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 mea- sured 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 chloro- phyll a l -1 . The clearance rates of 'standard' 1.5 mg dry wt E. papillosa and 'standard' 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 'mini- mal scaling' and adaptation to extremely low food concentrations. When the algal concentration was increased from 2000 to 10 000 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 com- pound 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.
Highlights
Ciliary filter-feeding occurs in many polychaetes (Fauchald & Jumars 1979, Nielsen 1987)
The clearance rates of ‘standard’ 1.5 mg dry wt E. papillosa and ‘standard’ 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
When the algal concentration was increased from 2000 to 10 000 cells ml–1 a 50% decrease in the clearance rate was observed in D. arietina, presumably because the gut capacity was exceeded
Summary
Ciliary filter-feeding occurs in many polychaetes (Fauchald & Jumars 1979, Nielsen 1987). Ciliated tentacle crowns functioning as downstream collecting sys-. Different aspects of filter-feeding in the sabellid polychaete Sabella pavonina have been studied during recent years. Jørgensen et al (1984) determined the particle-retention efficiency; Riisgård & Ivarsson (1990) measured clearance rates; Mayer (1994) measured the particle velocity during the capture phase; and recently Mayer (2000) made a numerical simulation of flow fields and particle trajectories. The particle-capture mechanism and the feeding structures of the serpulid tentacle crown of Spirorbis tridentatus has recently been studied by Riisgård et al (2000). It was found that S. tridentatus uses the same basic principle of ciliary ‘catch-up’ of particles as adopted by the entoproct Loxosoma pectinaricola and the cycliophore Symbion pandora
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