ABSTRACT
Abstract Energy values of biological material (expressed in J per unit of weight) are widely used in studies of energy budgets of organisms and of energy transfer in ecosystems. The methods to estimate caloric values are rather cumbersome. In many publications, already published records of the same or a related species are used instead. The present review summarizes records of caloric values in several hundreds of species of marine invertebrates. Estimates in more than 70 species of marine bivalves (Mollusca: Pelecypoda) by about 25 authors are discussed in detail to judge their reliability. Bivalves are a suitable group for a study of the variability in energetic values because they differ widely in the contents of two different types of reserve material: the low-caloric carbohydrates (glycogen) and the high-caloric lipids. Moreover, many bivalve species have been analyzed for these substances. On the basis of their chemical composition, the soft parts of nearly all bivalves must show caloric values within the range of about 5.3-6.3 cal (or 22-26J)mg−1 AFDW (ash-free dry-weight). A high proportion of the published records of direct bomb-calorimetric estimates proved to be below this range as a consequence of methodological errors. Particularly, the omission of separate ash determinations and incomplete drying appear to cause underestimates in energy per unit of ash-free dry-weight. A representative value for marine bivalves appears to be close to 5.5 cal (or 23J)mg−1 AFDW. This proposed value is substantially higher than averages of uncritical compilations. Representative values for other taxa of animals are probably also higher than means of literature records and will exceed this bivalve value of 5.5 cal by 0.1 or 0.2 cal mg−1 AFDW in most major taxa (with organisms using primarily lipids instead of carbohydrates as a reserve material). Pros and cons of the direct and indirect method of estimating caloric values are discussed.
