Periphyton grazing byAmnicolalimosa:An enclosure-exclosure experiment

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Abstract
An enclosure-exclosure experiment was performed in Nonquit Pond, Rhode Island to test the effect of grazing by Amnicola limosa (Say) (Gastropoda) upon lentic periphyton. Periphyton from enclosures with A. limosa had higher organic content in May and July, and lower standing crops in May, July, August, and September than periphyton from exclosures without A. limosa. Small diatom (< 18 μm long, other than Cocconeis placentula) abundances on glass slides were significantly lower in the enclosures than in the exclosures. Cocconeis abundances were not significantly affected by grazing. Cocconeis relative abundances on glass slides exposed in the littoral zone of Nonquit Pond also increased with increased grazing pressure from A. limosa. Because characteristics of Nonquit Pond do not seem to be unusual, and grazer abundances were not extreme, these data may have general importance to the study of lentic periphyton community structure.