Feeding ecology of platynereis dumerilii (audouin & milne-edwards) in the seagrass posidonia oceanica system: The role of the epiphytic flora (Polychaeta, nereididae)

Abstract

The feeding ecology and the ecological role of the herbivorous polychaete Platynereis dumerilii (Audouin & Milne-Edwards) (Nereididae) in the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile was investigated under natural and laboratory conditions. Experiments were devised to define the preferred items, their consumption rate and degree of assimilation of chlorophylls. Results of faecal pellets analyses, food-choice experiments and photosynthetic pigment analyses demonstrated that P. dumerilii feeds preferentially on erect filamentous algae. Worms of length above 10 mm may graze also on living tissue of Posidonia leaves, when starved. This behaviour has rarely been reported for invertebrates, and especially for poly-chaetes in Posidonia ecosystems. Small individuals had a lower feeding rate on large macroalgae (e.g., Cystoseira), but higher digestive efficiency. Platynereis dumerilii thus feeds preferentially on erect micro- and macroalgae which are more easily cut by the jaws of its eversible pharynx. This selective herbivore thus has a special microniche, with respect to other mesograzers inhabiting the Posidonia meadows.

Key-words:

• Platynereis
• Nereididae
• Polychaeta
• Posidonia oceanica
• seagrass
• feeding
• epiphytes
• Mediterranean Sea