Andrew J. Davies, Mark P. Johnson, Christine A. Maggs

Published in Marine Ecology-Progress Series (2008)

Limpets, predominantly Patella vulgata, have been associated with damaged or receding canopies of Ascophyllum nodosum. Although the damage results from limpet grazing, the benefits that limpets gain from this behaviour are unclear as A. nodosum is thought to be well defended from grazers by anti-herbivore compounds. In this study, P. vulgata individuals were enclosed at densities between 80 and 320 m-2 at two sites within Strangford Lough. Limpet growth and limpet survival were compared between unsubsidised controls and treatments in which limpet diets were subsidised by fronds of A. nodosum. When subsidised, limpet residual growth rates were significantly higher and mortality was lower than in unsubsidised control treatments. Individual limpets consumed a similar amount of A. nodosum regardless of limpet density. Higher densities of limpets therefore consumed more A. nodosum per replicate. The effects of A. nodosum in maintaining limpet densities could resonate through sheltered rocky communities. The importance of a macroalgal subsidy in supporting limpet populations may have been underestimated or overlooked in earlier studies. Therefore, the extensive and productive macroalgal canopies that characterise many sheltered temperate rocky shores could be more sensitive to increased limpet abundances than previously thought.

Full citation

Davies, A.J., Johnson, M.P. & Maggs, C.A. (2008) “Subsidy by Ascophyllum nodosum increases growth rate and survivorship of Patella vulgata” Marine Ecology Progress Series, 366: 43-48.

http://dx.doi.org/10.3354/meps07453

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Pushkar M. Wadke, Michael T. Burrows, David Meldrum and Andrew J. Davies
Published in the conference proceedings of Oceans 2007, Vancouver (2007)

Magnetic sensors have existed for many years and are widely used in different applications such as navigation systems, automation, position detection and current detection (amongst others). In this paper we explore a unique application of underwater magnetic sensing using a magneto-resistive sensor to monitor animal behaviour. Animal behaviour researchers have used several different techniques to study the behaviour of limpets. Most common are motographic methods using time-lapse photography. This technique is limited by low resolution, time consuming data analysis and sometimes an obscured field of view. Here, we present preliminary results from the use of a magneto-resistive sensor attached to the common limpet Patella vulgata. The (Honeywell HMC1052) 2-axis anisotropic magneto-resistive (AMR) sensor was fixed using epoxy putty to the shell of a limpet. The sensor has the capability to capture the limpet’s orientation with a resolution of 0.05°. This high resolution allows us to describe a range of behavioural responses which was not possible using earlier techniques. Limpet movement was truthed using time-lapse infra-red videography. Magneto-resistive sensors can quantify orientation behaviour, be used in extreme environments and provide superior data to qualitative and interpreted observations obtained from previous techniques. Several future developments may increase the applicability of this technique, such as using an artificial magnetic field to precisely locate animals at sub-GPS resolution.

Full citation

Wadke, P.M., Burrows, M.T., Meldrum, D. & Davies, A.J. (2007) “Using magneto-resitive sensors to monitor animal behaviour: a case study using limpets” Proceedings, Oceans 2007 MTS/IEEE Vancouver.

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