MEPS 322:213-224 (2006)  -  doi:10.3354/meps322213

ABSTRACT: The present study shows that when suspended phytoplankton cells are present at sufficiently high concentrations the tube-dwelling marine amphipod Corophium volutator (Pallas) filter feeds, but when the phytoplankton biomass reaches a certain low level, both laboratory and field video observations support the hypothesis that C. volutator can switch to surface deposit feeding. Feeding behaviour and quantification of water processing were studied in individuals transferred to glass tubes. Simultaneous clearance of algal cells of different size showed that the setae filter on the second gnathopods retains particles ≥7 µm. The pumping rate (P, ml h^–1) was measured by video particle tracking, and the relationship between P and body dry weight (W, mg) was found to be P = 53.3W^0.76. The relationship between P and body length (L, mm) was P = 0.24L³ + 7.8, and the relationship between temperature (T, °C) and P was P = 5.55T + 3.3. The respiration rate of a 6.5 mm length individual was 0.7 µl O₂ h^–1 (15°C), and by relating respiration to P of an individual of this size, it was estimated that C. volutator pumps 108 l water ml^–1 O₂ consumed, thus fulfilling the conditions for classification as a true filter feeder. Monthly samples were collected for 1 yr from the shallow (0.8 m) inner part of Odense Fjord (Denmark) in order to follow size and density distribution of C. volutator. By combining filtration rate data with size- and temperature-dependent P data, the area-specific population filtration rate varied between 0.9 in January and 19.4 m³ m^–2 d^–1 in June. The half-life of phytoplankton (assuming 100% particle retention efficiency and efficient vertical mixing of the water column) ranged from 14.5 h in January to 0.7 h in June and July. This suggests that the grazing impact of C. volutator may be significantly important in the inner Odense Fjord and other shallow water areas with dense populations of C. volutator.

KEY WORDS: Feeding · Pumping rate · Particle retention efficiency · Respiration · Effect of temperature · Grazing impact