STREAM MACROINVERTEBRATE COMMUNITIES IN THE ISLAND OF TENERIFE

Macroinvertebrate communities in seven Tenerife streams were investiga ted in spring and autumn 1991. AU Tenerife streams are small and run f or limited distances. Six of the study streams represent a majority of the permanent streams in Tenerife, the seventh being seasonal. A tota l of 127 taxa were identified. Species richness ranged between 34 and 74, and there was a threee-fold difference in abundance between the ri chest and poorest sites. The lowest richness value was found at a laur el forest stream site and the highest at an exposed, low elevation (19 0 m a.s.l.) site. In a partial least square regression analysis, pool size, algae, pH, and temperature were factors that influenced species richness positively. Altitude had a negative influence. The two orders richest in species in all streams were Diptera followed by Coleoptera . Only nine taxa were common to all streams, viz. the gastropod Ancylu s striatum, the oligochaete Eiseniella tetraedra, the dytiscid beetles Nebrioporus canariensis, Agabus biguttatus, and Laccobius canariensis , and the dipterans Dixa tetrica, Simulium tenerificum, Zavrelimyia nu bila and Thienemanniella ?clavicornis. Another 14 species occurred in six streams. In spring, the overall most numerous taxa were Hydroptila sp. (Trichoptera), Baetis canariensis (Ephemeroptera), and Orthocladi inae (Diptera), and in autumn, the dipterans Simulium ruficorne and Ta nytarsini. Some taxa occurred in a clear seasonal pattern whereas othe rs did not. About half of all taxa could be characterized as habitat s pecialists defined as those in which > 90 % of all individuals were fo und in either pool or riffle habitats. All stream sites contained uniq ue taxa that were not found at other sites. Each stream site also show ed major individual differences in the composition of functional feedi ng groups stressing the individuality of the different streams. The re sults are discussed in the light of threatening habitat loss for strea m-living animals in Tenerife.