Decomposers and Autotrophs
Aquatic Decomposers:
Viruses, Archaea, Bacteria, Protists, Fungi
Autotrophs:
Chemoautotrophs, Anoxygenic Phototrophs,
Cyanobacteria, Eukaryotic “Algae”,
Non-Vascular Plants, Vascular Plants
Ecological Trophic Roles
• Autotrophs (fix carbon dioxide into organic matter)
–
–
–
–
Allochthonous (organic matter production from outside)
Autochthonous (organic matter production within)
Chemosynthesis (reduced inorganics as energy source)
Photosynthesis (light as energy source)
• Anoxygenic (Purple Sulfur and Green Sulfur bacteria; anaerobic)
• Oxygenic (cyanobacteria and all eukaryotic algae and plants)
– Some production lost from cells as DOM via exudation (leaking)
• Decomposers (organic matter mineralized to P & N nutrients)
– Microbial Heterotrophs: (major component of the “Microbial Loop”)
• Prokaryotes and Fungi
– mostly osmotrophs and some parasites
– convert DOM or dead POM back to living cells and nutrients.
• Protists (predators of prokaryotes; important link to main foodweb)
• Overall, represents an important control of energy flow in the ecosystem.
– Viruses (Facilitate DOM release by lysis of prokaryotes and algae.)
– Detritivores (Consumers specialized in eating detritus.)
• Consumers:
– Grazers (primary consumers)
– Predators (secondary and higher consumers)
All interactions leak
DOM; bacteria are
important in this back to
living cells (prey).
Taxonomy of Cellular Life
(Three Domains)
Taxonomy: classification (hierarchical
grouping based on characteristics);
nomenclature (naming); identification
(define characteristics that match taxa).
Phylogeny: study of
evolutionary relationships.
Comparison of rRNA base
sequences is most common.
Viruses:
Archaea
• Biochemically and
phylogenetically distinct from
Bacteria cells, with some
characteristics more similar to
Eukarya cells
• Adapted to extreme
environments (heat, acids, salts,
anaerobic).
• Methanogenesis is unique to
archea; obligate anaerobes that
respire using carbon dioxide to
methane, an important
“Greenhouse Gas”.
• New archaea groups are being
discovered from non-extreme
environments; little is known
ecologically or physiologically
about these new discoveries.
Methanococcus sp.
Bacteria:
•
Extremely diverse; biomass greater than all other life combined.
•
Less than 1% of the bacteria species in the world have actually been
described. Not all species can be cultivated and studied successfully with
present culturing techniques.
Bacterial Distribution in Lakes
Planktonic
• Epilimnion density
high; trophic activity and
DOM release is greatest
in euphotic zone (yellow
line = light)
• Hypolimnion density
decreases (less DOM)
and does not increase
until immediately above
the sediments.
Benthic
• Surface sediment
density is about 1000times greater than
surface water density,
and decreases with
depth, largely due to lack
of oxygen.
Heterotrophic Protists
Protists are a polyphyletic group
(many distinct evolutionary
lineages). Includes many
species also considered algae, or
mixotrophs.
Heterotrophs are important
as predators of bacteria and
as parasites.
Includes familiar subphyla
Sarcodina (which includes
the Amoeba), Ciliophora
(includes the ciliated
Stentor), and zooflagellates.
Oomycota and Fungi
• Most fungi are saprophytic, decomposers of dead organic
matter, very important in the breakdown of organic detritus
from terrestrial sources.
– Anamorphs (asexual forms) of Ascomycota and some Basidiomycota
are most abundant on detritus (leaves, wood).
– Along with bacteria, they increase the nutritional quality of detritus.
– Some are very adapted for this role in aquatic environments (see
example of amphibious fungi below)
• Some Oomycota and all Chytridiomycota are parasitic, killing
their prey and decomposing the tissues.
• Others form symbiotic associations with cyanobacteria or
green algae called lichens.
• Because of low amounts of organic matter, fungi not usually
present in pristine groundwater.
Amphibious Fungi
Many taxa have tetraradiant conidia (asexual spores) via
convergent evolution. Shape helps anchor them to leaf
surfaces in stream flow. Colonization enriches CPOM for
shredder amphipods, which are important to the fish diet.
Parasitic Oomycota and
Chytridiomycota
A rotifer caught by one of the “lethal
lollipops” of the oomycete, Zoophagus sp.
Both a copepod (sexual; gametophyte host) and
chironomid larvae (asexual; sporophyte host) are
required for chydrid, Coelomomyces sp.
Lichens
Most common in wetlands; rare
in lakes and rivers, never
groundwater.
foliose (leaf-like)
crustose (encrusting a surface)
fruticose (projections)