Every year, tons of plastics from various sources find their way into the ocean. Rather than decomposing, these plastics break down into smaller and smaller pieces called microplastics. Microplastics are small plastics, and they are difficult to quantify and remove from the environment.

of unicellular algae. When certain dinoflagellates grow rapidly and become harmful algae blooms called red tide. Additionally, some species of dinoflagellates are also known for being symbiotic with coral reefs. When these dinoflagellates produce an excess of Reactive Oxygen Species(ROS), it degrades the coral host cells and causes the host cell to expel the dinoflagellates leading to coral bleaching and coral death. The purpose of the study was to look at the effects of the microplastics on the growth and ROS production of the gymnodinium. The hypothesis of the study was that the microplastics would have initial negative effects on the gymnodinium, but the gymnodinium would be able to adapt.

Gymnodinium were cultured in a tank of seawater, and then separated into petri dishes and exposed to three concentrations of polyethylene microplastics, 250mg/L, 500mg/L, and 1g/L. Ten microliters from each culture was inserted into a hemocytometer which was used to track the growth of over the course of two days. The ROS production of the gymnodinium was measured by using a UV spectrophotometer to record the absorbance at 254.7nm increased with an increase of ROS production.

For the growth experiments, there were a total of four trials conducted with five replicates Plastics were found to decrease the average percent change in growth of the dinoflagellates. Over the course of the two days exposed to plastics, the control had an 80% change while there was a 54%, 50%, and 43% change for the 250mg/L, 500mg/L, and 1g/L concentrations respectively. The results show that the general trend was that the plastics had a negative effect on the growth of the gymnodinium. For the ROS production experiment, there was one trial conducted. The highest percent change in absorbance occurred at three days for both the control group and the microplastic group. There was a peak of 305% change in ROS production on day three in the microplastic group which was far larger than the 172% change that occurred in the control group. However, at day four the ROS production in both the control and microplastic group decreased from day zero. This showed that after four days the gymnodinium could be adapting to the plastic and are experiencing less stress which led to the decrease in ROS production.

This study produced statistically significant results that showed a decrease in the growth of the gymnodinium as the plastic concentration increased. It also found that the microplastics induced stress on the dinoflagellates which might also be adapting to the plastic. The study showed that the microplastics had an overall negative effect on the dinoflagellates and suggests a possible relationship between microplastics and coral bleaching. Future studies include testing the effects of different types of microplastics that have different electrical charges, sizes, and densities.