Annual Production by Gammarus pseudolimnaeus among Substrate Types in Valley Creek, Minnesota

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Abstract
Annual production by G. pseudolimnaeus Bousfield in Valley Creek, Minnesota, was computed, using the size-frequency method, separately by substrate type for the 5-yr period, 1968-1972. Four substrate types were identified: sand (0-0 through 8); sand-gravel (0-5 through 8); gravel (0-1 through -5), and cobble (0-6, -7). Annual production was higher in fine-particle substrates than in coarse; 5-yr means were: sand, 21.4; sand-gravel, 21.8; gravel, 15.0, and cobble, 11.0 g/m2 (dry weight). Siltation reduced production more in the fine-particle substrates than in coarse. The ratios of annual production to annual mean standing stock ranged mostly from 5.5-6.5, with 6.0 being the 5-yr mean of all substrates combined. Densities and standing stocks were also higher in fine-particle substrates and were also affected more by the siltation in fine-particle substrates.