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Interpretation of Invertebrate Drift in Streams
Author(s) -
Waters Thomas F.
Publication year - 1965
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1936336
Subject(s) - mayfly , streams , invertebrate , gammarus , upstream and downstream (dna) , biological dispersal , hydrology (agriculture) , hydropsychidae , environmental science , baetidae , stochastic drift , ecology , water column , geology , biology , upstream (networking) , amphipoda , computer network , population , statistics , demography , geotechnical engineering , nymph , mathematics , crustacean , sociology , larva , computer science
Various experiments were conducted in a small Minnesota trout stream to determine if data on the drift of stream invertebrates obtained with stationary nets set in the stream, may be interpreted as indication of permanent downstream displacement. A mayfly, Baetis vagans McDunnough, and the scud, Gammarus limnaeus Smith, were the two species primarily involved in the drift. Drifting invertebrates were collected in arrays of several shallow nets stacked on their supporting rods to obtain the vertical distribution of the drift through the water column. Both species entered the drift nets, not only along the stream bottom, but in all water strata. A comparison of the standing crops with drift net accumulations indicated that the drift was too large to be supplied only by the standing crops in the vicinity of the drift nets and that the organisms must have drifted down from upstream areas. Measurement of the dispersal of organisms moving into a denuded stream bottom area, alternately open to movement from upstream and downstream, indicated that both species did so primarily at night and from upstream. Experimentally blocking the drift with nets set from bank to bank reduced daily drift rates downstream from the block position through a distance of 38 m, including two riffles and an intervening pool, indicating that the organisms normally drifted through at least this distance. In general, it appears that the accumulation of organisms in drift nets is the result of a permanent displacement of the organisms downstream, and not the result of nondirectional activity in the immediate vicinity of the nets.