Date of Award

Summer 8-31-2018

Document Type

Thesis: Open Access

Degree Name

MS Marine Science


Environmental and Ocean Sciences

Committee Chair

Jennifer Prairie

Committee Co-Chair

Nathalie Reyns

Committee Member

Moira Décima


Observations of fine-scale behavioral dynamics of zooplankton may shed insight into much larger-scale ecosystem patterns and phenomena. Some zooplankton, such as copepods, are known to aggregate near density gradients; however, it is not clear the extent to which density gradients alone affect copepod distribution and behavior, since these gradients are often associated with phytoplankton layers. In this study, we investigated the behavior of Calanus pacificus in response to salinity gradients through laboratory experiments observed with high-resolution video and analyzed using computational techniques. Image data were collected using two cameras recording continuously for a duration of 30 minutes or more, allowing us to construct 3D swimming paths of copepods. In stratified treatments, we observed a decrease in the swimming velocity of some copepods as they transitioned through the density gradient. In addition, in the treatment with the strongest density gradient, we found that jump frequency was significantly increased for copepods when they were in the middle of the tank, in the vicinity of the density gradient. However, when averaging copepod tracks throughout the entire tank, we found no consistent differences in behavioral properties, including velocity, jump frequency, and net-to-gross displacement ratio (NGDR), between the stratified treatments and the control treatment without a density gradient. Our results indicate that physical cues from density gradients elicited some behavioral responses from copepods; however, the observed behavioral responses in our experiments did not result in aggregations, indicating that chemical cues may be important for these aggregations to occur.