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Outdoor mass production of marine diatoms for bivalve hatcheries using saline groundwater: a case study in Yerseke (Netherlands) and the improvement of the culture systems in Bouin (France)
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Advisor(s)
Abstract(s)
The level of the bivalve production in hatcheries and nurseries let to the need to
develop a low cost mass microalgae production to be used as food. The saline
groundwater has been used successfully as culture medium for marine diatoms, as well
as for some fish and crustaceans. The objective of this work was to evaluate in two
different sites, at Yerseke and in Bouin, the groundwater quality to be used in diatoms
production.
At Yerseke the effects of acclimatization and coverage of tanks (to avoid the
decrease of water temperature during the night) on the cellular concentration were also
evaluated. The first essays revealed that the groundwater had very high nutrient
concentration, where the diatom Skeletonema costatum grew up to 1.3*10P
6
P cells/mL in
7 days. In another experiment the iron concentration was very high (reducing the light
penetration) but the cultures of Chaetoceros mulleri (previously grown in the algae
room) supported these conditions and reached cellular concentrations of 5.6*10P
5
P
cells/mL, minimizing the importance of the effects of acclimation in growth. The use of
a trickling-block system reduced the iron concentration of the groundwater used in the
third experiment. No significant differences were observed in the cellular concentration
(1.9*10P
5
P cells/mL) due to the covering of the tanks, being the water temperature higher
in the covered tanks. It can be concluded that although the nutrient concentrations are
elevated the observed variability in the groundwater makes it unreliable. However, the
outdoor production of marine diatoms in Yerseke could be possible, given the
promising results of these first essays.
The second part of the work aimed to contribute to the improvement of a wellestablished
batch system using groundwater and the improvement of productivity by the
introduction of continuous production systems in Bouin. Results showed that the
duration of the batch cultures with Skeletonema costatum and groundwater as culture
medium was influenced by water temperature and available light, because under higher
light conditions cellular concentrations reached 1.4 *10P
6
P cells/mL (within 3 days). The
light penetration profile showed that light attenuation in the production tanks was very
high, indicating that the depth of the tanks should be reduced. In the Batch cultures the
nitrogen and phosphorus were completely consumed. The productivity of these systems
could therefore been increased in the summer, with more light and with the adding of
these nutrients to the cultures. The continuous culture at a daily dilution rate of 80 % of
the tank’s volume per day was maintained for 34 days without cleaning. The culture
was productive throughout the all period, with constant pH values. The 6 days
experiment using different dilution rates showed that in lower renewal rates the growth
rate is lower, whereas the cellular production, turbidity of the cultures and the light
attenuation in the tank are higher. The opposite occurs with higher dilution rates,
leading to the conclusion that the better dilution rate for the tested period was of 80 %,
since it is necessary to find a compromise between the washing of the culture and the
risk of collapse. The cellular productivity of the continuous systems with a dilution rate
of 80% dayP
-1
P was similar to the one of the batch culture tested. This shows that the
outdoors continuous systems are a reliable alternative to the batch culture that can be
used in the low irradiance periods and in countries with less light.
Description
Dissertação de mest., Biologia Marinha, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2007
Keywords
Teses Aquacultura Pescas Diatomáceas Produtividade