Bio-foam enhances larval retention in a free-spawning marine tunicate

Abstract

Here we report a mechanism that reduces dispersal of early developing stages and larvae in a free-spawning intertidal and shallow subtidal tunicate, Pyura praeputialis (Heller 1878), in the Bay of Antofagasta, Chile. The spawning of gametes by the tunicate into the naturally turbulent aerated seawater decreases their surface tension and induces the formation of a bio-foam. Water collected from foamy intertidal pools and tide channels showed a high concentration of P. praeputialis early developing stages and tadpole larvae in the foam. Because gametes are synchronically spawned for external fertilization and larvae settle near adults, our results suggest that this bio-foam increases fertilization success and effective settlement of their short-lived larvae in the vicinity of the adults spawning the gametes. This mechanism reinforces published evidence suggesting that local retention of intertidal and inshore marine invertebrate larvae may be more common than previously thought, offering, for instance, new perspectives for the design and networking of marine protected and management areas.

Fig. 1.

Photographic record of P. praeputialis spawning and field sampling. (A) Synchronous release of gametes from intertidal P. praeputialis during exposure to air. (B) Sperm and egg suspensions retained on the surface of intertidal specimens. (C) Thick foam (≈2 m height) covering the surface of tide channels. (D) Sampling of sea water from the surface in tide channels. ES, egg suspensions; SS, sperm suspensions.

Fig. 2.

Abundance of developing stages and tadpole larvae of P. praeputialis per 10 liters of water collected from tide channels at different times of a tide cycle. (A) Symbols give the average number and standard error of developing embryos (circles) and tadpole larvae (squares) found in water samples collected during the day from three tide channels with (filled symbols) and without (open symbols) foam over two alternate days. (B) Symbols depict the average number and standard error of developing embryos (squares) and tadpole larvae (circles) found at diurnal hours in three water samples collected from tide channels with (filled symbols) and without (open symbols) foam along two consecutive days. Dashed lines indicate tidal cycles. Asterisks indicate direct observations of gamete spawns in the field.

Fig. 3.

Comparison of surfactant properties (tension) as a function of the protein concentration for BSA (open circles) and male gonad tissue (open squares) and female gonad tissue (filled triangles) of P. praeputialis. Error bars show 2 SD (n = 3).