PLANKTIVOROUS FISHES AS SELECTIVE AGENTS FOR REPRODUCTIVE SYNCHRONY

Most shallow-water crabs release larvae during nocturnal maximum ampli tude high tides, when larvae are rapidly transported by strong ebb tid es to deeper waters at night. Larvae released at this time may avoid b eing eaten by planktivorous fishes, which abound in shallow water and feed during the day. Eurypanopeus planus (Smith, 1869), Uca beebei (Cr ane, 1941) and Pachygrapsus transversus (Gibbes, 1850) live on the Pac ific coast of Panama and often release larvae during the day. Eurypano peus planus also releases larvae without regard to tidal amplitude. Un like most crabs, larvae of these three species will encounter, not avo id, planktivorous fishes. The predator avoidance hypothesis predicts t hat these larvae should be relatively well protected from predation co mpared to larvae of species that are released when predators are avoid ed. We tested this prediction experimentally by exposing larvae of the se species and the sympatric crab, Cataleptodius taboganus (Rathbun, 1 912), which exhibits the common hatching pattern, to silversides, Memb ras gilberti an abundant diurnal planktivore that feeds where all spec ies release larvae. The rank order of silversides' prey preferences ma tched that predicted from the timing of larval release; Larval vulnera bilities to predation were related to the apparent conspicuousness of larvae, which is determined by the color of yolk and chromatophores. A survey of 30 other species of crabs further indicates that conspicuou sly colored larvae are released when they best avoid predators and tha t inconspicuously colored larvae may be released at other times. Copyr ight (C) 1997 Elsevier Science B.V.