Algal zones on a very sheltered shore (Ballantine scale 7) between the two bridges on the Menai Strait, North Wales. August 2009.
Large tidal range, about 10 metres at extreme spring tides, so tidal zones are well defined.
1: as no waves or spray, terrestrial vascular plants grow to high water mark.
2: luxuriant Ascophyllum nodosum with large L. obtusata s.s.
3: Fucus vesiculosus and Ascophyllum nodosum intermingled. For initial experience, avoid sampling in this zone, and where it adjoins other zones, as L. obtusata and L. fabalis may be intermingled.
4: abundant Fucus serratus with small L. fabalis.
5: abundant Laminaria digitata.
Menai seawater carries much sediment, but in many places the strong current keeps algae free of deposits that can smother them or disrupt feeding by molluscs. At a few locations, the impact on rocks directly facing the current stunts or prevents algal growth, so there will be few or no Littorina obtustata s.l., see image 48Dof 48 Differentiation L. obtusata/L. fabalis
Full account at: 02 Differentiation L. obtusata/L. fabalis

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