The effect of water level fluctuations on a littoral fauna

The littoral fauna of Llyn Tegid, North Wales, in 1968/9 is compared with the results of similar faunal investigations made by Rothwell(née Dunn) in 1951/2 (Dunn, 1953) and Hynes in 1957 and 1959 (Hynes, 1961). The results show the long term effects upon the littoral fauna of the change in mean water level and the increased water level fluctuations produced for a time by the controlled outflow scheme, which came into operation in 1955. In 1961 Hynes recorded big reductions in numbers and variety of invertebrates living in the littoral zone. The reduced water level fluctuations in recent years has resulted in a re‐establishment of some of the fauna.