Comparative morphology of the feeding appendages of four mesozooplankton species in the Sundays River estuary

Abstract

The morphology of feeding appendages of the coexisting estuarine copepods, Pseudodiaptomus hessei and Acartia longipatella, and mysids, Rhopalophthalmus terranatalis and Mesopodopsis wooldridgei, were examined and compared as an aid in elucidating dietary differences. The robust mandibles of P. hessel copepodids compared to the more painted and slender teeth with no molar region, of A. longipatella suggest that the latter species relies on more fragile food particles. Mandible edge indices indicate, however, omnivorous feeding by both species. No clear dietary differences could be deduced from the dimensions of the second maxillae of these copepods. Mandible edge indices calculated for the mysid species suggest a more herbivorous feeding mode in M. wooldridgei and a more carnivorous one in R. terranatalis, supporting previous studies on their diets. No interspecific differences between the mysid size classes were evident from edge indices. Significant increments in setae and setule lengths and spacing with increasing mysid size class were evident, reflecting differences in food particle sizes utilized. The morphological differences in the feeding apparatus could reflect differences in the diets between species and indicate differences in food particle sizes utilized by the various developmental stages within species. These differences in diet should reduce inter- and intraspecific competition.