Feeding, growth and respiration in the polychaetes Nereis diversicolor (facultative filter-feeder) and N. virens (omnivorous)-a comparative study

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The polychaetes Nereis divers~color and N. virens were fed various amounts of shrimp meat in laboratory experiments and h e a r relationships between specific growth rate and specific respiration rates were found.From this relation the energy cost of growth ('specif~c dynamic action', SDA) was found to be 20 to 26% of the growth.The starvation respiration rate (maintenance) (R,,, p1 O2 h-' ind.-') as a function of body mass (W, g dry wt) was: R, = 1306 W' and R, = 704 W' O for N. diversicolor and N. virens, respectively.For worms fed shrimp meat the maximum specific growth rate was 7 % d-l in N, diversicolor and 5.9% d-' in N. virens.In filter-feeding N. diversicolor fed algal cells (6.2 pm &ameter Rhodomonas sp.) there was a strong correlation between ingestion rate and growth rate, the maximum specific growth rate being 3 O/o d.' No functional response was seen even at the highest algal concentration of 2 X 104 cells ml-l.It is possible that filter-feeding In N. diversicoloris a relatively recent adaptation which has resulted in a broader fundamental n ~c h e compared to that of the closely related N. virens.This filter-feeding adaptation may possibly explain the coexistence of the 2 polychaetes in certain braclush water areas.