Macroinvertebrate frequency data for the RIVPACS III sites in Northern Ireland and some comparisons with equivalent data for Great Britain

1. A total of 313 macroinvertebrate taxa were recorded from the 70 running- water sites in the River (I) under barn (V) under bar ertebrate (P) under b ar rediction (A) under bar nd (C) under bar lassification (S) under bar yst em (RIVPACS III) dataset for Northern Ireland, after the application of a s tandardization procedure to ensure that all samples were identified to the same taxonomic level. The listing includes a small number of oligochaetes n ot previously reported from Ireland. The frequency of occurrence of the 313 taxa within the Northern Ireland dataset is also presented. 2. The taxonomic composition and frequency of occurrence of taxa in the Nor thern Ireland dataset were then compared with the 614 site dataset for Grea t Britain, which included 637 taxa, and a 75 site subset within Britain at a similar latitude to Northern Ireland with 333 taxa. 3. The macroinvertebrate fauna of Northern Ireland is dominated by taxa rec orded at the highest frequencies of occurrence in Britain. Some notable abs ences are highlighted and, in particular, a small number of lotic mayflies and stoneflies which are common in Great Britain. There is documentary evid ence of the introduction by man of a number of non-insect taxa, either deli berately or by accident. 4. A detailed knowledge of the present composition of the macroinvertebrate fauna of running-water sites in Northern Ireland, and an active research p rogramme on the potential for new colonists to pose a threat to native spec ies, are important factors in the future conservation of the freshwater fau na. Copyright (C) 2000 John Wiley & Sons, Ltd.