Marine Macroalgae

Local tide tables need to be consulted in advance of any shore work
Efforts should be focused on living, attached seaweeds. Drift specimens washed onto the shore by the tide have ambiguous origins which could lead to misleading distribution records. In some instances drift material may be worth recording if the species has not otherwise been found attached in the survey area, though it is important to note these records as ‘drift’.
1. Intertidal collecting
For intertidal work, it is best to arrive about 2 hours before the time of the predicted low tide and to work from the high to the low levels as the water recedes. Seaweeds should be removed by hand from rocks at low tide. A geological hammer, chisel or knife is essential for collecting crust-like seaweeds. Care must be taken to limit damage to the natural environment and consider which samples are essential.  Special care is required when collecting less conspicuous seaweeds; often these are minute, delicate and commonly grow epiphytically on larger ones.  Separate small seaweeds from a mixed collection in the field and store specimens in polythene bags or vials. Any collected material should be examined as soon as possible before the specimens start to deteriorate. It is possible to keep the seaweeds fresh for a short while by storing in polythene bags (with any excess water drained off) in a fridge for a couple of days.
2. Subtidal collecting
A diving mask or glass-bottomed bucket is useful for searching for shallow water specimens; sometimes these are to be discovered in larger and deeper tidepools at lower shore levels. Shallow water collecting can be achieved by snorkel diving whilst deeper water sampling is only possible by dredging or SCUBA-diving. When collecting underwater the containers may be conveniently carried in a fine mesh draw-string bag. Small containers (e.g., plastic specimen tubes) should be filled with seawater so as to prevent them from floating away or buoying up the draw-string bag.  Information regarding subtidal collections can be recorded in situ by writing with a wax crayon or a lead pencil on a pad of roughened white plexiglass or a slate.

If samples cannot be examined within a few days of collection they should be preserved in spirit or by drying. Preservation of permanent voucher specimens may be required as a reference collection. 
1. Dried herbarium specimens
This method is ideal for preserving the macro marine algae. The specimen should be placed in a shallow tray of water. Freshwater is tolerable for robust seaweeds but saltwater is needed for delicate forms. It is at this stage that the essential collection information (locality; date etc) should be written in pencil on a mounting sheet of good quality acid-free paper. Carefully float the specimen above the paper sheet in the tray of water.  The sheet should be slowly raised and slightly tilted and as the water drains away a needle, brush and forceps should be used to tease out the specimen to display to best advantage its characteristic form. Any overlapping branches can be further minimized by removing at this stage any branches or fronds that obscure the form of the mounted specimen.
The specimen on its mounting sheet should be placed in a plant press to dry. This comprises to rigid press boards (latticed wood strips is most effective) with absorbent drying paper added in layers between specimens to remove the remaining water. The specimen needs covering with nylon gossamer fabric, muslin or cotton to prevent it  sticking to the upper drying paper. Further drying paper should be placed over the specimen and more specimens and drying papers added. The press should not be strapped too tightly if segmented lime-impregnated seaweeds or stoneworts are included since on drying they often disintegrate.    
To avoid the risks of the seaweeds starting to decay in the press it is essential to replace the absorbent paper with dry sheets approx. 12 hours after first pressing the specimens and on subsequent days until the specimens have dried. If conditions for drying are poor then it will be necessary to expose the press to a gentle heat source, though be aware that excess heat can damage the specimens.
Most seaweeds adhere naturally to the mounting sheets, but more robust forms and segmented coralline forms may be loose on the mounting sheet after drying. Such specimens may be stored in a small envelope and appended to a herbarium sheet. Coralline seaweeds and very lime-encrusted stoneworts should be dried with very little pressure and the former may be stored in boxes or envelopes. Each sheet, envelope or box should bear a label containing the sample's collection information. Dried specimens are more or less permanent and retain their colour almost indefinitely if stored in the dark and are not normally subject to attacks by animals such as herbarium beetles, though if you suffer an infestation they may well eat the labels!
2. Liquid Preservation
Formalin: despite posing a health hazard this is still the most popular liquid preservative. It is used at a strength of 2.5-4% (1 part 40% formaldehyde: 9 parts of water) and is neutralised by the addition of borax or calcium carbonate. Glycerol is commonly added since algae are readily damaged if the sample completely dries out. Appropriately sized polythene bags need to be used for larger algae and the surplus preservative drained before transportation
Glutaraldehyde: increasingly widely recommended for preserving freshwater algae and seaweeds, although different concentrations are recommended depending on the material. Often a concentration of 2.5% is recommended for macroalgae made by diluting 25% glutaraldehyde and adding a pinch of calcium carbonate. It is recommended that a final concentration of below 0.5% is more suitable for more delicate forms such as naked flagellates. It is recommended that 1 ml of 40%  glutaraldehyde is added to each 100 ml of algal material to give a final concentration of 0.25–0.5
Lugol’s Solution: some laboratories and organisations have banned the use of formaldehyde completely and have often turned to using Lugol’s solution despite its limitations. Several variants exist, differing in the ratio of potassium iodide to iodine. Some have a ratio of about 7:1 whereas others have a ratio of 2:1 - 2 g potassium iodide and 1 g iodine in 300 ml water to give a deep straw colour. Lugol’s solution is often used for preserving planktonic algae by adding it to make a final concentration in the sample of 0.5%.