Adaptive value of the volume of perivitelline fluid in the eggs of euphausiids (Crustacea: Euphausiacea)

The perivitelline space of the euphausiid egg serves to maintain eggs buoyancy. It is believed that in oceanic species the volume of the perivitelline space is smaller than in neritic 32, 37, 40]. Published and original data suggest a more complicated tendency for perivitelline space volume and, correspondingly, egg buoyancy in euphausiids, which decrease in the direction: continental slope → shelf → ocean. This tendency is well explicable by adaptations of euphausiid species to the specific conditions of these biotopes. The possible mechanisms of these adaptations are discussed.