Summer Series 4: Would you like seaweed with that?

Next time you bring home fish and chips, consider a sprinkling of health-giving seaweed.

Karengo is the Māori name for edible red seaweeds that belong to the genus Porphyra, known in Japan as nori (used to wrap sushi) and in Wales as laver (mixed with oatmeal and bacon fat to make laverbread). 

New Zealand shores are home to a very diverse array of seaweeds (about 800 known species), and the karengo group is no exception. We have about 35 known karengo species, the most familiar one being Porphyra columbina.

Karengo is found on rocky shores in the upper intertidal zone, close to the high-tide mark. You can find one or more species in most parts of the country year-round. Their blades (the equivalent of leaves on land plants) can be pink, purple, gold, or greenish and range from huge sheets with the texture of cellophane to delicate ribbons. To the non-expert eye, they’re easily confused with sea lettuce (Ulva species), which have a similar ‘ruffly’ blade shape.

“Some are really tough and some are really tender, but all are just one cell thick – making them unique among seaweeds,” says NIWA Principal Scientist and seaweed expert Wendy Nelson.

Karengo is considered taonga by Māori and sometimes given as a gift. “Wherever Porphyra seaweeds are found, people prize them really highly, and you can find native names for them all over the world,” says Dr Nelson. “They have quite a rich flavour and are high in vitamins, protein, iron, and iodine – they’re very nutritious!”

In New Zealand, they can be gathered from the wild for personal use. Only one person holds a licence to harvest them commercially and they’re not farmed here as they are in Japan.

If you want to try karengo, Dr Nelson suggests that you only take small quantities sufficient for a meal and leave plenty for maintaining the population, so never remove all the tufts/blades from a particular rock. Research by NIWA on two karengo species at Kaikoura (Porphyra virididentata and P. cinnamomea) shows that the blades are able to re-grow from the base after harvesting. Like other plants, their main growing period is spring.

Porphyra seaweeds belong to a really ancient group of seaweeds – the Bangiales – with fossils up to 1.2 billion years old found in northern Canada and China.

 “Their long evolutionary history is probably down to their ability to cope with a whole range of environmental challenges and different conditions,” she explains. “They’re incredibly resistant. They can dry out to a crisp, then the tide comes in and away they go, photosynthesising again. That’s why they’ve survived for so long!”

Wendy's suggestions for serving karengo

First air-dry your karengo in the sun, then use it dried:

• crumbled and sprinkled into savoury dips (e.g., mayonnaise, yoghurt, sour cream, avocado), served with fresh vegetables or chips, or to accompany fish or spiced fish cakes
• added to omelettes or scrambled eggs
• sprinkled on mashed or baked potatoes or kumara
• broken into small pieces and added to soups (particularly good with spicy chicken or Asian-flavoured soups
• boiled or steamed until it softens and then fried lightly in butter.

Bon appetite! 

Scientist bio

Dr Wendy Nelson is an expert in seaweed ‘taxonomy’ (the science of formally identifying and describing species) and a Principal Scientist at NIWA, where she co-leads research programmes in marine biodiversity and biosecurity. Some of her recent research with colleagues at NIWA and the University of Otago has discovered a lot of hidden diversity among the Bangiales seaweeds, including several new species, using DNA analysis.

Species Fact File