The Controversy Over Rockweed Harvest

Unharvested rockweed beds on Kent Island

Unharvested rockweed beds on Kent Island

The extensive rockweed beds that I have explored on Kent Island with Christine Walder, who is studying intertidal biodiversity, are also an economic resource that has caused controversy in the coastal communities where it proliferates. Harvesting rockweed is fundamentally different from the harvest of other marine species, because not only is it an important primary producer in the food web, but it also provides habitat for hundreds of species. By reducing the biomass of rockweed through harvest, countless other species are also reduced. Despite these ecological concerns, wild seaweed harvesting is a global industry that is growing every year, with millions of tons harvested for such varied uses as fertilizers, food additives, and cosmetics. Rockweed harvesting is a growing industry in Maine and in the Maritimes, which landed 88.1 million tons in 2010 (reviewed by Seeley and Schlesinger, 2012).

Regulations on rockweed harvest are different in Maine and Canada, and vary locally. In New Brunswick, Canada, private property rights only extend to the top of the intertidal zone, below which is open to public access. In Maine, however, waterfront property owners own everything down to the low tide mark. But Maine law provides public access to privately owned intertidal lands for the purposes of “fishing, fouling, and navigating.” The question is whether rockweed harvesting should be considered “fishing,” which is how the state currently defines harvesting.

In Canada, the federal government is responsible for managing rockweed resources through the Department of Fisheries and Oceans (DFO). However, DFO has signed a Memorandum of Understanding with the provinces of New Brunswick and Nova Scotia that delegates management authority to the provinces. These provincial governments have granted long-term harvesting leases to large companies that own the harvesting boats and equipment (Vandermeulen, 2013). In the United States, by contrast, the federal government is not involved in regulation, and until now, harvest has been largely owner operated. Maine is currently in the process of developing a management plan that resembles New Brunswick’s operation model, which favors vertically integrated harvesting companies. There are also different methods of rockweed harvest: hand-harvesting from boats is the typical method used in New Brunswick, while mechanical harvesting is used more widely in Maine (reviewed by Seeley and Schlesinger, 2012). Mechanical harvesting ensures a more uniform cutting height, but may cause more long-term damage to the rockweed holdfasts than hand harvesting (Seeley and Schlesinger, 2012). In both countries, there is no closed season for Rockweed harvest, but it is mostly cut in the early summer when the weather is better. Unfortunately, the Rockweed is at its reproductive peak in the summer, making the timing of the harvest a short-sighted management practice (Vandermeulen, 2013).

Uncut Rockweed on Kent Island, which can grow to 3m in length

Uncut Rockweed on Kent Island, which can grow to 3m in length

Rockweed cut to the 16'' harvest limit from one of Christine's experimental areas

Rockweed cut to the 16” harvest limit from one of Christine’s experimental areas

In New Brunswick, harvest is capped at 26 million pounds per year, and the regulatory guideline theoretically limits the industry to removing 17% of available rockweed biomass, which is based on the assumption that there is 50% regrowth in three years (reviewed by Seeley and Schlesinger, 2012). This harvest rate may not be sustainable in all areas, however, because rates of regrowth are dependent on many factors, and biomass can take anywhere from 3 to 11 years to recover. Furthermore, local patches of Rockweed are harvested at up to 50% of biomass (Ugarte et al, 2006), and a report from the Canadian Science Advisory Secretariat concluded that the present hand harvest rate is often between 20 and 30% in Nova Scotia, far above the 17% guideline (Vandermeulen, 2013).

Harvesting rockweed on a large scale would not only change the landscape of the intertidal, but it would also have ecological effects that could reverberate through the food web. As I have mentioned in previous posts, rockweed is the “old growth forest” of the intertidal, and provides vital habitat for hundreds of species. The rockweed industry claims that their harvesting operation is sustainable because the strands grow back, and are therefore a renewable resource that can be managed. This definition of sustainability is not what most ecologists would consider sustainability, because when rockweed is cut it no longer provides the same habitat for the species that depend on it. While rockweed may grow back at a faster rate after it is harvested, the regrowth is shorter and bushier than the uncut strands (reviewed by Seeley and Schlesinger, 2012). This fundamental alteration of the rockweed habitat structure will inevitably have ecological consequences, because of the high degree of interdependence of organisms in a food web.

Of particular concern is the impact of the rockweed harvest on Common Eiders. The Common Eider population has declined in the Bay of Fundy in recent years, (Ronconi and Wong 2003). The reason for this decline is not completely understood, but rockweed harvesting may play some role. Eiders feed in the Rockweed canopy, and the long Rockweed strands protect foraging Eider ducklings from predators. One study found that Rockweed clumps over 130 cm that are harvested are reduced up to 55% of their length and 78% of their biomass (Ugarte et al, 2006). The Rockweed strands on Kent Island can reach to three meters in length, and removing 78% of their biomass would make much less food available for Eiders. Reducing rockweed biomass and length that much would decrease cover for the eider ducklings, and would make much less food available. Shortening the rockweed will also force the eiders to dive more often and to greater depths for their food. Adult eiders are capable of diving, but it is energetically demanding, while young ducklings are incapable of diving for their food. Existing studies have found that rockweed harvested sites with a steep slope supported fewer Eider ducklings on Grand Manan, and harvested sites had fewer ducklings on mainland New Brunswick than did unharvested control sites (Blinn et al, 2008).

Studies have also shown indirect impacts of Rockweed harvesting on fish biomass and biodiversity, both of which are important to the health of the coastal ecosystem (Seeley and Schlesinger, 2012). Furthermore, rockweed is an important primary producer in intertidal ecosystems, therefore removing it could have a large long-term impact on commercial fisheries (Vandermeulen, 2013). Rockweed harvest is, in fact, highly contentious among lobstermen and fishermen because the algae provides habitat for juvenile lobster and herring.


Rockweed harvesting boats in Seal Cove, Grand Manan, an Island in the Canadian province of New Brunswick

The designs of many of the existing studies of these impacts of rockweed harvesting, including Christine’s, are based on the assumption that the rockweed cutting height is restricted to 16 inches, a limit that is in reality often surpassed (Seeley and Schlesinger, 2012). The danger of overharvest is a very real one, especially because the industry must remove large volumes of seaweed to make a profit, as rockweed is only valued at two cents a pound (Seeley and Schlesinger, 2012). There is already a history of rockweed overharvest, and areas were closed in Nova Scotia beginning in 1988 (Seeley and Schlesinger, 2012). Studies have shown that if beds are completely denuded, they are replaced by other seaweeds such as Chondrus and Fucus (Jenkins et al 2004), which don’t provide the habitat structure offered by rockweed, and overharvested areas may take years to recover back to an ecologically and commercially viable standing stock (Vandermeulen, 2013).

It is a common theme in environmental policy that science and management efforts lag behind natural resource exploitation, and Ecosystem-based Management (EBM) is rarely used or enforced until a collapse occurs. EBM is very difficult to implement because it requires a large amount of scientific data to support it, and often faces the additional hurdle of political opposition from resource user groups. As of now, government standards for Rockweed are not based on cumulative impact assessments that study the long-term effects of repeated cutting on a large scale (Maine Department of Marine Resources, 2011). The comprehensive stock assessments that inform regulations in Nova Scotia are at least twenty years old (Vandermeulen, 2013) and mostly small-scale experiments have been conducted to determine the ecological effects of harvesting.

Continued research on rockweed will help to fill in the gap in the scientific understanding of the relationship between rockweed structure and the productivity of intertidal ecosystems. The recent report from the Canadian Science Advisory Secretariat on assessment and management of marine “plants” in Nova Scotia (Vandermeulen 2013) recommended establishing areas that are closed to harvesting to be able to distinguish between the long-term ecological effects of harvesting and those of climate change. Without areas closed to harvesting for study, ecological change in the rockweed community may go entirely unnoticed. Rockweed is an integral part of a delicate ecosystem, and a fuller understanding of its function will inform policy that integrates ecology, which in the long run will benefit commercial as well as conservation endeavors.

Another perspective on the Rockweed controversy:


Blinn, B. M., V.Violette and A. W. Diamond. 2006. Osprey, Pandion haliaetus, depredates Common Eider, Somateria mollissima, duckling. Canadian Field-Natu- ralist 120(2): 236-237.

Jenkins, S., Norton, T., and Hawkins, S. 2004. Long term effects of Ascophyllum nodosum canopy removal on mid shore community structure. Journal of the Marine Biological Association of the United Kingdom, 84: 327-329.

Maine Department of Marine Resources. 2011. Rockweed: ecology, industry, management. Re- trieved February 1, 2012, from rm/rockweed/2011facts.pdf.

Ronconi, R. A. and S. N. P. Wong. 2003. Estimates of changes in seabird numbers in the Grand Manan archipelago, New Brunswick, Canada. Waterbirds 26(4): 462-472.

Seeley, R., and Schlesinger, W. 2012. Sustainable seaweed cutting? The rockweed (Ascophyllum nodosum) industry of Maine and the Maritime Provinces. Annals of the New York Academy of Sciences, 1249: 84-103.

Ugarte, R., Sharp, G., and Moore, B. 2006. Changes in the brown seaweed Ascophyllum nodosum (L.) Le Jol. Plant morphology and biomass produced by cutter rake harvests in southern New Brunswick, Canada. Journal of Applied Phycology, 18: 351-359.

Ugarte, R. & G.J. Sharp. 2011. Management and production of the brown algae Ascophyllum nodosum in the Canadian maritimes. J. Appl. Phycol. doi: 10.1007/s10811-011-9753- 5.

Vandermeulen, H. Information to Support Assessment of Stock Status of Commercially Harvested Species of Marine Plants in Nova Scotia: Irish Moss, Rockweed and Kelp. Canadian Science Advisory Secretariat (CSAS), Department of Fisheries and Oceans, Maritimes Region. 2013.


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