MEPS 267:195-208 (2004)  -  doi:10.3354/meps267195

ABSTRACT: An automated image analysis system was used to monitor sediment surface feeding activity of 2 bivalves (Abra ovata and A. nitida) inhabiting contrasting environments. A larger variety of feeding behaviours was recorded in A. nitida, whereas A. ovata mostly fed at the sediment surface. There were also clear differences in the behaviour of the 2 species during surface deposit feeding (i.e. a wider extension of the inhalant siphon in A. ovata, and the exhalant siphon being located below the sediment-water interface in A. ovata and above this interface in A. nitida). In A. nitida, increase in feeding activity resulted mostly from an increase in feeding intensity, and not from an increase in the amount of time devoted to feeding. In A. ovata, the most active bivalves tended to increase their activity mostly by increasing the amount of time devoted to feeding. This suggests that feeding intensity was limited in A. ovata but not in A. nitida. Food dilution and food addition experiments were carried out to assess the functional response in the 2 species. The results of the food dilution experiments were statistically insignificant due to high inter-individual variability. Food addition significantly affected feeding activity in A. ovata and A. nitida, although in different ways. In A. ovata, feeding activity was highest at intermediate food concentrations, and inhibited at the highest ones. In A. nitida, increased feeding activity was induced at higher concentrations than in A. ovata, and feeding activity was greatest at the highest food concentration. Such discrepancies in feeding behaviour and functional response in closely related species characterise the difficulty in delineating functional groups in benthic deposit-feeders.

KEY WORDS: Deposit feeding · Behaviour · Image analysis · Bivalves