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The Combined Impact of Ocean Warming, Acidification and Eutrophication on a Green Seaweed

Paper Reviewed
Gao, G., Clare, A.S., Chatzidimitriou, E., Rose, C. and Caldwell, G. 2018. Effects of ocean warming and acidification, combined with nutrient enrichment, on chemical composition and functional properties of Ulva rigida. Food Chemistry 258: 71-78.

Writing to introduce their work, Gao et al. (2018) say there currently is "growing interest in using seaweeds as food because they are rich sources of dietary fiber, protein, vitamins and minerals," citing Bolton et al. (2016). And in this regard, green seaweeds (Ulva species) are particularly rich in fiber, omega-3 fatty acids and vitamins A, B2, B12, C and tocopherol.

Despite the important dietary benefits of green seaweeds, little is known about how these species might respond to model-based predictions of ocean warming, ocean acidification and eutrophication. Thus, it was the objective of Gao et al. to investigate the impacts of these three supposed stresses on the chemical properties and food quality of Ulva rigida.

To accomplish their work, the five scientists subjected U. rigida samples they collected from the low intertidal reaches of Cullercoats beach, United Kingdom, to two temperature levels (ambient and elevated summer values of 14 and 18 °C), two pH levels (ambient and future predicted levels of 7.95 and 7.55) and two nitrate levels (ambient and elevated values of 6 and 150 µmol L-1) for a period of 12 days. Thereafter, they performed a series of analyses on the seaweed samples, including amino acid and fatty acid analyses and determinations of plant swelling capacity, water holding capacity and oil holding capacity.

In discussing their findings, the authors report that high temperatures "increased the content of every amino acid and thus the total amino acids," adding that "high temperature, high pCO2, and high nitrate ... enhance the content of some amino acids synergistically, indicating [the] future ocean environment may promote [the production] of amino acids in Ulva species." With respect to fatty acids, Gao et al. similarly state that high temperature, high pCO2, and nitrate also increased their contents, suggesting that "the production of fatty acids in Ulva species may benefit from global climate change."

Plant swelling capacity, water holding capacity and oil holding capacity also increased in the high temperature, high pCO2 and high nitrate environment. Such increases, according to the researchers, are expected to provide a number of benefits. And in this regard, they state that (1) the swelling capacity of Ulva "can enhance satiety and reduce calorie intake (i.e. carbohydrate, sugar, fat, saturated fat and protein intake), and hence can be applied in an adjunctive therapy for obesity (Dettmar et al., 2011)," (2) the improved water holding capacity "can avoid syneresis and modify the viscosity and texture of formulated food," adding that "the increased viscosity due to water absorption could lead to slower rates of intestinal absorption ... and make Ulva clinically useful in reducing blood cholesterol and postprandial glycaemia, decreasing risks of obesity and Type II diabetes (Willett et al., 2002)," and (3) the enhanced oil holding capacity can allow Ulva species to be used "as stabilizers in formulating food products," as well as to be utilized to "reduce blood lipid level, obesity and coronary heart disease risk and thus can be a valuable functional food." In short, Gao et al. conclude that "future ocean conditions may promote the value of Ulva species as a healthy food."

In light of these several findings, the future looks bright (and healthy!) for producers and consumers of green seaweeds, which observationally-based optimism stands in stark contrast to the gloom and doom predictions of both climate and ocean acidification alarmists who ever so struggle to acknowledge that anything good can come from rising atmospheric CO2 concentrations.

Bolton, J.J., Cyrus, M.D., Brand, M.J., Joubert, M. and Macey, B.M. 2016. Why grow Ulva? Its potential role in the future of aquaculture. Perspectives in Phycology 3: 113-120.

Dettmar, P.W., Strugala, V. and Richardson, J.C. 2011. The key role alginates play in health. Food Hydrocolloids 25: 263-266.

Willett, W., Manson, J. and Liu, S. 2002. Glycemic index, glycemic load, and risk of type 2 diabetes. The American Journal of Clinical Nutrition 76: 274S-280S.

Posted 10 June 2018