Sea lettuce strains in the laboratory. Photo: Antoine Fort, NUI Galway.
Feb 21 2019 Posted: 10:20 GMT

Sea lettuce seaweed strains show extensive variation in growth and metabolism, demonstrating a large potential for boosting biomass and metabolite yields in aquaculture in Ireland

Researchers from the Ryan Institute and School of Natural Sciences at NUI Galway have carried out a study aimed at identifying strains of seaweed which are good for aquaculture and agriculture in Ireland. The study discovered that sea lettuce, a fast growing seaweed with excellent nutritional value for animal feed and industrial uses could return higher yields when the right strains are used. This seaweed is also responsible for green tides in Cork and the East coast of Dublin.

The year-long study which was published in one of the top 10 Plant Science international journals, Plant Physiology, analysed 50 seaweed strains of sea lettuce, mostly from Ireland and is the first study of its kind to be carried out.

Sea lettuce plays a key role in coastal ecosystems and is of increasing commercial importance. However, physiological differences between strains and species have yet to be described in detail. Furthermore, the strains of Ulva (seaweed blooms) used in aquaculture usually originate from opportunistic collection in the wild without prior selection of best performing strains. As a result, efforts are required to detect the potential variability in growth and metabolic accumulation between seaweed strains to ultimately select the best performing strains, like sea lettuce, under certain environmental conditions.

Lead author of the study, Dr Ronan Sulpice from the Plant Systems Biology Lab in the Ryan Institute and School of Natural Sciences at NUI Galway, said: “This study is an important stepping stone towards the development of modern breeding approaches for seaweed aquaculture.”

The sea lettuce strains were collected from around the coastlines of Co. Galway, Co. Clare and the East coast. Beaches included Roundstone, Derrygimla, Dog’s Bay, Clifden, Tievegarriff, Ventry Bay, Lahinch, Bunowen Beach, Eastern Scheldt (Netherlands), Tolka and Courtmacsherry beach.

The growth, physiological and metabolic characteristics of 50 seaweed bloom strains were investigated in the laboratory, using a custom-made growth monitoring platform set by researcher Dr Antoine Fort.

Mr Antoine Fort from the Ryan Institute at NUI Galway, said: “The study paves the way towards the domestication and breeding of elite strains of seaweed blooms (Ulva) for aquaculture, similar to what has been done for crop plants since the beginning of agriculture.”

The researchers found a large natural variation for a wide range of growth and metabolic characteristics, with growth increases varying from 9% to 37% per day amongst strains. They also found that sea lettuce strains possess a unique diurnal growth pattern and primary metabolism compared to land crop plants, with higher growth rates during the night than during the light period. This sea lettuce was not primarily using starch and sucrose to sustain its growth at night, contrary to plant crops. Nitrates were accumulated during the night in the seaweed tissues, and nitrate accumulation and consumption was positively correlated with high growth.

The large variability in growth and nutritional quality recorded amongst sea lettuce strains justify future efforts in strain selection for increasing biomass, metabolite yields and nutrient removal in the growing aquaculture industry.

The next stage of this research will sequence the genomes of all the sea lettuce strains collected and analyzed during this study, and aims to identify the genes responsible for fast growth and high nutritional content, while extending the research to 300 strains of sea lettuce which be collected across Europe.

The study was funded by the EU Horizon 2020 project, GenialG.

To read the full study in Plant Physiology visit: http://www.plantphysiol.org/content/early/2019/02/12/pp.18.01513

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