Annual occurrence and algal preferences of the kleptoplastic sea slug, Elysia papillosa

Abstract

Kleptoplastic, sacoglossan sea slugs are some of the best known examples of specialist marine herbivores. However, while their chloroplast symbiosis (kleptoplasty) has been studied in many species, little is known about sacoglossan life histories or their seasonal and temporal variation in natural populations. Most sacoglossan species are associated with one or a few closely related algal species that provide the chloroplast source for the kleptoplastic association. Elysia papillosa, a small sacoglossan with a distribution ranging throughout the Caribbean to Florida, primarily feeds on the alga, Penicillus capitatus, although it has also been found on several additional species of algae. A yearlong field survey of E. papillosa in a rhizophytic algal bed in Tarpon Springs, FL, USA revealed a low density of slugs throughout the year except during April, when mean density sharply peaked to 7.0 ± 5.9 slugs (0.25 m2)−1 . Slugs were not found on any algae other than P. capitatus, except occasionally on P. lamourouxii, suggesting that the latter alga serves as a secondary chloroplast source for E. papillosa. The presence of slugs throughout the year implies a broad tolerance of both salinity and temperature although the peak numbers in April may indicate a physiological preference for warming spring temperatures and, perhaps, day length.