Common Kelp (Ecklonia radiata)

The common kelp represents a habitat-forming seaweed growing up to two metres high and creating a dense underwater jungle, which consequently is home to a plethora of flora and fauna. As such, Ecklonia radiata is one of our most important underwater species.

The kelp itself provides food for the many herbivores: fish such as butterfish and silver drummer, gastropods like Cook’s turban shells, down to tiny herbivorous amphipods. These grazers in turn become a food source higher up the food chain. Furthermore, as the kelp breaks down at its margins, its detritus floats around in the water providing both organic matter and nutrients to plankton and planktivores alike. And of course, Ecklonia is food for the endemic sea urchin, kina.
A dense stand of common kelp usually signals a healthy rocky reef. However, the depletion of many of the large reef predators such as snapper and crayfish mean the balance between predators and grazers can become tilted; kina can graze the kelp forest down, literally eating themselves out of house and home, as the effects of this cascade, leaving a barren habitat, and little food, behind.

Ecklonia can be found right across the globe in all the major oceans. In addition to being ubiquitous across New Zealand, it is also found in far flung places such as southern Australia, Madagascar, the Canary Islands, South Africa, Senegal and Oman, the latter at 17 degrees North, well within the tropics. Such a distribution is somewhat unusual for a temperate seaweed given that at some point in its current form, it would have had to cross the warm seas of the equatorial region.

Interestingly, when there is a single or few kelp plants, the common kelp remains fairly short. But, in the presence of a dense crowd of the plants they grow fast and tall, as they make sure not to be shaded out. In this way tall stands of common kelp occur.

In southern New Zealand, the giant kelp (Macrocystis pyrifera) outcompetes Ecklonia leaving it in the understory. In terms of reproducing, Ecktonia’s spores land only a few metres from the adult which limits its dispersal. The only other way for it to spread is when storm-ripped adult plants are carried down current, but bear in mind they do not float.

Fast Facts
1. Rimu or Rimurimu in Māori.
2. A laminarian or true kelp.
3. Anchor themselves to the reef with holdfasts.
4. Is found in certain regions of all the major oceans - Pacific, Indian and Atlantic.
5. Usually grows to about 1m tall but can reach 2m high.
6. Foundational species- creating the forest that supports high diversity on rocky reefs.
7. Reproductive spores land only a few metres from the adult.
8. Compounds such as alginates extracted from kelp can be used in a plethora of commercially produced foods.

"As the kelp breaks down at its margins, its detritus floats around in the water providing both organic matter and nutrients to plankton and planktivores alike.