WATER FILTRATION BY THE BAY SCALLOP, PECTEN IRRADIANS, AS OBSERVED WITH THE USE OF RADIOACTIVE PLANKTON

¹ Shellfish Laboratory, U. S. Fish and Wildlife Service, Beaufort, North Carolina

1. The water filtration by the bay scallop, Pecten irradians, was studied by following the clearing of suspensions of plankton cells that had been made radioactive. The use of radioactivity measurement techniques for such studies of the rate of water propulsion of filter-feeding invertebrates by the indirect method allows detection of slight changes in cell numbers in dilute suspensions and is advantageous for investigation of the feeding activities of lamellibranch molluscs.

2. The scallops were observed to filter the water passed through their gills very efficiently with apparently complete retention of Chlamydomonas and Nitzschia cells after adjustment to the immersion in the suspensions. The rapid rate of decrease of suspended plankton was not continued, however, for there was evidence of a decrease in the efficiency of the gills and increasing return to the suspension of phytoplankton cells previously removed.

3. The bay scallop has a relatively high rate of water propulsion, probably cortrelated with its rapid rate of growth and active mode of life. The average rate for small scallops, 38-44 mm. in length, was 3.26 liters per hour. The largest scallops, about 12 to 14 months of age and measuring 64-65 mm. in length, averaged 14.72 liters per hour. The maximum rate observed was 25.4 liters per hour. The smaller scallops had a rate of about one liter per hour per gram of tissue, whereas the older scallops pumped an average of about 0.7 liter per hour per gram.