- The document summarizes a study that investigated the effectiveness of marine macroalgae in maintaining water quality in a closed tropical marine water system over 24 days. - The addition of two macroalgae species (a green moss and Halimeda spp.) to one of the tanks (tank B) appeared to significantly lower concentrations of nitrate, nitrite, and ammonium compared to the control tank (tank A) without macroalgae. - The macroalgae removed a total of 27.3g of inorganic nitrogen from the water through nutrient uptake, with ammonium uptake averaging 0.05 mg/L/day and nitrate/nitrite uptake averaging 28.4 mg/L/day

1. Maintaining water quality using marine macroalgae
‘Creating a dynamic environment’
By
Jack S.F. Little (2016)
University of Liverpool, School of Environmental Sciences

2. 2
Contents
Preface and terminology 3 – 4
Abstract 5
Introduction 5 – 6
Method 6 – 7
Results 7 – 9
Discussion 9 – 10
Acknowledgements and references 10 - 11

3. 3
Preface
The replication of natural ecosystems appears an impossible undertaking due to their delicate and complex
natural processes. Although true replication in reality could be too complex or problematic for large-scale
water systems, the possibility may exist that various advantageous characteristics of an ecosystem’s process may
be sustainably and effectively utilised. Conditioning water through the bio filtration of marine macroalgae and
aquatic plants could prove to be an effective approach in creating a dynamic environment in both small and
large scale water systems which can range from public aquariums to water treatment plants.
The primary aim of this study is to investigate the efficiency of marine macroalgae in maintaining water quality
in a closed tropical marine water system over a 24-day period. The secondary aim is to promote the
effectiveness and benefits that bio filtration through marine plants and algae can offer by creating dynamic
(artificial) marine habitats in both commercial aquariums and large-scale systems for effluent water. Through
the natural processes of nutrient uptake in algae, the deduction of harmful concentrations of inorganic
nitrogen compounds can be achieved and also function as an effective method in maintaining a higher
standard in water quality.
Above all, marine macroalgae not only offer practical advantages in public aquariums, but also create a more
natural and atheistically pleasing system for both animals and visitors. Marine macroalgae can be integrated
with relative ease into almost any water system with minimal care and attention while providing maximum
appeal.

4. 4
Useful terminology
Dynamic ecosystem – An artificial representation or reproduction of a natural system, applying the biochemical
interlinking advantages of both plants and animals.
Fish and algae species
Macroalgae – A large multicellular, plant-like organism found primarily around marine environments, which
come in varying colours and sizes. Most commonly known as seaweed.
Halimeda spp. – A green macroalgae which is mostly inedible to most herbivores, due to the calcium carbonate
formed in the tissue and is found commonly around the north east coast of Australia (Guiry and Guiry, 2000).
Green moss – This species was unidentified. However, this is most likely a tropical species found around East
Asia.
Dascyllus aruanus – Commonly known as ‘Humbug Damselfish’. They are typically 6cm in length and are
widespread throughout the tropics and indo-pacific region
Inorganic nitrogen compounds
Ammonium (NH4
+
) – nitrite and nitrate are formed from ammonia through a process called nitrification.
Ammonia can be dangerous for marine animals by impairing respiration
Nitrite (NO2‾) – Nitrite is a strong toxic intermediate for fish and invertebrates. High concentrations can cause
inhibition of oxygen transport in the blood.
Nitrate (NO3
‾) – Nitrate is the final stage in nitrification. Nitrate in low concentrations are not toxic to fish.
Higher concentrations can influence the quality and comfort of fish and invertebrates.
Units
Mg L⁻¹ day⁻¹ – milligrams per litre per day
Statistics (Minitab 17 Software)
Two sample t-test = Determines whether the mean differs significantly between two groups
P – P-value (Strength against the null hypothesis I.E there are significant differences in environmental
conditions between tank a and tank b)

5. 5
Abstract
Macroalgae is used in a variety of ways, for example as fertilizer, food and medicine. Additionally, macroalgae
and macrophytes (Large aquatic plants) have recently been used as a natural method for filtering water and
lowering toxic concentrations of dissolved nutrients such as inorganic nitrogen compounds. Some of which
are problematic in large concentrations. Recent studies (including this study) have shown the effectiveness of
improving water quality by using macroalege in large open water treatment systems and also smaller closed
water systems such as those in public aquariums. Strong interlinking features of plant and animal interactions
may be the key in improving water quality and environmental conditions in aquariums by creating a ‘dynamic
environment’, which can be beneficial for water quality and environmental conditions. The aim of this study
was to further investigate the effectiveness of marine macroalage in maintaining water quality in a small closed
water system. This study took place over a 24-day period at Sea Life Manchester. The addition of macroalgae
appears to have a significant effect on lowering nitrate, nitrite and ammonium concentrations (P=<0.005).
Nutrient uptake rates of ammonium averaged to be around 0.05 mg L⁻¹ day⁻¹. Nitrate and nitrite uptake rates
averaged to be around 28.4 mg L⁻¹ day⁻¹. The addition of macroalgae led to a removal in total of 27.3g of
inorganic nitrogen, utilized by the macroalgae in tank b. Dissolved oxygen concentrations and pH levels were
raised with the addition with the addition of the macroalgae. Finally, the use of the macroalgae is not limited
to use in only small closed water systems, but also large open water treatment systems.
Introduction
Marine macroalgae are a group of multicellular
plant-like organisms found in a wide variety of
marine and sometimes mixed fresh water systems
such as estuaries (Kaiser et al., 2005).
The application of macroalgae (commonly known
as seaweed) expands well beyond the fundamental
source of nutrients for a range of marine
herbivores (Jiménez et al., 2015). Marine
macroalgae are harvested and exploited in a
number of ways for example, dietary supplements
in commercial farming (Cyrus et al., 2015), biofuel
(Herrmann et al., 2015), water filtration (Adey et
al., 2007), medicine and fertilizers (Abbott, 1990,
1996)
Macroalgae are known to have high nutrient
uptake rates which can be harnessed as an effective
method in reducing harmful concentrations of
inorganic nitrogen from effluent waters (Taboada,
2009). The potential in macroalgae being used to
‘clean’ water is further supported and seems a
notable approach, especially in small or large water
systems such as estuaries. Ryther et al. (1979)
estimated that macroalgae were capable of
removing up to 15.4kg of nitrogen ha⁻¹ day⁻¹ in
large open water systems. As a result, some species
of algae are used in wastewater treatment and
recycling of nutrients, more commonly in some
parts of Europe and in marine fishpond effluents
for commercial uses in Israel (Gao and McKinley,
1994).
Additionally, marine macroalgae have been used as
a natural approach in refining water quality in
some commercial and non-commercial aquariums
(Adey et al 2007). Dr Walter Adey is an influential
researcher in algae ecology and pioneered the
development of algae scrubbers or filters to
maintain water quality.
The advantages of utilizing macroalgae for reasons
previously stated are clear to see. However, during
the last 20 years, Adey et al (2007) discovered the
majority of large public aquaria settled to display
their animals in front of representations portraying
their respective natural habitats. Additionally, and
perhaps most importantly, Adel et al (2007)
emphasise the importance of ecosystem modelling
and how best to manage the biochemical
environment-as well as contrast the successful
interconnecting functions of plants and animals
needed for a dynamic ecosystem.

6. 6
Large commercial aquariums such as Sea Life do
endeavour (with reasonable success) to replicate the
marine environment. High quality water from
complex water filters, pumps and automated
systems provide the fluid home for a wide variety of
marine species. However much of the aquarium
perhaps lack the true biodiversity and interlinking
functions provided by macroalgae (and other
aquatic plants) in maintaining water quality. Can
the proven, natural methods pertaining to the use
of macroalgae create a dynamic system by providing
a method in maintaining water quality?
Within closed water systems like Sea Life,
organically bound nitrogen from leftover food and
excrements cause an increase of inorganic nitrogen
(N) compounds which are synthesised by protein
splitting bacteria and released in the form of
inorganic ammonium ions (NH4+). These
ammonium ions can then be oxidised to other
forms of inorganic N such as nitrate (NO3
‾) and
nitrite (NO2
‾), through the nitrification process
performed by nitrifying bacteria (Alexander and
Clark, 1965). Nitrate, nitrite and ammonium are
the primary problematic compounds, which if left
untreated can cause adverse biochemical damage to
the adjacent marine organisms. However, large
quantities of nitrate and ammonium are required
for sufficient growth in plants (Tischner, 2000).
The aim of this study was to measure the
effectiveness of marine macroalgae in maintaining
the quality of water by lowering concentrations of
inorganic N compounds. The difference in water
quality was compared between a control water
system and a dynamic system with macroalgae. The
use of macroalgae in maintaining water quality in
large water systems such as waste treatment plants,
rivers and estuaries will also be discussed.
This study took place at Sea Life Manchester over a
24-day period. Two species of macroalgae were
used during the observations. The first species used
was a tropical green marine moss. The second
macroalgae species used was a Halimeda spp., which
has calcium carbonate deposits in its tissue and
make it inedible to most herbivores (Guiry and
Guiry, 2000).
Methods
Practical set up
Two forty-litre water tanks (tank A and tank B)
were used to each house a population of a tropical
species of fish, Dascyllus aruanus and a marine
macroalgae species (Figure 1). Both tanks were set
up to occupy identical environmental conditions
e.g. water temperature (24°C), salinity and pH.
Both tanks were thoroughly cleaned and prepared
to safely house the populations of D. aruanus. Both
algae species were prepared and cleaned by
carefully removing any invertebrate herbivores and
any additional species, which may lead to variation
in results. Additional lights were set up above the
tanks to ensure ample light availability for the
macroalgae. Once both thanks were prepared and
ready, water temperature, salinity, dissolved oxygen
and pH were measured in both tanks prior to
observations.
D. aruanus individuals were carefully selected and
randomly allocated into either tank A or tank B
with a total of ten D. aruanus per tank in total.
Tank A was used as a control environment,
housing only a population of D. aruanus. Tank B
was used as the dynamic environment and house a
species of macroalgae as well as a D. aruanus
population. Two algae species were chosen to be
Figure1. From top left clockwise: Tank A and Tank B,
Green marine moss algae (algae species 1) , Halimeda spp (algae
species 2) and Dascyllus aruanus.

7. 7
used in this study. Only one algae species was used
at a time over two twelve-day observations.
Measuring dissolved constituents and
environmental conditions
Concentrations of nitrate (NO3
‾), nitrite (NO2
‾)
and ammonium (NH4+) were measured and
recorded once around noon each day. Nitrite and
ammonium concentrations were measured directly
using a Spectrophotometer from a 5ml water
sample. Nitrate concentrations were measured
using a chemical drop test with corresponding
coloured concentration charts. Temperature,
dissolved oxygen, salinity and pH were also
measured and recorded daily by using their
respective digital meters and probes. Both
populations of D. aruanus in each tank were fed
with identical amounts of food. Following the daily
measurements and feeding, the water in both tanks
was finally drained by 50% and refilled with fresh
tropical marine water (~24°C). All the water
quality tests, feeding and water changes were
repeated once a day over a 24 day testing period.
After 12 days, the macroalgae in tank B was
replaced with the second species.
Once all observations were completed and
recorded. All animals and algae were carefully
returned to their original respective tanks. All
water quality data records were compiled for
statistical analysis water quality and environmental
conditions in tanks A and B.
Statistical analysis
Concentrations of Ammonium, nitrate, nitrite,
temperature, dissolved oxygen, pH and salinity
from both tanks were compiled for statistical
analysis using statistical software Minitab 1.7.
Comparisons of water quality and environmental
conditions between tank A (no algae present) and
tank B (with algae) were assessed using two sample
t-tests to assess any significant differences.
In addition to water quality comparisons, nutrient
uptake rates were also calculated for each
macroalgae species (see equation below). Assuming
the environment is equal in tank A and B, we can
theorise that the difference in dissolved nutrient
concentrations (Nitrate, nitrite and ammonium)
between tank A and tank B is caused by the uptake
of nutrients by the addition of macroalage.
Estimations of nutrient uptake rates were
calculated using the following equation:
(𝐴𝑇𝑛𝑢 − 𝐵𝑇𝑛𝑢)
𝑡
ATnu=Total N nutrient concentration in tank A
[mg/L]
BTnu=Total N nutrient concentration in tank B
[mg/L]
t=time (Days)
[Nutrient uptake of inorganic Nitrogen in mg L⁻¹
day⁻¹]
Results
Salinity and water temperature
Water salinity and temperature were set up to be
identical in both tanks. Measurements of salinity
and temperature were taken to test if the
environmental conditions were homogenous under
varying conditions (high light and macroalage).
Salinity remained nearly identical in both tanks
and showed no significant difference between tank
A and tank B over the 24-day period of the study
(P=0.930). Water temperature was also identical in
tank A and B and no significant differences were
found during statistical tests (P=0.833).
Inorganic nitrogen concentration
The prevalent difference was observed between
nitrite and nitrate concentrations (P=<0.005)
(Figure 2). Over the entire 24-day testing period,
nitrate and nitrite concentrations were lower by
nearly a third in tank B (algae) compared to

8. 8
BA
100
90
80
70
60
50
Tank
Nitrate+Nitritemg/L
BA
105
100
95
90
85
Tank
Dissolvedoxygen%
Figure 4. Mean dissolved oxygen concentrations (%) in tank
A and B
concentrations found in tank A (Figure 2). Tank A
nitrite and nitrate concentrations were consistently
higher throughout the testing period.
Ammonium concentrations displayed similar
patterns to nitrate and nitrite concentration
differences. Over the 24-day period, the mean
concentration of ammonium was significantly and
consistently lower in tank B (P=0.043). The
concentration of ammonium in tank B was lower
by around a quarter of the mean concentration
recorded in tank A (Figure 3).
Nutrient uptake rates between two macroalgae
species
Because two macroalgae species were used over the
24-day testing period (one per 12 days), an
opportunity to compare nutrient uptake rates
between the two species was undertaken. Using the
nutrient uptake equation (see page 7), nitrite,
nitrate and ammonium uptake rates were
calculated (Table 1.)
Table 1 displays uptake rates of nitrate, nitrite and
ammonium, which show strong differences in
efficiency between the two algae species. Halimeda
spp. (Species 2) has higher uptake rates of nitrite
and nitrate than green marine moss (species 1) used
during this study. Uptake rates of ammonium
appear to be moderately lower in both species of
macroalgae compared to the nitrate and nitrite
uptake rates (Table 1). Uptake rates appear to
reflect the respective concentrations of nitrite,
nitrate and ammonium (See Figure 2 and 3).
Dissolved oxygen
Results from dissolved oxygen are limited due to
technical issues. However, the concentration of
dissolved oxygen in the water in tank A and tank B
that was recorded did indicate significant
differences. Dissolved oxygen in tank B was on
average significantly higher than concentrations
recorded in tank A (P=<0.005) (Figure 4).
Algae uptake Rate (mg L⁻¹ day⁻¹)
Inorganic nitrogen compound
Species
1
Species
2
Mean daily uptake
rate Total N removed over 24 days (Grams)
Ammonium (NH4+) 0.0085 0.09 0.05 0.0473
Nitrate+Nitrite (NO3-+NO2-) 19.6 37.1 28.4 27.216
BA
0.175
0.150
0.125
0.100
0.075
0.050
Tank
Ammoniummg/L
Table 1. Macroalage uptake rates of inorganic N nutrients and total N removed
from system
Figure 3. Mean ammonium concentrations (mg/L) in tank
A and B
Figure 2. Mean nitrate and nitrite concentrations (mg/L) in
tank A and B

9. 9
pH
Levels of pH fluctuated greatly in both tanks. Over
the study, mean concentrations did show
significant differences between tank A and tank B
environments. Levels in pH were notably higher in
tank B (algae) compared to tank A (figure5)
(P=<0.005). The mean pH level in tank A was
around 7.8 while tank B concentrations had a
mean level of around 8.1 (See figure 5).
Discussion
The addition of a macroalage species in tank B
appears to have a significant effect on lowering the
concentration of ammonium, nitrate and nitrite.
Convincing differences in mean nitrate and nitrite
concentrations over the 24 days can be clearly seen
in Figure 2. Ammonium concentration are more
variable between both tanks, yet significant
differences between tank A and tank B were
observed (Figure 3). The presence of algae does
have an effect on ammonium concentrations,
which were lowered by around 25% over the
course of the experiment.
Nutrient uptake rates
Nutrient uptake rates of the macroalgae in table 1
appear to reflect the respective concentrations of
inorganic nitrogen compounds shown in Figures 2
and 3. Uptakes rates of nitrate and nitrite appear
to be reasonably high with a mean of 28.4 mg L⁻¹
day⁻¹ as compared to ammonium mean uptake
rates, which were around 0.05 mg L⁻¹ day⁻¹ (Table
1). Considering the relatively small amount of
macroalgae used during this study, uptakes rates
were very effective relative to the amount used.
During the experiment, the macroalgae was able to
remove, through nitrogen assimilation, 27.22g of
nitrate and nitrite as well as 47.3mg of ammonium
(see table 1). These figures are relatively low
quantities, however in considerable larger
quantities, Ryther et al. (1979) estimated that
macroalgae were capable of removing up to 15.4kg
N in large open water systems.
The elevated rates of N assimilation utilized from
macroagale is a desirable trait to possess.
Comparing the uptake rates between uptake rates
between aquatic plants and algae should be
considered in any water treatment system.
Macroalgae appear to be more effective in nutrient
uptake rates paralleled to rates recorded in aquatic
plants. Comparatively, some macrophytes (large
aquatic plants) in wetlands have been shown to
have removal rates of nitrates to be 0.63 to 1.26 g
NO3 m⁻2
day⁻¹ or 12.6kg N ha⁻¹ day⁻¹ (Lin et al.,
2002).
Overall, the uptake rates estimated from the
macroalgae species used has an overwhelming
effect on lowering concentrations of inorganic N.
Different species will vary on the efficiency,
however both species did demonstrate effective
uptake rates which will increase with increasing
biomass of algae used in the system.
Water quality
The addition of macroalgae will have an effect on
the environmental conditions. Water temperature
and salinity were almost identical in tank A and
tank B, which were the initial intentions. Despite
an increase of light exposure needed for the
macroalgae growth, there were negligible
differences on both salinity and temperature,
which both were well within the normal
environmental conditions throughout the study.
Levels of pH were an environmental condition that
fluctuated with the addition of macroalgae in tank
B (Figure 5). Tank B mean pH was slightly higher
at around 8.1 compared to the mean pH in tank A,
which was 7.8. Throughout the study, the pH did
fluctuate between about 7.7 and 8.2 in both tanks.
BA
8.1
8.0
7.9
7.8
7.7
Tank
PH
Figure 5. PH levels in tank A and B

10. 10
However, the pH level is consistently higher in
tank B (with algae). Many reasons could explain
further however, a change in balance of dissolved
chemicals in the water caused from uptake of the
macroalgae may be a primary explanation.
Generally, in closed water systems (such as
aquarium tanks), there is equilibrium between
ammonium (NH4
+
) ions and ammonia (NH3),
which have a strong effect on the pH. As
ammonium, nitrate, and nitrite are used by
macroalgae, there will be additional ammonia
(NH3) ions left in the water. This ‘unbalancing’
between ammonia and ammonium may be the
cause of the slight increase of pH in tank B.
Additionally, macroalgae species 2 (Halimeda spp.)
does precipitate calcium carbonate (CaCO3) in its
tissue, which could also affect the alkalinity of the
tank water (Kleypas and Yates, 2009).. However,
further investigation is needed to understand fully
the interlocking functions of plant and animal
interactions. The pH of seawater is on average
around 8.1-8.3 which is subject to fluctuate
depending on the amount of carbon dioxide (CO2)
absorbed from the atmosphere, however, pH levels
do tend to surpass 8.4 in lagoons and estuaries
(University Team Open University Team, Wright,
and Colling, 2014).
Dissolved oxygen concentrations were another
environmental condition that seems to be affected
with the presence of macroalgae. Dissolved oxygen
concentrations are significantly higher with the
addition of macroalgae (Figure 4). The liberation of
oxygen during photosynthesis may account for this
difference in oxygen concentrations.
Both species of macroalgae used in this study were
a green species, which seems to be the most
efficient type of macroalgae for removal of
nutrients. Considering both the potential of large
and small scale usage of macroalgae, there seems to
be supporting evidence showing green macroalgae
species hold some additional advantages compared
to red and brown species. Adams et al, (1999)
found that unlike most red and brown species,
some green macroalgae, (especially filamentous
types) are able to survive in a wide array of salinities
along the environmental gradients in rivers and
estuaries. Similarly high removal rates can be
observed using Ulva lactuca (light green algae),
which is commonly found in and around intertidal
rock, pools. Studies demonstrate that the efficiency
of removing ammonium and phosphate in
polluted seawater and marine fishpond effluent in
24 h reaches up to 95.8% and 93.5%, respectively,
using Ulva reticulata (Taboada, 2009). Resistance
against varying salinities and effective uptake rates
is an advantageous trait to support the potential
introduction of macroalgae into various water
systems, whether natural or commercial.
The introduction of marine macroalgae into a
water system seems to have significant and
desirable effects on the water quality. Both
macroalgae species demonstrated high nutrient
uptake rates and effectively utilized a total of 27.7g
of N from the water system (Table 1). Macroalgae
can transform a system both in aesthetics and
quality. Introduction of macroalgae into any water
system will need careful planning in deciding
which species to use and position respective to the
system’s needs (commercial or industrial). Further
study is needed on the effect of pH larger
quantities of macroalgae has on the water quality.
Finally, the relatively small amount of macroalgae
used proved its effectiveness in maintaining water
quality over nearly a month. Macroalgae can with
relative ease serve as a bio filter and maintain water
quality without hindering environmental
conditions in both commercial and industrial
water systems.
Acknowledgments
Thank you Sea Life Manchester for providing your
time, equipment and facilities needed for this
study to take place. Also many thanks for the
aquarists and displays team who assisted and took
time for this study.
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