Effects of high versus low light irradiance on biomass and abundance of four orders of invertebrates in depositional zones at various sites throughout the east Maple River.

Abstract

Depositional habitats of streams in Northern lower Michigan are characterized by fine substrate called fine particulate organic matter (FPOM), which is comprised of silt, sand and detritus. These areas are occupied by numerous invertebrates and benthic algae in which light availability affects both biomass and relative abundance. The purpose of this study was to examine the effects of high and low light availability on biomass and relative abundance of four orders of aquatic invertebrates. This was done by collecting data in the East Maple River at four sites 150 m apart. Two ten cm cores were taken at each site, one in low light and one in high light. Average biomass for high and low light were calculated, in addition to calculations for relative abundances of four orders (Diptera, Copepoda, Nematoda and Ephemeroptera). Statistics were run comparing the means for total biomass in high versus low light habitats and comparing the means for each order in high versus low light. High light areas showed significantly higher means for total biomass, which were attributed to higher photosynthetic output in high light areas. Copepoda showed significantly higher abundances in high light habitats when compared with low light habitats. This difference is attributed to Copepoda possession of chemosensors and photoreceptors that aide in detection of high nutrient food resources. These food resources are high in nutrients due to large quantities of primary production in high light areas. Therefore invertebrates prefer high light over low light habitats.