MEPS 409:107-119 (2010)  -  DOI: https://doi.org/10.3354/meps08618

ABSTRACT: In Chile, the ascidian Pyura praeputialis is an introduced species that occurs in intertidal and subtidal habitats restricted to Antofagasta Bay where it commonly forms extensive colonies that dominate mainly the rocky intertidal. Here we report the results of laboratory experiments conducted to determine the patterns of gamete spawning, and the consequences of the mode of reproduction, sperm age and sperm concentration on fertilization success. Our laboratory experiments indicate that the synchronous release of gametes takes place after the specimens are exposed to air, which is then followed by the formation of a biofoam in the rearing containers. Self fertilization with gametes obtained either by stripping or natural spawning failed to produce larvae or normal development, which occurred only when allosperm were used. Under laboratory conditions, fertilization success significantly decreased with sperm age and sperm concentration. Under field conditions, we recorded a negative effect of distance from areas with biofoam associated with spawning individuals on fertilization success. These findings suggest that it is selectively advantageous for this broadcast species to release gametes at low tide or after a period of emersion followed by biofoam formation. We suggest that this mechanism might have evolved to mitigate the difficulties of fertilization in turbulent aerated seawater, and to maximize fertilization success of short-lived gametes.

KEY WORDS: Broadcast spawner · Gamete longevity · Sperm concentration · Reproductive success · Synchronous spawning · Biofoam · Ascidian