Bioremediation potential, growth and biomass yield of the green seaweed, Ulva lactuca in an integrated marine aquaculture system at the Red Sea coast of Saudi Arabia at different

Bioremediation potential, growth and biomass yield of thegreen seaweed, Ulva lactuca in an integrated marineaquaculture system at the Red Sea coast of Saudi Arabia atdifferent stocking densities and effluent flow ratesYousef S. Al-Hafedh1, Aftab Alam2 and Alejandro H. Buschmann3

1 Center of Excellence for Wildlife Research, Natural Resources & Environment Research Institute, King Abdulaziz City for Science & Technology,

Riyadh, Kingdom of Saudi Arabia

2 Center for Desert Agriculture, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and

Technology, Thuwal, Kingdom of Saudi Arabia

3 I-mar Research Center, University of Los Lagos, Casilla, Puerto Montt, Chile

*Correspondence

Dr. Yousef S. Al-Hafedh, Center of Excellence

for Wildlife Research, Natural Resources &

Environment Research Institute, King

Abdulaziz City for Science & Technology,

P.O. Box 6086, Riyadh 11442, Kingdom of

Saudi Arabia.

Email: [email protected]

Received 21 November 2013; accepted

3 February 2014.

Abstract

Growth, production and biofiltration rates of seaweed, Ulva lactuca were investi-

gated at two stocking densities (3 kg and 6 kg m�2) and two effluent flow rates

(5.4 and 10.8 m3 day�1) to optimize an integrated mariculture system at Saudi

Red Sea coast. effluents from fish-rearing tank, stocked with 200 kg fish (Oreochr-

omis spilurus), fed to six seaweed tanks via sedimentation tank. Fish growth

(weight gain 1.75 g fish day�1), net production (NP, 10.16 kg m�3) and survival

(94.24%) were within acceptable limits. Ulva showed significantly higher

(F = 62.62, d.f. 3, 35; P < 0.0001) specific growth rates at lower density compared

with higher density and under high flow versus low flow (SGR = 5.78% vs. 2.55%

at lower flow and 10.60% vs. 6.26% at higher flow). Biomass yield of Ulva at low-

and high-stocking densities (111.11 and 83.2 g wet wt m�2 day�1, respectively) at

low flow and (267.44 and 244.19 g wet wt m�2 day�1, respectively) at high flow

show that high flow rate and lower density favoured growth. Removal rates of

total ammonia nitrogen (TAN) (0.26–0.31 g m�2 day�1) and phosphate phos-

phorus (0.32–0.41 g m�2 day�1) by U. lactuca were not significantly different

(F = 1.9, d.f. 3, 59; P = 0.1394 for TAN and F = 0.29, d.f. 3, 59; P = 0.8324 for

phosphates) at both the flow rates and stocking densities. Results show that the

effluent flow rate has significant impact over the performance of the seaweed than

stocking density.

Key words: bioremediation, Oreochromis niloticus, Red Sea, Ulva lactuca.

Introduction

Rapid development of fed aquaculture (e.g. fish and

shrimp) in coastal areas throughout the world has raised

increasing concerns on environmental impacts of such

practices (Wu, 1995; Mazzola et al. 1999; Diana et al.

2013). Aquaculture effluents laden with feed wastage, fish

excretion and faeces, rich in inorganic nitrogen (N) and

phosphorus (P), may significantly contribute to the nutri-

ent loading of coastal waters (Kautsky et al. 1997) leading

to the problems of considerable concern in many parts

of the world including coastal eutrophication, loss of

biodiversity and diseases (Gowen & Bradbury 1987; Folke

& Kautsky 1989; Ackefors & Enell 1990; Read & Fernandes

2003; Neori et al. 2007).

The promotion of more sustainable aquaculture prac-

tices for the coastal aquaculture is now being strongly

emphasized (Naylor et al. 2000; Wurts, 2000; Troell et al.

2003; Neori et al. 2004; Costa-Pierce 2010). Integration of

finfish aquaculture with macroalgae (seaweeds) culture is

one such practice for bioremediation of the waste laden

effluents in which seaweeds are grown downstream from

animals (McVey et al. 2002). Eutrophic inputs of nitrogen

and phosphorus from finfish farming can be reduced using

an integrated approach that combines aquaculture of mar-

ine macroalgae with finfish (Folke et al. 1994; Krom et al.

© 2014 Wiley Publishing Asia Pty Ltd 1

Reviews in Aquaculture (2014) 6, 1–11 doi: 10.1111/raq.12060

1995; Fei et al. 1998; Chopin et al. 2001; Yang and Fei,

2003; Neori et al. 2004). The marine macroalgae benefit

from the co-culture with finfish because the algae require

dissolved nitrogen and phosphorus that are waste products

in finfish aquaculture from uneaten feed and fish excretion.

Besides its ecological aspect, integrated aquaculture also

has economic incentives as the nutrients contained in efflu-

ents, such as N and P, could be channelled into the produc-

tion of valuable products that are otherwise flushed from

the system (Chopin et al. 2001). The use of macroalgae as

nutrient strippers in integrated aquaculture has been dem-

onstrated as an excellent example of ecotechnology (e.g.

Neori et al. 2004). The benefits of integrating the produc-

tion of macroalgae with the fed mariculture of fish or inver-

tebrates to recapture waste nutrients are well known (Neori

et al. 1996; Troell et al. 1997; Chopin et al. 2001). Modern

integrated mariculture systems, seaweed-based in particu-

lar, are bound to play a major role in sustainable develop-

ment of coastal aquaculture (Neori et al. 2004). This issue

is highly relevant for a growing aquaculture industry in

Saudi Arabia (FAO 2010) to reduce environmental risk of

an oligotrophic sea that is rich in biodiversity (Khalil & Ab-

del-Rahman 1997; Baars et al. 1998; Al-Hafedh et al. 2012).

Seaweeds have been proven to be very efficient in restor-

ing water quality of the mariculture effluents and to reduce

the environmental impact derived from the high load of

nutrients contained in these effluents. Systems of integrated

aquaculture are ideal because the N and P in the animal

effluent are necessary requirements for the growth of the

seaweeds. Obviously, the best seaweed to integrate into an

animal aquaculture operation is one characterized by rapid

growth, the accumulation of N and P to high levels in tis-

sue, and some added value (Neori et al. 2004). Species of

the genus Ulva are usually preferred in biofiltration studies

due to a high biomass production and biofiltering effi-

ciency (e.g. Neori et al. 1996).

As part of an effort to develop integrated aquaculture

technology, we have been evaluating the tank-based inte-

grated system for the bioremediation of effluents using

green alga, Ulva lactuca, which is locally available in the

Red Sea at Jeddah coast in Saudi Arabia. A previous study

demonstrated that a red (Gracilaria arcuata) and a green

alga (U. lactuca) were good candidates to establish a land-

based IMTA system in the Saudi Arabia coast (Al-Hafedh

et al. 2012). However, as the efficiency of seaweeds as bio-

filters depends on several culture conditions, such as the

water flow and nutrient concentration (Buschmann et al.

2001), it is important to optimize the physiological poten-

tial of the selected seaweeds to design an efficient integrated

aquaculture system (Troell et al. 2003). This research com-

pares the growth, production and bioremediation potential

of the seaweed, U. lactuca at two stocking densities and two

effluent flow rates in an integrated marine aquaculture sys-

tem to culture marine tilapia (O. spilurus) and seaweeds at

the Red Sea coast of Saudi Arabia.

Materials and methods

Integrated aquaculture system

Integrated marine aquaculture system was installed at Fish

Farming Centre of the Ministry of Agriculture at Obhur

(Jeddah), Saudi Arabia as per the design depicted in Fig-

ure 1 by using fibreglass tanks. The system comprises of

one round conical bottom fish culture tank (3.1 m diame-

ter, 1.65 m depth in the centre and 1.4 m depth on the

periphery, total volume approximately 11 m3), one round,

conical bottom cylindrical sedimentation tank (1.3 m in

diameter, 1.25 m depth in the centre and 1 m depth on the

periphery, total volume approximately 1.44 m3) and six

oval round bottom seaweed culture tanks (each with total

length of 1.85 m, width 1.24 m, total water volume of 1 m3

and a surface area of 2.15 m2 per tank). The system was

Figure 1 Diagrammatic presentation and

layout of the integrated tank based aquacul-

ture system for the marine fish and seaweed

culture experiments. The figure at the base

indicates water sampling points in the culture

system as indicated in Table 1.

Reviews in Aquaculture (2014) 6, 1–11

© 2014 Wiley Publishing Asia Pty Ltd2

Y. S. Al-Hafedh et al.

covered by an asbestos roof with some transparent plastic

panels over the seaweed tanks to allow desired light while

avoiding direct sun. Moderate aeration with ambient tem-

perature and natural carbon dioxide concentration was

provided to the system. Aquaculture tank was aerated using

polythene tubes (2.5 cm in diameter) and airstones con-

nected to an air blower, whereas the aeration was provided

at the bottoms of the seaweed tanks by placing one perfo-

rated pipe in each tank which was connected to the air

blower through polythene pipes. Each pipe (1.5 m long

and 2.5 cm in diameter) had 2.5–3 mm diameter holes

spaced at 10 cm intervals along the length, so that the air

bubbles produced through the holes allowed to stir and

move the seaweed inside each culture unit.

Experimental set-up

Two independent experiments were run to compare the

effects of seaweed stocking density as well as flow of efflu-

ents on the bioremediation potential and biomass yield of

green alga, U. lactuca. Ulva lactuca was collected from the

shallow water of Jeddah coast and brought to the experi-

mental site in buckets. The inoculums were washed and

cleaned from the debris and associated algae or any possible

epiphytes before the stocking.

The experimental fish culture tank received filtered sea-

water from the well and stocked with 200 kg of Oreochr-

omis spilurus with an average weight of 101.3 � 4.0 g (at a

stocking rate of 20 kg m�3). The fish were fed twice daily

(at 0800 and 1300) with a 30% protein diet at 2% of the

biomass (1% at each feeding), and the total feed given per

day was recorded. A centre drain was used to remove solids

from the cone-bottom sedimentation tank. Fish effluents

from the sedimentation tank were allowed to flow by grav-

ity to the six seaweed culture tanks. Three seaweed tanks

were stocked with 3 kg of U. lactuca per tank, whereas each

of the other three tanks was stocked with 6 kg of U. lactu-

ca. The water flow in each tank was set to a low rate

(225 L h�1 which was equivalent to 3.75 L min�1) achiev-

ing six water turnovers per day in each seaweed tank. The

airflow was adjusted to be strong enough to allow the rota-

tion of seaweed at a rate of 3–4 times per minute in the

tanks. Seaweed biomass was harvested after every 10 days,

drained to eliminate the superficial water and then

weighed. The seaweed biomass was weighed, mixed and

then randomly re-distributed among the culture tanks

between trials to the initial density in each tank to avoid

position effects. The experiment was repeated for three

times (total 30 days).

The whole procedure was repeated by adjusting the water

flow to a high rate (450 L h�1, equivalent to 7.5 L min�1)

achieving 12 water turnovers day�1 in each seaweed tank.

The system was run 3 times again for 10 days using this

higher effluent flow rate. In this case, the U. lactuca stock-

ing density was the same and as in the previous experiment

and at every 10 days interval the biomass was weighed,

mixed and re-stocked to the initial density in each tank.

Water quality and other parameters

The water quality parameters (Ammonia-N, Nitrite-N,

Nitrate-N and Phosphate-P) were determined by using

Hach spectrophotometer (DR2800, Hach Lange, Dussel-

dorf, Germany) from the samples collected at four different

points in the system at different frequencies as shown in

Table 1 and Figure 1. The fresh weights of the seaweeds

were determined at the initial point and after every 10 days

using drainage procedure by taking all the seaweed from

one tank and letting the water trickle for 5 min, then shak-

ing the seaweed up and down for 3–5 times and then taking

total wet weight. The seaweed stocking was adjusted to ori-

ginal at every 10 days by taking out the excess seaweed. The

experiment was repeated three times for 10 days each.

Fish growth

Daily weight gain (DWG) expressed as g fish day�1, NP

expressed as kg m�3 day�1, and feed conversion ratio

(FCR) were calculated by using the following formulae:

DWG = (final weight�initial weight)/no. of fish/time

(days);

Net production (NP) = [final biomass (kg m�3)�initial

biomass, (kg m�3)]

FCR = total dry feed fed, kg/[final fish biomass (kg)�initial fish biomass (kg)]

Seaweed growth

Seaweed specific growth rate (SGR = % wet wt day�1) and

biomass yield (Y = g wet wt m�2 day�1) were determined

according to Evans (1972) and calculated as follows:

SGR ð%Þ ¼ 100� ½lnWt � lnW0Þ�=t

Y (g wet wt m�2day�1Þ ¼ ½ðWt �W0Þ=t�=SA

where W0 and Wt are initial and final wet weights (wt)

in grams, t is time in days and SA is the surface area.

Biofiltration efficiency of the seaweeds

Twice a week, water samples were taken at the inflows and

outflows of the seaweed tanks for TAN, nitrite and nitrate

analyses. The average reduction in TAN concentration

between the inflows and the outflows of the tanks (n = 3

for each culture condition) is expressed as a percentage and



Bioremediation potential of Ulva lactuca

defined as TAN uptake efficiency or TAN removal effi-

ciency. The amount of TAN removed per unit of time per

unit of area by the seaweeds represented the nitrogen

uptake rate or TAN removal rate and will be calculated

according to the formula adapted from Evans and Langdon

(2000).

TAN uptake efficiencyð%Þ ¼ ðSi � SoÞ=Si � 100

TAN uptake rateðg m�2day�1Þ ¼ QðSi � SoÞ=A=T

where Q = flow rate; Si = TAN inflow (g L�1); So = TAN

outflow (g L�1); A = tank surface (m2) and T = time. The

same formulae were used to calculate phosphate uptake

efficiency and phosphate uptake rate.

The fish excretion rates are associated with feeding

regimes (Zakes et al. 2006) and therefore, vary significantly

along the day. The biofiltration efficiency parameters (refer

to previous paragraph to see calculation formulas) for the

experiment using the two stocking densities (3 and

6 kg m�3) and the two flow rates (5.4 and 10.8 m3 day�1

were used to establish daily variations. The nutrient data

were taken in the morning (08:00 h), in the afternoon

(14:00 h) and in the late afternoon (17:00 h) in the same

points described above.

Statistical analysis

The biomass yield and specific growth rate were analysed

with a one-way ANOVA using the stocking biomass as the

experimental factor separated for both flux rates. As three

independent trials were run, each trial was used as a

repeated measurement. Daily variations in nutrient uptake

and uptake efficiency of U. lactuca during the culture per-

iod were compared using a two-way ANOVA. No statistics

were run to compare the water fluxes as the experiments

were not carried out on the same time period. All the tests

were performed after assuring the normality and homoge-

neity using Shapiro–Wilk’s and Levene’s tests, respectively.

The HSD Tukey’s a posteriori test was used to determine

statistical difference for the daily variations of biofiltration

efficiencies (P < 0.05). All the statistical tests were per-

formed using IBM SPSS Statistics version 19 (SPSS Inc.

2009).

Results and discussion

Culture conditions

Daylight irradiances over the seaweed tanks ranged from

950 to 1200 lmol photon m�2 s�1 in almost all sunny

days, while the experiment was running. Values of water

temperature, dissolved oxygen, pH, total ammonia nitro-

gen (TAN), nitrite (NO2–N), nitrate (NO3–N) and phos-

phate (PO4–P) in the fish culture tank are computed in

Table 2. Not much fluctuation was noted in seawater tem-

perature and salinity during the experiments, the tempera-

ture fell in a range of 28–31°C, while salinity was always

recorded to be around 42 ppt. Dissolved oxygen (DO) in

the seawater entering into the fish tank was in the range of

2.66–4.54 mg L�1. Also important to mention is that pH

Variables Measurement points Frequency

Seaweed Biomass Seaweed Tanks Every 10 days

Temperature Point 1, 3 and 4 Daily at early morning,

noon and late afternoon

Salinity Point 1, 3 and 4 Daily at noon

Dissolved Oxygen Point 1, 3 and 4 Daily at noon

pH Point, 1, 3 and 4 Daily at early morning,


Nutrient Concentration Point 1, 3 and 4 Day 2, 5 and 9 of each

experiment at early morning,


Organic Material Point 1, 2 and 3 Day 2, 5 and 9 of each

experiment and taken at noon

Sludge Point 2 After finishing every experiment

(every 10 days)

Carbon, Hydrogen, Nitrogen Seaweed tissues At the starting (day 1) and end

(day 10) of each experiment

Water Flow Point 3 Daily Daily

Seaweed Aeration Control Seaweed Tank Weekly

Fish Feeding Point 1 Daily

Fish Biomass and Density Fish Tank Every 10 days

The table also indicates the measurement frequency during the study period.

Table 1 Summary of variable that must be

monitored during the seaweed culture experi-

ments using the fish effluents. The position of

the measurements in the culture system is

established after Fig. 1




fluctuated between, 6.8 and 7.9. TAN concentrations in the

fish culture tank ranged between 0.0 and 0.07 mg L�1,

nitrite nitrogen ranged from 0.0 to 1.6 mg L�1, nitrate

nitrogen was found to fluctuate between nondetectable val-

ues and 2.7 mg L�1 and phosphate–phosphorus values

were recorded to fall in the range of non-detectable values

to 1.22 mg L�1. Figures show high mean values of nitrite

in the inflow to seaweed tanks indicating rapid rate of nitri-

fication in the system.

Fish growth

Data for the fish growth are summarized in Table 3. Initial

and final average weights for the fish during the experiment

in the integrated system were 98.7 g fish�1 and

200.3 g fish�1, respectively. Initial biomass in the fish-rear-

ing tank was 199.2 kg, and the final fish biomass was

recorded to be 380.8 kg. The daily weight gain was 1.75 g

fish day�1, while total weight gain and the NP were calcu-

lated to be 101.6 kg and 10.2 kg m�3, respectively. The

value for FCR was found to be 1.73 and survival was

94.24% during the experimental period of 8 weeks.

Marine tilapia, O. spilurus was selected for this experi-

ment because of its adaptability, better growth potential,

ease of handling and tolerance of this species to seawater.

Commercially, O. Spilurus, weighing 30–120 g is reared at

a stocking rate of 200–300 fish m�3, fed 30–34% protein

diet, and the commercial production is reported to be 30–40 kg m�3 (FFC 2007). Thus, similar stocking rate and

feeding was adopted for the fish in the present study to

indicate the relevance and reality of the outcome to the

commercial practices. Preliminary work on this species by

Al-Amoudi (1987) indicated the potential of this species

for marine culture in Saudi Arabia based on its tolerance to

seawater.

During 58 days rearing in integrated system, the fish was

fed with 2% body weight daily following Al-Ahmad et al.

(1988) who studied growth and production of O. spilurus

in the seawater tanks, raceways and cages in Kuwait and

determined a daily feed ration of 2% body weight to be

optimum for fish ranging in size from 70 to 130 g. Accord-

ing to Al-Ahmad et al. (1988), the growth rate of O. spilu-

rus in seawater tanks was 1.28 g fish day�1 with a

production of 6.1 kg m�3 month�1, FCR of 1.37 and sur-

vival from 93.0 to 98.7%. These results are comparable with

our results except daily weight gain (1.75 g fish day�1) that

is much better in our integrated system; however, their

FCR is superior. Cruz et al. (1990) also reared O. spilurus

in flow-through seawater tanks and reported much higher

daily weight gain, ranging from 2.07 to 3.49 g/day with a

FCR between 1.47 and 2.13 and survival rates from 94.99 to

97.71%.

Table 2 Water quality at the fish culture tank supply (point 1) in the morning, afternoon and evening during the whole experimental period of

2 months

Parameters Fish culture tank

Morning Afternoon Late afternoon Mean

Range Mean (SE) Range Mean (SE) Range Mean (SE) Range Mean (SE)

Water temperature 28.0–30.7 29.76 (0.07) 28.0–31.0 29.87 (0.09) 28.0–32.0 30.31 (0.01) 28.0–31.0 29.98 (0.06)

Dissolved oxygen 2.66–4.54 2.78 (0.15)

pH 6.80–7.85 7.38 (0.1) 6.80–7.87 7.40 (0.05) 7.0–7.85 7.43 (0.05) 6.80–7.87 7.40 (0.67)

Salinity 42 42 42 42

Ammonia-N 0.0–0.33 0.07 (0.02) 0.0–0.15 0.08 (0.01) 0.0–0.30 0.08 (0.02) 0.0–0.07 0.08 (0.01)

Nitrite-N 0.0–1.1 0.38 (0.11) 0.0–1. 6 0.50 (0.13) 0.0–1.4 0.48 (0.13) 0.0–1.6 0.45 (0.12)

Nitrate-N 0.0–2.4 1.41 (0.32) 0.0–2.7 2.46 (0.46) 0.0–1.6 2.20 (0.42) 0.0–2.7 2.02 (0.40)

Phosphate-P 0.0–1.09 1.09 (0.18) 0.39–1.22 1.22 (0.05) 0.28–1.1 1.10 (0.05) 0.00–1.22 1.14 (0.09)

Temperature in °C, salinity in g L�1 and all other parameters are in mg L�1. Data represent mean values and the standard error (SE).

Table 3 Fish, Oreochromis spilurus stocking and growth data in the

integrated system

Parameters Values � SD

Average initial fish weight (g) 98.71 � 5.11

Total initial fish biomass (kg) 199.20

Total initial fish number 2018

Average final fish weight (g) 200.3 � 6.21

Total final fish biomass (kg) 380.77

Total final fish number 1901

Fish survival rate (%) 94.24

Culture period (days) 58

Weight gain (g fish day�1) 1.75

Total gain (kg) 101.59

Net production (kg m�3) 10.16

Feeding rate (%) 2

Total feed consumed (kg) 175.5

Feed conversion ratio (FCR) 1.73

FCR, feed conversion ratio.




Seaweed growth and production

Growth and fresh biomass production of the green sea-

weed, U. lactuca was compared at two stocking densities

(3 kg and 6 kg m�2) and two flow rates (5.4 and

10.8 m3 d�1) (Fig. 2). At a low fish effluent flux, U. lactuca

yield achieved values of 50 to almost 150 g (fresh)

m�2 d�1) and the initial biomass did not affect significantly

(F = 1.55; d.f. 1, 12; P > 0.24) the biomass yield. However,

there was a statistically significant difference (F = 6.45; d.f.

2, 12; P < 0.013) between the three experimental trials sug-

gesting that even subtle environmental changes can pro-

duce some production differences. On the other hand, the

specific growth rate reached values of 6% d�1, did not vary

significantly between both initial biomass tested (F = 1.99;

d.f. 1, 12; P > 0.18) and between the experimental repeti-

tions (F = 2.66; d.f. 2, 12; P > 0.11) (Fig. 2).

When this experiment was repeated under a high fish

effluent flow (10.8 m3 d�1), the yield increased from 250

to over 300 g m�2 d�1 and the specific growth rates varied

from 6 to 12% d�1 (Fig. 2). As these values are higher than

the previous experiment (low fish effluent flux), they sug-

gest that nutrient may have been limiting the biomass pro-

duction at a low seawater flux. At the higher fish effluent

flow rate, the biomass yield did not vary significantly

(F = 0.21; d.f. 1, 12; P > 0.65) between both initial biomass

tested in this study and also there were no significant

(F = 1.66; d.f. 2, 12; P > 0.23) variation between the three

experimental trials (Fig. 2). However, the specific growth

rate showed a significant (F = 21.64; d.f. 1, 12; P < 0.001)

difference between initial biomass of 3 kg m�3 as com-

pared to the treatment using 6 kg m�3 (Fig. 2). Three rep-

etitions of the experiment clearly show that the specific

growth rates did vary significantly (F = 4.04; d.f. 2, 12;

P > 0.05), suggesting that the changes in certain subtle

environmental conditions can modify the experimental

results.

These experiments suggest that an increment of the fish

effluent flow in the seaweed culture tanks allowed to dupli-

cate the biomass yield obtained in a 10 days experiment.

This evidence further suggested that nutrient flux might

not become a limiting factor for seaweed production, as we

did not detect differences in temperature, pH, salinity or

other relevant environmental factors. Our results indicate

that the specific growth rate of U. lactuca reached upto

12% day�1. In previous studies, U. clathrata that was cul-

tured in tanks receiving waste water from a shrimp aqua-

culture pond (Copertino et al. 2009) and U. lactuca (Neori

et al. 1991) and U. rigida cultured in effluents from a mar-

ine fish pond (Jim�enez del R�ıo et al. 1996) showed high

daily SGRs attaining 12%, 17.9%, 13.8%, respectively.

These values are in the same range as those found in this

study.

Considering the results described in the above para-

graphs, we can state that the increase in water flow to

10.8 m3 day�1 (12 water turnovers d�1) is adequate to

maintain a high yield and that the stocking rate 3 kg m�3

for U. lactuca seems to be the best choice. If the biomass is

Figure 2 Average (�SD) fresh biomass pro-

duction (Yield; g m�2 day�1; upper graphs)

and specific growth rate (SGR;% day�1; lower

graphs) at the low (5.4 m3 day�1) and high

(10.8 m3 day�1) fish effluent flow rate in the

seaweed culture tanks. T1, T2 and T3 indicate

the three independent 10-days repetitions of

the experiments.




increased the growth rate is reduced to values that do not

allow an increment in the biomass yield. The biomass yield

of U. lactuca at lower as well reached values of 250 g fresh

m�2 d�1, at high flow rate either at 3 or 6 kg m�3. Khoi

and Fotedar (2011) reported that the growth rate and yield

of Ulva increased with increasing stocking densities but

decreased at the highest stocking (2.00 kg m�2). As tank

configuration, water movement and flux are relevant for

seaweed production in land-based tank systems (e.g. Bus-

chmann et al. 1994) the increment of water exchange rate

using fish effluents was crucial to increase productivity. Ne-

ori et al. (1991) found that under N-sufficient conditions,

increasing stocking densities can decrease the yield of

U. lactuca. In addition, light limitation, even though each

thallus was cycled from the top to the bottom of the tanks

may affect also biomass yield (Vandermeulen 1989). Lapo-

inte and Tenore (1981) suggested that insufficient carbon

supply may decrease seaweed growth at higher stocking

densities. In our case it seems that also as in other previous

studies (e.g. Buschmann et al. 1994) the carbon addition

by fish respiration seems relevant allowing that pH never

increased above 8 indicates that CO2 was never limiting the

growth in our seaweed tanks.

Nutrient uptake rate and removal efficiency

Ulva lactuca removed a fair amount of total ammonia

nitrogen (TAN) at removal rates ranging from 0.26 to

0.31 g m�2 day�1 and phosphate/phosphorus from 0.32 to

0.41 g m�2 day�1 but the values were not significantly dif-

ferent at both the water fluxes and the stocking rates

(Tables 4 and 5). In statistical terms, TAN removal efficien-

cies were not found to be responding significantly to the

stocking rate of the seaweed (54.36 at low-stocking density

and 67.56% at high-stocking density under lower flow rate

and 93.15 at low-stocking density and 92.69% at high-

stocking density under higher flow rate) but were positively

affected by the flow rate and were recorded to be signifi-

cantly higher (F = 14.66, d.f. 3, 59; P ≤ 0.0001) at higher

flow. Phosphate removal efficiencies were also indifferent

from either stocking density or flow rate and were ranging

from 16.4 to 24.03% (F = 0.43, d.f. 3, 59; P ≤ 0.7323). In

terms of stocking density in a square meter, we had 1.4 and

2.8 kg m�2 of U. lactuca as each of our seaweed tanks pro-

vided 2.15 m2 surface to seaweeds.

Khoi and Fotedar (2011) reported a maximum TAN

removal rate (81.14%) for U. lactuca at a stocking density

of 1 kg m�2 and their result was in accordance with the

data reported by Debusk et al. (1986) and Neori et al.

(1991) for U. lactuca in intensive fishpond systems. TAN

removal efficiency in the present study were much higher

(54.36 at low-stocking density and 67.56% at high-stocking

density under lower flow rate and 93.15 at low-stocking Table

4Dailyvariationofuptake

rates(g

m�2day

�1)an

duptake

efficien

cies

(%)ofUlvalactuca

inthemorning,afternoonan

dlate

afternoonat

twostockingden

sities

(3an

d6kg

m2)at

aseaw

a-

terturnoverrate

of5.4

m3day

�1

Parameters

U.lactuca

stockingden

sity

3kg

m2

6kg

m2

Morning

After-noon

Late

Afternoon

F-value(d.f.)

P-value

Morning

After-noon

Late

Afternoon

F-value(d.f.)

P-value

TANuptake

rate

(gm

�2day

�1)

0.20�

0.03a

0.26�

0.03a

0.26�

0.05a

0.56(2,41)

0.575734

0.22�

0.02a

0.31�

0.02a

0.31�

0.05a

2.49(2,38)

0.097084

TANuptake

efficien

cy(%

)53.25�

5.43a

54.36�

6.99a

48.82�

5.93a

0.23(2,41)

0.795604

50.95�

3.86a

67.56�

4.42b

57.74�

5.12ab

3.44(2,38)

0.042940

Phosphateuptake

rate

(gm

�2day

�1)

0.20�

0.9

a41.0

�0.12a

0.13�

0.05a

2.44(2,41)

0.100360

0.09�

0.04a

0.40�

0.11b

0.35�

0.12ab

2.95(2,38)

0.064114

Phosphateuptake

efficien

cy(%

)8.09�

3.61a

19.65�

5.69b

7.78�

3.20a

2.46(2,41)

0.098593

4.04�

1.94a

18.20�

4.56b

16.48�

5.13b

3.52(2,38)

0.039321

Values

representmea

ns(�

SE)an

ddifferentsuperscriptindicates

statistically

significantdifferences(HSD

Tuke

ytest;P<0.05).TA

N,totalammonianitrogen

.




density and 92.69% at high-stocking density under higher

flow rate) than 49–56% (Neori et al. 1991) from the marine

fishpond effluents and 55% (Neori et al. 1998) from an

integrated culture system of abalone and macroalgae.

Schuenhoff et al. (2003) reported 64% TAN removal for an

integrated fish and seaweed (U. lactuca) system.

The daily variations of the removal efficiencies of TAN

and phosphate at lower nutrient flux are presented in

Table 4 and at higher nutrient flux in Table 5. There was

no significant daily variation in the TAN removal rates at

both the stocking densities and the flow rates. Statistically

significant positive differences, however, were noted in

TAN removal efficiencies at higher stocking density under

low nutrient flux showing lower values in the morning and

better performance in the afternoon (Table 4). Daily varia-

tions in the phosphate uptake rate and removal efficiencies

were also significantly better at higher stocking density

under low nutrient flux (Table 4 and 5). The removal effi-

ciency of orthophosphate in our macroalgae biofilter tank

was similar to other studies (Cohen & Neori 1991; Neori

et al. 1998; Schuenhoff et al. 2003).

Conclusions

Seaweed species suitability for integrated aquaculture

depends on the culture conditions and the local environ-

mental conditions. The selection of seaweed species for

their commercial use as biofilters depends principally on

two aspects. The interest of investors for a new species to

be incorporated depends firstly on the commercial value

and, secondly, on the physiological capabilities for growth

in culture conditions together with its capacity to remove

dissolved nutrients (Buschmann et al. 2001; Chopin et al.

2001). The economic value of Ulva species is generally not

as high as Gracilaria or other seaweed species that are used

for raw materials for phycocolloid production as well as for

edible seaweeds. However, Ulva can be utilized as a nutri-

tive feed for herbivorous mariculture animals such as abal-

ones and sea urchins (e.g. Osako et al. 2004; Dworjanyn

et al. 2007). Species of Ulva have been studied mainly from

the viewpoint of the treatment of land-based pond/tank

effluent (Danakusumah et al. 1991; Neori et al. 1991;

Msuya & Neori 2002; Hern�andez et al. 2005; Robertson-

Andersson et al. 2008; Copertino et al. 2009). In this study,

we have selected U. lactuca to test its relevance under inte-

grated aquaculture at the Red Sea coast of Saudi Arabia,

and our purpose was mainly to assess its physiological

capabilities in local culture conditions.

Results of this study confirms the conclusion made by

Neori et al. (1996), who found that tank-cultured green

alga, Ulva was highly effective for treating fish culture

effluent. Various strategies for integrating seaweed cultiva-

tion with fish culture have been successful and we found aTable

5Dailyvariationofuptake

rates(g

m�2day

�1)an

duptake

efficien

cies

(%)ofUlvalactuca

inthemorning,afternoonan

dlate

afternoonat

twostockingden

sities

(3an

d6kg

m2)under

asea-

water

turnoverofflow

rate

10.8

m3day

�1

Parameters

U.lactuca

stockingden

sity

3kg

m2

6kg

m2

Morning

After-noon

Late

afternoon

F-value(d.f.)

P-value

Morning

After-noon

Late

afternoon

F-value(d.f.)

P-value

TANuptake

rate

(gm

�2day

�1)

0.15�

0.02a

0.21�

0.02a

0.33�

0.11a

2.02(2,62)

0.141579

0.14�

0.02a

0.25�

0.04a

0.18�

0.02a

3.2

(2,44)

0.050872

TANuptake

efficien

cy(%

)97.54�

1.19a

93.15�

4.41a

87.34�

3.92a

2.17(2,62)

0.123057

91.78�

4.47a

92.69�

3.77a

96.89�

2.33a

0.39(2,44)

0.679542

Phosphateuptake

rate

(gm

�2day

�1)

0.74�

0.18a

0.32�

0.07a

0.35�

0.06a

4.15(2,62)

0.020508

0.41�

0.01a

0.33�

0.05a

0.47�

0.01a

0.6

(2,44)

0.553447

Phosphateuptake

efficien

cy(%

)30.10�

5.77a

24.03�

6.19b

86.22�

3.33ab

42.59(2,62)

<0.0001

22.28�

6.54a

16.40�

2.22a

22.59�

4.13a

0.56(2,44)

0.575415

Values

representmea

ns(�

SE)an

ddifferentsuperscriptindicates

statistically

significantdifferences(HSD

Tuke

ytest;P<0.05).TA

N,totalammonianitrogen




lower density at higher flow rate work remarkably well for

U. lactuca because of large thin thalli that need more sur-

face rather than the volume of culture vessel to absorb

enough light for photosynthesis. Ulva is suitable for inte-

grating with prawn systems because these species have high

tolerance and affinity for ammonium uptake (Lehnberg &

Schramm 1984). Previous studies have focused on the inte-

gration of Ulva with finfish (Jim�enez del R�ıo et al. 1996),

abalone (Neori et al. 1998, 2000) and prawns (Litopena-

eus vannamei) (Copertino et al. 2009; Cruz-Su�arez et al.

2010). Yamasaki et al. (1997) showed that integration of

kuruma prawn, Penaeus japonicus larvae and Ulva lactuca,

resulted in higher survival and better growth of prawn

larvae and lower bacterial density in seaweed treatments.

In the present study, Ulva lactuca performed well with

marine tilapia (O. spilurus) as has also been found to do

well with effluent from the culture of the gilthead bream,

Sparus aurata in Israel (Vandermuelen and Gordin, 1990).

It is also illustrated in this work that the concept of inte-

grated production can be applied in the management of

commercial aquaculture systems in Saudi Arabia as has

been shown in many studies (Cohen & Neori 1991; Neori

et al. 1991; Schuenhoff et al. 2003). Seaweeds used for

human consumption, bio-fuels and chemical extraction

may be of relatively high economic value and can contrib-

ute substantially to the economic viability of integrated

aquaculture systems. Sze (1998) stated that Ulva tolerate

pollution better than most macroalgae. They can be used as

bio-indicators of nutrients in the water column as their

ability to assimilate surrounding nutrients is rapid which is

clearly reflected by their tissue nutrient content within a

relatively short period of time (Ryther et al. 1975).

The integrated culture system described here can

improve the feasibility of land-based mariculture as it can

reduce the risks of the nutrient release into the environ-

ment and offers opportunities for Saudi Arabian Red Sea

coast and other areas with similar environmental condi-

tions that are especially relevant to maintain the oligo-

trophic condition of this sea reducing the environmental

impacts of a rapidly growing coastal aquaculture.

Acknowledgements

The authors acknowledge the financial support from

King Abdulaziz City for Science and Technology, Riyadh

and the facilities provided by the Fish Farming Center of

the (Ministry of Agriculture), Jeddah for conducting this

research.

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Documents

Bioremediation potential, growth and biomass yield of the green seaweed, Ulva lactuca in an integrated marine aquaculture system at the Red Sea coast of Saudi Arabia at different