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The Seashore

Spiral or Twisted Wrack (Fucus spiralis)

The Spiral Wrack

The Spiral Wrack grows up to 35 cm. Usually the frond is spiralled or twisted although that is not always obvious. However, when mature the swollen tips of the fronds are rounded and almost like a bunch of grapes. These are the receptacles (reproductive structures). Along the olive-green/yellow fronds are smooth edged, not serrated (as in F. serratus) and lack bladders. Considerable hybridisation occurs between Fucus making identification on some shores difficult.

The upper shore is a hazardous place for marine algae. Prolonged emersion exposes the seaweed to desiccation, temperature stress and reduced nutrient supply. Adaptations include: the spiralling of the frond to trap water and slow down evaporation, although not as effective as Pelvetia; they have thick cell walls although not as thick as Pelvetia and they lack the oiliness; hence, the slightly lower level on the seashore. However, the growth is more rapid than Pelvetia and where overlap between the two occurs, Fucus will shade out the latter and dominate. Spiral Wrack shows better stress-tolerance than other wracks found further down shore. Like Pelvetia, this plant is also hermaphrodite. No other species of Fucus is. The frond shows variation in its shape from one shore type to another and will be greatly affected by salinity fluctuations and wave action. It hybridises (crosses) with F.vesiculosus under certain conditions e.g. low salinity. Specimens at the bottom of the zone are less able to tolerate stress. This is due to individuals adapting (acclimatising) to the stresses over a period of weeks. This is not genetic and is similar to drought hardening found in flowering plants.

The niche has some slight overlap with Pelvetia, although found to a lower level within the upper rocky seashore. Found around the Atlantic shores, in the English Channel and up into the North Sea.


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