Taxonomic and size structures of phytophilous macroinvertebrate communities in Vallisneria and Trapa beds of the Hudson River, New York

Phytophilous macroinvertebrates (PMI) were sampled from the surfaces and surrounding water of two aquatic plant species, Vallisneria americana and Trapa natans, which have substantially different morphologies. It was expected that the plants would harbor invertebrate communities of different structure. Total density of PMI was consistently greater in Vallisneria than inTrapa, e.g. 6x greater per m(3) water and 21x greater per m(2) leaf surface in August. Each macrophyte harbored taxa that were either significantly more abundant or present only with that macrophyte; the herbivore Galerucella nymphaceae (Coleptera: Chrysomelidae) was abundant on Trapa. Vallisneria harbored 34 taxa vs. 40 taxa in Trapa, but similarity was low (Morisita's C=0.55-0.66). Predaceous invertebrates were more prevalent in Trapa than in Vallisneria, as were larger individuals. Both PMI communities exhibited shifts in size distribution between July and August. Standing crop of Trapa was 3x greater than for Vallisneria. These two macrophyte beds clearly support PMI communities of different taxonomic and size structure, which is believed to be related to the differences in macrophyte morphology.