LARVAL DEVELOPMENT OF PAGURUS LONGICARPUS SAY REARED IN THE LABORATORY. III. BEHAVIORAL RESPONSES TO SALINITY DISCONTINUITIES

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Abstract
1. Each zoeal instar of P. longicarpus was exposed to salinity discontinuities of varying magnitudes. Three distinct behavioral responses were observed: telson flips regardless of the magnitude of the discontinuity; downward swimming when the magnitude of the discontinuity was moderate; passive sinking when the magnitude of the discontinuity was extreme. 2. All zoeal instars avoided water with a salinity of ca. 20‰ or less, well within the range of salinity permitting complete development to the juvenile. 3. Avoidance of low salinity layers in stratified columns by Zoea I and II appeared to be a function of an absolute salinity (S≃20-22‰) when the salinity of the lower layer (S) was less than 25‰ and a function of salinity difference (ΔS) when S was greater than 25‰ (ΔS≃8‰ for Zoea I; ΔS≃5‰ for Zoea II). Avoidance of bow salinity layers by Zoea III and IV appeared to be a fuction of absolute salinity (S≃20‰) regardless of S over the range of S tested. 4. Evidence is presented that the antennules and antennae may not be involved in detection of salinity discontinuities.

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