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Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources
Thompson, R.C.; Roberts, M.F.; Norton, T.A.; Hawkins, S.J. (2000). Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources, in: Jones, M.B. et al. (Ed.) Island, Ocean and Deep-Sea Biology: Proceedings of the 34th European Marine Biology Symposium, held in Ponta Delgada (Azores), Portugal, 13-17 September 1999. Developments in Hydrobiology, 152: pp. 357-367
In: Jones, M.B. et al. (Ed.) (2000). Island, Ocean and Deep-Sea Biology: Proceedings of the 34th European Marine Biology Symposium, held in Ponta Delgada (Azores), Portugal, 13-17 September 1999. Reprinted from Hydrobiologia, 440(1-3). Developments in Hydrobiology, 152. Kluwer Academic: Dordrecht. ISBN 0-7923-6846-0. XII, 391 pp., more
In: Dumont, H.J. (Ed.) Developments in Hydrobiology. Kluwer Academic/Springer: The Hague; London; Boston; Dordrecht. ISSN 0167-8418, more

Also published as
  • Thompson, R.C.; Roberts, M.F.; Norton, T.A.; Hawkins, S.J. (2000). Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources. Hydrobiologia 440(1-3): 357-367, more

Available in Authors 
    VLIZ: Proceedings [66288]

Keywords
    Biofilms; Density dependence; Intraspecific relationships; Phytobenthos; Patella depressa Pennant, 1777 [WoRMS]; Patella vulgata Linnaeus, 1758 [WoRMS]; Marine

Authors  Top 
  • Thompson, R.C.
  • Roberts, M.F.
  • Norton, T.A., more
  • Hawkins, S.J., more

Abstract
    Distinct seasonal variations in the abundance of photosynthetic microbiota and limpet grazing intensity were recorded at Port St Mary, Isle of Man between January 1994 and June 1996. Microbial abundance was negatively correlated with insolation stress, while grazing intensity was positively correlated with sea and air temperature. These patterns result in a mis-match between the supply of and the demand for microbial resources with maximal grazing intensity during the summer and autumn, but maximal microbial standing stock during the winter and early spring. The importance of top-down control of microbial assemblages by grazing was demonstrated by experimental exclusion of limpets during autumn 1993. This resulted in a four-fold increase in the abundance of cyanobacteria within 6 days, followed by a more gradual proliferation of ephemeral algae during the next 4 weeks. The abundance of diatoms remained relatively constant and was not influenced by the removal of grazers at this time of year. The influence of microbial resource availability on the growth and mortality of limpets was examined using experimental enclosures of differing densities of either Patella vulgata or P. depressa. After 6 months, there were significant relationships between grazer density and both mortality and growth with increased mortality and reduced growth for P. vulgata at increased densities, and reduced growth for P. depressa at increased densities. Hence, the availability of microbial resources may also influence the biomass of grazers on rocky shores from the bottom upwards. A conceptual model is presented which describes seasonal and annual variations in microbial resources and grazing intensity and their potential consequences for other shore dwellers.

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