Feeding by Chaetognatha: Energy Balance and Importance of Various Components of the Diet of Sagitta elegans

Abstract

Daily rations, in terms of number and energy content of food items, were estimated for three developmental stages of Sagitta elegans Verrill in Bedford Basin, Nova Scotia (Canada) at two times of year, and compared to estimated energy requirements. In mid July, the younger two stages appeared to be meeting their metabolic needs but the oldest stage did not. This corresponded to a major annual period of spawning and disappearance of mature S. elegans. The opposite seemed to be the case in December, which was not a spawning period: while the older two stages appeared to be obtaining sufficient energy, the youngest stage seemed to experience a substantial deficit. Population data for the following 3 years inlplies that the youngest individuals suffered very high losses during this period. The previously noted simplicity of the chaetognath's population cycle in Bedford Basin may be due in part to such an annual loss of individuals hatched late in the season. While copepods were always numerically dominant among prey items, tintinnids and rotifers were important in the diets of small individuals in July, and cannibalism played an important part in the energy intake of the larger stages in December