Five seaweeds that look like exotic caulerpa (but aren’t)
New Zealand has over 1,000 species of seaweeds. Here are five that have been mistaken for exotic caulerpa:
Sea Lettuces (Genus ulva)
These seaweeds are commonly found in the region. Like exotic caulerpa, it’s bright green, but there are differences in its fronds. When washed up on beaches, it can look similar at first glance.
Ulva intestinalis (pictured left underwater and in the centre as beachcast) is very similar to exotic caulerpa. Ulva prolifera (right) is also similar but has a centre stem with leaves radiating from it.
2. Common flapjack
While exotic caulerpa is green, this species (Carpophyllum maschalocarpum) is mid brown to golden brown, with a firm texture and round vesicles (bladders) with points or leafy tips. It is similar in appearance to Sargassum.
Tip: Wind and waves wash seaweed up high on the beach during storms! After a storm is a great time to go and search for exotic caulerpa.
3. Seagrass
Native seagrass is an important part of the ecosystem. While the fronds of exotic caulerpa are shaped like oar blades, seagrass has thin, olive-green ribbon-like leaves.
4. Native caulerpa
There are native species of caulerpa that can be found washed ashore. As natives, these are not invasive. Pictured is Fern caulerpa (Caulerpa flexilis). Its fronds are more three dimensional than the invasive exotic species (Caulerpa brachypus, and Caulerpa parvifolia) which have flat leaf blades. Another native caulerpa, Caulerpa articulata, has round, bead like lumps on its stem.
A native species of caulerpa, Caulerpa geminata
5. Ecklonia radiata (Paddle weed)
A seaweed common to our shores. Unlike exotic Caulerpa, it is thick, brown and leathery.
If you think you see exotic Caulerpa, note the location, take a photo and report it to Biosecurity New Zealand on 0800 80 99 66 or online at report.mpi.govt.nz
What does exotic caulerpa look like?
The exotic seaweeds Caulerpa brachypus and Caulerpa parvifolia are closely related and appear identical.
They have green fronds up to 10 centimetres long in the shape of oar blades that rise from long runners or roots known as stolons. There are more images of Caulerpa, both in the sea and washed up on shore, to help you recognise it on the Biosecurity NZ website.
Thank you to the Auckland Council and Northland Regional Council Marine Biosecurity Teams for their expertise. Photo credits: Wendy Zapart / Auckland Council, Dimitri Collella / Auckland Council, Northland Regional Council, Zoe Hawkins / TON Marine Biosecurity Partnership, Jacqui Geux / iNaturalist.