1. Sampling macroalgae
The larger freshwater algae can be collected by hand in shallow water and by snorkelling or SCUBA diving in deeper water. In clear and shallow water it is helpful use a glass-bottomed box to view the underwater habitat. Forceps are easier than fingers to gather small delicate specimens. A three-pronged grapnel or dredge is required for the remote sampling of macroalgae such as stoneworts (charophytes) and other aquatic plants. Large specimens should be shaken or gently squeezed on collection to remove excess water before storing in suitable containers such as polythene bags, with smaller individuals placed in vials or jars together with a little water.
2. Sampling algae associated with surfaces
An old toothbrush or small spoon are very useful implements for brushing or scraping small algae from a surface into a collecting tube or bottle. The edge of the spoon can be used to scrape the surface and the sample kept within the bowl of the spoon by using the thumb before transferring to a suitable vial. A knife or scalpel is useful for scraping encrusting forms from hard surfaces and removing slivers of wood such as when sampling subaerial forms on tree trunks. A geological hammer or stone chisel is useful for removing portions of a surface with very firmly encrusted forms such as Hildenbrandia – safety glasses need to be worn.
Small attached epiphytes and loosely associated forms are commonly present on filamentous algae, bryophytes and other aquatic macrophytes. These microalgae may be sampled by removing access water from collections of finely divided flowering plants (e.g. Utricularia, Myriophyllum), mosses or larger filamentous algae (e.g. Cladophora, Vaucheria) by shaking them a few times before gently squeezing and collecting the water and microalgae into a wide-mouthed container. Flocculent material that sometimes tenuously coats submerged portions of macrophytes is best removed by very carefully inverting a jar over the plant to be sampled, cutting it and then capping it with the plant and associated flock inside. After settlement of the algal-rich sediment to the floor of the container, the excess water can be carefully removed and the sample pipetted into small tubes or vials. This squeezing technique is useful for sampling epiphytes and free-living algae associated with aquatic plants in shallow water (tychoplankton) along with forms that are normally in open water (euplankton, true plankton).
Greenish or brownish slimy films of microalgae and other organisms frequently cover submerged parts of reeds and other emergent aquatics. These can best removed with forceps or by running a thumb and forefinger up a stem and collecting the film into a suitable container. If the film is very loose, it can be removed by suction using a pipette with a large bulb, or by cutting a portion of film-bearing surface and carefully transferring it underwater to a container. Submerged twigs, dead culms, portions of the roots and stems of aquatic plants and other hard surfaces (e.g. rocks, glass, plastic and wood) are all suitable surfaces for algae.
3. Sampling microalgae associated with sediments
Free-living algae associated with mud or silt (epipelic algae) are predominantly diatoms, blue-green algae, green algae and euglenophytes. In shallow water the best method for sampling is to draw a large pipette slowly across the sediment surface. The mixture should be allowed to settle and much of the water drawn off after allowing the particles to settle in the dark. The remaining mixture is then thoroughly shaken to distribute the sediment and algae evenly.
4. Sampling phytoplankton
Minute free-floating planktonic algae are best collected by towing a fine net of bolting silk
(plankton net) through water. A 20-33 µm mesh is a convenient size of mesh since any smaller size might soon clog if planktonic algae are present in quantity. The disadvantage of this method is that it allows smaller forms to escape and concentrates grazing zooplankton. Ideally the net should be drawn just below the surface and, if those algae loosely associated with surfaces are to be sampled, then the net should be allowed to brush against submerged plants. The net should not be towed too rapidly otherwise it pushes the water ahead rather than filtering it.
The simplest method of obtaining a plankton sample from static or slow-moving water is to use a bucket, jug or a piece of flexible tubing. Large plankton are very sparse in nutrient-poor lakes (oligotrophic), whereas the nanoplankton and picoplankton are too small to be sampled with a net.
Algae forming a surface scum, entrapped as a surface film (neritic algae) or in sufficient quantity as to discolour the water (‘water bloom’) are easily sampled by partly filling a bottle or vial with the algae-rich water.
5. Sampling algae on soil-free surfaces (subaerial form)
Algae forming a greenish/yellowish dusty layer or red/orange-coloured crusts/felty covering can be scrapped using a knife or scalpel and placed in a paper envelop or vial and air dried. Sometimes a portion of the substrate and closely attached alga might need to be removed using a geological hammer or chisel if rock and a scalpel or knife used to remove slivers of wood such as when sampling tree trunks.
6. Sampling soil algae (limno-terrestrial algae)
Soil algae sometimes form visible growths in the form of gelatinous layers, crusts and mats that can be collected using a knife blade, scalpel, spatula or spoon. However, such samples are frequently mixed with fungi, moss protonema and lichens. Before sampling the soil for diatoms, remove any layer of plant matter and collect the top 1-2 cm of the soil, and put it in a sample vial. Air dry the sample or add a few mls of liquid preservative
For further information on sampling protocols, see:
- Bellinger EG, Sigee DC (2015) Freshwater Algae: Identification, Enumeration and Use as Bioindicators. Wiley & Sons. 296 pp.
- John DM, Whitton BA, Brook AJ (eds) (2011) The Freshwater Algal Flora of the British Isles an Identification Guide to Freshwater and Terrestrial Algae. Second Edition. Cambridge University Press, Cambridge. 878 pp.
- Ehrlich L. (2011) Sampling and Identification: methods and strategies. In: Algae: Source to Treatment American Water Works Association Manual M57, First Edition. Denver, pp. 25-69.