Distribution and abundance of macroinvertebrate communities in artificial beds of submerged aquatic vegetation (SAV)

Macroinvertebrates inhabiting natural and artificial beds of submersed aquatic vegetation (SAV) were sampled in a small embayment of the tidal freshwater Potomac River. Three different densities of artificial vegetation beds, composed of floating polypropylene rope threaded through a mesh base, were placed in areas of barren sediment areas in Gunston Cove. Chironomid larvae, which reached peak population numbers in May, were the numerically dominate taxa found in both the artificial SAV beds and Vallisneria americana beds. Significantly more invertebrates were found in the SAV beds than in unvegetated control areas. A trend of increasing numbers of invertebrates per strand with increasing artificial bed density was observed with significantly more chironomids in high and intermediate density beds than in lower density beds. Using ANOVA, the effect of season, and to a lesser extent, bed density, explained the variation in the number of midges found on strands of artificial SAV. Within high density beds, significantly more midges were found on inner strands of artificial SAV beds as compared to outer strands, although variation in sites and months was apparent. When exclosure cages were placed over intermediate density artificial SAV beds, consistently more chironomids, damselfly larvae, ostracods, aquatic mites and planarians were found on the SAV strands in the exclosures than on strands in uncaged beds, suggesting that predation limits these taxa. Limpets and caddisflies were found in significantly greater numbers on strands of Vallisneria than on the artificial SAV. In contrast, oligochaetes and chironomids were found in significantly greater densities in the artificial SAV strands, with chironomids showing a ten fold greater density on artificial vegetation strands than on the same surface area of Vallisneria leaves.