Types of Aquatic Organisms - Freshwater Ecology: Concepts and Environmental Applications - page 120

Classification of Organisms by Energy Source and Nutrient Requirements a TABLE 7.2

Energy source/

Carbon source Mode electron donor Electron acceptor Organisms (example)

CO 2 Photoautotroph Light/ H 2 O O 2 Cyanobacteria/

eukaryotic algae/
macrophytes

CO 2 Photoautotroph Light/ H 2 S Organic C Green and purple

sulfur bacteria
(anaerobic)

CO 2 Photoautotroph Light/ H 2 , organic C Organic C Purple nonsulfur

bacteria (anaerobic)

CO 2 Chemoautotroph Reduced inorganic O 2 Bacteria (e.g.,

compounds (e.g., Nitrosomonas, iron

NH 4 , H 2 S, Fe 2 , bacteria, hydrogen

H 2 ) bacteria)

Organic C Heterotroph Organic C Organic C Fermentative bacteria

(anaerobic)

Organic C Heterotroph Organic C O 2 Aerobic bacteria,

protozoa, and
animals

Organic C Heterotroph Organic C Oxidized Anaerobic bacteria

compounds that respire

such as NO 3 , organic C

SO 4 2 , Fe 3

a Reproduced with permission from Yanagita (1990). See Chapters 8, 9, and 11-13 for further discussion of types
of organisms. Not all types are shown.

A variety of additional classifications are used to describe the func-
tional role of organisms in aquatic foodwebs (functional feeding groups).
Organisms that sieve particles from the water column are called filterers .
Organisms that acquire their nutrition from small particles in the benthos
are called collectors. Shredders break up larger benthic organic material for
their nutrition, and scrapers remove biofilms from hard benthic substrata.
Predators are often classified further by their position in the food web. For
example, grazers or herbivores (primary consumers) eat algae, plants, or
sometimes bacteria (primary producers). Top carnivores eat animals but
are generally eaten by no larger animal. Thus, a classification scheme based
on mode of obtaining nutrition is one way to classify organisms.
Additionally, organisms may be classified by the habitat they occupy and
some of the special terminology for this purpose is presented in Table 7.3.
Such classification can be useful because it allows an investigator to make
predictions about abiotic and biotic conditions important to organisms. For
example, an epilithic alga (living on rock) in a rapidly moving stream may
experience a relatively high water velocity. An epiphytic alga on a macro-
phyte may have competitive or facilitative interactions with the macrophyte.
Organisms can also be classified by how they interact with other or-
ganisms (interspecific interactions). Many different types of interspecific in-
teractions are possible, and I adhere to the interaction scheme shown in
Table 7.4. There are direct interactions and indirect interactions . Direct in-
teractions occur between individuals of two species and involve no others;