December 18 marked the end of a 90-day exposure study. During this time, we exposed the mussel Mytilus Californianus to regular doses of the drug, Fluoxetine which is the active ingredient in Prozac, a selective serotonin reuptake inhibitor (SSRI) antidepressant. For this project, we wanted to determine if environmentally relevant levels of fluoxetine affect the mussels’ biological functions, namely their ability to grow and clear algae from the water column. We set up the experiment with different exposure levels to cover a spectrum of concentrations measured in water samples worldwide.  We wondered if the higher exposure levels would cause more disruption to the biological functions we were measuring. We were most interested in whether fluoxetine affects the mussels ability to clear algae from the water. The reason is because this important function, when magnified across an area of mussel bed, has been shown to be an important ecosystem service. While mussels are an important fishery on their own, some might argue that their role in the rocky intertidal community far exceeds their value as seafood. Since mussels are sessile filter-feeders they filter the water of algae, excess nutrients, and frankly anything in the water that passes by their gills. This makes them highly vulnerable to contamination from toxins in the environment. As other organisms consume mussels (e.g. sea stars and whelks) any contaminant stored in their tissues could accumulate in the tissues in higher trophic organisms. Run off that contain the chemical residues of pharmaceuticals and personal care products (PPCPs) could affect marine life dramatically, and warrants more intensive study.

While there are numerous studies that show negative effects of PPCPs on aquatic organisms, they are mostly acute toxicity studies lasting only 7-10 days. Very few have done chronic exposure trials lasting longer than 30 days, and even fewer have looked at marine organisms. We wanted our study to mimic how fluoxetine could be persistent in the rocky intertidal environment. Often contaminants enter the coast through ‘pulse’ events, where rain drives more run-off and the compounds are essentially ‘flushed’ into estuaries and neighboring nearshore communities. We housed our mussels in tanks and dosed the mussels with fluoxetine every 10 days, to mimic these pulse events rather than constant exposure at the same concentration. We coordinated our measurements around the days we dosed the tanks. We measured mussel clearance rates using a Coulter Cell Counter. This involved feeding the mussels and taking water samples just after feeding and another sample 3 hours after the first sample was taken. The cell counter allowed us to process each water sample in under 15 seconds, which was terrific given that each algal sample day yielded 60 samples that needed immediate processing! We also measured growth by taking the length and width of each mussels every 30 days. While not as exciting as algal clearance rates, we wanted this baseline data to see if this fluoxetine could affect mussel growth. On days 30, 60, and 90 we harvested mussels to save their tissues for additional biological and chemical analyses.  We were interested in how mussels body condition might be affected, so we compared the biomass of tissues necessary for the gonadosomatic index.

Currently, we are in the beginning stages of another experiment that will assess how mussels ability to induce defenses (e.g. thicker shells) in response to predator cues may be affected by the presence of fluoxetine in the water. This experiment should be finished in April or May. Also, our undergraduate student Dylan Dayrit who has been assisting with sample processing throughout the course of this experiment, is currently developing his Honors Thesis to determine the concentrations of fluoxetine in the mussel tissues. This is a big undertaking because we currently have 500 frozen mussels to process. We feel that this information could be very important in determining how much of the fluoxetine in water is taken into the mussels tissues.

I will be filling you in on the findings of this first experiment in the next post.

Have a good new year!

Joey