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Experimental prey species preferences of Hexaplex trunculus (Gastropoda: Muricidae) and predator-prey interactions with the Black mussel Mytilus galloprovincialis (Bivalvia: Mytilidae)

Hexaplex trunculus is one of the most widespread Mediterranean species of muricid gastropod and lives on rocky, sandy-muddy and mud substrata. Although common in the Adriatic Sea, relatively little is known about its ecology especially its feeding behaviour. The aim of this study was to explore aspects of the feeding behaviour of H. trunculus using Arca noae, Modiolus barbatus and Mytilus galloprovincialis as experimental prey. Prey species preference, predator size, prey size choice, feeding rates, handling times and mode and place of attack were analysed. Typically, only M. galloprovincialis was attacked: A. noae rarely at the byssal gape and M. barbatus never. Small (40 mm) H. trunculus could not easily attack large M. galloprovincialis (65 mm) and preferred small (20 mm) and medium (35 mm) sized prey. Conversely, medium (55 mm) and large (70 mm) H. trunculus fed randomly on M. galloprovincialis of all three sizes. The feeding strategy adopted by the H. trunculus individuals varied with respect to size. A tendency to drill the prey shell was recorded for small individuals whereas marginal chipping was adopted more frequently by large predators. Average small, medium and large H. trunculus consumed 2.4 &plusmn ; ; ; ; 1.6 (range 0 - 4), 1.2 &plusmn ; ; ; ; 1.6 (range 0 - 4) and 2.0 &plusmn ; ; ; ; 2.1 (range 0 - 6) M. galloprovincialis, respectively. There was a statistically significant difference in prey handling time with respect to method of access adopted, predator size and prey size. The time required to access a M. galloprovincialis individual by marginal chipping was considerably less than the time required for drilling. Hexaplex trunculus consumed an average of 0.42 &plusmn ; ; ; ; 0.72 g M. galloprovincialis tissue dry weight over five week period, suggesting that a single individual would, over a period of five weeks, consumed ~40% of its own tissue body weight (this sentence might have to go out depending on changes we make in results). Hexaplex trunculus showed no preference to drill either the left or right valves of M. galloprovincialis but generally attacked the posterior shell margin.

Predation; whelk; bivalve; Hexaplex trunculus; Mytilus galloprovincialis; Arca noae; Modiolus barbatus

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