Decomposers and Autotrophs

Decomposers and Autotrophs
Aquatic Decomposers:
Viruses, Archaea, Bacteria, Protists, Fungi
Chemoautotrophs, Anoxygenic Phototrophs,
Cyanobacteria, Eukaryotic “Algae”,
Non-Vascular Plants, Vascular Plants
Taxonomy of Cellular Life
(Three Domains)
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).
• Biochemically and
phylogenetically distinct from
Bacteria cells, with some
characteristics more similar to
Eukarya cells
• Adapted to extreme
environments (heat, acids, salts,
• 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.
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 techniques.
Bacterial Distribution in Lakes
• 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.
• 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
Includes familiar subphyla
Sarcodina (which includes the
Amoeba), Ciliophora (includes
the ciliated Stentor), and
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
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.
Most common in wetlands; rare
in lakes and rivers, never
foliose (leaf-like)
crustose (encrusting a surface)
fruticose (projections)
• Distinguished from anoxygenic
photosynthetic bacteria by
presence of chlorophyll a (more
evolutionarily advanced than
bacteriochlorophyll of Purple and
Green bacteria).
• Oxygenic Photosynthesis, Well
studied compared to other bacteria
as they are large (1 μm to 100 μm)
and have distinct morphologies
(spherical, filamentous, and
• Many can fix-N2 gas into ammonia
for assimilation into cell biomass;
thereby, never N-limited growth;
only occurs in the absence of
oxygen, such as in specialized
cells called heterocysts.
• In filamentous forms, cells
are arranged end-to-end to
form trichomes which may
be contained within a
• Akinetes are like spores, or
“resting” cells. They can
develop while still attached
to the filament.
• Hormogonia are small
fragments of the the parent
trichome and move away to
develop a new filament.
Filaments and gelatinous forms are
quite resistant to protist phagocytosis
as illustrated in this video.
• Gas vesicles give some cyanobacteria buoyancy, and when
blooms occur these can form surface scums. Affords them
an advantage in the competition for light at the surface.
• Some produce noxious odors and toxins.
• May accumulate high biomass in eutrophic waters, causing
night time fish kills by depleting oxygen.
• Cyanobacteria contain phycobillins, which are pigments
that absorb light in the green region where chlorophyll does
not absorb. Allows them to photosynthesize at greater
depths than other organisms.
• An ecological grouping of Eukaryotic taxa
that perform, oxygenic photosynthesis.
• This is an extremely taxonomically and
morphologically diverse group of organisms
(unicellular, multicellular, immobile, motile,
sessile, etc.)
• Major taxonomic groups are distinguished
by accessory photopigments.
• Rhodophyceae (Red Algae) - Poorly represented in
freshwater systems; none are planktonic. Mainly
restricted to fast-moving streams of cool, well
oxygenated water. Contain phycoerythrin (reflects red
light, absorbs blue light).
• Chrysophyceae (Golden-brown Algae) - Commonly
found as planktonic in oligotrophic lakes; mostly
unicellular (possessing flagellum), sometimes colonial.
– Unicellular species very small; colonial species very
large so it limits grazing by herbivores.
– Some species of Dinobryon genus able to take up
phosphate at very low ambient levels.
• Bacillariophyceae (Diatoms) –
Extremely important algae
group, both planktonic and
– Possess a characteristic frustule, a
clear glass-like cell wall.
– Frustule is divided into halves; halves
fit together in either a pennate
(elongate) or centric (circular) form.
– Centric forms = radial symmetry,
pennate forms = bilateral symmetry
– These can attach to form to hard
substrate, and form filaments
– Benthic diatoms of stream periphyton
are an indicator of good water quality.
• Diatoms are generally large and often not motile; they rely on slow
sink rates, oil droplets and upwelling dynamics to stay in the surface
• The frustule is made of silicon and is not very soluble. Silica is a
limiting nutrient to their growth.
• Typically bloom in spring, fastest growth when there are plenty of N,
P, and Si; during summer they are less abundant (grazed or sank).
• When diatoms die, they sink to the bottom and the frustule is
incorporated into the sediments.
• Historic patterns of planktonic community structure can be studied in
sediment cores containing diatom frustules. Isotopic composition of
frustules can be used to date sediments, study past patterns of
abiotic conditions. This is the field of paleolimnology.
• Dinophyceae (Dinoflagellates) – Unicellular, motile, have
– Many species develop an armor-like cell wall, which can be very
elaborate in shape and even possess horn-like projections.
– Some dinoflagellates produce toxins and are problematic when
they experience blooms; Pfisteria commonly implicated in fish
kills, and can harm humans.
• Euglenophyceae (Euglenoids) – Unicellular, motile,
some have flagella.
– Many capable of both autotrophy and heterotrophy
(phagotrophic) = mixotrophy.
• Chlorophyceae (Green algae) – Diverse group, from
unicellular to complex multicellular assemblages.
– Found in all surface habitats (wetlands, damp soils, lake and
river benthic zones, etc.)
– Unicellular species most common as lake plankton.
– Filamentous species usually epibenthic (e.g stream periphyton).
Can be problematic, forming large populations during periods of
nutrient enrichment.
Aquatic Plants: Macrophytes
• The term macrophyte often includes macroalgae as well
as vascular and non-vascular plants.
• Macroalgae include Chlorophyceae (Green algae) and
the Charophytes (stoneworts).
• Nonvascular plants (Bryophytes) can be very abundant
in some freshwaters:
– Lack vascular tissue for transporting water; absorb water like
sponge, distribute via capillary action to extremities.
– Sphagnum dominant in the shallow acidic waters of peat bogs,
high-latitude wetlands. Buildup of acidity in Shagnum bogs
reinforces dominance of the moss, leads to buildups of peat.
– Some aquatic mosses able to survive at great depths (> 120 m).
• Charophytes (stoneworts) are morphologically more
complex than chlorophytes; have reproductive
structures similar to land plants. May be evolutionary
precursors to land plants.
• Stoneworts very sensitive to nutrient enrichment and are a
useful indicator of nutrient pollution.
Bryophyte Sphagnum
Aquatic Vascular Plants
• Aquatic vascular plants predominantly angiosperms
(flowering plants).
• It is believed the aquatic angiosperms are evolved from
terrestrial species:
– Relatively low species richness compared to terrestrial
– Many possess vestigial relics of terrestrial life, such as stomata,
or waxy cuticle.
– Aquatic angiosperms demonstrate a high degree of phenotypic
plasticity to adapt to changing environmental conditions, i.e. the
same species may take on many forms.
Adaptations of Aquatic Plants
• Aquatic plants generally lack the rigid structures that
land plants have (woody material, etc.)
• Often have air spaces within the plant to provide
buoyancy and decrease density
• Smaller or highly dissected leaves (in submerged plants)
to reduce resistance to flowing water
Emergent Vascular Plants
• Emergent aquatic plants are found
along the shorelines and shallow
littoral zone. They are attached to
the soil and extend their leaves
above the surface to the air.
• Emergent plants are common in
wetlands, and high densities can
lead to transpiration rates higher
than the expected evaporation from
surface water.
• To slow water loss during dry
periods, emergent plants can close
stomata just like terrestrial plants.
Floating Attached Vascular
Almost exclusively angiosperms
(e.g., flowering water lilies).
Leaves are usually round, strong,
and the petiole attaches at or near
the middle. These are
adaptations for dealing with the
harsh surface environment of the
Red on underside to collect green
light scattered from below.
Petioles proportionately longer
than the water depth, so that the
leaf can remain on the surface
during periods of wave activity.
Less common on large lakes
(depth, wave action)
Submerged Vascular Plants
• All structures and processes (except flowering) take
place under the surface of the water.
• Vascular system reduced, with all major conducting
vessels absent from stems.
• Leaves tend to be highly divided and reticulated than
those of land plants. Commonly ribbon and thread-like
in form; long, pliable leaves resist tearing in water.
Highly dissected leaves increase SA:V ratio.
Floating Plants
• These plants are free-floating, with
roots unattached to the
• Highly diverse in morphology and
habitat. Can be problematic if
population blooms; can choke out
other vegetation or limit water
traffic by humans.
• Generally restricted to sheltered
habitats and rivers with lowvelocity flow. All nutrient
absorption is from water (except in
carnivorous species, which
augment with nutrients from prey)