Decomposers and Autotrophs Aquatic Decomposers Viruses Archaea Bacteria

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 r. RNA 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 1000 times greater than surface water density, and decreases with depth, largely due to lack of oxygen.

Heterotrophic 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)