Welsh Journals

SOME STREAM INVERTEBRATES FROM SKOMER ISLAND, WALES D. DUDLEY WILLIAMS AND NANCY E. WILLIAMS A few collections of freshwater invertebrates were made from Iwo streams on Skomer Island, Dyfed, during June, 1974. Although these samples were not sufficiently large to enable definite conclusions to be drawn about the distribution and abundance of the fauna, record of those species found seems worthwhile. Skomer Island lies approximately 1 km due west of the southern tip of St. Brides Bay in what was the old county of Pembrokeshire. The streams examined, one near South Pond and the other near South Haven, were both mere trickles when visited and their features suggested that they may have been of a temporary nature. Samples were taken by disturbing the substrate and aquatic vegetation by hand and allowing the debris and animals to drift into a small 135 micron mesh hand net held downstream. We can find no previous data on the freshwater fauna of Skomer, although the nearby island of Skokholm (2 km due south) has been relatively well studied (see Davis, 1956). The following animals were TRICLADIDA: NEMATODA: OLIGOCHAETA: HIRUDINEA: MOLLUSCA: CLADOCERA: OSTRACODA: COPEPODA-CYCLOPOIDA: -HARPACTICOIDA: AMPHIPODA: ISOPODA: ACARI-ORIBATEI: INSECTA-COLLEMBOLA: TRICHOPTERA: COLEOPTERA: DIPTERA-CHIRONOMIDAE: found: Polycelis sp. (Unidentified) Nais elinguis Miiller Nais communis (variabilis?) Piguet Chaetogaster sp. Clitellio arenarius (Miiller) Enchytraeidae (unidentified) Helobdella stagnalis (Linn.)* Hydrobia ventrosa (Mont.) H. ulvae (Pennant) Alona rustica T. Scott Candona sp. Eucyclops agilis (Koch, Sars)* Bryocamptus pygmaeus (Sars)* Gammarus duebeni Lilljeborg* Asellus meridianus Racovitza* (unidentified) 2 species (unidentified) 2 species Plectrocnemia geniculata McLachlan* Limnephilus fuscicornis (Rambur) Wormaldia subnigra McLachlan Agabus melanocornis Zimmermann* Hydroporus sp.t Laccobius sp.t Micropsectra sp. Corynoneura scutellata Winn. Cardiocladius ? capucinus (Zett) Orthocladiinae (unidentified) 1 species