Influence of macrophyte spatial architecture on periphyton and macroinvertebrate community structure in shallow water bodies under contrasting land management

The role of aquatic macrophyte architecture (leaf architecture complexity) in structuring and determining associated algal and invertebrate communities was studied in shallow ditches in coastal marshes under contrasting management (pasture and arable agriculture) and hence nutrient regime (eutrophic and hypertrophic). Variations in colonisation rates between functional feeding groups (macroinvertebrate community) and periphyton colonisation patterns were examined on artificial substrata units recreating three macrophyte leaf architectures-dissected, broad and flat-floating. Units increased in architectural complexity but total colonisable area was constant (255 cm 2). Habitat complexity had a major effect on macroinvertebrate colonisation in the pasture ditch units, particularly on predator species (Coleoptera, Hemiptera and Odonata) as well as for grazers, particularly Gastropoda. Macroinvertebrate abundance was significantly higher on the dissected leafed units. Rates of taxon colonisation (colonisation rates - decolonisation rates) were higher on the dissected and flat-floating leaf units (1.57 and 1.4 species day-1, respectively) as was species richness (46 and 27 species, respectively) reaching equilibrium, when rates became equal, in about three weeks. Habitat complexity also modified periphyton assemblages. Algae-substrata associations and species richness were higher on the broad and dissected units in the pasture ditch (47 spp. and 43 of diatoms spp.; 11 and 15 non-diatoms spp., respectively). Conversely, arable ditch units had a significantly higher density of periphyton and variations in community size and composition, with a few dominant non-diatom taxa, such as Lyngbya birgei, Anabaena spiroides, Spirulina princeps and Oedogonium sp., associated with reduced macroinvertebrate diversity and colonisation, in particular for grazer species. Thus, the experiments demonstrated that high architectural complexity plays an important role in shallow coastal ditches, promoting variation in food availability - more heterogeneous algal assemblages - and macroinvertebrate community succession. Hence, external variables, such as system productivity (eutrophic vs hypertrophic; bottom-up implications), seem to regulate and modify the effects of habitat spatial heterogeneity through epiphytic community growth and consequently macroinvertebrate colonization (species turnover rate). © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.