Does seabird carrion contribute to the diet of the shore crab Carcinus maenas on the Isle of May, Scotland? An isotopic perspective

• Published in: Journal of the Marine Biological Association of the United Kingdom 2011-11, Vol.91 (7), p.1459-1464
• Main Authors: Watts, A.J.R., McCafferty, D.J., Newton, J., Bailey, D.M.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Aquatic birds; Aves; Biological and medical sciences; Breeding seasons; Crustaceans; Ecosystem services; Food chains; Food webs; Foraging behavior; Fundamental and applied biological sciences. Psychology; Hypotheses; Intertidal zone; Invertebrates; Isotopes; Marine ecosystems; Marine environment; Mortality; Nutrient cycles; Organisms; Predators; Scavengers; Sea water ecosystems; Shellfish; Stable isotopes; Synecology; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0025-3154; 1469-7769
• DOI: 10.1017/S0025315410002286

Scavengers are common in marine environments and provide an essential ecosystem service, helping to return nutrients and energy contained in carrion to the system. Knowledge of the prevalence of scavenging is required to fully understand marine food webs. As most scavengers are also predators it is usually unclear what proportion of their diet is derived from carrion, and if this proportion varies in time. In this study we set out to determine whether the input of seabird or other carrion could be detected in the stable isotope composition of the shore crab (Carcinus maenas). Shore crabs were captured in the intertidal zone of the Isle of May (Scotland) before and after the peak fledging of Atlantic puffins (Fratercula arctica). The stable isotope (δ15N and δ13C) compositions of crabs and the proposed carrion source were determined. Fifty crabs were selected (25 from before (IOM1) and 25 after the fledging period (IOM2)). IOM1 had a mean δ15N value of +13.85‰ and IOM2 a mean of +13.53‰. The mean δ13C values were –15.46‰ for IOM1 and –15.87‰ for IOM2. In contrast to our expectations, there was no evidence that shore crabs were feeding on seabird carrion following the post-fledging period of Atlantic puffins. Future sampling in autumn months following the grey seal (Halichoerus grypus) breeding season may be useful in establishing if there is another route for nutrient and energy cycling between higher predators and marine scavengers at this location.