Macrocystis pyrifera (Linnaeus) C.Agardh (BC)

Yet another charismatic kelp species in our BC flora, Macrocystis pyrifera cannot be confused with anything else when mature (Image A), whereas juveniles lack the distinguishing features (Image B). Individuals start off as simple blades with a stipe and holdfast (Image B) in which dichotomous ontogenic splitting of the transition zone (junction of the stipe and blade; Image C) establishes frond initials. The latter undergo a series of unilateral divisions to form the apical scimitar (Image D), which grows rapidly to produce the long fronds characterized by their stipe and multiple vegetative blades each subtended by a pneumatocyst (gas filled sac; Image A) buoying the fronds to the surface.

There were once thought to be two species along the Pacific coast. They were distinguished in part by habitat and a strap-like (‘integrifolia‘-type; Image E) versus mound-like (‘pyrifera‘-type; Image F) holdfast. We now know that there is a genetic difference associated with these two morphologies, but it is a population rather than species level distinction. Whereas the strap-like holdfast is widely distributed in coastal waters throughout this species’ range, including in BC, the mound-like holdfast is associated with exposed offshore populations in California. However, we also find the latter in subtidal and intertidal populations at some locations in Hadia Gwaii, which has led to some interesting biogeographical speculation (see Saunders 2014).

Macrocystis integrifolia is one of two major canopy forming species in the BC flora, the other being Nereocystis luetkeana (K.Mertens) Postels & Ruprecht. Individuals are distributed from the low intertidal to subtidal where they reportedly reach up to 30 m in height in our waters.

Image A. Mature Macrocystis pyrifera left high and dry on a low tide at Blackburn Point, Gwaii Haanas; BC (EGWS000231).

Image B. Juvenile individual lacking the distinguishing features of this species (low intertidal on rock, Haswell Bay, Gwaii Haanas, BC; GWS028246).

Image C. Juvenile initiating the dichotomous ontogenic blade splitting observed in this species (low intertidal on rock, Seppings I., Bamfield, BC; GWS003990).

Image D. Close up of the apical scimitar from which the long fronds develop (low intertidal on rock, Tahsis, BC; GWS006687).

Image E. Strap-like ‘integrifolia‘ holdfast typical to this species in BC (low intertidal on rock, Newberry Cove, Gwaii Haanas, BC; GWS038344).

Image F. Mound-like ‘pyrifera‘ holdfast typical to offshore populations in California, but also recorded in both subtidal and intertidal populations at some locations in Haida Gwaii (low intertidal on rock, Newberry Cove, Gwaii Haanas, BC; GWS038372).