Image analysis as a tool for measuring particulate matter concentrations and gut content, body size, and clearance rates of estuarine copepods: validation and application

Abstract

The performance of image analysis in measuring suspended particulate matter concentrations was compared with that of the Coulter counter in different samples including latex spheres, diatoms and natural estuarine waters. The two techniques gave comparable numerical concentrations. Image analysis results also correlated positively with dry weight measurements of estuarine suspended particulate matter samples. The conversion of particle areas measured by image analysis into volumes was addressed by trying to determine the average height of the particles. This was done by plotting volume concentrations from the Coulter counter against area concentrations from image analysis. The resulting linear relationships were found to be significant in homogeneous samples like the spheres and diatoms but not in natural estuarine samples. Further measurements were done on cross-section views of natural particulate matter to estimate the actual height, which was found to be on the average 34% of its average diameter. Also validated is the use of image analysis in measuring body sizes and gut contents of copepods. Results show that the gut resembles a cylinder and its measurement is independent of the animal's orientation at the time of measurement. Body size measurements converted into carbon compared favorably with literature data.