Dataset: Observations of Copepod Reactions to Sinking Aggregates Experiments 2019

During the summer of 2019, two sets of experiments were conducted on July 1 and July 11 to observe reactions of the copepod Calanus pacificus to sinking aggregates.

C. pacificus was collected using a small boat near Scripps Canyon in La Jolla, CA (32° 51.720' N, 117° 16.816' W) at least 4 days before each experiment with a 333 µm mesh plankton net (0.5 m diameter mouth). Samples were sorted in the lab to isolate individuals of the species C. pacificus. Copepods were maintained with regular water changes in an incubator in the dark at 18°C until the experiment and fed Thalassiosira weissflogii. Copepods were starved for 24 hours prior to each experiment by transferring them into beakers with filtered seawater which were wrapped in aluminum foil to maintain darkness and kept at room temperature. Starved female C. pacificus were tethered the morning of each experiment and placed in a beaker with filtered seawater at room temperature without food until they were used for the experiment.

Prior to each experiment, phytoplankton cultures of the species T. weissflogii were started in 2L flasks and were grown in f/2 media at room temperature under 12:12 hour LED light:dark cycle for 3-5 days corresponding to the exponential growth phase. Three days before each experiment, the cultures were diluted to 30,000 cell/mL, using filtered seater that had a density between 0.001-0.002 g/cm3 less than the density of the filtered seawater used in the experimental tank (densities were measured with a handheld density meter). This was done to slow down the sinking velocity of the aggregates. The diluted cultures were then added to cylindrical acrylic tanks (each with a volume of 2.2 L). These cylindrical tanks were allowed to rotate in the dark on roller table for 3 days at a rate of 3.3 rpm to form aggregates.

Individual copepods, tethered to a strand of hair to ensure they stayed in the field of view of the camera, were placed in a 30.5 cm x 16 cm x 8 cm tank filled with filtered seawater. Individual aggregates were then pipetted into a funnel in the top of the tank, and allowed to sink towards the tethered copepod. A Point Grey Grasshopper camera (Model GS3-U3-41C6NIR-C) was used to image the interactions between the copepods and aggregates, recording at rate of 30 fps. The experiments were filmed completely in the dark with the exception of a near-infrared LED light from below, which was used to ensure there was no effect of light on copepod behavior. In Experiment 1, 4 different copepods were each exposed to 6 different aggregates. In Experiment 2, 10 individual copepods were each exposed to 4 different marine snow aggregates (with the exception of the first copepod which was just exposed to one aggregate). In Experiment 1, some copepod/aggregate interactions were not successfully recorded or the aggregate never entered the field of view of the camera and so these were not included in the data sheet.