The role of the predator Trophon geversianus in an intertidal population of Mytilus chilensis in a rocky shore of the Beagle Channel, Tierra del Fuego, Argentina

Abstract

Predation influences changes in the abundance and the limits of spatial distribution of organisms on rocky shores. We quantified the effect of the predation pressure of the gastropod Trophongeversianus on the mytilid Mytilus chilensis in a rocky intertidal community of the Beagle Channel, Tierra del Fuego. We quantified the density of T. geversianus along with the density of T. geversianus preying on M. chilensis and examined the potential relationship between sizes of both T. geversianus and M.chilensis. Additionally, we carried out laboratory experiments to quantify the drilling and ingestion rates of T. geversianus on M.chilensis at different aerial exposure times. At mid intertidal levels, unlike at low intertidal levels, T. geversianus consumed more frequently the available size range of mussels. On average, sizes of predator and prey consumed were positively correlated. The drilling rate decreased with increasing time of aerial exposure. Additionally, permanently submerged predators invested less time consuming the same amount of food than individuals exposed for 4 out of 12 h (4/12 h). Predators exposed for 9/12 h invested less time and consumed less food than those exposed 4/12 h. Our results suggest that T. geversianus is an efficient predator of M. chilensis, due to both its high density and feeding rate. Our results suggest that the strong predation pressure of T. geversianus on M. chilensis prevents this key competitor from monopolizing space at the low level through controlling their abundance, and further limits their vertical distribution.