Freshwater invertebrates from the Bermuda Islands and their zoogeographical affinities

The Bermuda Islands lie in the western Atlantic Ocean with the closest main land being North Carolina, some 965 km to the west. The islands have underg one considerable change since permanent settlement around 1612 and this has affected their freshwater habitats which now are limited to small lakes (v ariously influenced by saltwater intrusion), ponds and drainage ditches. Al though there exist some patchy records of freshwater invertebrate taxa, goi ng as far back as 1859, there had been no single attempt to survey a variet y of habitat types across the islands. The latter was done in 1990-1992 and the results are reported here. Because of the proximity of many sites to t he coast, this survey reports some species with brackishwater tolerance, an d also, as in the case of the mites, species that were riparian in distribu tion. The samples revealed a total of 51 fresh/brackish water species, with 24 of these being recorded from the islands for the first time. Predominan t amongst this fauna were oligochaetes, gastropods, microcrustaceans, perac arids, odonates, corixids, hydrophilid beetles, and chironomid, ceratopogon id and ephydrid dipterans. Based on distributional records in the literatur e, it is concluded that these freshwater taxa have colonised the islands pr imarily from the southwest (from the Caribbean and Gulf of Mexico regions), likely carried by the prevailing northeasterly winds and the Gulf Stream. There are, however, other taxa whose sources must lie in the North American continent, particularly on its eastern seaboard. A single species, the bra ckishwater chironomid Halocladius stagnorum, seems to have colonised from s ource areas along the coast of the eastern Atlantic, possibly via ocean-goi ng vessels.