making it through the border.
Caulerpa also grows on ships' ropes and bumpers. We have standards in place to reduce the risk of pests, like caulerpa, hitchhiking to New Zealand on ships.
How to identify caulerpa
- long horizontal runners (stolons) with many upright, flattened fronds
- fronds up to 15cm long
- a bright green colour
- fronds with a smooth midrib
- paired branchlets, all flattened in the same plane.
If you think you've found caulerpa
- photograph it
- note the location and any landmarks
- call 0800 80 99 66
Note: This information is a summary of caulerpa's potential impacts on New Zealand.