Size and organic content of eggs of marine annelids, and the underestimation of egg energy content by dichromate oxidation.

Dichromate oxidation is a simple technique that is often Ilsed to estimate the energy content of eggs in studies of marine invertebrate life histories (1). We used this method to measure the energy contents af the eggs of 12 species of marine annelids. In combinati on with measures of egg ash­ free dry weight (AFDW), these data yielded estimates of AFDW-specific energy density that were mostly lower than the average weight-specific energy density of carbohy­ drates. This seemed unlikely to be correct, as invertebrate egg ... typically camain little carbohydrate and ill stead are composed primarily of energy-dense protein and lipid (1, 2), After validating our methods (by u.'Iing them to estimate energy content and AFDW of the eggs of a previ� ously studied echinodenn) and reexamining published data on the energy contents of echinodenn eggs, we conclude that dichromate oxidation oft en underestimates the energy contents of small eggs of marine invertebrates. This system­ atic error, .which is likely related to the tendency of the assay to incompletely oxidize proteins, can only be cor­ rected with substantial independem data on egg biochemi­ cal composition. We thus suggest that dichromate oxidation should not be used for routine measurement of the total energy content of marine invertebrate eggs. Maternal investment of energy per offspring is a variable of fundamental importance in models of the evolution of life histories (3, 4). It is relatively easy to quantify in free· spawning marine invertebrates, where maternal investment is primarily limited to the organic material provided in the egg. Among echinoderms· , egg energy and organic content (as AFDW) are both positively correlated with egg volume in interspecific comparisons (I, 5). Few data on relation� ships between egg size and organic or energy content are available for members of other phyla of invertebrates (i. 6. 7). We measured these variables in 12 species of marine annelids, with the aim of testing hypotheses on differences between annelids and echinoderms in relationships between maternal investment and larval nutritional mode. We used the technique of dichromate oxidation to estimate egg en­ ergy content (8, 9). Though it is prone to several problems (10. II, 12), previous analyses have suggested timt dichro­ mate oxidation estimates agree well with those made by other techniques (l, 13), and it is frequently used to measure