This study examined the ability of oysters to filter algae from water. Researchers set up continuous and batch reactor systems to study this. In the batch reactor, oysters were able to filter algae effectively over 10.5 hours. Data analysis showed the oysters filtered algae at a rate of 0.025 L/hour. A model was developed that closely matched experimental data and can predict algae concentration over time. The study demonstrated oysters' important ecological role in controlling algal blooms.

1. Filtration of Marine Algae by Oysters
Mattie Rourk, Bryan Robinson, Dr. Drapcho
BE 4100 Biological Kinetics, Biosystems Engineering,
Clemson University, Clemson, SC, 29632
Abstract
The experiment was used to determine the rate at which oysters filter
marine algae from a system and how it can be modelled. A CSTR made
first to begin the growth of algae and after the algae has reached an
optimal concentration, a sample of it was placed into the oyster system
and set up as a batch reactor. After 10.5 hours of sampling, we
concluded that the model Ct= 370.5/e[(15*FR*t)/2] can be used to determine
the concentration of algae in our system at any point.
Introduction
Oysters are considered to be a keystone species for a number of
reasons, including that they help prevent erosion and provide a
habitat for other organisms. However, one of their most important
roles is their ability to filter feed. They selectively feed on
phytoplankton or algae, which was used in this experiment, and filter
organic and inorganic matter from the water. Filtering the water
improves water clarity, which is beneficial to photosynthetic
organisms, and water cleanliness. The objective of this study was to
analyze the ability of marine oysters to filter marine algae from the
water in a lab setting.
Materials and Methods
Materials:
•Pump
•Tank
•Reactors
•Oysters
•Marine Algae
Methods:
Initially, this study was set up as a continuous flow reactor where the
saltwater mix was pumped into an algae reactor and the contents of
the algae reactor flowed into the oyster reactor, which drained to the
sink and the OD was recorded for the algae and oyster reactors at
750nm. Then, the oyster reactor was converted into a batch reactor
and 15ml of algae was added into the reactor and the OD, pH, and
alkalinity were recorded as frequently as possible for the day. The
next day, 5ml was added to the reactor and the procedure was
repeated. The OD recorded was used to determine the change in the
amount of algae in the reactor, then the rate of filtration of algae by
oysters.
Results and Discussion
Figure 1 and Figure 2 display the two different setups used for this
experiment.
Figure 1. CSTR Setup Figure 2. Batch Setup
The Continuous flow setup was originally set to have approximately a 24
hour hydraulic retention time for the flow into the algae reactor, but this
caused the oysters to not receive enough algae and give random results. So,
the hydraulic retention time was lowered to allow the oysters to receive
more algae. However, once the retention time was lowered, there was an
indication of growth in our saltwater mix, which would affect our system
and results. This led us to switch to a batch reactor and see how much
algae could be filtered by the oysters over the span of a day. Throughout
the day, the pH stayed between 8.33 and 8.63, and the Alkalinity stayed
between 0.020 and 0.024.
Using another group’s trend line equation for marine algae,
OD=0.0021*TSS, we determined amount of algae filtered at each time
based on the Optical Density. Next, we used an equation found from an
online reference, FR = (V/nt) ln (C0/Ct), to determine our filtration rate.
Instead of using number of cells for the ‘C’ values, TSS was used and ‘n’
represents the number of oysters. Based on these calculations, the Filtration
Rate would be about 0.025 L/hour. This filtration rate is used in the
modeling to determine the change in the amount of algae in the oyster
reactor over time.
The results of the study for the batch reactor were very close to the
simulation results, as shown by Table 1 below.
Table 1. Calculated Amount of Algae in Batch Reactor over Time
.
Conclusions
This study highlighted how well and quickly oysters can filter
microorganisms like algae from the water and truly demonstrated the
importance of their ecological role. When a body of water has a large
growth of algae, or an algal bloom, this can cause the DO of the water to
be reduced severely and lead to problems for other marine organisms like
sickness or death. With oysters being able to control the concentration of
algae in a body of water, this ensures the safety of other marine organisms.
In addition, the equation used from the online reference is reliable and can
be used to fit different conditions to determine what variables are needed.
References
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5131657/
http://hatchery.hpl.umces.edu/oysters/importance-of-oysters/
Riley & Pa-Sweet
Acknowledgements
We would like to thank Dr. Drapcho for her advisement and the BE Department.
Model Development
Figure 3. Change in Algae Concentration over Time
Figure 3, above, displays the actual data found from the experiment
compared to the simulated data found from modeling for the amount of
algae present in the reactor over time.
• Spectrophotometer
• Stir Plates
• Tubing
• Saltwater Mix
• pH Probe
• Various Beakers
• 0.1 N H2SO4
• 25ml Pipettes
• Aerator
Time Algae in Reactor– Experimental
(mg/L)
Algae in Reactor-–Theoretical
(mg/L)
9:30 AM 370.5 370.5
12:00 PM 245.7 226.5
1:00 PM 182.9 186.0
5:00 PM 92.4 84.6
8:00 PM 50 48.9