Seaweeds - of Helford and beyond

Algae are not only abundant in the seas but they have also colonised freshwaters as well as the land where species grow on soil as well as on hard substrate, even on trees. Many are single-celled and in water they may 'bloom' so prodigiously that their decaying remains can suffocate other sea-bed organisms.

A species of sloth owes its green colour to a single- celled alga living on its hairs, whilst the freshwater Hydra has a green alga actually living in its cells. Their universality, range and habitat indicate that they are very ancient.

The term 'seaweed' generally implies the multi-cellular species that clothe the surfaces of the rocky shore, each in their own ecological niche. Here they reflect the degree of exposure to wave and wind whilst the zones express the time they are exposed to air/water. Offshore, seaweed grows in water just as deep as light can penetrate.

Japweed
Sargassum muticum
© AAT
An introduced brown species found anchored
in sandy areas or attached to other weeds
and rocks often in sheltered
places such as rockpools

The following broad categories are usually easily recognised although there have to be exceptions to every rule! The groups are commonly known as the red (Rhodophyceae), green (Chlorophyceae), brown (Phaeophyceae) and the genus Vaucheria (Xanthophyceae). Many of the commoner species can be identified accurately without specialist knowledge.

A close look will show that each algal species tends to occupy a particular ecological niche on a shore and the presence of certain seaweeds, the width of zones and the position up the shore bears a close relationship to the topography, geology and aspect of a site.

As with all British fauna and flora, there are 'southern' species favoured by the warmer conditions in the south-west. Others have been introduced in recent times. Japweed (Sargassum muticum) is known to most of us, and another probable introduction is Anotrichium furcellatum, known only in the Helford River. The sheltered yet fully-marine nature of the River, combined with its large number of habitats, ensures that it has a large number of these rarer British species.

There are about 640 British species with an impressive 400+ species having been found in Cornwall and the Helford VMCA in particular - red 246 (H=148) , green 49 (H=30), brown 113 (H=61) and a few Xanthophyceae.

Various species of seaweed are used as food, extracted for gelling agents and medicine in many parts of the world. They are also used as soil-improvers and formerly kelp was burnt and the ash purified for glass making.

Coming attraction! Pamela and I are preparing an annotated check-list of the seaweed of Helford VMCA. All will be revealed!

Stella Turk

Extract from HVMCA newsletter No.28 Spring 2004