On my last post, I mentioned that we were breaking down the 90-day experiment, where we exposed mussels to environmentally relevant levels (0, 0.3, 3.0, 30.0, and 300 ng/L) of fluoxetine. We had measured mussel length and width as well as mass and water clearance rates, so see if fluoxetine had an effect on mussel physiology. After some preliminary analyses, we found that mussels grew at a slower rate when exposed to the highest levels of fluoxetine (30 and 300 ng/L). While all mussels survived the exposure, some did exhibit negative growth with respect to total mass. I am currently looking at the other data to see if there were similar trends. We are also assessing body condition using a condition and gonadosomatic indices. These indices assess mussel health by measuring the the dry weight of mussel tissue over the length and width of its shell and the proportion of gonad and somatic tissues for each individual mussel, respectively. Once we get the dry weights of each individual mussel, we will have the results from comparing the values between treatments.
The next exciting part of this study is how fluoxetine may affect mussel shell thickening in response to a predator cue. The experiment is designed to test four fluoxetine treatments (0, 0.3, 3, and 30 ng/L) with and without the presence of whelk predator cues (+/-). In total there are 8 treatment types with 10 mussels per treatment, and 2 whelks per (+) treatment. Our facilities have limited space and holding tanks, so I decided to construct an experimental water table to house 800 mussels and 40 whelks that will be used in the experiment (Figure 1). This water table holds fresh water that is chilled at 12.5 °C, and has an air manifold that connects to each vessel housing mussels and whelks (n=80, 10 replicates per treatment).
The individual vessels are simply a 32 oz. wide mouth mason jars. This was a cost effective way to increase replication and ensure independence between replicates. To each fluoextine treatment jar we will add 0.75L of filtered saltwater and the appropriate volume of fluoxetine. In (+) predator cue jars, we cage the whelks in plastic 50mL perforated sample vials (Figure 2).
We will be monitoring this experiment over the next few months. I will be inform you on our progress when it has completed. If you would like to follow my more frequent posts, please visit my new personal website: josephrpeters.weebly.com. Also, please comment here if you have have questions or suggestions about the experiment.