Influence of diet on sex differentiation of Hippolyte inermis Leach (Decapoda: Natantia) in the field

The gut contents of the shrimp Hippolyte inermis were investigated for 1 year along a depth transect through a seagrass bed. Besides size, sex and weight of all individuals were recorded. The diets of immature and adult individuals were compared to detect any influence of food on sex development, since previous investigations indicated a correlation of the life cycle of this protandric species with the abundance of algal food in the environment, and laboratory experiments demonstrated the effect of diatoms of the genus Cocconeis on the direct development of females. Results indicated that the shrimp is an opportunistic herbivore, able to feed on both plant and animal items, with a preference for macroalgae and diatoms present on the leaves of Posidonia oceanica. Small females, deriving from direct differentiation, had a diet significantly different from that of males. The difference was due to a larger abundance of microalgae in the guts of young females. The influence of microalgal food on the sex reversal mechanism of this species, previously detected through laboratory experiments, was demonstrated to control the life cycle of H. inermis in the field.