Macroinvertebrate colonization of acrylic plates in a large river

From April 1977 through June 1978, scuba divers used a double-cup bar-clamp sampler to monitor colonization rates and standing crops of macroinvertebrates on acrylic plates near the rocky bottom of the Susquehanna River in northeastern Pennsylvania. Monthly, bimonthly, and cumulative plates were exposed for about 30, 60, and 124–362 days, respectively.The upper surface of monthly plates was colonized from June through September at rates ranging from 125 organisms/m²/day in June 1978 to 3,200 org/m²/day in August ({xx\-x} = 1,300 org/m²/day). Chironomids (Rheotanytarsus spp.) and hydropsychids (Hydropsyche phalerata and Cheumatopsyche spp.) composed 97% of the total. The lower surface of monthly plates was colonized from May through September at rates ranging from 110 org/m²/day in June 1977 to 760 org/m²/day in May 1977 ({xx\-x} = 260 org/m²/day). Naidids (Nais spp. and Chaetogaster spp.) and chironomids (Nanocladius spp.) composed 89% of the total.Macroinvertebrates remained on cumulative plates after colonization of monthly plates ceased. The upper surface of cumulative plates was inhabited from June through October at densities ranging from 5,800 org/m² in June 1977 to 78,000 org/m² in August ({xx\-x} = 40,000 org/m²). The lower surface of cumulative plates was inhabited year-round, at densities ranging from t,000 org/m² in December to 15,000 org/m² in June 1977 ({xx\-x} = 6,100 org/m²).This study was supported by Pennsylvania Power and Light CompanyThis study was supported by Pennsylvania Power and Light Company