How Climate Driven Ocean Warming May Affect Filtration Rates in Blue Mussels

An Investigation into how Climate Driven Oceanic Warming may effect the
Filtration Rates of the Blue Mussel Mytilus edulis L.
Ciara Condit.
School of Environmental Sciences, University of Ulster, Coleraine, BT52 1SA, U.K.
The worlds oceans are progressively warming at an unprecedented rate as a direct result of global
warming. It is predicted that by 2100 mean global sea surface temperatures will have rose by between
1.1 to 6.4°c (IPCC 2007). It is predicted that intertidal ecosystems will be significantly effected by
global warming. The mollusc, Mytilus ediulis, are a dominant intertidal species of economic and
biological importance. Thus is is necessary to engage in studies that attempt to predict the species
reaction to increasing temperatures. This study is concerned with how thermal increases within water
temperature will effect the filtration rate of individual M.edulis. An indirect method is utilized where
the reduction in yeast particle concentration over time acts as an estimate of the filtration rate of the
mussel between four temperature treatments of 7, 16, 20 and 25 ºc. This study proves that the within
the experimented temperature range the rate of filtration of individual M.edulis will continually
increase with increasing temperature. It is uncertain whether production rates will increase within a
warmer climate. It is more likely that they will in fact decrease due to the integrated climatic effects
of increasing temperatures, ocean acidification and reduced food availability.
Key words: Mytilus edulis; temperature; oceanic warming; filtration rate; climate change; aquaculture
Introduction
Climate change is now firmly established as a scientific reality that will result in a variety of
emergent challenges for the Earth’s systems’ in the coming decades (Huertas et al, 2011).
Anthropogenic activity such as deforestation and fossil fuel combustion have facilitated a continual
rise in the the levels of the principle greenhouse gas CO₂. (IPCC, 2007) The atmospheric
concentration of CO₂ is currently estimated at around 385ppm, the highest concentration recorded
in the last 800,000 years (Luthi et al, 2008), high atmospheric concentrations of CO₂ are driving the
global warming phenomenon. The worlds oceans are progressively warming at an unprecedented
rate as a direct result of global warming. Sea temperatures around the UK and Ireland have been
warming at between 0.2 and 0.6 ºc per decade for the past 30 years (Rayner et al, 2003). It is
predicted that by 2100 mean global sea surface temperatures (SST) will have rose by between 1.1
to 6.4°c, with the best estimates ranging between 2 to 4.5°c (IPCC 2007). There is a high degree of
uncertainty surrounding the precise temperature augmentation to be expected by the end of the
century, due to the uncertainty surrounding the levels of future carbon emissions. Global
greenhouse gas emissions are currently increasing at an accelerating rate, assessments subsequent
to the latest IPCC Fourth Assessment Report (AR4) have found that current emissions are tracking
the worst case scenarios predicted for the 21st century (Steffen, 2009).
Increasing temperature is considered the most pervasive impact of climate change on the marine
system (Halpern et al, 2008; Brierley & Kingsford, 2009). It is therefore necessary that research be
directed towards understanding the ecological effects of oceanic warming. It is predicted that
intertidal ecosystems will be significantly effected by global warming, due to the high variability in
daily and seasonal temperatures, exposure and the harsh range of abiotic conditions that already
exist within this zone (Jones et al, 2009). The bivalve mollusc, Mytilus ediulis are a species that
dominate the intertidal zone along the coastlines of the Atlantic Ocean (Jones et al, 2009). They are
an important species for both economic and biological reasons and they are therefore the chosen
species for this study.
April 2013 Ciara Condit
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Mussels are the primary food source for organisms such as fish, sails and seastars (Jones et al,
2009), these filter feeders feed on phytoplankton communities and thus provide an important energy
pathway from the primary producers to species at higher trophic levels. These marine invertebrates
are described as “ecosystem engineers” as they provide energy and nutrient flows for the coastal
marine ecosystem (Gazeau et al, 2007). The species recycle nutrients through resuspension during
the production of their psudofaeces (Asmus & Asmus, 1993).
Mussels are important economically due to their high commercial value. Aquaculture is currently
the fastest growing food supply sector worldwide and blue mussels are the main shellfish cultivated
in terms of both value and tonnage. The UK is the third most important European producer of the
species, with the main contributions coming from Northern Ireland. The mussel fishery is the most
valuable fishery within Northern Ireland, in 2010 the region gained an estimated revenue of £7.70
million from the cultivation of Mytilus edulis (Seafish, 2012).
Due to the ecological and commercial viability of these organisms it is important to engage in
investigations that can provide an insight into how they may be effected in a changing climate.
“The direct effects of warmer water temperatures, changes in ocean currents, reductions in nutrient
supply and ocean acidification on reproduction, growth and distribution of shellfish are expected to
cause progressive reductions in the productivity of coastal fisheries” (Roberts et al, 2004). A study
carried out by the SMILE project in Strangford Lough, Northern Ireland indicated that oceanic
warming will be detrimental to shellfish aquaculture. Elevated water temperatures were positively
correlated to a reduction in the mean weight and length of M.edulis individuals. An Increase of 1ºc
in annual average water temperature caused a 10% reduction in productivity, while 4ºc increases
decreased productivity by 50%. The trend was the most pronounced for M.edulis due to
physiological reasons (SMILE, 2007).
“Climate change in Northern Ireland will effect shellfish species directly through changes in
environmental conditions such as seawater pH, temperature, salinity and oxygen
availability” (Heath et al, 2012). This study is solely concerned with the effect of temperature on the
organism. In particular the rate of filtration with increasing temperature will be monitored to
determine whether the feeding rate of the mussel Mytilus edulis will increase in a warmer climate,
and if so will the species cope with the elevated temperatures that are to be expected within the near
future.
Methodology
Blue mussel, Mytilus edulis specimens were collected from the Lough Foyle aquaculture site,
Northern Ireland. Any sediment, epibionts and epiphytes and were removed from the surface of the
individuals within 24 hours of collection. The 50 individuals were stored in an aquarium tank
containing 15 liters of fresh sea water, that was incubated to 11ºc and aerated with an oxygen pump.
The seawater within the aquarium tank was sourced from Portstewart Herring Pond, Northern
Ireland. The tank water was changed every 72 hours, providing a natural planktonic diet for the
mussels present.
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Experimental Procedure:
Experiments were carried out during the month of March, 2013. Mussels were measured using a
vernier caliper and weighed using 100 g electronic laboratory scales, three individuals of similar
weight (± 0.03 g) and length (± 0.03 cm) were were selected for experimental analysis. Artificial
sea water was made up to the same salinity as the tank sea water (50 µS/cm) using a ratio of 197g
of marine salt to five liters of distilled water. The use of artificial sea water ensured that no
undesirable particles were present during experimentation. Measurements of 1900 ml of the
artificial sea water were added to four, geometrically identical 3000ml beakers. The three chosen
mussels were then each placed into a beaker. The fourth beaker would act as a control. The four
beakers were placed in an incubator which maintained the water to the desired experimental
temperature. This allowed a 24 hour period for the individuals to become acclimatised to each
temperature treatment, while also ensuring a common starvation period. After the acclimatization
period natural yeast particles were weighed into four portions of 0.2 g. Each yeast portion was
added to a l00 ml flat bottom flask which was diluted with 100 ml of artificial sea water, and mixed
into a solution. Each 0.002 g/ml yeast solution was added to its corresponding beaker, and stirred
well using a glass rod. In this experiment the control beaker was subject to all the same
experimental conditions as the others, apart from the presence of an individual mussel. The control
determined the rate at which yeast particles fell out of solution, as opposed to being filtered out by
an individual.
Once the yeast solution was mixed into all the beakers, a sample was drawn from the centre, surface
of each beaker using a 10 ml pipette. The turbidity of each sample was measured using the HI
93730 Hanna Portable Microprocessing Turbidity Meter. The initial turbidities were recorded and a
further 90 minute acclimatisation period was allowed. After the 90 minutes, samples were drawn
from each beaker every 20 minutes for a period of three hours. The turbidity of the samples from
each beaker were recorded during this period. The turbidity readings for each sample are an
average of three readings.
The same experimental process was repeated for four temperature treatments of 7, 16, 20 and 25ºc.
The 7ºc treatment represents the temperature minima recorded in Lough Foyle from 2009 - 2011,
the 16ºc treatment represents the average maximum temperature from 2009 - 2011, 20ºc represents
the possible temperature maxima for the Lough (AFBI, 2013) and the 25ºc treatment represents the
possible maximum high temperature that could be reached within the lough by the end of the
century. Three biological replicates and a control were used for each temperature treatment. The
same three mussel individuals were utilized across all treatments.
After experimentation the overall turbidity loss within each beaker was calculated by subtracting
the initial turbidity from the final. Finally the overall turbidity loss calculated within the control
beaker of each treatment was subtracted from the overall turbidity loss of each of the three other
beakers within that treatment. This provides three turbidity loss values per treatment, that signify
the amount of particles filtered by each of the three replicates within each treatment. These values
are subsequently divided by 180 (experiments ran for 180 m), so as to present the results per unit
time. The final result is a value that signifies the rate of filtration of an individual, it is
presented as Natural Turbidity Units (NTU) per minute. The variation in the filtration rates of the
individuals between the treatments are statistically analysed.
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Data Analysis
The data analysis tools of the spreadsheet application, Microsoft Excel 2007 were used to test for a
significant statistical difference between the filtration rates of the individuals both between the
treatments, and within the treatments. To begin the results were inputed into an Excel spreadsheet.
They were then examined using a two-factor ANalysis Of VAriance (ANOVA) and a two sample
paired t-Test assuming unequal variance. Within both tests the alpha levels were set to 0.05,
therefore it was possible to state with 95 % confidence whether the analysed results are significantly
statistically different. Where p < 0.05 results are said to be significantly statistically different and
where p > 0.05 the results are not said to be significantly statistically different.
Results
Mussel # Length
(cm)
Weight
(g)
Individual Filtration Rate (NTU / m)
for treatments:
for treatments:
for treatments:
for treatments:
Mussel # Length
(cm)
Weight
(g)
7 ºc 16 ºc 20 ºc 25 ºc
1 6.52 21.86 0.036 0.050 0.058 0.067
2 6.54 21.89 0.032 0.048 0.055 0.070
3 6.51 21.87 0.030 0.051 0.057 0.065
Table 1. Table listing the individual filtration rates of the mussel replicates at the four temperature treatments and their
corresponding length and weight.
Fig 1. Two-Factor ANOVA testing the significant difference of filtration rates between temperature treatments and
between the biological replicates within temperature treatments. (Alpha 0.05)
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A two factor ANOVA was conducted to determine whether the filtration rate of an individual
significantly differed, both between the temperature treatments and within the temperature
treatments. Temperature had a significant effect on filtration rate across the treatments “F(3) =
119.140, p = 9.78x10⁻⁶”. Individual mussel filtration rates did not vary significantly at the same
temperature “F(2) = 0.813, p = 0.487”. The 16 ºc treatment (M=0.050, SD=1.53x10⁻³) and the 20
ºc treatment (M=0.057, SD=1.53x10⁻³) have an equal variance of 2.33x10⁻⁶, it was therefore
necessary to run a second ANOVA specifically analyzing the variance between these two factors.
Fig 2. Two-Factor ANOVA testing the significant difference of filtration rates between the 16 ºc and 20 ºc treatments
and between the biological replicates within these treatments. (Alpha 0.05)
The above two factor ANOVA found that there was a significant statistical difference in the rate of
filtration between 16 ºc and 20 ºc “F(1) = 147, p = 0.007”.
Two sample
combination of
treatments
P (T<=t) two-
tail
7 ºc & 16 ºc 0.00328257
7 ºc & 20 ºc 0.001194315
7 ºc & 25 ºc 0.000110087
16 ºc & 20 ºc 0.004952037
16 ºc & 25 ºc 0.001900281
20 ºc & 25 ºc 0.008168503
Table 2. Table listing the paired samples t-Tests conducted and their corresponding p-values. (Alpha 0.05)
Six paired samples t-Tests were conducted to further assess where the greatest significant statistical
differences lay between groups. Within the above table p < 0.05 this confirms that the mean rates
of filtration are statistically different between all of the paired groups. The statistical difference in
the mean rate of filtration is greatest between 7 ºc (M = 0.033, SD = 3.05x10⁻³) and 25 ºc (M =
0.067, SD = 2.5x10⁻³ ); “t(4) = - 15.170, p = 0.0001”. The statistical difference in the mean rate of
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filtration is smallest between 20 ºc (M = 0.057, SD = 1.5x10⁻³) and 25 ºc (M = 0.067, SD =
2.5x10⁻³); “t(3) = - 6.276, p = 0.008)”
Discussion
The results of this study indicate that the filtration rate of the blue mussel will progressively
increase with the elevated temperatures associated with oceanic warming. Studies by Jorgensen et
al (1990) have also drawn this conclusion. The ANOVA results evidence a significant statistical
difference in the rate of filtration between the temperature treatments, but not between the
biological replicates within the temperature treatments. This is consistent with the fact that rising
temperature is the factor that is increasing filtration rates. The paired t-Tests reveled that the
greatest statistical difference of the mean filtration rates exists between the 7 ºc and the 25 ºc
treatments. Also that the smallest statistical difference in mean filtration rates exists between the 20
º c and the 25 ºc treatments. The results of the paired t-Tests are consistent with a positively
correlated gradational increase in filtration rate with temperature.
Mussels pump water with the lateral cilia situated on their gills, the species can control their
filtration rate through the mechanism of altering the size of their shell gap (Jorgensen et al., 1996),
measurement of the gap size is often utilized as an estimate of filtration rate. The highest filtration
rates occur when M.edulis individuals are fully open with extended mantle edges and siphon,
filtrations rates decline with a reduction of valve gape and retraction of mantle and siphon
(Jorgensen et al., 1990) Filtration rate studies are majorly conducted in situ, as it is a complicated
parameter to observe in the field (Dolmer, 2000). There are a variety of experimental techniques
that are used in an attempt to estimate the filtration rates of the suspension feeders M.edulis, this
makes it difficult to then compare and interpret the findings (Petersen et al., 2004). Three main
techniques exist, these include the bio-deposition method, in which filtration rate is estimated on the
basis of egested material. The flow-through method, where filtration rate is estimated by the inflow
particle concentration minus the outflow concentration. Finely the indirect method which estimates
the filtration rate as a function of the reduction in particle concentration over time, within a closed
container (Petersen et al., 2004), this study utilizes the indirect method. Estimations of M.edulis
filtration rates make it possible to determine the efficiency of the transport of energy from the
pelagic to the benthic system (Dolmer, 2000). Variability in arial and water temperatures can
regulate filtration rates, absorption and utilization of the available food by the species (Lesser et al,
2010). As mussels M.edulis are exposed to harshly variable environmental conditions (e.g., air and
seawater temperatures), their ability to physiologically adapt and seasonally acclimatise, are crucial
for their survival and capacity to competitively dominate the rocky intertidal (Bayne, 2004;
Thompson et al., 2002; Lesser et al, 2010). Currently, quantifying the mussels capacity to
acclimatise to changing environmental conditions is especially critical, as climate driven changes in
water temperature, seawater pH, and primary productivity will have profound effects upon the
organism.
The rise in the rate of filtration with temperature is explained by the fact that M.edulis are
ectothermic organisms, and so temperature directly determines their vital physiological processes
such as acid–base regulation, resting metabolic rate, metabolic scope for growth and maturation
(Heath et al, 2012). It is scientifically acknowledged that metabolically temperature augmentation
has an ubiquitous stimulatory effect that should felicitate increased growth and biomass within
organisms, providing there is no limit of resources (Padilla-Gamino and Carpenter, 2007), and their
6

thermo-tolerance is not exceeded (Gibson et al, 2011). The M.edulis individuals utilized within this
study were exposed to temperature maxima of 25 ºc, as individual filtration rates continued to
increase at this temperature there is no indication that the thermal range of the mussels native to
Northern Ireland, will be exceeded before the end of this century. Although it is possible that the
organisms could be subject to periodic stress from increasing aerial temperatures and the increased
frequency of heatwave occurrences that are related to climatic change. From this study it is not
evident that when temperatures Increase beyond the acclimatisation potential, the species produce a
stress response whereby increasing amounts of energy are devoted to the synthesis of heat shock
proteins. Therefore as temperatures rise, so to will the costs of maintaining heat stress.
Consequently, organisms that are thermally stressed will possess less energy for reproduction and
growth, and will require a greater food intake to supplement the expended energy (Lesser et al,
2010). Therefore even though M.edulis may begin to filter faster as the climate warms there may be
less energy available to increase the organisms productivity.
The sessile filter feeder, M. edulis consume a mixed diet, comprised of phytoplankton, macrophytes
and detritus. Where possible phytoplankton constitute the main component of the diet (Lesser et al,
2010). A study carried out by Dolmer (2000) shows that the filtration rate of the mussel is
dependent upon the existence of sufficient food quantities. At lower algal concentrations mussels
reduce or stop filtering, the purpose of this is to reduce oxygen uptake and thus respiration, to
conserve energy (Jorgensen, 1990). Studies have shown that M.edulis stop filtering when algal
concentrations drop below 1500 cells per cm³ or 1 mg Chl-a per m³ (Dolmer, 2000). Thus reduced
filtration rates within the organism may become a future problem as the abundance of
phytoplankton is set to decline globally as the climate warms (Behrenfeld et al, 2006). Species
dependent on planktonic food, such as M.edulis are the most likely to demonstrate rapid responses
to climate change (Heath et al, 2012). A study carried out by Boyce et al (2010), depicted a global
phytoplankton decline over the past century, that was strongly correlated to increasing sea surface
temperature. Continued oceanic warming will affect phytoplankton indirectly due to changes to
ocean circulation, water column stability, resource availability and intensified heterotrophic grazing.
It is predicted that thermal intensification will serve to reduce primary productivity and the timing
and extent of the phytoplankton spring bloom. As phytoplankton provide the basis of the marine
food web (Sommer & Winder, 2012) the repercussions of such effects would negatively impact the
entire marine food chain (Thuiller, 2007), through directly effecting phytoplanktonic consumers,
such as M.edulis that provide important linkages at the bottom of the food chain. Furthermore, as
phytoplankton are photosynthetic organisms they possess the ability regulate atmospheric CO₂
abundance through functioning as a carbon sink (Huertas et al, 2011). Therefore, a reduction in
their abundance would increase the concentration of CO₂ that remains within the atmosphere,
intensifying the effects of global climate change.
Oceanic warming of surface waters increases the stability of the water column therefore enhancing
stratification. As a result greater amounts of energy are required to mix the deep, nutrient rich water
into the surface layers (Richardson, 2008). This decrease of resources to the euphotic zone will
reduce phytoplankton abundance (Richardson and Schoeman, 2004). Predicted change to large-
scale oceanic circulation will also decrease nutrient availability. Studies suggest that the predicted
warming-induced melting of the Greenland Ice cap will significantly reduce the surface salinity of
the ocean, consequently reducing the Atlantic meridional overturning circulation by a factor of five,
or greater. The Atlantic meridional overturning plays a key role in thermohaline circulation, hence
its reduction would globally shallow the mixed layer depth, restricting surface nutrient abundance
and therefore primary productivity. It is possible that the phytoplankton biomass within the North
7

Atlantic could be halved, which would also severely impact on the majorly bottom-up controlled
zooplankton populations. Therefore it is possible that primary and secondary production within the
North Atlantic could severely decline as a result of climate change and if so a decline in
Aquaculture and fisheries production would be imminent (Brierley & Kingsford, 2009). This
highlights the question, what does the future hold for an organism whose feeding rates are
increasing but whose food source is rapidly declining globally ?
Climate change is resulting in a range of oceanic impacts that will become detrimental to the
mussel, it is therefore necessary to undertake experiments that assess multiple impacts and can
therefore provide a more realistic perspective as to how the species may be affected in the future.
Temperature & pH, are among the most important environmental factors controlling the
distribution, physiological performance, morphology and behavior of marine invertebrates (Gibson
et al, 2011). From the currently available research on the ecological effects of climatic change it is
not clear whether the effects of increasing temperature or ocean acidification pose the greatest
future threat to the mussel M.edulis. Although, to date the majority of studies relating to the
impacts of climate change on the marine invertebrates have focused on ocean acidification as a sole
stressor (Gibson et al, 2011). The pH of the ocean is falling in a direct response to the continual rise
in atmospheric CO₂ concentrations. As the ocean acidifies it reduces the carbonate availability and
increases carbonate dissolution (Hall-Spencer et al, 2008). Ocean acidification is therefore
predicted to majorly impact calcifying organisms that rely on carbonate for their skeletal or shell
formation (Fabry et al, 2008). As a result calcifying organisms such as M.edulis will have to work
harder in an attempt to produce shells and maintain calcification rates, therefore there will be less
available energy for reproduction, growth, defending against disease and predation (Harrould-
Kolieb and Savitz, 2009). Studies have shown that if the thermal thresholds of embryos are
exceeded the organisms may not reach the calcifying stage, therefore if the species bottleneck is
embryonic thermo-tolerance compromised calcification loses its relevance. Although for all the
species that do not reside within or near their lethal temperature limits future deleterious species
impacts may occur as the combined result of acidification and thermal stress. Future research
should be directed towards multi-stressor experiments that investigate the combined effects of
warming and acidification on marine fauna (Gibson et al, 2011).
The stresses of climatic change have begun to impact upon the species, this is evident from the
declining trend in shellfish production within Europe. Over the last five years production of
molluscs has fallen by 9 % (SeaFish, 2012). To ensure that aquacultural and fisheries production
remains sustainable as the climate changes, it will be necessary to re-evaluate the carrying capacity
of the coastal systems in which the sites are found. Therefore ensuring that possible future
reductions in primary production, which is the major factor determining the carrying capacity for
the cultivation of bivalves (Moore & Service, 2001), do not collapse the fisher and disrupt
ecosystem services and function.
As M.edulis are intertidal organisms they alternate between terrestrial and aquatic existence, often
spending more time in air than in water. Future research into the thermal biology of the organism
should investigate the effects of exposure to increasing aerial temperatures. “Numerous studies have
documented the effects of submerged body temperature and food on survival and reproduction.
However, surprisingly few have examined the interactions of aerial (low tide) body temperature and
food supply on the fitness of intertidal organisms” A study carried out by Schneider et al, (2010)
suggests that aerial body temperature, like submerged temperature affects survival (Schneider et al.,
2010).
8

This study does not come without limitation, firstly the fact that the particles that were being
filtered within the experiment were composed of yeast mean that the filtration behavior observed
may not have been ecologically relevant (Strohmeier et al, 2012), as yeast particles are not
representative of a M.edulis natural diet. Also the study uses a small number of biological
replicates and no technical replicates, increasing the amount of biological and technical replicates
would increase the reliability of the results. Furthermore increasing the length of time over which
the experiment was run would allow more acclimatisation time and increase the accuracy of the
filtration rate results recorded. The flow through method may have provided more reliable results
than the indirect method for estimating filtration rate. The flow through method flows fresh
seawater through an aerated tank containing a population of mussels and subsequently measures the
particle concentration of the out flow of water, therefore the mussels would not have been further
disturbed from the experimental conditions which they had become acclimatised to. However a
study by Petersen et al (2004) evidences the fact that the clearance rate estimates of the blue mussel
varies according to the experimental method used. This highlights the need for future research, to
establish a method which determines filtration rate more accurately, the establishment of a universal
method for the estimation of filtration rates would increase the reliability of future comparisons
between studies. A better study may have examined how the individual mussels would cope with
the combined effects of predicted future climatic stressors such as temperature, food availability and
ocean acidification.
Conclusion
This study proves that the rate of filtration of individual M.edulis will increase with increasing
temperature. If no other factors are considered it could be deduced that the increased rates of
filtration may result in increased productivity for the species. However due to the complexity of the
various abiotic and biotic factors that integrate to impact upon the organism within its natural
environment it is not always correct to make a simple deduction based on a singular parameter, as
such deductions may not always translate accurately into future scenarios.
Future studies investigating the integrating the effects of thermal intensification, ocean acidification
and reduction in food availability on M.edulis could prove to be invaluable for predicting how the
species will respond to changes within the future climate. Such studies would also provide the
information necessary to construct appropriate conservation and management strategies, there is a
growing acceptance of the need for an ecosystem based approach to management (Brierley &
Kingsford, 2009).
A large reduction in global CO₂ emissions is crucially required to minimise future anthropogenic
climate change (Brierley & Kingsford, 2009). However our planet is currently committed to rapid
and intensifying climatic changes for the foreseeable future (Bell et al., 2011), and so our challenge
is to avoid the unmanageable by managing and be prepared for the unavoidable (Scientific Expert
Group on Climate Change, 2007).
9

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11

Personal Development Planning
I have found the process of undertaking an undergraduate dissertation invaluable in terms of
actively learning how to begin to undertake the personal research that is required to progress into
the career of a scientist. Also conducting my own laboratory experiment made the process very
interesting, I have learned that I would like laboratory work to become a component of my future
career. The dissertation process has allowed me personally to appreciate the amount of effort and
research that is required to investigate small scale topics of interest within the earth sciences. As
you process through the dissertation process your knowledge within your chosen topic grows and
therefore with hindsight there are always going to have been better ways to have progressed.
However in order to have gained such knowledge I believe you must have first been through the
process.
My dissertation does not come without limitation. A major but easily changeable limitation is that
yeast particles were utilized to estimate the rate of filtration. However as yeast are not
representative of the natural diet of Mytilus edulis, the observed filtration rates lose their ecological
relevance. The study could also increase the amount of biological and technical replicates which
would serve to increase the reliability of the results. Furthermore increasing the length of time over
which the experiment was run would allow more acclimatisation time and increase the accuracy of
the filtration rate results recorded. The flow through method may have provided more reliable
results than the indirect method for estimating filtration rate. The flow through method flows fresh
seawater through an aerated tank containing a population of mussels and subsequently measures the
particle concentration of the out flow of water, therefore the mussels would not have been further
disturbed from the experimental conditions which they had become acclimatised to.
An overall better study may have examined how the individual mussels would cope with the
combined effects of predicted future climatic stressors such as temperature, food availability and
ocean acidification. However I believe undertaking such a work load may have been beyond the
scope of an undergraduate dissertation.
I believe that the topic I chose to research is a currently relevant and extremely important issue
within the field of marine science. I have now realized that I would like to undertake further study
within the field of marine biology and more specifically relate my research to the ecological effects
of climate change.
12

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