PRESENTATIONONMICRO-ALGAE

PREPAREDBY

MD. INJA-MAMUN HAQUE

ABDUR RAZZAK HASAN

TAHTEHAL ENAM BORNO

The base of the food chain in the marine environment comprises Phytoplankton

Phytoplankton is the main producer in marine enviornment

Most frequently used in commercial culture operations

What is micro-algae???

commonly known as seaweed

• Also referred to as phytoplankton, microphytes, or planktonic algae

Produce mass quantities of zooplankton (rotifers, copepods, brine shrimp)

This zooplankton serves as food source for larval and early-juvenile stages of crustaceans and fish

Major classes of cultured algal species

More than 40 different species isolated and cultured as pure strains in intensive systems

currently used 8 major classes and 32 genera

Diatoms

Skeletonema costatum

Thalassiosira pseudonana

Chaetoceros gracilis

C. calcitrans

Flagellates

Isochrysis galbana

Tetraselmis suecica

Monochrysis lutheri

Class

Cyanophyceae Bacillariophyceae Haptophyceae Chrysophyceae Prasinophyceae Cryptophyceae Xanthophyceae Chlorophyceae

Figure 2.2. Some types of marine algae used asfood in aquaculture (a) Tetraselmis spp. (b)Dunaliella spp. (c) Chaetoceros spp. (Laing,1991)

A generalized set of conditions for culturing micro-algae Parameters Range Optima

Temperature (°C) 16-27 18-24

Salinity (g.l-1) 12-40 20-24

Light intensity (lux) 1,000-10,000 (depends on volume and density

2,500-5,000

Photoperiod (light: dark, hours)

16:8 (minimum)

24:0 (maximum)

pH 7-9 8.2-8.7

Temperature controlled room for maintenance of algalstock cultures in a bivalve hatchery: stock cultures in test tubes (left)and inoculation hood (right).

AERATION/MIXING

Why mixing is necessary??? To ensure all cells of the population

equally exposed to the light and nutrients

To prevent sedimentation of the algae

To avoid thermal stratification

To improve gas exchange between the culture medium and the air

Mixing achieved by

stirring daily by hand (test tubes, erlenmeyers), aerating (bags, tanks)

using paddle wheels

jetpumps (ponds)

NB: not all algal species can mixing tolerate vigorous

Aeration filter (Fox, 1983)

Growth dynamics 

Growth of an axenic culture of micro-algae characterized by five phases  

1. Lag or indution phase 2. Exponential phase3. Phase of declining growth rate4. Stationary phase5. Death or "crash" phase

Lag or induction phase

little increase in cell density occurs

relatively long when an algal culture is transferred from a plate to liquid culture

attributed to the physiological adaptation of the cell metabolism to growth

Lag phase(Cont.)

the increase of the levels of enzymes and metabolites involved in cell division and carbon fixation

exponentially growing algae have short lag phases, which can seriously reduce the time required for upscaling

Exponential phase

key to the success of algal production

the cell density increases as a function of time t according to a logarithmic function

Ct = C0.emt Ct and C0 being the cell

concentrations at time t and 0

m =specific growth rate (dependent on algal species,light intensity and temperature)

Phase of declining growth rate

Cell division slows down when

nutrients light pH carbon dioxide other physical and

chemical factors

begin to limit growth.

Stationary phase

the limiting factor and the growth rate balanced,

results in a relatively constant cell density

Death or "crash" phase

water quality deteriorates

nutrients are depleted to a level

incapable of sustaining growth.

Cell density decreases rapidly

Culture eventually collapses.

Algal culture techniques

Algal culture techniques Indoor Outdoor

allows control over illumination, temperature, nutrient level, contamination with predators and competing algae

make it very difficult to grow specific algal cultures for extended periods

Algal culture techniquesOpen Closed.

uncovered ponds and tanks (indoors or outdoors)

are more readily contaminated

closed culture vessels such as tubes, flasks, carboys, bags, etc

Algal culture techniques

Axenic =sterile Xenic.

free of any foreign organisms such as

bacteria and require a strict sterilization of all glassware, culture media and vessels to

avoid contamination.

impractical for commercial operations

Advantages and disadvantages of various algal culture techniques

Culture type Advantages Disadvantage

Indoors A high degree of control(predictable)

Expensive

Outdoors Cheaper Little control (less predictable

Closed Contamination less likely

Expensive

Open Cheaper Contamination more likely

Advantages and disadvantages of various algal culture techniques

Culture type Advantages Disadvantages

Axenic Predictable, less prone tocrashes

Expensive, difficult

Non-axenic Cheaper, less difficult

More prone to crashes

Advantages and disadvantages of various algal culture techniques

Culture type Advantages Disadvantages

Continuous Efficient, provides a consistentsupply of high-quality cells,automation, highest rate ofproduction over extendedperiods

Difficult, usually only possible toculture small quantities, complex,equipment expenses may be high

Semicontinuous Easier, somewhat efficient

Sporadic quality, less reliable

Batch Easiest, most reliable

Least efficient, quality may beinconsistent

Batch culture method

Batch culture method

Consists of a single inoculation of cells into a container of fertilized seawater

Followed by a growing period of several days

Finally harvesting when the algal population reaches its maximum or near-maximum density

In practice, algae are transferred to larger culture volumes prior to reaching the stationary phase

Batch culture method

larger culture volumes are brought to a maximum density and harvested

The following consecutive stages might be utilized: test tubes,

2 l flasks, 5 and 20 l carboys, 160 l cylinders, 500 l indoor tanks, 5,000 l to 25,000 l outdoor tank

Batch culture method

According to the algal concentration, the volume of the inoculum amounts to 2- 10% of the final culture volume

Where small amounts of algae required indoor culture employs 10 to 20 l glass or plastic carboys (may be kept on shelves backlit with fluorescent tubes)

Batch culture systems for themass production of micro-algae in 150 lcylinders.

Batch culture method ADVANTAGE

Batch culture systems widely applied because of

Simplicity and flexibility

Allowing to change species

To remedy defects in the system rapidly

Batch culture method DISADVANTAGE

Batch culture not necessarily the most efficient method

harvested just prior to the initiation of the stationary phase

must thus always be maintained for a substantial period of time past the maximum specific growth rate.

the quality of the harvested cells may be less predictable than that in continuous systems

need to prevent contamination during the initial inoculation and early growth period

require a lot of labour to harvest, clean, sterilize, refill, and inoculate the containers

Batch culture method

Carboy culture shelf (Fox, 1983

Carboy culture apparatus(Fox, 1983).

Continuous culture

Continuous culture

Culture in which a supply of fertilized seawater continuously pumped into a growth chamber

The excess culture simultaneously washed out, permits the maintenance of cultures very close to the maximum chamber

Two categorie

Turbidostat culture chemostat culture

Continuous culture

turbidostat culture chemostat culture

the algal concentration is kept at a preset level

by diluting the culture with fresh medium

by means of an automatic system.

a flow of fresh medium is introduced into the culture at a steady, predetermined rate.

The latter adds a limiting vital nutrient (e.g.nitrate) at a fixed rate

in this way the growth rate and not the cell density is kept constant.

Continuous culture

Algae Culture density forhighest yield (cells per μl

Usual life of culture(weeks)

Tetraselmis suecica 2 000 3-6

Chroomonas salina 3 000 2-3

Dunaliella tertiolecta 4 000 3-4

Isochrysis galbanaMonochrysis lutheriPseudoisochrysis paradoxa

20 000 2-3

Continuous culture methods for various types of algae in 40 linternally-illuminated vessels (suitable for flagellates only) (modified fromLaing, 1991),

Continuous culture

Diagram of a continuous culture apparatus (not drawn to scale):

(1) enriched seawater medium reservoir (200 l); (2) peristaltic pump; (3)resistance sensing relay

(50- 5000 ohm) (4) lightdependent resistor (ORP 12); (5) cartridge filter (0.45 μm); (6) culture vessel (40 l); (7) six 80 W fluorescent

tubes (Laing, 1991).

ADVANTAGE OFContinuous culture

Producing algae of more predictable quality

Amenable to technological control and automation

DISADVANTAGE OFContinuous culture

Relatively high cost and complexity Requirements for constant illumination

and temperature mostly restrict continuous systems to indoors

This only feasible for relatively small

production scales.

Harvesting and preserving micro-algae

High-density algal cultures concentrated by either chemical flocculation or centrifugation

Products such as aluminum sulphate and ferric

chloride cause cells to coagulate and precipitate to the bottom or float to the surface

Recovery of the algal biomass is then accomplished by

1.siphoning off the supernatant 2.skimming cells off the surface

Harvesting and preserving micro-algae

Coagulated algae no longer suitable as food for filter-feeders

Centrifugation of large volumes of algal culture

usually performed using a cream separator

Cells deposited on the walls of the

Centrifuge head as a thick algal paste

The resulting slurry stored for 1-2 weeks in the refrigerator or frozen

Harvesting and preserving micro-algae

Cryoprotective agents (glucose, dimethylsulfoxide) added to maintain cell integrity during freezing

Cultures stored in hermetically sealed vials lose their viability more rapidly than those kept in cotton-plugged vials

Concentrated cultures of Tetraselmis suecica kept in darkness at 4°C maintain their viability

Nutritional value of micro-algaeDepends on

1. cell size 2.digestibility 3. production of toxic compounds 4.biochemical composition

There marked differences in the compositions of the micro-algal classes and species

Nutritional value

Protein 12-35%

Lipid 7.2-23%

Carbohydrate 4.6-23%

Micro-algae can also be considered as

a rich source of ascorbic acid (0.11-

1.62% of dryweight,

a mixture of

algal species supplies the animals

with an adequate amount of both

nutrients

Use of micro-algae in Aquaculture

Bivalve molluscs

Intensive rearing of bivalves relied on the production of live algae

Comprises on average 30% of the operating costs in a bivalve hatchery

use of micro-algae in Aquaculture

Pinhead shrimp

Added during the non-feeding nauplius stage

algae available immediately upon

molting into the protozoea stage.

Penaeid shrimp

Requirements for cultured algae in hatchery andnursery culture of bivalve molluscs (Utting and Spencer, 1991

Use of micro-algae in Aquaculture

Marine fish "green water technique" part of the

commonly applied techniques for rearing larvae of

Gilthead seabream Sparus aurata Milkfish Chanos chanosHalibut Hippoglossus hippoglossus

Effects of the presence of micro-algae in the larval rearing tank

stabilizing the water quality in static rearing systems(remove metabolic by-products, produce oxygen);

a direct food source through active uptake by the larvae with the polysaccharides present in the algal cell walls possibly stimulating the non-specific immune system in the larvae

Effects of the presence of micro-algae in the larval rearing tank

an indirect source of nutrients for fish larvae through the live feed (i.e. by maintaining the nutritional value of the live prey organisms in the tank)

increasing feeding incidence by enhancing visual contrast and light dispersion

microbial control by algal exudates in tank water and/or larval gut

Effects of the presence of micro-algae in the larval rearing tank

an indirect source of nutrients for fish larvae through the live feed (i.e. by maintaining the nutritional value of the live prey organisms in the tank)

increasing feeding incidence by enhancing visual contrast and light dispersion

microbial control by algal exudates in tank water and/or larval gut

References

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