ANALYSIS OF THE ASSOCIATIONS BETWEEN MACROINVERTEBRATES AND MACROPHYTES IN A FRESH-WATER POND

The interactions between aquatic macrophytes and macroinvertebrates ar e complex, with macrophytes often providing both refuge and food, eith er directly or indirectly, for invertebrates. Macroinvertebrate-plant relationships have been studied extensively in terrestrial environment s, but much less so in aquatic environments. The objective in this pap er was to explore some of the factors that affect macroinvertebrate-ma crophyte relationships in the littoral zone of a freshwater pond. A to tal of 53 macroinvertebrate Laxa were found associated with six macrop hyte species in Cannery Pond, a small, shallow, eutrophic pond in Skag it Co., WA (USA). A graphical inspection of the data revealed that the macroinvertebrate densities and biomasses on the emergent macrophyte species (Scirpus tabernaemontani, Typha latifolia, and Polygonum hydro piperoides) were more similar to each other than to the submerged macr ophyte species (Potamogeton natans, Ceratophyllum demersum, and Potamo geton pusillus). Multivariate analyses (MANOVA) confirmed that there w ere significant differences among the plant taxa based on macroinverte brate densities and biomasses. Cluster analyses (parametric and nonmet ric) further revealed that the strongest grouping was into two groups (emergent and submerged plants) rather than the original six. The grea test differences between submerged and emergent plants were due to dif ferences in the abundances of Mollusca, Annelida, Platyhelminthes, Cru stacea and Diptera, all of which were common taxa. Morphological simil arities among plants appeared to influence macroinvertebrate-macrophyt e associations, with the greatest abundances of macroinvertebrates bei ng found on submerged plants that had a large surface-to-weight ratio and soft stems or leaves. Structural stability and persistence of vege tative structures throughout the year appear to be important for at le ast some of the macroinvertebrates. Most of the macroinvertebrate taxa in Cannery Pond were substrate generalists that are not confined to a particular species of macrophyte, but instead were found in similar a bundances on all morphologically similar macrophytes.