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

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1 Energy Pathways in Streams Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Photosynthesis Allochthonous primary production exudates Dissolved organic matter exudates Groundwater Stream Autotrophs Benthic Algae Macrophytes Benthic algae -- composition 1) diatoms 2) green algae 3) blue-green algae 1

2 Benthic Algae 1) Diatoms (Bacillariophyta) - small, silicon frustules - Many growth forms - Unicellular or colonial - How do diatoms remain attached? - Mucilage - low C/N ratio - Significance? Diatoms are attached to substrates Epi- lithic (on streambed particles > gravel) pelic (on mud) psammic (on sand) phytic (on plant) (a = epiphytic diatoms, b = blue green algae filament) 2

3 Didymosphenia geminata (aka Didymo) A stalked diatom aka rock snot Distribution in North America (2008) Didymo is spreading from historical northern, low nutrient waters to lower latitudes with more nutrientrich waters Poudre River A threat in New Zealand FIGURE: Map of the world showing regions where suitable stream habitats for D. geminata are located. (Map by Kris McNyset, US Environmental Protection Agency). 3

4 Benthic Algae 2) Green Algae (Chlorophyta) different growth forms In streams mostly filamentous (chains of cells that may or may not branch) - distinct chloroplasts - high C/N ratio - Significance? - How do they resist erosion? - Holdfast (specialized basal cell) Holdfasts for some marine algae Oedogonium holdfast 4

5 Benthic Algae 3) Blue green Algae (Cyanophyta) - Mostly filamentous in streams - no chloroplasts! (chlorophyll is distributed throughout cell) - Convert N 2 gas to NO 3 - (nitrate) in anoxic heterocysts (specialized cell) - advantage in N-poor water - high C/N ratio A commensalism between blue green alga and chironomid! (common in Colorado mountain streams) Nostoc alga Cricotopus midge Commensalistic relationship? Midge benefits, algae unharmed 5

Benthic algal mats a confusing terminology Periphyton: ( around the plant ) Includes algae, microbial biofilm and detritus Most commonly used in context of algal biomass Algal component alone is

5] includes bacteria and fungi (heterotrophs); may include some algae Aufwuchs: everything: periphyton + biofilm + micro-metazoans (rather antiquated term now) BIOFILM Autotrophic inputs: algae

architecture of algal (periphyton) mats 1) Ideal Periphyton: much like a forest, with different growth forms that are analogous to shrubs and trees - Understory species (unicellular diatoms) -

6 Benthic algal mats a 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 The architecture of algal (periphyton) mats 1) Ideal Periphyton: much like a forest, with different growth forms that are analogous to shrubs and trees - Understory species (unicellular diatoms) - Overstory species (stalked diatoms and filamentous green and blue green algae) [Fig. 3, Steinman] prostrate (adnate), stalked, filamentous, filamentous w/epiphytes 2) Real Periphyton: addition of detritus to mat disrupts ideal architecture 6

7 Algal mats grow over time then slough autogenic process [Fig. 5, Tuchman] a repeating cycle Colonization and cell growth Increasing cell density Shading and death of anchor cells Sloughing ~ 4 weeks What can cause a bare substrate in the stream? Energy Pathways in Streams Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Photosynthesis Allochthonous primary production exudates Dissolved organic matter exudates Groundwater 7

shadeadapted) Difference among species (BG s do well at high light intensity) What factors control light in a stream?

8 What factors control the amount of algal (periphyton) biomass in a stream??? (1) Light growth rate [Fig. 4.3] Shape of response (note light saturation) Growth history (note light vs. shadeadapted) Difference among species (BG s do well at high light intensity) What factors control light in a stream? insolation, depth, turbidity Attenuation of light in mat [draw] shade light What 2 patterns are shown in the graph above?? 100 % of ambient light How well would cells grow at bottom of mat? min 0 max Distance from surface of mat 8

molecular ratio of organic compounds in algae when nutrients are not limiting: C:N:P = 106:16:1 - Phosphorous - most often limiting in freshwater - Nitrogen - bluegreen algae can fix atmospheric N 2

9 (2) Nutrients what are some? Phosphorous as PO -3 4 [phosphate] Nitrogen, mostly as NO - 3 [nitrate] Carbon, mostly as HCO - 3 [bicarbonate], some CO 2 Silicon, as H 4 SiO 4 [orthosilicic acid] excess PO 4-3 REDFIELD RATIO - molecular ratio of organic compounds in algae when nutrients are not limiting: C:N:P = 106:16:1 - Phosphorous - most often limiting in freshwater - Nitrogen - bluegreen algae can fix atmospheric N 2 gas to NO Carbon - can be limiting in soft water (low HCO 3 - availability) [Fig. 4.11] - Silicon - rarely limiting for diatoms (3) Current Enhances diffusion rates (?) Delivery of nutrients Disposal of wastes But increases shear stress Different growth forms favored (?) Diatoms in faster velocities; filamentous G, BG in slower Inverse relation of algal biomass with current (Figures) Algae grown in streamside troughs for 30 days on clean tiles 9

10 (4) grazers (remove algae!) Mouthpart morphology determines depth of foraging in algal mats Baetis mayfly gathering & biting Heptagenia mayfly scraping & gathering Snail radula rasping & scraping (some caddisflies) (5) 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) autogenic sloughing (no disturbance!) 10

11 Macrophytes (multi-cellular, vascular system) Bryophytes (mosses) Angiosperms (flowering plants) - Characteristics of BRYOPHYTES - attached - Require free CO 2 (can t use HCO 3 ) for photosynthesis - Common in turbulent streams with low ph why?? - High CO 2 from mixing with air - angiosperms absent so reduced competition for attachment sites - sensitive to disturbance [Fig. 4.10] Characteristics of ANGIOSPERMS - Often with roots (to prevent downstream export) - none restricted solely to lotic - most common in low energy habitats (silt, low gradient) Phytoplankton Are there true lotic plankton? 11

caddisflies and mayflies Snails Vertebrates: some fish and

12 Herbivory (text, Ch. 9, pp ) Definition: consumption of primary producers by heterotrophs Primary Producers: Benthic algae (Periphyton) Consumers = Herbivores: Insects: 6 orders, 38 families Majority caddisflies and mayflies Snails Vertebrates: some fish and larval amphibians Use term grazers for consumers that rely on algae. In the scraper functional feeding group. 12

Algal-based Food Web Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Allochthonous primary

1) Algal Characteristics (growth form and C:N ratio) 2) Grazer Characteristics (mouthparts size, organism mobility, and need for different elements (N, P, etc.

13 Algal-based Food Web Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Allochthonous primary production exudates Dissolved organic matter Photosynthesis Groundwater exudates What regulates energy flow from algae to consumers? 1) Algal Characteristics (growth form and C:N ratio) 2) Grazer Characteristics (mouthparts size, organism mobility, and need for different elements (N, P, etc.)) 3) Environmental Characteristics (current, disturbance) Algal-Grazer interactions Algal characteristics: A) growth form [Fig. 4.1] filaments vs. low-lying diatoms B) food quality/ nutritional value (C:N ratio) generally, diatoms > unicellular green algae >> filamentous greens/bluegreens 13

14 Grazer characteristics: A) size and mobility - larger organisms are: - more generalists because mouths are large compared to size of algae) - More mobile and better able to to track algal resources that vary across the streambed in response to current velocity, history of disturbance, etc. - e.g., fish, crayfish - smaller organisms more specialized and select types (growth forms, not specific species) of algae (e.g., diatoms vs. filamentous algae) depending on mouthpart size and on C:N quality - Grazing insects B) mouthpart morphology (depth of feeding in algal mat) 3 major groups SNAILS rasping mouthparts (the radula)» Very unselective but efficient at removing almost all algal overstory and understory Heptagenia - scraping & gathering Snail radula rasping & scraping CADDISFLIES scraping (sclerotized mandibles)» Can remove small diatoms from understory (scissor-like mandibles) Baetis - gathering & shredding MAYFLIES (forage most effectively at mid-depth into mat) 14

Remove overstory algae and reduce shading of mid- to understory algae Enhance water flow through mat and nutrient delivery Regenerate nutrients through consumption and defecation mayfly snail caddis

15 Algal responses to grazers: Grazers change the structure of algal mats by selectively removing different growth forms. When overstory growth forms are removed, what happens to understory growth form production? Remove overstory algae and reduce shading of mid- to understory algae Enhance water flow through mat and nutrient delivery Regenerate nutrients through consumption and defecation mayfly snail caddis Overstory Understory mayfly snail caddis Fish/ tadpoles QUESTION: Does Grazing control stream algae biomass? Early evidence correlative [Fig. 5, Douglas diatoms decline with increasing caddisfly density] Lots of correlative evidence 1980s -- experimental evidence showing grazer reduction of algal biomass Fig. 8.4b is a colonization experiment where bare tiles are introduced into a stream and then algal biomass is measured over time for tiles that have no grazers (exclusion) or that have grazers (no exclusion) Density of diatom cells No. grazers Helicopsyche, a grazing caddisfly 15

Example effect of a mayfly grazer (Ameletus validus) on algae Caged mayflies at

Streambed ambient (1) Compare the streambed ambient to the 1X density of caged

(3) What is general effect of increasing grazer density on algal biomass?

html Take home message: Mayfly grazer reduces biomass but stimulates primary

What do we see in the experimental results in 9.3b?

(2) What is general effect of increasing grazer biomass on algal productivity?

?? Ratio of grazer to algal biomass in streams up to 20:1 How can so much grazer

16 Example effect of a mayfly grazer (Ameletus validus) on algae Caged mayflies at different densities What do we see in the experimental results in 9.3a? Streambed ambient (1) Compare the streambed ambient to the 1X density of caged mayflies. (2) What happens if 0 grazers? (3) What is general effect of increasing grazer density on algal biomass? photos_invertebrates_mayflies.html Take home message: Mayfly grazer reduces biomass but stimulates primary productivity by removing removing all but fast-growing diatoms. What do we see in the experimental results in 9.3b? (1) What are the X and Y axes in this figure? (2) What is general effect of increasing grazer biomass on algal productivity? (new biomass produced over time of experiment) -How do you explain this???!! Paradox??? Ratio of grazer to algal biomass in streams up to 20:1 How can so much grazer biomass be supported? Need to distinguish biomass from production People biomass Food biomass versus Low-biomass diatoms (why?) have high production rate (meaning?) and can thus support high grazer biomass (moreso than filamentous algae) 16

Draw on board algal production and algal biomass versus grazer biomass across a number of streams that differ in grazer biomass How do grazers track algal patchiness?

17 Draw on board algal production and algal biomass versus grazer biomass across a number of streams that differ in grazer biomass How do grazers track algal patchiness? 1) Patchiness within a habitat (e.g., on cobble surface or among cobbles within a reach) Individual response: Area restricted search stay in good algal patch (Fig ) Move slow, search thoroughly with high algae (Fig. 9.1) Drift to new habitat when food depleted (drift lecture) 2) Patchiness at larger scales (e.g., between reaches or between streams) Population response: population size larger where whole-stream algal production is high, so grazers can still suppress algae 17

11/4/15 Which is more important in regulating algal biomass: grazers or current velocity?

pattern What are some hypotheses? Algal AFDM (g) Stream survey 0.24 0.18 0.12 0.06 0.

treatment has more algae? Fast Controls Electric shock Algae AFDM (mg cm-2) 1.2 1.

18 11/4/15 Which is more important in regulating algal biomass: grazers or current velocity? (Opsahl, Wellnitz, and Poff, 2003, Hydrobiologia) Current Grazers Algae The streambed pattern What are some hypotheses? Algal AFDM (g) Stream survey Experiment: grow algae on tiles Current velocity (cm/s) Slow Which treatment has more algae? Fast Controls Electric shock Algae AFDM (mg cm-2) Grazers present! (like above fig.) Current Velocity (cm s-1) 18

2 0 20 25 30 35 40 45 50 55 Current Velocity (cm s-1) Pattern Reversal: Without electricity, grazers have easier access to algae in slow flow, so less grazing in

19 11/4/15 Using electric shock to exclude grazers Electrified wire Results Electric shock (- grazers) Slow Which treatment has more algae? Fast 1.2 Algae AFDM (mg cm-2) Controls (grazers +) 1.0 wi th o ut gr az h wit er s s r ze a r g Current Velocity (cm s-1) Pattern Reversal: Without electricity, grazers have easier access to algae in slow flow, so less grazing in fast flow leads to more algae in fast flow habitats. With electricity, grazers excluded, and faster-growing algae in slow accumulates more biomass than in faster current (erosion). Current velocity mediates herbivory and algal biomass on streambed! 19

Grazer density with electricity All grazers Mayflies Caddisflies Chironomids Effect ê ê ç è é

05 Predominant algae on tiles Cyanophytes Chlorophytes Diatoms Controls Electricity 99% 78% 0.

5% 15% à Grazer species have different sensitivities à Why does relative abundance of algal

Herbivore Tracking of Periphyton Heterogeneity Across Scales (Just FYI, not responsible for

) Scale of algal Patchiness Herbivore tracking mechanism(s) Example taxa Reference in text

20 Grazer density with electricity All grazers Mayflies Caddisflies Chironomids Effect ê ê ç è é P-value Predominant algae on tiles Cyanophytes Chlorophytes Diatoms Controls Electricity 99% 78% 0.5% 7% 0.5% 15% à Grazer species have different sensitivities à Why does relative abundance of algal types change? Herbivore Tracking of Periphyton Heterogeneity Across Scales (Just FYI, not responsible for this on exams!) Scale of algal Patchiness Herbivore tracking mechanism(s) Example taxa Reference in text Among streams Population recruitment Baetis Wallace & Gurtz (1986) Among reaches Individual search, Population recruitment Ancistrus (catfish), Baetis Power (1983) Fuller et al. (1986) Among rocks Among patches on rock Individual search behavior Individual search behavior Baetis, Campostoma (fish) Baetis, Dicosmoecus (caddis) Richards & Minshall (1988), Power & Matthews (1983) Kohler (1984), Hart (1981) 20

Energy Pathways in Streams

Energy Pathways in Streams Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Photosynthesis Allochthonous primary