Biomedical Engineering Reference
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(a)
(b)
(c)
(d)
Figure 9.1
Microalgal morphological diversity viewed with the scanning electron microscope: (a) the
diatom
Bacteriastrum
; (b) naviculoid diatom; (c) the coccolithophorid (Prymnesiophyceae)
Emiliania
huxleyi
; (d) the dinoflagellate
Gymnodinium catenatum
(CSIRO images).
adverse environmental conditions with genetic variability (Blackburn and Parker, 2005).
Most microalgae are phototrophic (autotrophic), that is they use the sun's energy through
photosynthesis, capturing it as chemical energy in biological molecules, for growth, using
carbon dioxide (CO
2
) and producing oxygen (O
2
) as part of that process. Indeed, microalgae
are responsible for over half of global primary productivity, more than all the land plants
together, and with their capacity to use carbon dioxide they play a key role in global
biogeochemical cycles.
Some microalgae are heterotrophic, that is they use organic carbon compounds, for
example, glucose, acetate, lactate and glutamate, and do not require light as part of the
process. Other microalgae have both autotrophic and heterotrophic capacity, depending on
the light and nutritional status of the environment they inhabit. This dual capacity is known
as mixotrophy (Lee,
2004 ).
Globally there is a vast biodiversity of microalgae. The numbers of different phytoplankton
species in the sea can only be guessed at. Twenty years ago, Sournia and co-workers (1991)
estimated that there were 474-504 genera and 3444-4375 species. Hallegraeff (2003) put
the figure at about 5000 species. Much larger estimates are commonplace. However, with
the use of modern molecular biology tools it is now appreciated that some microalgae are
not culturable using standard methods and that there is an incredible diversity at each
taxonomic level including infra-specific diversity, down to the level of within and between
populations (Norton
et al
., 1996 ; Simon
et al
., 2009). Even within the known species there
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