Energetics of Chiton pelliserpentis (Quoy & Gaimard, 1835) (Mollusca: Polyplacophora) and the importance of mucus in its energy budget

Abstract

Energy budgets are reported for high- and low-shore groups of the chiton Chiton pelliserpentis (Quoy & Gaimard, 1835) from a sheltered shore, Kaikoura Peninsula, New Zealand. Annual energy flow through the high-shore group (532 kJ · m −2) was about half of the low-shore flow (1131 kJ · m −2). Most components of the budget were measured; i.e. growth production, reproductive production, production of mucus, respiration, defaecation, excretion and consumption. Previous studies of molluscan energetics have usually ignored mucus and excretion, and calculated consumption by summing all other terms. However, mucus appears to be a major component of molluscan production. The largest single component of the budgets of both chiton groups was production of mucus which accounted for 74 and 66% of assimilated energy on the high and low shores, respectively, whereas respiration (generally assumed to be the largest component of energy expenditure by animals) accounted for only 21 and 29% of assimilation, respectively. No significant differences in utilisation of energy between the two groups were apparent despite considerable differences in population structure. High-shore chitons exhibited adaptations enabling them to maintain consumption in the face of reduced available feeding time, reduce metabolic costs in the face of exposure to greater environmental temperatures, and reduce losses of energy via egestion, and hence maintain a maximal rate of growth.