Are filtration rates for the rough tunicate Styela plicata independent of weight or size?

The filtration rate of the rough tunicate Styela plicata was determined as an aid for potential use as a bioremediator of algae and bacteria contamination in estuarine waters. Filtration rates were calculated hourly over a period of six hours for tunicates (16.8 to 57.8 grams) exposed to two targeted concentrations (105 and 106 cells mL(-1)) of the microalgae Nannochloropsis sp. (n = 7 per treatment) and the bacteria Escherichia coli (n = 6 per treatment). Filtration rates for individual tunicates exposed to microalgae differed as much as 3520 mL hr(-1) within an hour and 2349 mL hr(-1) with bacteria. However, the average filtration rate of tunicates exposed to microalgae at 10(5) cells mL(-1) was 3065 mL hr(-1) animal(-1) (+/- 1284 mL hr(-1) s.d.), 3252 mL hr(-1) animal(-1) (+/- 1039 mL hr(-1) s.d.) at 10(6) cells mL(-1) and 3158 mL hr(-1)animal(-1) when combined. The average filtration rate with bacteria at 10(5) cells mL(-1) was 4654 mL hr(-1) animal(-1) (+/- 810 mL hr(-1) s.d.), 2296 mL hr(-1) animal(-1) (+/- 1460 mL hr(-1) s. d.) at 10(6) cells mL(-1) and 3475 mL hr(-1) animal(-1) when combined. There was no relationship between average hourly filtration rate and whole animal weight (r(2) = 0.0001) ordry organ weight (r(2) = 0.0067) indicating that filtration rate should not be reported on a live or dry weight basis. It is suggested that averaging the filtration rate of a population of animals over time would yield a more accurate value, especially for use in modeling of bioremediation effects.