4.1 Taxonomy of Microorganisms in Aquatic Environments 83
Fig. 4.24 Illustrations of some algae (All items in the table
reproduced with permission) a) Red algae are red because of
the presence of the pigment phycoerythrin; this pigment
reflects red light and absorbs blue light. Because blue light
penetrates water to a greater depth than light of longer
wavelengths, these pigments allow red algae to photosynthesize
and live at somewhat greater depths than most other algae.
The picture of the red alga, Dichotomaria marginata, shown
here was taken and kindly supplied by Keoki Stender,
University of Hawaii. b) Sargassum fluitans. Sargassum
seaweed, Gulf Weed (brown alga). This is a major component of
the algae in the Sargasso Sea in the pelagic Atlantic. It has long,
serrated fronds with a distinctive midrib, and smooth berrylike
spherical gasfilled bladders, pneumatocysts, which assist the
floatation of the alga.The photo of Sargassum above was kindly
supplied by the South Carolia Department of Natural Resource,
courtesy of H. Scott Meister. c) Synura spp, a member of the
Chrysophyceae (golden or goldenbrown algae on account of
their content of fucoxanthin which in the presence of chlorophyll
makes them look brown or golden brown), forms swimming
colonies from a variable number of cells joined together at their
posterior ends in a spherical or elongated cluster. Synura is
important because it gives drinking water a bitter taste and a
“fishy” cod liver oil type of odour. Synura is freshwater; some
marine members such as Olisthodiscus luteus, produce
neurotoxins which may kill aquatic fauna and may affect
humans through eating shell fish raw. Credit: Dr Graham
Matthews, [email protected] (http://www.
gpmatthews.nildram.co.uk/microscopes/pondlife_plants01.html).
Dr Graham Mathews is also Hon Secretary of the Secretary of
the Quekett Microscopical Club) d) Bacillaropyceae (Diatoms)
are one of the largest and ecologically most significant groups
of organisms on Earth. Diatoms are microscopic algae which
are easily recognizable because of their unique cell structure,
silicified cell wall and life cycle. Diatoms are found anywhere
there is water and light: in oceans, lakes and rivers; marshes,
fens and bogs; damp moss and rock faces. They are an
important part of the food chain in aquatic environments,
especially in nutrient-rich areas of the world’s oceans, where
they occur in abundance.Photograph of diatoms kindly supplied
by Dr David Carling) e) Dinoflagellates are minute marine
unicellular algae with diverse morphology, the largest,
Noctiluca, being as large as 2 mm in diameter!. Many are
photosynthetic, while some are parasites of fish. In temperate
climates they form blooms in summer months which may be
golden or red. Their blooms produce neurotoxins marine
animals eating and humans who consume them raw (such as
shellfish)