A comparison of absorption and utilization of food energy in two species of tropical Aplysia

Abstract

Growth of the tropical sea hare, Aplysia juliana Quoy & Gaimard, on a number of seaweed diets at 28 °C, was most rapid for animals eating Ulva fasciata; this alga is abundant in the habitat, is preferred by both laboratory and field animals, and is the food which gave both the highest efficiency of energy absorption (84 %) and highest growth efficiency (33 %). In contrast, Aplysia dactylomela Rang grew most rapidly on a diet of Enteromorpha sp., an alga scarce in the habitat but readily eaten by laboratory animals and the one that gave the highest absorption efficiency (68 %), but not the highest growth efficiency (67 %). Calorimetric determinations, on which the data for absorption and growth efficiencies were based, yielded the following values: Aplysia body tissues and spawn (4666–4920 cal./g ash-free material), seaweed foods (3228–4908 cal./g ash-free material) and faeces of Aplysia eating these foods (2445–4233 cal./g ash-free material). Spawn production, measured as a proportion of the total energy of growth (including spawn), was greater for A. Juliana (66 %) than for A. dactylomela (23 %).