Warming oceans threaten commercially harvested seaweeds in Atlantic Canada

Increased ocean temperatures can cause changes in species’ distributions, particularly for those species already living in waters that are warmer than what is optimal for their growth and reproduction. In our study, we asked how future increases in ocean water temperatures might affect the distribution of commercially important seaweeds that grow in waters off the coast of eastern Canada and the northeastern United States.

We focused on rockweed, serrated wrack, knotted wrack, carrageen moss, and three species of kelp. For each seaweed species, we determined the range of ocean temperatures (south of the frozen Arctic Ocean) where it presently grows. We then used the projections of future sea surface temperatures for the year 2100 produced by four global climate models to estimate where these temperatures would occur.

Our analysis included the most favorable model projection (change in average global air temperature would be less than 2.6°C) and the direst projection (change in average global air temperature could be greater than 4°C). Particularly sensitive areas are the southern Gulf of St. Lawrence and waters around Capes Cod and Hatteras.

Some models indicate that even at the lower temperature all species except rockweed are threatened on the southern Gulf of St. Lawrence. With greater increases in temperature, the areas of loss increase and become more certain. The loss of area of these seaweed populations will have significant ecological and economic effects including impacts on commercial fisheries and harvest rates, losses of biodiversity, and abundance of species. These changes in distribution should be considered in future management of harvests and the designation of marine protected areas to include future ranges of the seaweeds.

Read the full paper — The effect of global climate change on the future distribution of economically important macroalgae (seaweeds) in the northwest Atlantic by Amina H. Khan, Elisabeth Levac, Lou Van Guelphen, Gerhard Pohle and Gail L. Chmura on the FACETS website.