For large diatoms and dinoflagellates you can use a drawn-out glass pipet under a low-powered microscope. With a steady hand you can pick individual cells.  Use a Pasteur pipet that has been drawn out to a very thin tip by holding it over a bunsen burner flame for several seconds, pull it to elongate and thin the tube, and snap off the excess at the end. Attach the pipet to a piece of flexible tubing attached to a bulb that is attached to a vice-like apparatus designed to gently squeeze the bulb by turning a screw. This is the only way to achieve the very gentle suction required to draw cells into the pipet. I suggest not drinking much coffee prior to trying this approach.

For smaller cells I recommend using serial dilutions of raw seawater into enriched sw medium (like F/2) , put them into growth chamber and observe each dilution until you find the one that has grown only a single species. This method only works for the rarest species though.

Good luck!

we usually use micropipetting to isolate microalgae from water sample, and an inverted microscope would be better.

You may follow the attached papers published by us.

can centrifuge the water sample in lower rpm to avoid the shape of algae  being destroyed. then, remove the supernatant and take the pellet to observe. scanning electron microscope (SEM) is better for identification of microalgae...

For large diatoms and dinoflagellates you can use a drawn-out glass pipet under a low-powered microscope. With a steady hand you can pick individual cells.  Use a Pasteur pipet that has been drawn out to a very thin tip by holding it over a bunsen burner flame for several seconds, pull it to elongate and thin the tube, and snap off the excess at the end. Attach the pipet to a piece of flexible tubing attached to a bulb that is attached to a vice-like apparatus designed to gently squeeze the bulb by turning a screw. This is the only way to achieve the very gentle suction required to draw cells into the pipet. I suggest not drinking much coffee prior to trying this approach.

For smaller cells I recommend using serial dilutions of raw seawater into enriched sw medium (like F/2) , put them into growth chamber and observe each dilution until you find the one that has grown only a single species. This method only works for the rarest species though.

Good luck!

Recently at a meeting, Cyto 2014, I heard about a number of researchers utilizing Flow Cytometers to sort, identify, and culture algae and other particulates of varying sizes.  They tended to use acoustic focusing instruments so that they could screen gallon of sea water per minute.  A lot of these were custom built instruments.  Obviously this may be beyond what you are looking for, but there may be other similar instruments that can be used on a smaller scale.  Just a thought.  Technologies built for one application may be very useful across multiple disciplines.

I am currently using a method modified from PhycoTech.   I am sieving my sample into three size fractions (>500um, 499-75um, and

I depends which group of microalgae You want to isolate. In my lab we are focused on cyanobacteria and i can highly  recommend You  this paper: Rippka, R. (1988). Isolation and purification of cyanobacteria. Methods in Enzymology, 167: 3-27.

Greetings!

All good ways to get an isolate in your responses.  I will add another I have used.  An atomizer, like the kind used for perfume.  I place the sample into the reservoir of the atomizer, then spray onto an agar-filled petri dish.  I tend to use the water from which the organisms were collected, which gives you most of the chemicals they may need (other than what might precipitate during autoclaving).  

Few suggestions from Basic Microbiology,

You can setup a winogradskys column for enrichment of the microalgae of the sample water, use pastuer pipette to withdraw sample from each layer and then observe under dissecting microscope or high power for the presence of the algae like organisms. If you find positive samples, repeated plating and enrichment on algae culture medium chu medium and f/2 medium will help you recover some culturable  algae. Besides its always better to enrich the algae using some antibacterials and antifungals before plating as the growth rate varies drastically and the bacteria and fungi will outnumber the algae before they colonize the plate.

Best wishes.

You can use BG11 agar medium in petriplates for Blue green algae (or cyanobacteria) isolation by using serial dilution spread plating technique. Just serially dilute your sample and spread plate the aliquot. Incubate at 25- 28 degree celsius under proper light (for photosynthesis). After growth of algal colonies on plate transfer them to BG11 broth for liquid culture and storage.

You can use any routinely used microscope for morphological study of the microalgae but high contrast and resolution microscope with camera will do the best for your study. 

Link for Composition of BG11 medium is attached.

Kunal

http://www.ccap.ac.uk/media/documents/BG11.pdf

Dispense 9 ml BG11 agar medium with trace element 0.1%of media into each of ten test tubes with sterile automatic dispenser or sterile 10 ml pipettes. Aseptically add 1 ml of enrichment sample to the tube and serial dilute it then Incubate test-tubes under controlled temperature and light conditions:

(a) Temperature and photoperiod adjacent to the natural environmental condition.

(b) Llight intensity should be good enough as natural environment for photosynthesis.

• Examine cultures microscopically after 2 to 4 weeks by withdrawing a small sample aseptically from each dilution tube.

For collection micro algae , first of all collect random samples, dispense them in centrifuge bottles and centrifuge at slow speed for 20 minutes, resuspunded the pellet and a smaller portion 2 ml of it on  BG11 agar medium with trace element 0.1%of media. Make serial dilutions aseptically and add 1 ml of enrichment sample to the tube and serial dilute it. Now icubate test-tubes under controlled temperature and light conditions. Sea the micro algae cells under inverted microscope. You can use hanging drop method fir culture of microalgae. For smaller cells use serial dilutions of raw seawater into enriched sw medium (like F/2) 

the are many ways to isolate algae from a water sample by using streaking method or serial dilution or inoculation lop each method depend on the type of algae that you need to isolate