Ecology of Water Columns
2
Fate of organic matter synthesized
by producers
1. Graphic: Classical Water
Column Food Web
Top Predators
(larger fish,
non-baleen whales,
man)
Predators (fish, insects)
Grazers (copepods, cladocerans)
Phytoplankton (diatoms, dinoflagellates,
greens)
2. Classical Water Column
Food Webs
-
Maximum of 5 trophic levels
-
Too much Energy dissipated by
respiration
-
Known to be an oversimplification
-
Energy flowed up the trophic levels
-
Organic matter not consumed was
degraded by bacteria and fungi
-
primary regenerators (= recyclers,
re-mineralizers)
-
System control
-
Nutrient supply to producers
-
Action of top predators: how many
prey eaten
3. Bioaccumulation
-
Application of trophic level hypothesis
-
Contaminants accumulate in food
webs
-
Chlorinated hydrocarbons (DDT,
PCBs, Dioxin)
-
Heavy metals (Hg, Pb, Cd)
-
Low in phyto --> high in top predators
(fish, birds) --> toxic at [high]
-
Why?
-
Compounds not degraded but sequestered
by consumers
-
Example:
-
DDT interfered with Ca metabolism
in osprey --> egg shells thinned and crushed before hatching.
-
Other factors: [fat] in prey,
consumer age (older=more)
4. Classic Marine Phytoplankton:
-
Fig. 2.7. Pico and nanoplankton
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Bacteria
-
flagellate
-
Flagellate
-
Coccolithophore
-
Pennate Diatom
-
Centric diatom
-
Bidulfid diatom
-
Armored dinoflagellate
-
Naked dinoflagellate
-
Foraminiferan
-
Cilliate
-
Tintinnid
-
Freshwater phytoplankton: diatoms,
dinoflagellates, chlorophytes, desmids, other phytoflagellates
5. Classical Marine Zooplankton
-
(Fig.2.8. ) Representative micro-
and mesoplankton
-
Copepod
-
Euphausid
-
Chaetognath
-
Pteropod
-
Jellyfish
-
Hyperid amiphipod
-
Appendicularian
-
Polychaete
-
Freshwater Zoops: copepods,
cladocerans, rotifers, insects => many marine representatives missing
6. Classical Nekton
-
Representative marine nekton
-
Squid
-
Shark
-
Deep sea fish
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Tuna
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Flatfish
-
Sea turtle
-
Seal
-
Penguin
-
Whale
-
Freshwater Nekton: less
diverse
-
Crustaceans, insects, fish, amphibians,
reptiles, fw mammals & birds
7. New Views - New Discoveries
-
Discovery of new kinds of producers
-
New methods of measurements of
production
-
New observations about activity
& abundance of microbes & metazoa
-
Size of organisms constrains function
8. New Producers?
-
New methods show importance of
picoplankton
-
Size: 0.2 - 2 µm, too small
for plankton nets
-
Methods
-
Old counting method: what
grew on agar plates
-
New
-
Fluorescence microscopy + fluorescent
stains (eg. DAPI) - living organisms ìglowî under UV light, chlorophyll
a autofluoresces
-
3H-Thymidine uptake
assays (only incorporated by prokaryotes) - amount of radioactivity taken
up related to how many cells present
-
Findings
-
105 to > 106
bacterial cells ml-1
-
200 X higher numbers than thought
9. Small photosynthesizers
-
Picoplanktonic Cyanobacteria
-
Ubiquitous
-
Important primary producers in
nutrient poor waters
-
Fix N2 when N is low
-
Examples: Trichodesmium sp.
10. Trichodesmium introduces
the largest fraction of new nitrogen to the euphotic zone (~30mg N/m2/day)
in the N. Atlantic Ocean (tropical + subtropical).
-
Graphic from Chisholm 2000, Nature
407:685-687
11. Other ìignoredî groups
-
Gelatinous animals
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Ctenophores
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Coelenterates
-
Urochordates
-
Difficult to collect with nets
or dredges
-
New methods: SCUBA, minisubmarines
-
May be as abundant as copepods
& at least as large as copepod biomass
12. The importance of size
-
Small size = faster physiological
rates
-
Uptake of nutrients: smaller round
objects, higher surface to volume ratio
-
The smaller the organism, the
larger the weight-specific respiratory rate
-
Picoplankton => 50 - 80% of N
uptake in aquatic systems
-
Small size = faster generation
times
13. Fig.2.10. Effect
of size of organism on metabolic processes.
-
Weight-specific respiration of
zooplankton
-
Weight-specific release of nitrogen
by planktonic protozoans and metazoans. Lines depict upper and lower
extremes of measured values. Ikeda (1970) and Caron (1991)
14. Size vs. Biomass Relationships
The bigger the organisms, the
more scarce
Predation rates affected by size
of prey
Optimal foraging theory: predators
tend to choose prey that yield high food value compared to the energy spent
chasing, subduing & eating prey.
15. Fig.2.11.
Relationship of organism size to abundance.
a. Estimates
of abundance of some major groups of different size in 2 oceanic environments.
b. Biomass of surface
plankton in the N. Pacific Gyre in relation to weight of the organisms.
16. Fig. 2.12. Frequencies
of assimilation efficiencies for a wide variety of animals feeding on detritus,
on live producers and on animals. Valiela (1984).
17. Other food selection
criteria
-
Nutritive quality
-
Detritus
-
relatively low quality
-
Assimilation efficiency tends
to be low
-
May contain [high] of defensive
compounds
-
Antiherbivore (tannins, phenolics)
-
Antipredator compounds as in sponges,
sea slugs, gorgonians and tunicates
18. How do you track who
eats whom?
-
Stable Isotope Analysis
-
Isotopes of elements that donít
decay
-
2H/1H, 13C/12C,
18O/16O,
34S/32S, 15N/14N
-
Isotopic ratios can be measured
using continuous-flow mass spectrometers
-
Biological processes may change
the isotopic ratio from that available in the inorganic portion of the
environment
-
You are what you eat: an
organismís stable isotope ratios indicate their food source
-
Used in
-
Defining energy pathways
-
Food-web structures
-
Importance of aquatic vs. terrestrial
inputs