SEASONAL-VARIATIONS IN THE DENSITIES OF FECAL PELLETS PRODUCED BY OIKOPLEURA-VANHOEFFENI (C-LARVACEA) AND CALANUS-FINMARCHICUS (C-COPEPODA)

Two abundant macrozooplankters, Oikopleura a vanhoeffeni (Lohmann) and Calanus finmarchicus (Gunnerus) were collected from the coastal water s off Newfoundland in different seasons during 1990-1991 and incubated in natural seawater to collect freshly egested, field produced, fecal pellets. The densities of fecal pellets from O. vanhoeffeni and C. fi nmarchicus were measured in an isosmotic density gradient. These are t he first reported seasonal measurements of fecal pellet densities from two different types of macrozooplankters, 0. vanhoeffeni, a larvacean , filter feeder and C. finmarchicus, a crustacean, suspension feeder. Pellet density ranges and medians were significantly different among s easons for both species, depending primarily on the type of phytoplank ton ingested and its ability to be compacted. Winter 0. vanhoeffeni an d fall C. finmarchicuss feces filled with nanoplankters and soft bodie d organisms had less open space [packing index (% open area) = 3.5 and 4% for 0. vanhoeffeni and C. finmarchicus, respectively] and were mor e dense (1.23 and 1.19 g cm(-3)) than spring feces filled with diatoms (packing index = 15 and 23%, density = 1.13 and 1.11 g cm(-3)). For c opepods, these results contrast with previously published density valu es and with the predicted copepod fecal pellet density calculated, in the present study, using the conventional mass/volume relationship. Co pepod spring and summer diatom-filled feces had a calculated density o f 1.12 and 1.24 g cm(-3) vs a measured median density of 1.11 g cm(-3) for both spring and summer feces; the fall feces containing nanoplank ters had a calculated density of 1.08 g cm(-3) vs a measured median de nsity of 1.19 g cm(-3). Knowledge of the seasonal variations in fecal pellet densities is important for the development of flux models.