I often get asked questions along these lines. Typically I throw out a number of 1000 species, and try to avoid discussions regarding endemics. However, my former student Amanda Savoie, now at the Canadian Museum of Nature, sent a note last evening asking for some thoughts on such issues as she too is now receiving these questions. So I decided to put a little energy into the queries for a change.
To get an idea of the number of species, I went through our database at UNB to count the number of ‘species’ for our ~24800 Canadian specimens (not all have been genetically studied). The results were actually close to my typical response of 1000 coming in at ~900 species (all values are quick tallies).
This is of course an underestimate as there are many microscopic epi and endophytic species for which representation in our database will be moderate (low?). We also have a sweet spot in the lab for red algae, which are by far our best studied group. However, I would contend that these values are reasonable estimates in that reds are by far the most diverse group in the Canadian, and indeed many floras.
To the question, are there endemics? Absolutely! We have endemics in all three of our oceans. As an example from each, we have Waernia sp. 2GH in Haida Gwaii (northern British Columbia), Torngatum varicrassum G.W.Saunders in the Arctic, and Porphyra corallicola H.Kucera & G.W.Saunders in the Bay of Fundy, New Brunswick. But are any of these truly endemic?
Firstly, the previous examples are all easily overlooked – only an expert specifically trying to collect them would even have a shot at finding each. Secondly, there are no barriers to dispersal – our three ocean floras are essentially continuous with adjacent waters of the United States and nearby Greenland (I’m intentionally ignoring the islands of St. Pierre and Miquelon off the coast of Newfoundland, which are literally part of France). Consequently, sampling artifact likely contributes more to Canadian seaweed ‘endemism’ than actual endemism.
Consider for example that we have ~7700 collections from Haida Gwaii (Waernia sp. 2GH only one collection), ~1600 from the Canadian Arctic of which ~450 are from Labrador (Torngatum varicrassum G.W.Saunders type and only collection) and ~4500 collections from the Bay of Fundy (Porphyra corallicola H.Kucera & G.W.Saunders type and only collection). I think we can be confident that the respective adjacent waters of southern Alaska, western Greenland and northern Maine are not so intensely sampled with genetic tools. With time, I expect that our Canadian endemic species will be found in these adjacent waters. As a case in point; when we first described Saccharina druehlii G.W.Saunders & McDevit (currently Hedophyllum druehlii (G.W.Saunders & McDevit) Starko, S.C.Lindstrom & Martone) it was only known in Gwaii Haanas and thus a Canadian endemic. However, continued surveys by other researchers not surprisingly extended this range to Alaska (Starko et al. 2018). If we are still making discoveries for things like kelp, then it is highly likely that the less charismatic species are far more widely distributed than currently recorded.
I would speculate that there are two regions in Canada that could harbour endemic species as they both differ in abiotic factors from adjacent waters. These are the Gulf of Saint Lawrence (if we again ignore the French Islands of St. Pierre and Miquelon, which border this region) and Hudson Bay. For the latter we have indeed found uncharacterized endemic species. However, we have collected ~860 specimens there, considerably more than adjacent Arctic waters. So all bets are off, there is plenty of coastline out there. For example, we had only rare collections of Phycodrys sp. 1NB largely from the Bay of Fundy until we went to Norway where this species was common (Bringloe et al. 2019b). Similarly, Platysiphon glacialis (Rosenvinge) K.Kawai & T.Hanyuda was only known from the Eastern Canadian High Arctic and nearby Greenland, but then we collected in Nome, Alaska, where this species dominated some habitats (Bringloe & Saunders 2019a). Consequently the notion of endemism has to be placed in the context of sampling effort, and not only for the Canadian flora, but also sampling effort of adjacent waters and beyond.
Seaweed of Canada 