Native marine aquaria are pretty scarce. Little information exists on how to be successful in maintaining healthy coldwater marine systems in domestic aquaria.

Hopefully this record of my failures, triumphs and ideas will assist others interested in keeping some of our fascinating, beautiful and often little known sea denizens in aquariums.

Sunday, 5 September 2010

The Importance of Snails

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.


  1. Your ideas, Gary, about the snail grazing as a tool to remove competitive Ulva species (U. intestinalis & linza) so allowing the less competitive Coralline algae to grow is an excellent one. Leave your idea of an experiment in the sea (too risky - the snail-proof cages would probably we swept away!!!) aside - what about simply doing it in your tank. A couple of those little fish breeder cages, that are readily available, put in the corner of your tank might do, one with and the other without periwinkles in it, should solve the grazing question!

  2. Like you Gary, I have used snails to reduce slime or filamentous algae from rocks or walls of tank (however, unlike you I didn't think of the possibility that snails may play an important role on the composition of macroalgal species. However I have found, as you have, that the periwinkles can be quite destructive as they happily seem to go for macroalgae too. According to the Collins pocket guide to the seashore (page 182), topshells (Gibbula species) graze rocky surfaces, feeding on microalgae and detritus". So, with the aim of limiting plant damage in the tank, I have now started to use these (topshells) to get rid of the brown or green slime/fuzz/filaments that seems to grow in an uncontrolled way if not checked.

    Interesting to hear that the hornwrack is thriving. I haven't found this one growing on the shore at Hastings but there is always the hope that seawater will bring in a few spores of some of the more interesting species to the tank where, again hopefully, they will germinate.

  3. I've spent the last week closely watching the eating habits of the 2 main snail species and rather surprisingly its the topshells which appear to be the more voracious grazers of macroalgae. They are more 'agile' than periwinkles and travel to the very ends of the plants to get the freshest shoots.

    No periwinkles have been noted on the long 'branches' of Cystoceira which a week ago were sporting the most attractive bright turquoise new shoots. Topshells were swift to exploit this food source and few shoots remain. Some Cystoceira branches are now completely bare!

    I'll be interested to see how you get on with them in your aquarium Mike.