1. Stream Autotrophs 1) diatoms 2) green algae 3) blue-green algae
Benthic Algae
Macrophytes
Benthic algae -- composition
1) diatoms
2) green algae
3) blue-green algae

2. Benthic Algae 1) Diatoms (Bacillariophyta) small, silicon frustules
Many growth forms
Mucilage
Stickiness
Motility
low C/N ratio

3. Figure: Movement along substratum (blue proteins, green mucopolysaccharides, black striated lines are the actin filament network, black circles indicate the central nodule)
Mechanism of Movement: Movement is possible on a solid substratum for the raphid Pseudo-nitzschia diatoms. There seems to be a secretion of polysaccharide into the raphe along the entire slit, often leaving a trail in their wake. But how exactly could this mechanism of movement work? It is hypothesized that the force that is able to propel these diatoms can be derived from interactions among actin filaments and transmembrane structures (proteins). These transmembrane structures are thought to contribute to movement because their extracellular portion associates with a substratum while their intracellular portion has freedom of lateral motion within the cell (the raphe). More specifically, there is thought to be a transmembrane protein that is associated to a network of actin within the cell and to filaments of sticky mucopolysaccharide on the outside of the cell. The actin proteins serve to tug the proteins along the raphe, while the sticky mucopolysaccharides and motors (ATPases) pull in the opposite direction. As the proteins travel along the raphe and reach the central nodule, it is hypothesized that they detach from the mucopolysaccharides, allowing the mucopolysaccharides to attach to another protein. When the mucopolysaccharides reach the end of the raphe, they detach from the transmembrane protein and leave a sticky trail on the substratum. The mucopolysaccharide material is found within cell vesicles called crystalloid bodies, but it is not known from where these polysaccharides are secreted into the raphe. It is thought that a single vesicle may secrete enough polysaccharide to travel half a cell length.

4. Didymosphenia geminata
A stalked diatom
Distribution in North America
Poudre River
aka “rock snot”
A threat in New Zealand

5. Benthic Algae 2) Green Algae (Chlorophyta) How do they resist erosion?
different growth forms
mostly filamentous in streams
distinct chloroplasts
high C/N ratio
Significance?
How do they resist erosion?
Desmid

6. Holdfasts for some marine algae
Oedogonium holdfast

7. Benthic Algae 3) Blue green Algae (Cyanophyta)
Mostly filamentous in streams
no chloroplasts
N2-fixing (heterocysts)
high C/N ratio

8. Commensalistic relationship
A commensalism between blue green alga and chironomid!
Nostoc alga
Cricotopus midge
Commensalistic relationship

9. Algal Mats and confusing terminology
Periphyton: (“around the plant”)
Includes algae, microbial biofilm and detritus
Most commonly used in context of algal biomass
Algal component alone is assessed either by examining under microscope, or by assaying for chlorophyll-a (measure of living biomass)
Biofilm: organic microlayer on substrates [Fig. 5.5]
includes bacteria and fungi (heterotrophs); may include some algae
Aufwuchs: everything: periphyton + biofilm + micro-metazoans
(rather antiquated term now)
BIOFILM
Autotrophic inputs:
• algae
Heterotrophic inputs:
• DOM-COM-POM
• bacteria, fungi
Matrix:
• Polysaccharide fibrils produced by bacteria and fungi
• Extacellular release and death release enzymes and other molecular products

10. Mat architecture -- 2 views [Fig. 3, Steinman]
1) Vertical placement of algal cells/species depends on growth forms
prostrate (adnate), stalked, filamentous, filamentous w/epiphytes
2) Addition of detritus to mat disrupts “ideal” architecture

11. 8 Factors that control algal growth and biomass
(1) Light
growth response [Fig. 4.3]
Shape of response (saturation)
Growth history (light vs. shade)
Difference among species (BG’s do well at high light intensity)
Factors controlling light:
insolation, depth, turbidity
Attenuation of light in mat [draw]
shade
light
Distance from surface of mat
max
% of ambient light
100
min

12. (2) Nutrients … what are some?
P (PO4-3) [phosphate]
N (NO3-) [nitrate]
C (HCO3-) [bicarbonate], some CO2 Si
excess PO4-3
REDFIELD RATIO - molecular ratio in algae when nutrients are not limiting: C:N:P = 106:16:1
Phosphorous - most often limiting in freshwater (ratio N:P is ____ 16:1)
Nitrogen - bluegreen algae can “fix” atmospheric N2 gas to NO3-.
Advantage when N:P ratio ____ 16:1
Carbon - can be limiting in “soft” water (low HCO3- availability) [Fig. 4.11]
Silicon - rarely limiting for diatoms
(Redfield Ratio - C:Si:N:P = 106:15:16:1)
For P to be limiting, N:P must be > 16:1
Bluegrees have advantage when N limiting, i.e., N:P < 16:1

13. (3) Current Enhances diffusion rates (?) Increases shear stress
Delivery of nutrients
Disposal of wastes
Increases shear stress
Different growth forms favored (?)
Diatoms in faster, filamentous G, BG in slower
Inverse relation of algal biomass with current (Figures)
Algae grown in streamside troughs for 30 days on clean tiles

14. (4) substrate Texture and Size (5) Temperature Epi- lithic (on stone)
pelic (on mud)
psammic (on sand)
phytic (on plant)
(5) Temperature
greens and bluegreens do better at higher temperatures
diatoms year-round
seasonal shifts not as pronounced as in lakes

15. (6) grazers Mouthpart morphology determines “depth” of foraging
Baetis mayfly
gathering & biting
Snail radula
rasping & scraping
(some caddisflies)
Heptagenia mayfly
scraping & gathering

16. (7) sloughing autogenic process [Fig. 5, Tuchman] why??
Colonization and cell growth
Increasing cell density
Shading and death of anchor cells
Sloughing
** What other process can cause bare substratum? **

17. (8) disturbance substrate instability, scouring [Fig. 1, Peterson]
response depends on
age of mat (timing) [Fig. 6, Peterson]
Which “successional age” most resistant (i.e., doesn’t change in response to scour)?
(succession = change in species composition and biomass over time)
Grazers also responsd to disturbance!

18. Model: accrual vs. Loss of algal biomass (Fig. 6.2)
Summarizes many previous slides

19. Characteristics of BRYOPHYTES
Macrophytes
Bryophytes (mosses)
Angiosperms (flowering plants)
Characteristics of BRYOPHYTES
attached
Require free CO2 (can’t use HCO3) for photosynthesis
Common in turbulent streams with low pH … why??
High CO2 from mixing with air
Reduced boundary layers
angiosperms absent
sensitive to disturbance [Fig. 4.10]

20. Characteristics of ANGIOSPERMS
rooted (Temperate streams)
none restricted solely to lotic
most common in low energy habitats (silt, low gradient)
phenotypic variation for lotic survival …
smaller leaves
shorter internodes
vegetative reproduction
Phytoplankton
Are there true lotic plankton?