The diets of the chaetognaths Sagitta enflata, S. serratodentata atlantica and S. bipunctata at different seasons in Eastern Mediterranean coastal waters

Abstract

The chaetognaths Sagitta enflata, S. serratodentata atlantica and S. bipunctata were caught in six sampling periods from September 1988 until July 1989 during both day and night in Kisamos Gulf (Cretan Sea, Eastern Mediterranean) in the upper layers (0-50 m). Gut content analysis showed that copepods were the predominant food organisms in the diet of these three predators. Positive selectivity indices were found for Corycaeus spp. and Oncaea spp. but negative for Clausocalamus spp. copepodites and Clausacalanus furcatus females, which were the most numerous among copepods. Cannibalism was observed mainly in S. bipunctata while S. serratodentata atlantica was found to be less cannibalistic. The size of the predator was reflected in the size of prey. Feeding intensity indicated by Food containing ratio (FCR) and Number of prey per chaetognath (NPC) increased just before the reproductive period of each chaetognath species. Differences between day and night feeding were only found in S. enflata.