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Behavioural components of prey selection by dogwhelks, Nucella lapillus (L.), feeding on mussels, Mytilus edulis L., in the laboratory
Hughes, R.N.; Dunkin, S. de B. (1984). Behavioural components of prey selection by dogwhelks, Nucella lapillus (L.), feeding on mussels, Mytilus edulis L., in the laboratory. J. Exp. Mar. Biol. Ecol. 77(1-2): 45-68. hdl.handle.net/10.1016/0022-0981(84)90050-9
In: Journal of Experimental Marine Biology and Ecology. Elsevier: New York. ISSN 0022-0981, more
Peer reviewed article  

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Keywords
    Nucella lapillus (Linnaeus, 1758) [WoRMS]; Marine

Authors  Top 
  • Hughes, R.N., more
  • Dunkin, S. de B.

Abstract
    Dogwhelks foraging for mussels in an aquarium followed tortuous search paths when recently fed and moved faster along straighter paths when hungrier. In nature this “area restricted searching” would tend to keep dogwhelks in areas of high prey density and the increased “directionality” of movement of hungry dogwhelks would tend to take them away from areas of low prey density.Dogwhelks encountered different-sized mussels in the aquarium in frequencies significantly different from those presented, both in terms of numbers and of surface area. Water currents may have caused the bias. Dogwhelks inspected encountered mussels by crawling over them for ˜ 1–2 h. A proportion of mussels were rejected after inspection. Relative abundances of different-sized accepted mussels were significantly different from those of encountered mussels, the mean size of mussels in the diet increasing significantly with increasing size of the dogwhelks. Size selection became more pronounced as dogwhelks, previously fed on barnacles, became experienced with mussels. A mussel encountered by an experienced dogwhelk was more likely to be attacked if closer to the preferred size of 20–25 mm shell length than the previously encountered mussel.Accepted mussels were inspected for longer than rejected mussels, perhaps as a result of selection of the drilling site. Dogwhelks previously fed solely on barnacles drilled in random positions on the mussel shell at first, but after consuming six to seven mussels they had developed a significant tendency to drill in the thinnest area of shells up to 25 mm in length and in the area over the digestive gland of larger shells. This learned behaviour reduced the drilling time for smaller shells by ˜ 27% and, whilst not reducing the drilling time for larger shells, it allowed direct access to the most profitable organs of the prey. Shells were penetrated at a rate of ˜ 0.36 mm·day-1.The percentage of mussel flesh extracted by adult dogwhelks decreased from ˜ 90% for 10-mm to ˜ 60% for 40-mm mussels, the discarded flesh being predominantly from the mantle and foot. The profitability of mussels, calculated as the ratio of predicted weight of flesh extracted to predicted handling time, increased monotonically with increasing mussel shell length. The learned tendency to drill in the thinnest part of the shell increased the profitability of mussels <25 mm by ˜ 17%.Dogwhelks engaged in handling mussels were sometimes interrupted or displaced by contesting dogwhelks, with a probability that increased as handling of the prey progressed. Interlopers devalued the prey of occupant dogwhelks by prolonging drilling and ingestion, by stealing flesh, or by displacing the occupant. The learned tendency of the dogwhelk to drill over the digestive gland of larger mussels, allowing quicker access to the most profitable tissue, perhaps maximizes the average energy return from larger mussels when at risk from interlopers.The preference of dogwhelks for mussels smaller than those predicted to be the most profitable could reflect the devaluation of larger mussels by the risk from interlopers or the increased risks of predation, dislodgement or desiccation associated with longer handling times for larger mussels.

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