Sphagnum mosses as a microhabitat for invertebrates in acidified lakes and the colour adaptation and substrate preference in Leucorrhinia dubia (Odonata, Anisoptera)

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Abstract
The increase of peat mosses. Sphagnum spp, in acidified lakes leads to a changed microhabitat structure for benthic invertebrates The importance of this change was investigated for some benthic invertebrates Comparisons between quantitative samples of Sphagnum and debris within the acidified Lake Stora Hastevatten, in the Lake Gårdsjon catchment of SW Sweden, showed significantly higher abundances of Chironomidae, Ceratopogonidae, Odonata, Trichoptera, Cladocera and Argyroneta aquatica (Araneae) in Sphagnum For Chironomidae and Cladocera the differences were tenfoldSpecial reference was made to the libellulid Leucorrhinia 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 correspond to the brown and green colour of Sphagnum This result was completed 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 visual predators Small larvae, 4‐5 mm, were significantly more prevalent in Sphagnum and they also showed significant preference for this substrate in the laboratory test For medium‐sized larvae, 12‐14 mm, a tendency to prefer Sphagnum was found in the laboratory testLarvae of L dubia were shown to be more successful as predators on Asellus aquaticus in Sphagnum substrate than in debris in the laboratory testLaboratory predation tests with Notonecta glauca, Corixa dentipes, Acilius sulcatus, Hyphydrus ovatus and L dubia showed that they could all feed on larvae of L dubia The complex habitat structure of Sphagnum is probably the reason for the high abundance of invertebrates since it may 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 with fishThe expansion of Sphagnum due to acidification will probably benefit many acid‐tolerant invertebrate species