From Plant Press, Vol. 20, No. 4, October 2017.
The coastal waters of Maine have seen a considerable rise in summer temperature during the last decade, and there is concern for the future of many coastal fisheries, including seaweed harvest. Along the immediate coast, seaweeds are the major supplier of primary productivity to the marine ecosystem. They also provide the major element of community structure, and are potentially the best indicators of long-term changes resulting from climate change.
During the early 1960s, Walter Adey developed an extensive and quantitative area cover database in the Gulf of Maine for the calcified and long-lived coralline red algae. This was followed up by similar research into the Arctic and across the entire North Atlantic. From 1990 to 2007, he extended his work to all fleshy seaweeds using biomass. This summer, from June 15 to September 22, 2017, Adey revisited the stations of this unique database in the eastern Gulf of Maine to develop comparative data and to examine changes underway in the region.
Joining Adey on his field trip were scientists Matthew Suskiewicz, doctoral student from Laval University in Quebec, Canada, and Douglas Rasher from the Bigelow Laboratory for Ocean Sciences in Boothbay Harbor, Maine. They utilized the 64-foot research vessel Alca i with Adey as the chief scientist and captain. Several of Adey’s former and current university students and post-docs assisted the project as official Smithsonian volunteers. Sue Lutz served as senior technician.
Preliminary results are currently being analyzed. Earlier research had shown that two cold-water indicator species, the corallines Clathromorphum compactum and Lithophyllum orbiculatum, are abundant in the colder eastern part of the Gulf of Maine. A combined analysis from the 1960s to 2017 of both species at 12 stations shows a mean drop in cover of 39 percent of total cover. In addition, 11 of 12 stations showed a drop in cover, with only a single station showing a slight rise.
Seaweed biomass in waters 10-20m deep on the outer Maine coast between 1995-2007 were highly dominated by three Subarctic species: the kelp Agarum clathratum (canopy), the red Ptilota serrata (understory), and red Euthora cristata (epiphytic). In the 2017 collections there was almost no algal biomass at 20m. At 10m, all three dominant seaweeds occurred only as very small plants or fragments. It appears that in the roughly ten-year interval between surveys, the deeper water Subarctic component of the seaweed community was radically reduced.
Several key invertebrate species (especially the keystone Subarctic species Strongylocentrotus drobachiensis, the green sea urchin, and Asterias vulgaris, the northern sea star), abundant in early surveys, were essentially absent. Crab species from southern waters and barnacles had taken their place. The barnacle abundance is especially interesting in that the research team can quantitatively demonstrate changes using the abundant collections of rocks bearing corallines in the U.S. National Herbarium. The great abundance of barnacles, competitors for space with the corallines, as compared to their absence in earlier collections, could be due to the presence of greater plankton populations (on which the barnacles feed), due to increasing nutrients, or the absence of a Subarctic predator.
The research team has uncovered significant changes (temperature, turbidity, nutrients, seaweed populations, and invertebrate populations) in the Gulf of Maine during the past decade, and these have serious implications for benthic community structure and for human coastal communities. In-depth analysis of data obtained during this summer’s cruise is required to sort out the role of each factor. Clearly rising seawater temperatures is a major factor, and a great reduction in the previously important Subarctic component of benthic community structure is the most striking result.
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