Fucus serratus (Serrated wrack, Toothed wrack, Saw wrack, Black wrack)
Serrated wrack grows in profusion in the lower part of the mid-littoral zone, parallel and below F. vesiculosus, but higher than the Laminarias. It battles for space with the Ascophyllum nodosum and Bladderwrack, but once established, can dominate the rocks on the lowest shore. At low tide, you can find it in dense sweeps over the rocks and reefs, blanketing them in dark olive-brown fronds with discernible jagged edges. Serrated wrack does not have air vesicles (bladders), rather, it is much more bilateral than Bladderwrack; flat, branching dichotomously from a clear mid-rib. It is shorter too, (only growing to about 80cm long) and so likes to colonise rocks as high up as possible at the lowest shore line so that it will not dry out too much.
F. serratus have both male and female plants (unlike the other Fucoids). In the late summer, the female plants develop pointed crab-claw shaped tips that holds its tiny reproductive bodies (looking like little pustules) in the last 2cms of the plant. These tips tend to turn a deep amber-orange and get very slimy to the touch as they come to fruition. Evidently these female gamates also produce pheromones, called fucoseratin, to attract the male.
The darkness of Serrated wrack’s colouring comes from the additional pigmentation that many of the Fucoids share which helps them to absorb a greater amount of light at the deeper depths. When growing in thick dense colonies, it also give a multitude of epiphytes and epizootics (such as worms) a perfect environment, providing access to the ebb and flow of nutrient-rich tides, a sturdy holdfast, and good coverage to keep them relatively wet when exposed to air. In and around the fucus clusters, shelter is also created for other mobile species such as sea squirts, sea mats and little periwinkles.
Serrated wrack grows all along the Atlantic coast of Europe, from Portugal to Norway, across to Iceland, and down to Maine on America’s north-east frontier. It contains the same constituents as Bladderwrack, and so has been used for similar purposes. In Norway it is used to feed cattle or pigs (where it is sometimes known as “Swine-tang”); in Finland and Sweden it has been used to cover cottages, or for fuel; in Ireland, France and Italy it is used in cosmetics (eye serums, moisturisers, shampoos, lotions, etc) and in therapeutic “sea baths” due to its high oil levels; here in Scotland we are more prosaic and make it into a liquid fertiliser. However, in addition to having excellent skin conditioning and hydrating effects it, like both Bladderwrack and Knotted wrack, also contains a huge amount of minerals and vitamins and so holds hope for use as a thyroid stimulant and for its estrogenic properties.
Serrated wrack should be harvested mid-summer, (cut about 15 – 25cms above the holdfast so that it can regenerate) and can be used fresh to steam fish and seafood, or dried for culinary use in soups and stews and tea.