Original paper

Invertebrate distribution on a macroalgae/macrophyte mixed mat in flowing water

Fernández, Hugo R.; Reid, Brian

Abstract

In flowing waters, aquatic fauna is typically concentrated in the benthos, wood or other fixed substrates. Aquatic plants and filamentous algae may also offer refugia for invertebrates within the water column, due to flow attenuation, relatively stable substrate and provision of food. We quantified invertebrate abundance, size distribution and species composition along linear, flow-oriented gradients of mixed Cladophora sp. and Elodea canadensis mats in Crow Creek, northern Montana (USA). Mats were divided into four sections (0-20, 20-40, 40-60 and 60-80 cm, ordered basal to distal) using a customized sampler. Mat biomass, invertebrate richness and abundance were significantly higher in the 20-40 cm section, driven primarily by Cladophora biomass. Meanwhile, Elodea biomass was correlated with invertebrate richness in the 60-80 cm section. Most taxa, however, were not individually related to Cladophora or Elodea biomass, except for a positive relationship between Elodea biomass and the amphipod Hyalella azteca in the 0-20 cm section, and with cladocerans and copepods (meiofauna) in the 60-80 cm section. Biomass size spectra showed no difference among mat segments, but were prominently skewed towards smaller size classes (meiofauna), demonstrating that mats allow the presence of the meiofauna well into the water column of flowing waters. Stream epiphytic invertebrate communities may exhibit complex patterns in abundance and composition, potentially following a neutral model of colonization, movement, and loss of individuals along a linear flow-oriented substrate, but with strong interacting effects of substrate biomass, possible inter-specific interactions, or distinct microhabitat preferences.

Keywords

macrophyte biomassmeiofaunaneutral modelsize distributioncladophoraelodea