Foraging and homing behaviour of the limpet, Patella vulgata: a geographical comparison

Abstract

As yet few generalizations have been formulated, concerning the tuning, distance and direction of foraging behaviour of Patella vulgata (Linnaeus, 1758). This limpet has previously been reported to be active during daytime high tides and during emersion at nighttime.' Various authors have investigated local factors affecting foraging activity patterns in P vulgata*' but little attempt appears to have been made to make geographical comparisons of populations of this species as proposed in a previous study. This aimed to investigate the foraging patterns and homing behaviour of the limpet Patella vulgata at two widely separated geographical sites within the British Isles. The two localities chosen, in North Wales and in Cornwall, permitted comparisons to be made, using identical observing techniques of limpets in similar positions on the shore, at two latitudes and in localities showing marked differences in the timing during the day of high spring tides. Limpets were observed at Menai Bndge (53°13'15N, 4°09'50*W), on the Isle of Anglesey, and at Porthoustock (50°03'10*N, 503'30rW) on the Lizard peninsula. The sites were sheltered and in each locality limpets were studied on a vertical wall constructed of granite blocks. Twenty limpets of similar size at the mid-shore level were observed at each site (Menai Bridge mean limpet shell length = 43.2 ± s.d. 8-33 mm; Porthoustock = 42.6 ± s.d. 8.6 mm, ttest for size differences gives p = 0.84). At Menai Bridge, the area used for study was located directly beneath the Menai Bridge pier. The wall faced in an East-south-easterly direction, its flora dominated by the macroalga Ascophyllum nodosum Le. Jol. and its fauna by P. vulgata. Semibalanus balanoides (L.) was present, covering less than 30% of the study area. The tidal range at Menai Bridge is 6.7 m on mean spring tides, and 3.6 m on mean neap tides,' with highest spring' tides phased around 0200 and 1400 h. At Porthoustock the study site was part of the 'West of England Pier*, an abandoned quarry with a sheltered West-south-westerly facing wall. Macroalgae were absent on the wall and the fauna was dominated by Semtbalanus balanoides and P vulgata. Barnacle coverage of the wall surface was estimated