Japanese Kelp - Invasive Species Information

Reproduction: prolific spore production and its ability to foul structures both in its macroscopic and microscopic forms. It spreads rapidly and geographically distant populations can appear in a short space of time. It is transported to new areas by human activities in both its highly visible sporophyte, or as the microscopic gametophyte and spore stages in its life cycle.

Japanese Kelp stand

Japanese Kelp, is a highly invasive seaweed that can grow to 3m in length and has green-brown fronds. It grows in sheltered temperate waters, forming dense forests at depths of up to 15m and can quickly displace native habitats.

This seaweed is green and golden-brown in colour with a lighter coloured stem and a branched holdfast (for attachment to the substrate). The stipe has very wavy edges, giving it a ridged appearance. Undaria has a broad, attened leaf shaped blade with a distinct midrib and wavy margins.

How To Identify Japanese Kelp?

Fonds: Green-brown fonds can grow up to 1-3m tall that stop short of base, Midrib up to 3cm wide with frilly hold-fast base

Japanese Kelp stand

Japanese Kelp leaves

Japanese Kelp - Undaria pinnatifida ID Guide

Why Is Japanese Kelp A Problem?

Can be highly invasive and grow rapidly into dense beds.

Overgrows and excludes native algal species preventing biodiversity and altering marine food chain. as an opportunistic species, takes advantage of areas disturbed by human activities or grazing by herbivores such as urchins and is also known to grow in areas not normally occupied by native seaweeds where it may have a high degree of impact.

Habitat: Aquatic, marine (costal areas).
Distribution in Ireland: Present around coastal waters

Status: Established
Family name: Alariaceae