MEPS 229:113-126 (2002)  -  doi:10.3354/meps229113

ABSTRACT: A comparative study of feeding rates and structures was made with the 2 ciliary filter-feeding polychaetes Ditrupa arietina and Euchone papillosa from the Mediterranean Sea (Gulf of Lions, France) and the Gullmarsfjord (Sweden), respectively. The feeding rate (clearance) was measured as the volume of water cleared of 6 µm diameter flagellate cells (Rhodomonas sp.) per unit time. Most experiments were conducted at algal concentrations equivalent to about 0.4 to 3.8 µg chlorophyll a l^-1. The clearance rates of Œstandard¹ 1.5 mg dry wt E. papillosa and Œstandard¹ 3.0 mg dry wt D. arietina showed that the maximum weight-specific clearance rate was 114.7 ml h^-1 mg^-1 for E. papillosa and about 7 times lower, 15.7 ml h^-1 mg^-1, for D. arietina. A relative large tentacle crown in E. papillosa, resulting in the higher specific clearance rate, may be the evolutionary result of Œminimal scaling¹ and adaptation to extremely low food concentrations. When the algal concentration was increased from 2000 to 10000 cells ml^-1 a 50% decrease in the clearance rate was observed in D. arietina, presumably because the gut capacity was exceeded. A more pronounced tendency to become satiated was found for E. papillosa. No tendency to reduce the filter-feeding activity at even very low algal concentrations was noticed in the 2 polychaetes, and the filtering activity of both worms seems to be a basically continuous process. Video-microscope observations of E. papillosa showed that suspended algal cells approaching the pinnules suddenly accelerate and move through an arc of over 180° to be delivered on the frontal side of the pinnule. The transfer takes place at a maximum distance (radius) of about 25 µm from the pinnule. Scanning micrographs show the compound lateral cilia to be 20 to 25 µm long in both D. arietina and E. papillosa and to consist of 1 row of 4 cilia. The feeding current is generated by these compound cilia, which, during their power stroke, catch up with the particles.

KEY WORDS: Suspension-feeding · Filtration rates · Particle-retention mechanism · Adaptation to the environment · Feeding structures