Drift and upstream movement of invertebrates in a springbrook community ecosystem

Structure, drift, and upstream movement of populations of benthic macroinvertebrates, in particular Synurella dentata Hubricht and Lirceus fontinalis Raf., were examined within a temperate spring ecosystem. Chemical and physical aspects of the springbrook were also investigated and life histories of the gammarids and asellids noted.Chemically and physically the spring proved both constant and predictable, much more so than other lotic systems.Species diversity was low from November through February and increased in March, April, and May. Equitability followed the same trends as species diversity. Both indices were most affected by large fluctuations in the populations of aquatic insects.Significant changes in the numbers of amphipods, isopods, and total macroinvertebrates was evident over a seven month period. Males were present in the isopod population year-round, but only from November to January in the amphipod population. Breeding by the isopods occurred throughout the year and peaked during winter. Amphipods copulated only in the late fall and early winter.Significant diel peaks in the amphipod, isopod, and total invertebrate drift negatively correlated with light intensity levels. Amphipods and isopods did not exhibit any preferential upstream movement during either the day or night; however, total macroinvertebrate upstream movement was greater at night. The total number of invertebrates moving upstream were lower than values reported from other lotic environments.