Seaweed beds: Gardens or sea prairies?

Wakame, nori, kombu, arame, hijiki – words from the Land of the Rising Sun, where consumption of seaweed is part of day-to-day living. In Japan, but in Korea and China as well, seaweed is served as vegetable side dishes, in salads, as a condiment, in soups and for rolling those famous sushi maki. In fact, it’s the popularity of sushi restaurants that led to the discovery of seaweed’s many possibilities as food.

Inhabitants of Celtic and Scandinavian regions have also included certain seaweeds – dulse (Palmaria palmata) and Irish moss (Chondrus crispus) – in their diets, thus contributing to the enrichment of the global phycogastronomic experience. That tradition crossed the ocean with Irish immigration and took root locally in the Atlantic.

Macroalgae, microalgae and phytoplankton

What is seaweed? For most people, any aquatic plant is “seaweed.” But that’s a misnomer. A number of flowering plants have adapted to aquatic life, even to marine habitats (eelgrass and glasswort, for example). But seaweeds have neither flowers nor roots, nor even true leaves. In addition, numerous seaweeds are unicellular (microalgae), and several species belong to the world of plankton, an essential basis of ocean ecosystems.

Macroalgae (or seaweed, in plain language), meanwhile, are much bigger. Immense forests of giant kelp (Macrocystis pyrifera) that are over 60 meters long can be found on the western coastline of the Americas. Seaweed forests on the Atlantic side are more modest, with the kelp normally reaching no more than two or three meters in length.

Seaweed and rocky seashores

Rocky seashores are the realm of seaweed. The reason for that is very simple: the seashore is an extremely rich environment, and the constant water movement produced by waves and tides generates an abundant circulation of nutrients. On the other hand, that agitation obliges any organism living thereabouts to fasten itself securely. Seaweed does not possess roots that would enable it to secure itself in soft sediments like mud or sand. However, they do possess holdfasts that literally glue them to coastal rocks.

Seaweeds are plants, and can therefore not inhabit great depths, where light doesn’t penetrate sufficiently to allow for photosynthesis. That’s what defines the lower limit of the littoral zone. In the Gulf of St. Lawrence, seaweed does not take up residence at depths of greater than 20 meters. Beyond that lies the realm of the sea anemones and other filter-feeding animals.

Seaweed fields: more than a garden, an ecosystem!

Seaweed forests thus make up true ecosystems that play a highly important role in the oceans. Numerous species find refuge and food there. Some researchers even claim that seaweed fields may contribute to carbon sequestration.

Like all plants, seaweed transform CO² into oxygen, by incorporating carbon into their cells. In doing so they curb the acidification of coastal waters and participate in their oxygenation. It’s therefore highly beneficial to combine seaweed and mussel production, as the seaweed captures in situ the carbon released by the mollusks. What happens is, when it dissolves, CO² makes water more acid and hinders the production of those bivalves’ shells.

Besides carbon, seaweed can integrate the nitrates and phosphates released by the animals into their proteins.

It’s this same principle that Nathalie-R. Le François, Ph.D., a researcher at the Biodôme, wants to use to clean the Gulf of St. Lawrence basins there.

Moreover this living addition would make it possible to draw attention to the crucial role played by seaweed on the rocky shoreline and in the ocean.

To learn more

• Les Algues de A à Z. Carole Dougoud Chavannes. Jouvence éditions, 2013
• Plantes sauvages du bord de mer. Fleurbec, 1985
• Algues et faune du littoral du Saint-Laurent maritime. Robert Rossignol et Anne Rossignol. Institut des sciences de la mer de Rimouski and Fisheries and Oceans Canada, 2003
• Seaweeds: Edible, Available, and Sustainable. Ole G. Mouritsen. University Of Chicago Press, 2013 - Translated from the Danish (2009)
• http://seaweed.ie
• Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation? (Duarte et al., 2017)
  http://journal.frontiersin.org/article/10.3389/fmars.2017.00100/full

Read also:

The unexpected spin-offs associated to seaweed culture at the Biodôme