the Shore Using Wrack Species
zoning only remains true for moderately exposed rocky shores.
grows here has to be able to withstand long periods of drying out
as it is only covered by the tides for a short time. The two species
that fit this niche are Channelled Wrack, Pelvetia canaliculata,
and the Spiral Wrack, Fucus spiralis. The channelled wrack colonises
higher up the shore than the spiral wrack. The channelled wrack
will completely dry out on hot summer days appearing dead but springs
back when wetted by the tide.
wrack Fucus vesiculosus is the dominant seaweed in this zone. Knotted
wrack Ascophyllum nodosum may be found in this zone and can form
extensive beds. The proportion of both species sharing this zone
depends on the degree of exposure, the more exposed the beach the higher
the proportion of Bladder-wrack. Both of these seaweeds may
be replaced where there is a flow of fresh water by the brackish
tolerant horned wrack Fucus ceranoides.
exposed shores the bladder wrack can be found in the form Fucus
vesiculosus linearis. This is a bladderless stunted form that
is badly worn from severe wave action. The lamina may be worn away
leaving only the mid rib and even when the plant does grow back
it may lead to a distorted form.
serrated or toothed wrack, Fucus serratus, colonises the lower part
of the shore.
of Identification Between Species of Wrack
the plants are heavily exposed to the elements the dichotomous branching
will not be seen. The fronds wear away and when they grow back they
can produce asymmetrical branching.
between the species produce hybrid forms which are difficult to
identify unless an expert.
heavily exposed shores species may only be there as a specific
form as in the case of Bladderwrack with its bladderless variety
Fucus vesiculosus linearis.