Effects of light intensity on biomass and abundance of invertebrates in detrital zones of a northern Michigan stream ecosystem.

Abstract

The detrital zones in stream margins are extremely understudied in the scientific community. These areas of fine particulate organic matter (FPOM) contain many nutrients and provide an important habitat for many stream-dwelling organisms. This study examines the effects of light intensity on the invertebrate populations that inhabit these detrital zones in the Maple River in Cheboygan County, Michigan. Detrital samples were taken from 4 separate sites along the stream margin. At each site, invertebrates were taken from both a high and a low light habitat. Mean biomass and relative abundance of four orders were compared statistically using the non-parametric Mann-Whitney U test. A significantly higher number of invertebrates were found in high light habitats than in the low light habitats. There was also a significantly greater number of copepoda found in the high light environment. No significant differences were found in the abundances of Diptera, Nematoda, or Ephemeroptera individuals. The differences that were observed could be a result of increased algal abundance or food quality in these areas. This study provides important insight into a microhabitat that has not been observed extensively in the past.