Presently, the entire global supply of alginate is obtained from brown seaweeds. These are also known as macroalgae or kelp. The major species of commercial interest are Ascophyllum, Laminaria, Ecklonia, Durvillaea, Lessonia and Macrocystis, with Ascophyllum, Laminaria and Macrocystis being heavily used for alginate preparation. Have you wondered whether climate change, specifically global warming and acidification due to dissolving of CO2 into ocean water affects the growth and survival of these commercially important species of seaweed? This is the topic for our Spring 2017 blog. In addition to alginate, these seaweeds also provide a habitat for fish, sea urchins and other ecologically important organisms. Also, the macroalgae sequester a large amount of the CO2 emissions, estimated to be ~one quarter of the yearly atmospheric carbon increase (1).
A study by Juetebock et al (1) builds on previous work that found temperature to profoundly affect the growth, reproduction and survival of seaweeds. One of seaweeds they studied was Ascophyllum nodosum, which has 95% of its content used as a source of alginate. This type of brown seaweed is mainly found in North-Atlantic rocky shores. The authors reached a number of conclusions from their study. First the warm temperate East Atlantic region between Portugal to Brittany in France will have their Ascophyllum nodosum and Laminaria species likely become extinct. In turn these species will likely migrate to the Southern Arctic region that includes Northern Canada, and Greenland. Harvesting of Ascophyllum nodosum indicates that the abundance of this seaweed has already decreased in New Brunswick and Nova Scotia, Canada. Also A. nodosum has essentially disappeared from Long Island, NY and its retreat northward maybe accelerating faster and further north than the author’s models predict. Part of this enhanced northward movement may be attributable to Gulf of Maine’s temperature increasing faster than most other ocean areas (http://www.pressherald.com/2015/10/25/climate-change-imperils-gulf-maine-people-plants-species-rely/). The authors conclude that the key question is whether the adaptive capacities of A. nodosum are sufficient to survive climate change and there is a possibility that certain populations of this seaweed may become extinct over the next 100-200 years. This obviously has significant implications for the supply of alginate.
New work on this problem was recently published by Marba et al (2). They tested the hypothesis that growth of A. nodosum near the northern distribution edge would increase with ocean warming. The growth of 8 A. nodosum populations from West Greenland and Northern Norway (640 – 690N latitude) collected between 2009 – 2012 at mid-tidal zone in August& September was retrospectively quantified. The results indicated that arctic climate change enhanced the growth of A. nodosum at these locations with those populations at the Northern limits (coldest) have the least amount of growth. A caveat to these observation is that robust seaweed communities develop in sheltered areas. This geographic constraint together with variation in climate in the subarctic to arctic region may constrain growth of A. nodosum and other commercially important macroalgae. Overall the authors conclude that the current warming of A. nodosum habitats could stimulate an expansion northward. However, the boundaries and rate of this migration will depend on the adaptability of this species of brown algae.
Two reports (3,4) examine the impact of rising seawater temperature on Ecklonia species around the coast of Japan. The average surface temperature for the seawater surrounding Japan has risen by +1.080C from 1891 – 2012. In this first report (4) the authors studied Ecklonia cava, a kelp found in temperature habitats and is the predominate macroalgae in the southern coast of Japan. This seaweed has declined rapidly since the 1990s and some populations disappeared from the coasts of southwestern Japan by 2000. They suggest that this decline is likely due to multifactorial causes such as coastal reclamation, water quality changes, increased seawater temperatures and grazing by herbivores. Their results suggest that continued warming will drive a poleward shift in the distribution of E. cava and if existing E. cava populations cannot adapt and redistribute they may become extinct due to stresses such as high temperature and continued grazing by herbivores in their present environment.
The second report examines both the effect of temperature and UVB exposure on growth & biomass accumulation of three canopy forming seaweeds, including E. cava (4). Their experiments showed a tendency for the growth rate of Ecklonia to decline under warmer conditions and it also had a significantly reduced biomass. Also, higher UVB exposure (due to ozone depletion) caused a further reduction in biomass. The authors conclude that their results are consistent with other published studies that a sustained increase in seawater temperature will likely reduce the growth and yield (biomass) of several types of brown seaweed, especially Ecklonia, which is used for the extraction of alginate.
What about Laminaria digitata, probably the most commercially important species for extraction of alginate? A report by Raybaud, et al (5) examines the effect of global warming on L. digitata. First off, it has been documented that this species of seaweed has been declining along the Western Europe coast for several years. Laminaria ranges from Brittany in France to Northern segments of the coast of Norway. Decline in Laminaria digitata was observed in Brittany, Normandy and the English Channel. Raybaud et al (6) applied a new Ecological Niche Model based on presence only data to make some predictions about the future changes in the distribution of L. digitata. A complete disappearance of this species from French and Danish coasts is predicted by the 2050s. Although some decline is expected along the Scottish coast, northern segments may persist until the end of the 21st century. Also, a poleward movement is predicted along the Norwegian coasts in the next few decades. While the majority of models predict the extinction of L. digitate from regions stated above, a few of the models suggest complete loss of this species even for the south coast of Norway. The authors state that in addition to global climate change, L. digitata is being affected by multiple stressors that are related to human activity such as increased turbidity, sea level rise and aggressive harvesting. All of these factors together with the ecology models raise concern about the future of the commercially important seaweed.
So, what conclusions can be drawn from the various studies? There seems to be a consensus that all the major alginate producing seaweed species have decreased growth and biomass in the temperate coastal regions and are undergoing, or will undergo according to a variety of models, a migration to sub-arctic or arctic regions. There still remain the questions of adaptability of the species to the ecologic environment and whether genetic changes that might occur to allow adaption will affect the production of alginate. If the models are correct and the seaweed population relocates, their new environment in places such a Greenland and the north shore of Norway could make harvesting of the seaweed more difficult or at least more expensive. These uncertainties regarding seaweed as a source of alginate provides additional impetus to accelerate the technology for commercialization of alginate produced by bacteria. Since this process is similar to the production of human products such as insulin and other polymers such as xanthan gum by bacteria, the main impediments are the yield and performance of the alginate. Progenesis has engineered its bacteria to produce high yields and performance similar to seaweed alginate. The next step is to scale up and maximize production for commercial feasibility and to engineer unique alginate polymers not found in seaweed.
Articles
1. Jueterbock A, Tyberghein L, Verbuggen H, Coyer HA, Olsen JL, Hoarau G. Climate change impact on seaweed meadow distribution in the North Atlantic rocky intertidal. Ecology and Evolution 3: 1356-1373, 2013.
2. Marba N, Krause-Jensen D, Olesen B, Christensen PB, Merzouk A, Rodrigues J, Wegeberg S, Wilce RT. Climate change stimulates the growth of the intertidal macroalgae Ascophyllum nodosum near the northern distribution limit. Ambio 46(suppl.1):S119-S131, 2017.
3. Takao S, Kumagai NH, Uamano H, Fujii M, Yamanaka Y. Projecting the impacts of rising seawater temperatures on the distribution of seaweeds around Japan under multiple climate change scenarios. Ecology and Evolution. 5:213-223, 2015.
4. Xiao X, de Bettignies T, Olsen YS, Agusti S, Duarte CM, Wernburg. Sensitivity and acclimation of three canopy-forming seaweeds to UVB radiation and warming. PLoSOne DOI:10.1371/journal.pone.0143031, Dec 2, 2015.
5. Raybaud V, Beaugrand G, Goberville E, Delebecq G, Destombe C, Valero M, Davoult D, Morin P, Gevaert F. Decline in kelp in West Europe and climate. PLoS ONE * e66044, doi:10.1371/journal.pone.0066044. 2013.
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