Aquascope Facts
Cliff and rocky beach ecology

Protection against grazing

Idotea balthica grazing
Isopods (Idotea spp., approx. 3 cm long) are one of the few animals that are able to eat fresh algae.

For certain crustaceans (e.g. rock lice), shelfish (e.g. Blue-rayed limpet) and sea-urchins (e.g. Psammechinus miliaris), algae is an important food source.
    Because grazing can injure algae, it is natural that they try to protect themselves. This is made possible by the tissues storing hard and distasteful calcium. This type of protection is utilized by encrusting red alga and the coral alga, Corallina officinalis.
    The body form of the alga is also a factor that effects how easy they are to eat.
The large amount of calcium in coral alga makes it hard and distasteful. These plants are about 10 cm high.

It can, for example, be difficult to eat tufts that are short and thread-like. Another form of protection is to use unpleasant or poisonous chemicals. There are specie that contain one or more of the following chemicals for protective use: sulphuric acid, alkaloid, phenol or chlorine, bromine and iodine compounds.
Spongomorpha´s grazing protection 17 kB
A certain amount of protection is achieved against grazers with a dense thread-like growth, as with Spongomorpha spp.
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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson