Fig. 1.

Key stages in the life cycle of the purple sea urchin, S. purpuratus, as individuals transit between open ocean and shoreline habitats. Persistent differences in the intensity of water motion are depicted qualitatively by the color gradient, with stronger turbulence indicated in white. (A) Adults release gametes that fertilize externally and develop into pluteus larvae. (B) Pluteus larva at the eight-arm stage with a juvenile rudiment on its left side, nearing the competence period for settlement. Four of its five primary podia are visible on the left. (C) Turbulence-exposed larva 1 h after induction with KCl-augmented sea water, showing the retraction of tissue from the tips of the skeletal arm rods, indicating the first stage of settlement. (D) Metamorphosed juvenile 24 h after turbulence exposure and settlement. The larval arms have been reabsorbed, the juvenile has everted, the calcitic spines are visible, and the individual moves using its tube feet. The juvenile stage continues for approximately a year or more before first reproduction. Diameter of the circular image equals 8 cm in A and 620 μm in B–D.