Abstract
Seagrasses are one of the most productive marine ecosystems in the world. Posidonia oceanica, an endemic Mediterranean seagrass, is under high and constant anthropogenic and natural pressure, including the introduction of invasive species and climate change. Percnon gibbesi, a small crab with a tropical and subtropical distribution, was first reported in the Mediterranean Sea in 1999, and today is established across the entire Mediterranean Basin, inhabiting the shallow rocky infra-littoral zone. Given that P. gibbesi and P. oceanica can co-occur in the same environments, an experiment was set up to study their plant-herbivore interaction. Using two experiments at two different temperatures (19°C and 25°C), the incidence of herbivory on the seagrass tissues (fruits, leaves, rhizome, and whole shoot) by the invasive crab was assessed. The fruits along with the rhizome were the most consumed tissues, and the leaves of P. oceanica were the least consumed, which could be a consequence of tissue structure characteristics and/or nutrient quality. The incidence of herbivory on the leaves of P. oceanica was not affected by temperature. The herbivory pressure of the exotic crab P. gibbesi on native seagrass P. oceanica will likely be limited to a shallow bathymetric range, but given the large scale of the invasion, the consumption of P. oceanica could become a relevant ecological issue in the area.