Seasonal changes in the chemical and physical characteristics of Calanus finmarchicus and Oikopleura vanhoeffeni fecal pellets

Urban, Juanita (1992) Seasonal changes in the chemical and physical characteristics of Calanus finmarchicus and Oikopleura vanhoeffeni fecal pellets. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (16MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Fecal pellets from Oikopleura vanhoeffeni and Calanus finmarchicus were analyzed in the spring, summer, fall and winter to determine if there were changes in their physical (size, phytoplankton content & density) or chemical (particulate organic carbon & particulate silicate) characteristics. Changes in phytoplankton content due to seasonal succession were observed in both feces types which resulted from a change from a diatom based food chain in the spring to one based on the microbial loop in the fall. Changing phytoplankton content also resulted in seasonal changes in the dynamic density of the fecal pellets, due to the differential compactness of the component particles. Changes in the dynamic density resulted in changes in the potential of both fecal pellet types to exit the upper mixed layer and contribute to vertical nutrient and particle flux. -- Current literature equations used for predicting the settling velocity of fecal pellets gave correct trends for my data but overestimated the actual rates by 2-100 times. Empirical settling velocity equations were developed for the two fecal types based on their physical characteristics. The resulting equations for both C. finmarchicus and 0. vanhoeffeni were modified Stokes equations. For O. vanhoeffeni, the settling velocity (Ws) can be expressed as: -- [special characters omitted] -- and for C. finmarchicus as: -- [special characters omitted] -- where μ is the viscosity of the water, ps is the density of the fecal pellet, p is the density of the water, g is gravity (981 cm s⁻¹, Dn is the diameter of an equivalent sphere, and L and D are the length and diameter of the fecal pellet. Using these equations, seasonal settling velocities were calculated for the copepod fecal pellets. Fall C. finmarchicus fecal pellets had the fastest settling velocities (25-95 m day⁻¹), indicating that these feces have a greater potential in contributing to the nutrient flux than do spring feces (7-35 m day⁻¹). The higher measured sinking velocities for 0. vanhoeffeni fecal pellets suggests that they are more likely to leave the upper mixed layer and contribute to the nutrient flux than are copepod feces. -- The decay rate for C. finmarchicus fecal pellets was the same in the spring, summer and fall in the field, suggesting that the seasonally dependent nutrient flux due to fecal pellets is determined not by how fast they decay, but by their ability to leave the upper mixed layer. Decaying and fragmenting fecal pellets release dissolved free amino acids (DFAA) into the surrounding water. Changes in the physical characteristics of the fecal pellets resulted in the fall C. finmarchicus fecal pellets and the winter O. vanhoeffeni fecal pellets having the greatest potential to leave the upper mixed layer. This implies that, seasonally, the microbial loop can contribute to the nutrient and particle flux through copopod and tunicate feces.

Actions (login required)

View Item