Diet of chaetognaths Sagitta nagae, S. crassa in Yellow sea inferred from gut content and signature fatty acid analyses

Abstract

Chaetognaths are known to be an important primary predator of zooplankton but are also prey organisms for planktivorous species (i.e. fish larvae, small fish, and other carnivores) in the Yellow Sea. Nevertheless, few studies have been conducted to understand their feeding ecology. Therefore, to identify the diet of the most predominant chaetognath species, Sagitta nagae and S. crass, in Yellow Sea, we analyzed the gut content and whole body fatty acids (FAs) of specimens sampled in April and August 2013 from Yellow Sea. About 20% of specimens (S. nagae (n=969) and S. crassa (n=838)) contained foods in their guts without detecting any significant differences betweenspecies. Most of gut contents (>70%) consisted with small copepods. For fatty acid composition, relatively high amounts of carnivorous FA (especially, copepod FA marker 20:1 and 22:1) were appeared in both species. Based on the results, chaetognaths are carnivores and mainly feed on the small copepod as their major food source in Yellow Sea. Therefore, chaetognaths could play ecologically important roles to transfer energy from copepods to planktivorous fishes and govern the abundance of small copepods, known as top-down forcing, in Yellow Sea.ucted to understand their feeding ecology. Therefore, to identify the diet of the most predominant chaetognath species, Sagitta nagae and S. crass, in Yellow Sea, we analyzed the gut content and whole body fatty acids (FAs) of specimens sampled in April and August 2013 from Yellow Sea. About 20% of specimens (S. nagae (n=969) and S. crassa (n=838)) contained foods in their guts without detecting any significant differences betweenspecies. Most of gut contents (>70%) consisted with small copepods. For fatty acid composition, relatively high amounts of carnivorous FA (especially, copepod FA marker 20:1 and 22:1) were appeared in both species. Based on the results, chaetognaths are carnivores and mainly feed on the small copepod as their major food source in Yellow Sea. Therefore, chaetognaths could play ecologically important roles to transfer energy from copepods to planktivorous fishes and govern the abundance of small copepods, known as top-down forcing, in Yellow Sea.