Costaria ( latin= rib) is a brown handsome kelp often growing with Laminaria sp.. It is found around the Race Rocks shallow sub-tidal area. Costaria‘s blade is up to 2 m long and it has five midribs running its length, three on one side and two on the other. The midribs are concave on the bottom. The blade tissue, sitting between the ribs, is elaborately contorted into a system of ridges and valleys. Costaria costata is an annual. distributed from Alaska to southern California in the low intertidal and upper sub-tidal regions.This brown algae displays a range of shapes, reflecting the degree of wave exposure it encounters. In wave-exposed sites the plants are narrow and thick. their stipes are ridged and a series of regular perforations run the length of the blade. Wave-sheltered plants are broad and thin, having smooth stipes and no perforations. Transplant studies have shown these differences in morphology to be environmentally induced. For example, a plant moved from a wave-exposed locality to a sheltered are will produce new blade tissue characteristics of wave-sheltered plants. this morphological response to environmental differences is called phenotypic plasticity. In sheltered waters the blade is long and narrow while in surf waters it grows in a big, wrinkled egg shape.

Classification
Domain: Eyukarya
Kingdom: Protochtista
Division: Phaeophyta
Class: Phaeophyaceae
Order: Laminariales
Family: Laminariaceae
Genus: Costaria
Species: costata
Common Name: five- rib kelp
References:
Druehl,Luis. “Pacific Seaweeds”,Harbour, Canada, 2000

Other Phaeophytes or Brown Algae at Race Rocks

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The Race Rocks taxonomy is a collaborative venture originally started with the Biology and Environmental Systems students of Lester Pearson College UWC. It now also has contributions added by Faculty, Staff, Volunteers and Observers on the remote control webcams. Jana Morehouse  PC 2002