Incidence of herbivory of the invasive crab Percnon gibbesi on the endemic Mediterranean seagrass Posidonia oceanica

Abstract

[eng] Seagrasses are one of the most important and productive ecosystems in the world. They provide a habitat for hundreds of different species of fish and invertebrates, some with a high economic value. They also play a key role in mitigating the effects of global warming. Posidonia oceanica is an endemic Mediterranean seagrass and is under high and constant anthropogenic and natural pressure, such as destructive fishing methods, nutrient enrichment, land use change, and climate change. The latter has led to increased grazing rates of many herbivores, including invasive herbivores. Percnon gibbesi is a small crab and an opportunistic feeder, primarily herbivorous with a subtropical distribution, which has established stable populations in the Balearic Islands, inhabiting the shallow rocky infralittoral zone up to 4 m depth. Given these two species can occur in the same bathymetric range, an experiment was set up to study their plant-herbivory interaction. Using two experiments at two different temperatures (19°C and 25°C), the herbivory incidence on the plant tissues (fruits, leaves, rhizome, and whole shoot) by the invasive crab was assessed. The fruits and rhizome were the most consumed tissues and with the leaves being the least preferred, which could be a consequence of nutrient quality and tissue structure characteristics. The herbivory pressure of P. gibbesi on P. oceanica will likely be limited to a shallow bathymetric range (0-4m), but given the large scale of the invasion (e.g., the Mediterranean Basin), the consumption of P. oceanica could become a relevant ecological issue in the area.