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Algal Ecology

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g gyAbiotic

I. Light

II. Temperature

Ecology: Living in a marine environment

Patterns, Processes, and Mechanisms

Some factors affecting Algal Ecology

Biotic

I. Herbivory

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p

III. Salinity

IV. Nutrients

V. Water Motion

VI. TIDES

VII. Sand Burial

II. Epiphytism

III. Competition

All act together in nature!

I. LIGHT

= Amount of radiant energy impinging on a unit of surface area

M

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Measurement: Irradiance measured as: amount of energy falling on a flat surface

Measured as a rate:

• Microeinsteins (= Micromole photons) per square meter per second

• Watts per square meter

Algal point of view: light is extremely variable in space and time:

- Predictable variation:

- Latitude

- Seasonal changes in day length

- Less predictable variation:

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- At the surface = waves, white-caps, foam

- In the water = turbidity from silt, particulate matter, phytoplankton blooms

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PAR = Photosynthetically Active Radiation(400nm - 700nm

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Attenuation of Light with Increasing Depth

irradiance

At ~ 100 m even in clearest water, only 1% of surface radiance makes it through

Different wavelengths transmitted to different depths

Attenuate: to lessen in severity, intensity, or amount

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dept

h Energy inversely related to wavelength

Violet = short wavelength/high energy (blue or green goes farther)

Red = long wave length/low energy (red drops out first)

Light attenuation is due to:

• Absorption (long wave length, low-energy wavelengths absorbed first, by water itself.)

• Scattering (high energy, short wave lengths scatter due

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Scattering (high energy, short wave lengths scatter due to water molecules and particulates)

Effect of Salinity?

Effect of Turbidity?

Clear oceanic water (I-III)• Max transmittance in clear water occurs at ~475nm• Blue/Green region• 98% of surface From Jerlov 1976

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Coastal/estuarine water (1-9)• Max transmittance in opaque water occurs at~575nm•Yellow/Orange region• 56% of surface

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Across species:

Different Divisions have different pigments, allow potentially different depth distributions

How do algae cope with attenuation? (1) Pigments

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Engelmanns Theory of Chromatic Adaptation (1884)

dept

h

Green Light OnlyChl c, Fucoxanthin

Chl b, lutien, neoxanthin

irradiance

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Appealing, but wrong (Saffo 1987)

Irradiance not spectral quality1) produce more accessory pigments2) produce more photosynthetic pigments3) morphology matters- thicker fronds, arrangement of

chloroplasts

Chl d, alpha carotene,Phycobilins

Ecological Reality:red, green, and brown algae mixed throughout intertidal and subtidalzonation complexity – abiotic and biotic forcings

Within species

Change ratio of accessory pigments

Up-regulation of pigments(make more of everything)

How do algae cope with attenuation? (1) Pigments

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Change size of PSUsantennae + reaction center

(bigger is more efficient at low light levels)

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osyn

thes

is

Model for comparison of P-E curves within species: photoacclimation

tosy

nthe

sis

More PSUs

Fewer PSUs

Larger PSUs

Smaller PSUs

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Phot

o

Irradiance or light intensity

Phot

Irradiance or light intensity

From Ramus 1981

Same size, different number ofPSUs

Same number, different sizes of PSUs

How do algae cope with attenuation? (2) Morphology

Vs.

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Surface area: More surface to capture light, crustose algae should do best in dim habitats, less self shading

Thallus thickness: Thicker thalli should have a growth disadvantage in dim habitats, also self-shading

Sun adapted

Shade adaptednt

hesi

s

Comparison of P-E curves across species: photoadaptation

Pmax?

Alpha?

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adapted

Phot

osy

Irradiance or light intensity

Alpha?

- Affects all levels of biological organization – molecules, cells, organisms, communities. In algae – photosynthesis, enzymatic activity

II. Temperature

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Too high? – Denatures proteins, damage enzymes, membranes

Too low? – Low enzymatic activity, disrupts lipids, membranes, ice crystal formation

**Lethal temp set by tolerance of most susceptible life history stage**

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All algae are single celled at some stage of life history, even the big kelps; a species’ distribution is determined by effect of biotic and abiotic factors across all stages of its life history

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Isotherms

• Boundaries defined by the same surface water temperature averaged over many years for a particular month

• Northern and southern limit dictated by February and August Isotherms

Seaweed Floristic Regions1. Artic- depauperate

2. Northern Hemisphere Cold Temperate- Laminariales- Atlantic & Pacific have distinct communities

3. Northern Hemisphere Warm Temperate

4 Tropical4. Tropical- 180 million years, 20 °C isotherm

5. Southern Hemisphere Warm Temperate

6. Southern Hemisphere Cold Temperate- Durvillaeales-similar around the southern hemisphere

7. Antarctic- 1/3 of 100 species endemic

Best correlate for algal biogeographic patterns: Temperature

Other correlates:

Day length Latitude Confounded w/ temp

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f p

Currents

So why temperature?

- Experimental evidence w/single spp- Northern cold temperate southern limits set by summer high- Warm temperate/tropical spp northern limits set by winter low- Thermal boundaries shift with global warming/cooling events

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Potential problems with invasive species?- Increase in dispersal rates, changes in dispersal patterns- Global warming and shifting boundaries

•Codium fragile is a pest in Japan•Colpomenia from Japan is a serious problem in European oyster

beds•Caulerpa spp. has become pest in the Mediterranean (San

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Caulerpa spp. has become pest in the Mediterranean (San Diego?)

Definition = Grams of salts per kilogram of solution Measurement = Refractometer: measures light refraction

• Unit of Measure – ppt or o/oo, parts per thousand.

III. Salinity

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pp p p(1kg seawater contains 34.7 g of salts ->34.7o/oo)

• Range – oceanic 32-38ppt, estuarine 1-32ppt

III. SalinityOsmoregulation in seaweeds

• Seaweed cells lack contractile vacuoles to pump water out

• Seaweeds prevent bursting due to water diffusing in by pumping ions both in and out

Seawater is hypotonic (less saline) than most algal cells

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ions both in and out

• Tolerance of hypersaline water (e.g. in tidepools) depends on elasticity of cell wall (prevents plasmolysis = cell wall tearing away from cell membrane due to water rushing out).

• Tolerance of freshwater (even more hypotonic) depends on ion pumping ability and strength/elasticity of cell wall

• Osmotic stress (in either direction) can act synergistically with temperature

• Gametes and spores are especially sensitive

III. Salinity

Euryhaline: Species that can handle a wide range of salinities

Stenohaline: Species that can only survive in a narrow range

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Stenohaline: Species that can only survive in a narrow range of salinities

High Salinity:- Tidepools

Low Salinity:- Estuaries- FW seeps

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III. SalinityThe Baltic Sea: a huge estuary = brackish water

• Marine seaweeds (e.g. Fucus) occur there but are smaller morphologically

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are smaller morphologically (smaller thalli or smaller cells) and have different abiotic optima

• Local adaptation

Macro-nutrients necessary for algal growth =

C H O K N S Ca F Mg P

IV. Nutrients

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C, H, O, K, N, S, Ca, F, Mg, P

N is often limiting in coastal waters, needed for amino acids, protein synthesis, nucleic acids

Seaweeds and Nitrogen:

Ammonium (NH4+) and nitrate (NO3

-) are the most common and used nitrogen sources; NH4

+ is preferred because it can be utilized directly (energy saving)

NO3- assimilation by nitrate reductase requires iron (phytoplankton

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NO3 assimilation by nitrate reductase requires iron (phytoplankton cannot exhaust high NO3

- pools in Fe-limited Antarctic oceans; famous Fe-addition experiment), more energetically costly

Cyanobacteria can fix atmospheric nitrogen = convert N2 to NH4+;

25-60% of this fixed nitrogen is released into the water

Variation in nutrient availability in space and time:Issues of depth stratification, role of upwelling

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Variation in nutrient availability in space and time:Issues of depth stratification, role of upwelling

• Chlorophyll = measure of photosynthesis• Irradiance higher in shallow water• Nutrients usually higher in deeper water

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p• Maximum Ps happens in the middle.

Processes that make nutrients available to algae:

- Upwelling

- Nitrogen fixation by Cyanobacteria

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- Bacterial decomposition

- Runoff in coastal areas

- Defecation by animals

- All macroalgae have a boundary layer of water around the thallus, affects contact with nutrients

V. Water Flow

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affects contact with nutrients, gasses.

-Algae depend on water motion to deliver gasses, nutrients, and remove O2 from their surfaces

-e.g, Macrocystis, nitrate uptake increases by 500%, and Ps by 300% if flow goes from zero to 4 cm/second

In relatively still water (e.g protected coves), surface area becomes really important (more surface area = more diffusion)

Interaction of Water Flow and Morphology

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Algae in these environments tend to have high SA:V = maximize uptake of nutrients

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Relationship between SA/V(morphology) and photosynthetic rate

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From Stewart and Carpenter, Ecology (2003)

A B C D E

Costs of high SA:V? In high flow environment = leafy, foliose shapes are a drag

- Variation in species composition on wave exposed vs. wave protected shores = particular morphotypes consistently found in particular flow environments

- Variation within species =

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- Variation within species = phenotypic plasticity in traits that affect water flow around the algal thallus

e.g. Nereocystis “ruffles” and wide blades in protected areas

Positive effects:

Reduce shading by re-arranging thalli

Mixing of nutrients

Negative effects:

Damage, destruction

Loss of settling zygotes/germlings

Complicated effects of water flow

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Reduce boundary layer

Dispersal of spores, gametes, zygotes

Energetic expense of structure

Inhibits external fertilization in some spp

VI. Tides

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Littoral zone = intertidal zone

Supralittoral = above mean high water, rarely submergedSublittoral = below mean low water, permanently submerged

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• Sun and moon pull in the same plane at full and new moon (= spring tides, big changes in tide ht), and compete at half moon (= neap tides, smaller change).

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X

12:00Noon

X

X

X

TideLevel

SUN

MOON

gravitational pull

Semi-diurnal (twice daily) tides

6:00 PM

X

X

X

X

6:00 AM

12:00Midnight

Spring tide sequence

Sun and moon have different gravitational strengths (previous slide) and topography of ocean basin modifies tidal current so that high (and low) tides are not same height. This is referred to as mixedsemi-diurnal tides

mean sea level

0 ft mark at MLLW (mean lower low water)= mean lowest tides over the year at that location

http://tbone.biol.sc.edu/tide/

Tides = Periodic “waves” that result in a change in water level generated by the attraction of the moon and the sun

Diurnal

Semidiurnal(equal)

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Semidiurnal(unequal = mixed)

• Frequency and amplitude of tides affected by the tilt of the earth and morphology of the ocean basin

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• Diurnal, mixed, and semidiural in different locations

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• Frequency and amplitude of tides affected by the tilt of the earth and morphology of the ocean basin

neap tides

spring tides

spring tides

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spring tides

neap tides

neap tides

spring tides

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spring tides

spring tides

neap tides

Tides are sinusoidal. Appearance of the sine wave tidal function might lead one to believe that the relationship between immersion time (time underwater) and tidal height decreases smoothly (and linearly or gently curvilinear) with increasing tidal height:

Tides help to determine zonation patterns in intertidal

Mean no. hr of immersion

(= submergence)

tidal level (= height in intertidal)

low high

Does this correspond intuitively to sharp breaks in zonation patterns?

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Pattern: sampled distributions of species of macroalgae along CA and Oregon coasts and found (at all sites):

Doty (1946, Ecology 27:315-328)

crustose coralline reds (cc)

Six distinct zones

Endocladia (En)

Mastocarpus(M)

elevation

high

Specific hypothesis: species zones will correlate with discrete zones of immersion (“critical tide levels”)

( )

Egregia (Eg)

fleshy reds (fr)Laminaria – kelp (L)

elevationin

intertidal

low

MLLW

General hypothesis: tidal fluctuation and differential tolerance to immersion causes zonation of species in intertidal

Test: Calculated the actual immersion times over the tidal range:

Doty (1946, Ecology 27:315-328)

Mean no. hr of immersion

(= submergence)

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8

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Literally cut and weighed tide tables!

Conclusion: physical factors - immersion - control species distribution and determine zonation of species in intertidal

Results: dramatic non-linear steps in immersion that correlated with algal zonation!

( g )

tidal level (= height in intertidal)

low high

0

4

CCMEnEgfrL

Harsh environment: temp, desiccation, wave stress, salinity, light

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Intertidal organisms show striking patterns of zonation

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Zonation Patterns

physical factors

Dave Lohse

bioticinteractions

Zonation Patterns- physical factors and biotic interactions Zonation Patterns

highzone

Dave Lohse

low zone

midzone

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Adaptations to living intertidally:

- Wicked holdfasts for attachment

- Morphology that minimizes drag, shear stress

- Tolerant of high temps (H2O temperature typically 10-17 degrees C along Central Coast; in tide pools up to 30 degrees C)

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degrees C along Central Coast; in tide pools, up to 30 degrees C)

- Desiccation tolerance (some algae can survive 60-90% water loss), some require low tide for survival

- Synchrony in gamete release (e.g. intertidal Fucoids, like Silvetia compressa)

- Photoprotective pigments

VII. Sand Burial

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How do algae deal with this?

Two basic strategies: recover or resist

Opportunistic spp:Chaetomorpha, Ectocarpus, Ulva

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Stress “tolerators”:Gymnogongrus, Laminaria sinclairii, Neorhodomela

Abiotic

I. Light

II. Temperature

Ecology: Living in a marine environment

Patterns, Processes, and Mechanisms

Some factors affecting Algal Ecology

Biotic

I. Herbivoryp

III. Salinity

IV. Nutrients

V. Water Motion

VI. TIDES

VII. Sand Burial

II. Epiphytism

III. Competition

All act together in nature!

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I. HERBIVORY(i.e. “predation” on algae)

I. HERBIVORY• Damage caused by herbivores varies a lot

Macrocystis and sea urchins

…versus certain crustose corallines and limpets

How do algae deal with herbivory? recover, avoid, or resist

“Recover”

Chiton example = minimal cost of grazing of algal fitness

R id thRapid growth

Opportunistic recruitment

How do algae deal with herbivory? recover, avoid, or resist

“Avoid”

Spatial escape Low herbivory habitats

Associational defenses

Temporal escape

Life history

SizeAssociational defenses

HypneaSargassum

Size

Mastocarpus spp.

sporophyte (2N) 26

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“Resist”

Structural defenses

How do algae deal with herbivory? recover, avoid, or resist

tough, spiny

Turbinaria

Endocladia

Turbinaria

Endocladia

Chemical warfare:

Secondary metabolites

• Polyphenolics and pholorotannins in browns

• Terpenes in tropical spp

calcified

So… why aren’t all algae defended?

- Geographic variation in levels of algal chemical defense

- Within-INDIVIDUAL variation in defense

Life history variation is all about trade-offs(limited energy, how do you spend it?)

$$$

Inducible defenses versus Constitutive defenses

-Inducible defense: Can turn on and off- Constitutive: Always on

Ascophyllum

When do you want one versus the other?

Cues?Predictability?Cost of Defense?

Toth and Pavia 2000

Interaction of grazing and morphologyPadina example

Increased Grazing

Prostrate,Branching thallus

Typical Fan-Shaped thallusliose Fan-Shaped thallus

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Some common, local intertidal herbivoresSnails

Littorines

Limpets

Tegula

Chitons

Urchins

Herbivory- determine the lower limit of species (Harley 2003)

Haven Livingston

Herbivory- determine the lower limit of species (Harley 2003) II. EPIPHYTISM

Benefits to epiphyte?- Access to resources (nutrients, sunlight, etc…)- Place to live

Costs to basiphyte?- Extra drag- Depleted resources

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How do algae deal with epiphytes?

- Outrun them (rapid growth, blade turnover)

Membranipora on Macrocystis

- Ditch them by sloughing off outer layer of cells

(e.g. Ascophyllum, Silvetia, other fucoids)

Laminaria blade but not stipe

- Resist with chemical defenses

Allelochemicals. E.g. phenolics and polyphenolic compounds originate in plastids,produced by browns, active as antifouling agents and herbivore deterrents

pH. rapid growing spp often have increased pH at thallus surface. e.g. Ulva, Enteromorpha

Chondrus crispus inhibits diatoms

III. COMPETITION in Algae

Exploitative: scramble for a limiting resource (no direct antagonism)

Interference: interactions between organisms (limiting resource not necessary)

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Explotive Competition-passive, consumptive

Exploitative Competition-passive, pre-emptive

Interference Competition-overgrowth

Interference Competition-chemical