One of the most invasive marine pests is wakame, (Undaria pinnatifida) and divers should be aware of its threat, and how to recognise it and report its presence.
Wakame (or Japanese seaweed) is a brown macroalgae native to the waters of Japan, China and Korea. It has been harvested and eaten for centuries in these countries – think miso soup and seaweed salad.
There is a type of carotenoid (fucoxanthin) that occurs naturally in wakame that is believed to have beneficial health properties. The claims for its therapeutic use in areas such as weight loss, diabetes and cancer prevention/control have not been proven. In fact, because wakame is rich in iodine, it is recommended that people should not consume large amounts of it as high levels of iodine can interfere with the functioning of the thryoid gland
In Australia and other areas where it is not native, wakame can become a major pest, able to grow 2m in length in a year.
It was first recorded in Australia in 1988 in Triabunna, Tasmania – possibly brought in with ballast water from ships transporting woodchips.
It spreads easily; by the millions of microscopic spores released by each fertile organism, and by attaching itself to hulls and marine farming equipment – so please, boat owners, divers and anglers clean your equipment.
Wakame can grow to 3m in length, displacing native seaweeds. It can be differentiated from native seaweeds by its distinctive mid-vein (which is a lighter brown) and a ‘frilly’ sporophyll (the reproductive part of the plant). It has a hold-fast, and its green-brown fronds do not reach its base. Native seaweeds such as common kelp and bull kelp don’t have a midrib.
Photo: Kate Pritchard