Description of [Sertularia cupressina] and [Hydrallmania falcata] on tide-swept sublittoral sand with cobbles or pebbles
Shallow sands with cobbles and pebbles, exposed to strong tidal streams, with conspicuous colonies of hydroids, particularly Hydrallmania falcata and to a lesser extent Sertularia cupressina and S. argentea. These hydroids are tolerant to periodic submergence and scour by sand. Both diving and dredge surveys will easily record this biotope. Flustra foliacea, Balanus crenatus and Alcyonidium diaphanum may also occur on the more stable cobbles and pebbles, with Urticina felina and occasional Lanice conchilega present in the sand. Infaunal components of the other biotopes in the A5.1 or A5.2 complex may occur in this biotope as may elements of the 'Venus' associations; indeed, this biotope may be at one extreme of the spectrum of such associations (E.I.S. Rees pers. comm. 1997) and this biotope may be best considered an epibiotic overlay.