Bionomics of invertebrates within an extensive Potamogeton pectinatus bed of a California marsh

Abstract

Fourteen samples of sago pondweed (Potamogeton pectinatus L.) and associated invertebrates were collected every two weeks over a single season of plant growth in a large monospecific pondweed-bed located in Coyote Hills Marsh (Alameda Co., California, USA), using pull-up samplers that collect plants, epiphytic macroinvertebrates, and microcrustaceans throughout the water column. The macro-invertebrate fauna was dominated by insects, primarily chironomids. Semi-aquatic neustonic taxa, including an aphid and a springtail, were common; this is in contrast with most aquatic plant-invertebrate studies, in which neustonic insects are seldom collected because of sampling bias. Over the entire season, P. pectinatus biomass and the densities of four insect taxa (Anopheles spp. mosquitoes, Hydrellia sp. brineflies, Ademon sp. parasitic wasps, and coenagrionid damselflies) were significantly correlated. These correlations resulted from both similar overall phenologies of the plant and each of the insect taxa, and ecological relationships in which P. pectinatus provides either a specialized habitat or food source. macroinvertebrate numbers were highest in mid-summer, when P. pectinatus forms a dense floating canopy; microcrustaceans were more common during plant senescence in early autumn. Individuals of some taxa may be distributed in proportion to plant biomass; this occurred commonly in damselflies, perhaps as a result of territoriality in these nymphs.