Insect emergence from a large river system in the presense and absence of bighead (hypophthalmichthys nobilis) and silver (h. molitrix) carp

Abstract

Aquatic insect emergence is an important resource for terrestrial insectivores that rely on aquatic insects while raising young, or when terrestrial production is low. Emerging insects also transfer valuable high-energy lipids from phytoplankton to terrestrial consumers. The objectives of this project were to: (1) quantify insect emergence in two large-river systems that differed in primary productivity, and (2) determine the impacts of bighead and silver carp on the emergent insect community. Floating traps (surface area = 0.25 m2) were used to sample emerging adult insects, and were placed in study sites with and without Asian carp. Insects were sorted, identified to family, and individually weighed to determine emergent biomass rates. Sites with carp displayed the greatest insect flux; however, insect diversity was greatest at sites without carp, and lowest at the sites with carp. Emergent insect diversity was correlated with the presence of aquatic vegetation. Insect abundance was also linearly related to algal standing stock (measured as chlorophyll a). This suggests that primary productivity in large river systems have a positive impact on the magnitude of insect emergence, and that the diversity of insects increases with aquatic vegetation. Bighead and silver carp may positively impact insect emergence by removing zooplankton competitors, but may decrease insect diversity by a reduction in large-sized phytoplankton food resources.