The growth of epiphytes (plant and animal) was investigated at various stages in the development of the low littoral alga Himanthalia elongate. The vegetative thallus, or button, is very resistant to the settlement of epiphytes on its upper surface, but susceptible to extensive coverage on its lower surface and stalk, especially by Bryozoa and spirorbid worms. The receptacles or straps are invaded by a microforest of filamentous algae, which in turn provides accommondation and in many cases food for many invertebrates, including gastropods, amphipods and larval Diptera. Spirorbid worms on the underbuttons are confined to sites sheltered from strong water currents and wave action, but other epiphytes of the underbuttons show little regard for these features. Microfores and its associated fauna are restricted to sheltered sites. Perspex discs set up as imitation Himanthalia buttons were colonized by the same epiphytes as real Himanthalia buttons, but on both sides, indicating the existence of a special protective mechanism for the upper surfaces of real Himanthalia buttons. |
