Strong current striking rocks of very sheltered shore on the Menai Strait, North Wales. .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 are few or no Littorina obtusata and Littorina fabilis.
August 2009
Full account at: 02 Differentiation L. obtusata/L. fabalis

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