Same old weapons against brand new enemies: A native anemone defensive mechanism can reduce predation from a novel invasive sea slug.

NICOLAS BATTINI; CLARA GIACHETTI; ALEJANDRO BORTOLUS; EVANGELINA SCHWINDT

Congreso; Marine and Freshwater Invasive Species: Ecology, Impact, and Management.; 2016

The opisthobranch Pleurobranchaea maculata, native to New Zealand and SE Australia, was recently found in Argentina. This species is highly voracious and an active predator that feeds on a wide variety of invertebrates, especially sea anemones, that represent their main prey item. Natives Actinothoe lobata and Parabunodactis imperfecta are the dominant sea anemone species in fouling and intertidal communities, respectivly, of shallow Patagonian waters.In order to determine if P. maculata preys on these two native sea anemone species, adults of these three species (predator and potential preys) were collected and transported to the CENPAT Experimental Aquarium. Trials were performed in individual tanks (n =10) each one of them with three equal compartments associated to the following treatments: one prey alone, one predator with control food and one predator with one prey species. After a 4 day starvation period, 48 hs feeding trials were performed and the percentage consumed was estimated for each prey. Although both sea anemone species were partially consumed, A. lobata showed a defensive behavior that tended to reduce the effect of predation. When initially attacked by sea slugs, A. lobata sea anemones extruded their acontia, leading to withdrawal response by P. maculata. This behavioral reaction was not observed when P. imperfecta was attacked by P. maculata. This work presents the first evidence of a differential response shown by an introduced, voracious and invasive predator towards two native sea anemones preys. The kind of defensive mechanism shown by A. lobata may have important implications in the structure and dynamics of the benthonic communities invaded by P. maculata within the study area.