Forgive the dramatic title but I'm increasingly convinced that grazing by herbivorous snails is an essential mechanism in the promotion of coralline algaes over the lower green algaes like hair algae and Enteromorpha.
Enteromorpha quickly grows over all surfaces and coralline algaes are unable to compete. A week ago I boosted the number of herbivorous periwinkles and topshells in my tank by about 400%. Adding another 60 or 70. I had noted that in areas of strong coralline algal growth, especially in Kimmeridge Bay the number of snails per square metre was very high, approx 40 - 50.
In a week almost all surfaces previously colonised by Enteromorpha have been grazed bare and in its place new corroline algae, both branching and encrusting has flourished. Furthermore new wrack growth has been noted on previous areas that had appeared devoid of anything but hair algae.
It would be interesting to be able to create a snail-proof 'cage' in a Kimmeridge rockpool and see if Enteromorpha takes over when the heavy grazing is stopped from occuring.
In the British reef aquaria, therefore, snails can be used to naturally create the conditions for coralline algae to flourish. As an added bonus I never need to clean the glass! Interestingly coralline algae growth seems restricted to rocks, shells etc. unlike in tropical tanks where encrusting growths quickly cover pumps and glass. perhaps British winkles and topshells are also able to feed on coralline algae on very smooth surfaces? The commonly used Turbo snails used in tropical aquaria may simply not feed on coralline algaes?
I am convinced that its not enough simply to mimic sea temperature, natural light levels, salinity and chemistry to promote corraline algae. Grazing appears to be an important factor. The conversion of green algae to soluble excreted snail waste for the skimmer is also an excellent nitrate and phosphate exporter whilst releasing minerals back into the water for use by higher and more desirable algaes.