Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 26

for supplementing nitrogen uptake in such adverse
conditions.

1.6.4 Yellow-green algae as bioindicators

Yellow-green algae have not been widely used as
bioindicator organisms, partly because they are not a
prominent group in the aquatic environment. Differ-
ent species do have clear environmental preferences,
however, that could be used to provide information
on ambient conditions. These are discussed by John
et al . (2002) and include algae that are prevalent in
acid bogs ( Botrydiopsis spp., Centritractus spp.),
calcareous waters ( Mischococcus spp., Ophiocytium
spp.), humic waters ( Botrydiopsis spp., Tribonema
minus ), organically rich conditions ( Chlorosaccus
spp.), inorganicnutrient-enrichedwaters ( Goniochlo-
ris fallax ) and brackish (partly marine) environments
( Vaucheria prolifera, Tetraedriella spp.).

G

FS

M

P

ES

N

1.7 Dinoflagellates

V

Dinoflagellates (Dinophyta) are mostly biflagellate
unicellular algae, although some (e.g. Stylodinium )
are without flagella and are attached. They are pre-
dominantly found in the surface waters of marine
systems (about 90% are marine), with only about
220 species present in freshwater environments.
Dinoflagellates contain chlorophylls- a and - c ,but
are typically golden- or olive-brown (Fig. 1.3) in
colour due to the major presence of carotene and
the accessory xanthophyll peridinin. The chloroplasts
can be plate-like (Fig. 4.57) in some species or elon-
gate in others. Pyrenoids are present, and the main
storage product is starch. Lipid droplet reserves may
also be found, and some dinoflagellates possess an
eyespot.

Figure 1.7 Line drawing of heterokont zoospore, typi-
cal of xanthophyte algae, with a long anterior flagellum
bearing two rows of stiff hairs plus a short posterior flag-
ellum. This is smooth and often bears a swelling (FS)
that is part of the light-sensing system. ES, eyespot; G,
Golgi body; M, mitochondrion; N, nucleus; P, plastid.
Graham & Wilcox, 2000. Reproduced with permission
from Prentice Hall.

and Ophiocytium (attached to filamentous algae) and
Chlorosaccus (attached to macrophytes).
As with other algal groups, some yellow-green
algae have developed alternative modes of nutri-
tion. Chlamydomyxa is an amoeboid, naked form
that has retained its photosynthetic capability (still
has chloroplasts) but has also become holozoic,
ingesting desmids, diatoms and other algae and
digesting them within internal food vacuoles.
Chlamydomyxa is typical of low-nutrient acid bogs,
and the holozoic mode of nutrition may be important

1.7.1 Cytology

Dinoflagellates have a number of distinctive cytolog-
ical features.
A large central nucleus (usually visible under
the light microscope) containing chromosomes