Costaria costata (C.Agardh) De A.Saunders (BC)

Another distinctive kelp species in the BC flora distinguished by its namesake ribs, five in total running the length of the blade (Image A; three are formed on one surface separated by two ribs on the opposing surface). Costaria is a simple kelp consisting of a hapteral holdfast, stipe, and a single undivided blade (Image B). In sheltered habitats the blades are wide and highly bullate adding to the distinctive appearance of this species in such habitats (Image C). In contrast, individuals at exposed sites have long strap-like blades that have reduced bullatation and at times rows of perforations between the ribs (Image D).

We have verified records from throughout BC, literally from southern Vancouver Island to the northern coast of Haida Gwaii. It is a conspicuous element of the low intertidal flora extending well into the subtidal (our deepest collection is from 20 m at Kloo Rock, Gwaii Haanas, but it extends deeper).

As a totally random bit of trivia, De Alton Saunders may be my ninth cousin twice removed. We have a possible link through one John Saunders of Agmondesham, Buckinghamshire (1535-1615). Small world and or seaweed is in the family genes.

Image A. Specimen in the low intertidal on rock at Botany Beach, BC. The five ribs are evident and set this species apart from others in the BC flora (GWS004441).

Image B. Pressed specimen showing the hapteral holdfast, stipe and costate (ribbed) blade (subtidal (8 m) on rock, Sooke, BC; GWS006351).

Image C. Individual from a sheltered habitat with a wide bullate blade (low intertidal on rock, Murchison Island Lagoon, Gwaii Haanas, BC (GWS013374).

Image D. Individual from an exposed habitat with a narrow strap-like blade and reduced bullation (mid intertidal on rock, Raft Cove, Vancouver Island, BC; GWS004712).