Diet composition and temporal changes in the trophic patterns of Plesionika narval (Crustacea-Decapoda) in the Aegean Sea (Eastern Mediterranean Sea)

Abstract

The feeding habits of the Plesionika narval, narwal shrimp, from the south-eastern Aegean Sea (E. Mediterranean) were studied monthly during an annual cycle between 2014–2015. A total of 2516 specimens (1631 females and 885 males) was studied from two depth zones (A = 10–30 m, C = 150–170 m). P. narval consumed a wide variety of preys, mostly dominated by crustaceans, molluscs and polychaetes. The Shannon–Wiener diversity index (H′), did not reveal significant differences in its diet composition, either between sexes or seasons. However, the female’s diet was found to significantly differ between months and depth zones. The diet varied within sex, the average dietary dissimilarities were 18.87% among males and 12.04% among females, possibly attributed to the sexual dimorphism and/or the size differences between sexes. The low variation (<16%) in the diet composition from shallow and deep water was most possibly related to migration of females to shallower waters during spring and summer and differences in benthic preys inhabiting the two depth zones studied. The high repletion index (%RI) values observed for females in late spring and summer and for males in autumn and winter could be associated with metabolic processes, such as reproduction and moulting. The highest number of stomach emptiness in females during August in the deeper depth zone coincides with the spawning period of this species in the area under study and migration of females to shallower waters.