THE INFLUENCE OF LIGHT INTENSITY ON GROWTH OF THE MARINE PLANKTONIC ALGA
CHLORELLA SP.UNDER LABORATORY CONDITIONS
Igor Brautovic
Institute of Oceanography and fisheries, Dubrovnik, Croatia - igor@labdu.izor.hr
Abstract
Chlorella sp.cultures were exposed to the light intensities of 900, 2000, 4000, 6000, and 12000 lux until the steady phase of growth was
achieved. Optimal growth at 6000 lux was established. The shortest period of log phase was recorded for the algae exposed at 6000 and
12000 lux, and the longest at 2000 lux. Algae at 900 lux were exposed to 12000 lux on the 23rd day of the experiment with successful
growth.
Keywords: Chlorella, light intensity, growth rate
Rapp. Comm. int. Mer Médit., 37,2004
322
Introduction
The green phytoplankton alga Chlorella sp.is normally used in
mariculture for human food, and for culturing zooplanktons in marine
fish hatchery. In a microalgal culture under illuminated conditions, the
production rate of cells depends on the distribution of light intensity
and growth rate of cells (1). The aim of the research was to establish
optimal light intensity in order to access maximal abundance of
Chlorella sp.in the shortest time.
Material and methods
Chlorella sp. was isolated from the coastal waters of Kaštelabay,
Central Adriatic Sea, and persistence in laboratory in a liquid medium.
For each experiment 20 l of filtrated and sterilized (by UV lamp) sea
water, 500 ml Chlorella sp. culture abundance 1.3x10
7
cell ml
-1
, 20.5
ml of nutrition medium “Walne” (2), and 0.25 ml of thiamine were
added in three bags. In each experiment three different bags with
algae culture were exposed to the certain light intensity estimated by
the luxmeter: 900, 2000, 4000, 6000 and 12000 lux. The bags at 900
lux were exposed at 12000 lux on the 23
rd
day of the experiment.
Light source for the intensities 900 – 600 lux were ?uorescent tubes
40 W (220-240 V), and for the highest light intensity of 12000 lux
VTFE lamp was used. Photoperiod 15 h light / 9 h dark was set by the
timer mechanism. Cultures were continuously mixed by air pumps.
Indoor and the temperature of the medium, as well as the salinity (psu)
were controlled. The algae cells were counted daily at 9 am by the
Bürcker-Türck counter.
Results and discussion
The initial abundance of algae was 3.3x10
5
cell ml
-1
. The seawater
salinity was 37.5 psu at the beginning and at the end of the experiment
it was between 42.0 psu (at 900 lux) and 43.3 psu (at 12000 lux). The
temperature was between 23.9°C and 25.8°C. Photo bioreactors with
diurnal cycles will save energy and improve organic carbon sources
removal (3). (4) were tested the use of submarine lamps (1.20 m
?uorescent tube, 90 W, 220-240 V) in large volume tanks (0.8 m
3
) for
the development of Chlorella sp. with the bloom technology. 10-16 x
10
6
cell ml
-1
were obtained after a week. In our experiment maximal
growth was at 6000 lux. After 7 days the abundance of Chlorella sp.
was 19.1 x 10
6
cell ml
-1
, and the maximal abundance was 85.9 x 10
6
cell ml
-1
on the 15
th
day of the experiment (Fig. 1). Algae previously
exposed at 900 lux, were in a steady phase on 23
rd
day, and then they
were exposed at a significantly higher light intensity of 12000 lux that
caused the growth after 48 hours, and a new steady phase was
established after 7 days (Fig. 2). It seems that in the first part of the
experiment the nutrition did not become depleted, so in the second
phase the higher light intensity was stimulating the growth until the
second steady phase was achieved.
Fig. 2. A new growth of Chlorella sp.after changing the light intensity.
References
1-Hirata S., Taya M., and Tone S., 1996. Characterization of Chlorella
cell cultures in batch and continuous operations under a photoautotrophic
condition. Journ. Chem. Eng. Jap., 29: 953-959.
2-Walne P.R., 1970. Studies on the food value of nineteen genera of algae
to juvenile bivalves of the genera Ostrea, Crassostrea, Mercenariaand
Mytilus. Minist. Agric., Fish. and Food (London). Fish. Invest., 25: 62 pp.
3-Lee K., and Lee C-G., 2001. Effects of light/dark cycles on wastewater
treatments by microalgae. Biotechnol. Bioprocess Eng., 6: 194-199.
4-Sanmartin M., Bengoa-Ruigomez M.V., Hatziathanasiou A., Divanach
P., and Kentouri M., 1995. On the use of submarine light tubes in large
volume intensive Chlorella sp. culture: definition of the optimum number
of lamps per unit of volume. Actas del V Cong. Nac. de Acuicul. Sant
Carles de la Rapita, 10-13 de Mayo 1995. F Castello i Orvay and A.
Calderer i Reig (eds.), Univ. de Barcelona Publ., 1000 p.
Fig. 1. The growth of Chlorella sp.under the different light intensities.
