Wednesday, May 22, 2024

Green pest offers greener solutions

Avatar photo
Sea lettuce is often the nasty dark green side of a Bay of Plenty summer at the beach – tangling around surfboards, getting in swimmers’ hair and fringing Tauranga harbour in stinking, rotting green layers on the high tide line. But work by Waikato University researchers might soon turn that nuisance plant into a valuable stock food additive, waste absorber and gourmet food option. Richard Rennie spoke to lead scientist Dr Marie Magnusson. 
Reading Time: 2 minutes


Amid bubbling tubs of sea lettuce on an industrial site only metres from Tauranga Harbour a team of researchers is starting to understand how this otherwise pesky maritime plant can found a thriving aquaculture industry.

“What makes this species worth studying is not only how prolific and fast growing it is but the array of interesting chemicals and soluble fibre it contains,” Waikato University macroalgal biotech programme leader Dr Marie Magnusson says.

“We are looking at a biorefinery process with it as feedstock, where it is capable of producing seaweed salt for human use and soluble fibre with bio-active properties for the likes of stock feed additive or nutraceuticals for human health benefits. 

“At the end of the process cellulose remains, which can be turned into micro-fibrous products for use in medical materials.”

The research is funded with $4 million from the Tertiary Education Commission and $9m from Waikato University.

Earlier work by Magnusson at James Cook University in Townsville also found seaweed can be refined and concentrated for its protein content.

“You can pretty much double the original protein level to 40%, with the rest of the material being mainly cellulose.”

The frilly, green, free-floating lettuce-like weed starts as tiny spores but when cultivated grows to harvest size in a matter of weeks, making it ideally suited to large-scale growth and harvesting operations.

While other seaweed species have received much attention lately for their efficacy in reducing enteric methane emissions from cattle, sea lettuce is more likely to have applications in general animal health.

Its sulphur content means feeding it straight to livestock is not an option but use as an additive to stock diets is more likely.

“There is also the potential there as a general gut health additive. Due to the level of soluble fibre it contains it has positive effects on the gut biome.”  

“And at a human level, again the gut health aspect shows promise from our early animal modelling work.”

The benefits of seaweed were well known to early Maori who used it in cooking, with varieties of sea lettuce eaten in salads and stews around the world. 

In a less processed form the lettuce has dietary equivalents to Japan’s highly prized aonori and aosa seaweeds, commercially cultivated in specific bays on the Japanese mainland and used in noodle, pancake and dumpling dishes.

Magnusson is encouraged by the Government’s aquaculture strategy released last September, which outlines plans to make an $800m a year industry worth $3 billion by 2035.

But the lettuce’s value also includes its ability to help mop up what are very land-based wastes, particularly nitrogen and phosphate.

Magnusson’s previous work in Australia used seaweed in bio-remediation, where a waste stream of nitrogen-rich water from a prawn farm had a final purification pass through a seaweed-dense pond. 

The filtered water contained less nitrogen than the original water used on the farm. 

These sorts of eco-system services could have application here in helping reduce phosphate and nitrogen levels in catchments, possibly as part of an overall catchment protection plan. 

Magnusson said New Zealand is blessed with large swathes of sea area already consented for ocean farming and sea lettuce is one option.

“Both the Hauraki Gulf and Bay of Plenty have that area and there is no shortage of groups wanting to grow it. 

“Work still remains in researching market opportunities and outlets for the product itself,” Magnusson said.

People are also reading