The Fresh and Brackish Waters of Bardsey Island (North Wales): A Chemical and Faunistic Survey

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Abstract
In several small ponds, temp., pH, alkali reserve, 0, silicates, phosphates, chlorides, Ca, and Mg were detd. Considerable variation occurred between ponds from the stable spring-fed ones to the fluctuating ones receiving their water from drainage. The effects of sea spray were usually marked. The fauna in these ponds and pools was not large, the chief noteworthy points being the occurrence of the brackish water Gammarus chevreuxi with truly freshwater forms absent; the occurrence of Asellus meridianus and not A. aquaticus; and the large number of Corixidae that occurred in the shallower ponds inland. Special attention towards a planarian, Procerodes (Gunda) ulvae, showed it to be most abundant in pools having a substratum consisting of moderate-sized stones resting on shingle. This species was sometimes found to tolerate rapid alternation between sea water and fresh water but was not limited to such conditions.