FAECAL PRODUCTION AND AN ESTIMATE OF FOOD INTAKE IN THE WILD OF THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL)

• Published in: Journal of Molluscan Studies
• Main Author: CLARKE, ANDREW
• Format: Text
• Language: English
• Published: Oxford University Press 1989
• Subjects: Articles; Antarctic; The Antarctic; Antarctic Peninsula; Austral; Signy Island; Nacella; Antarc*
• Online Access: http://mollus.oxfordjournals.org/cgi/content/short/55/2/261; https://doi.org/10.1093/mollus/55.2.261

The Antarctic limpet Nacella concinna is common in shallow waters around the Antarctic Peninsula, and has a mean density of 125 individuals/m2 at Signy Island (Picken, 1980). In the austral summer 1986/87 ammonia excretion and faecal egestion were measured as part of a programme to develop a detailed individual energy budget for this species. Ammonia production was measured in 102 individuals ranging from 3 to 720 mg dry weight. For a standard limpet of 200 mg dry weight, ammonia excretion was 0.13 μg-at/hr. Compared with previous measures of oxygen uptake these data suggest an O:N atomic ratio of between 15 and 25. The relationship between ammonia excretion and dry weight could be expressed by a power curve with a weight exponent of 0.82 (SE 0.042). Faecal production was measured in limpets freshly sampled from the field, and placed in dean seawater for 4 days. During this time faecal production decreased (since the limpets were not feeding), although only data from the first 24 hours were used. Again the relationship between faecal egestion and dry weight could be expressed by a power curve, although this time the weight exponent was 0.94 (SE 0.101). The ash content of the faecal strings increased significantly with the size of the limpet, possibly because larger limpets were ingesting a greater proportion of substrate during feeding. If this is so, then this would also explain the weight exponent dose to 1.0, rather than the value of about 0.8 to be expected from metabolic measures (since larger limpets would be passing relatively more faecal material). If assimilation efficiency is known, then food intake in the wild may be estimated from a measurement of faecal egestion and faecal organic content (Clarke et at ., 1988). Applying typical values of assimilation efficiency for limpets (40 to 60%) suggests a daily food intake in Nacella of 2 to 3% body weight per day. This is a quite typical figure for a grazing limpet, and suggests there is no resource limitation for Nacella at Signy in summer.