SPHAGNUM MOSSES AS A MICROHABITAT FOR INVERTEBRATES IN ACIDIFIED LAKES AND THE COLOR ADAPTATION AND SUBSTRATE PREFERENCE IN LEUCORRHINIA-DUBIA (ODONATA, ANISOPTERA)

The increase of peat mosses, Sphagnum spp., in acidified lakes leads t o a changed microhabitat structure for benthic invertebrates. The impo rtance of this change was investigated for some benthic invertebrates. Comparisons between quantitative samples of Sphagnum and debris withi n the acidified Lake Stora Hastevatten, in the Lake Gardsjon catchment of SW Sweden, showed significantly higher abundances of Chironomidae, Ceratopogonidae, Odonata, Trichoptera, Cladocera and Argyroneta aquat ica (Araneae) in Sphagnum. For Chironomidae and Cladocera the differen ces were tenfold. Special reference was made to the libellulid Leucorr hinia dubia which is common in acid lakes. In a laboratory test, late instar larvae of L. dubia were shown to be able to change colour to co rrespond to the brown and green colour of Sphagnum. This result was co mpleted with a field test where larvae of L. dubia were significantly more common in Sphagnum of the same colour as the larvae. The ability to change colour may have an adaptive value when coexisting with visua l predators. Small larvae, 4-5 mm, were significantly more prevalent i n Sphagnum and they also showed significant preference for this substr ate in the laboratory test. For medium-sized larvae, 12-14 mm, a tende ncy to prefer Sphagnum was found in the laboratory test. Larvae of L. dubia were shown to be more successful as predators on Asellus aquatic us in Sphagnum substrate than in debris in the laboratory test. Labora tory predation tests with Notonecta glauca, Corixa dentipes, Acilius s ulcatus, Hyphydrus ovatus and L. dubia showed that they could all feed on larvae of L. dubia. The complex habitat structure of Sphagnum is p robably the reason for the high abundance of invertebrates since it ma y serve as both shelter against predation and as foraging sites. It is probably important as a key habitat for young instars of, for example , L, dubia. In lakes with large Sphagnum mats, L. dubia can coexist wi th fish. The expansion of Sphagnum due to acidification will probably benefit many acidtolerant invertebrate species.