- University of Toronto
- Queen‘s University
Macroinvertebrate populations associated with Myriophyllum exalbescens, Potamogeton richardsonii, and Vallisneria americana were compared with those on plastic ‘plants’ similar in morphology to P. richardsonii. The density of organisms varied according to macrophyte species (Myriophyllum ≫ Potamogeton > Vallisneria). The plastic imitations did not differ significantly from Potamogeton in the total numbers of macrophytes they harboured at two different sampling periods during the growing season. A similar macroinvertebrate species composition occurred in association with the three plant species and with the artificial substrates.
This study was carried out in 1974 in Lake Opinicon, Ontario (Lat. 44° 33'N, Long. 76° 20'W), where the Biological Station of Queen's University is located. This is a hard-water mesotrophic lake, 750 hectares in area. About one half of the lake is sufficiently shallow to support the growth of macrophytes, of which there are about 15 common submerged species (Crowder et al. 1977). Plants of Myriophyllum exalbescens Fern., Potamogeton richardsonii (Benn) Rydb., and Vallisneria americana Michx. were collected from the lake on 18 May 1974 and planted in pots, which were then set out in 2 m of water in a bay relatively free of other aquatic macrophytes. Alongside the live experimental planting, ten plastic imitation 'plants' were set out. These were made from stiff white plastic and black electric tape attached to an anchored string 'stem' with a styrofoam float attached to the stem tip: they had the general 'leaf size and form of P. richardsonii foliage. Samples for analysis were collected by a diver, who lowered a plastic bag over each plant or substrate and broke off the stem or string at the sediment-water interface. Ten samples of each species were collected at 2-week intervals between 74/6/5 and 74/8/5, and at 4-week intervals from 74/8/5 until 74/10/6. The plastic plants were sampled on two occasions, 74/6/18 (4 replicates) and 74/7/73 (6 replicates). In each sample, individual eggs (or egg groups when these were obvious), larvae, pupae, and other forms were numerated if they were attached to the plant or were retained by a 0.2 mm nylon mesh screen into which the contents of the plastic bag had been washed. A list of macroinvertebrates found is available from the authors on request. Following Korinkova (1971), the number of invertebrates per unit plant surface area was chosen as the preferential method of expressing results. To do this the dry weight of the sampled plants was obtained and converted to area. Calculated areas in cm2 g-l dry weight (± SE) were as follows: - Myriophyllum 761 ± 98, Potamogeton 546 ± 28, Vallisneria 1417 ± 67. One-way analysis of variance was used to compare different species sampled on the same date. In cases where the data were not parametric, a Kruskall-Wallis test was used.