Ecological efficiency
Pn
n 
Pn  1
Ecological
efficiency of
zooplankton is
usually
around 10%
of NPP in
lakes
Fecal pellets
Zooplankton such as Daphnia filter-feed using currents generated by
their thoracic appendages. Fecal pellets sediment rapidly to the bottom
80-95% of energy is lost at each trophic step, much of it as feces
Assimilation efficiency
Herbivores
≈100% for sugary nectar
≈40-80% for small
phytoplankton and
filamentous algae
<20% for mud and detritus
Carnivores
60-70% for aquatic insects
70-90% for meat
Fecal pellets
The undigested material in the zooplankton fecal pellets was not assimilated.
Assimilation efficiency depends on the digestibility of the diet
Cellulose or other undigestible material makes AE low
Ingested energy ─ egested energy = assimilated energy
Assimilation efficiency (AE, %)= assimilated energy/ingested energy x 100
Exploitation efficiency or Consumption Efficiency (EE)
In
EEn 
 100
Pn  1
n  EEn  GPEn
Exploitation efficiency is the consumption rate at a given trophic level divided by
the productivity of the trophic level it feeds on.
If EE for herbivores is low then plant detritus will be readily available for
detritivores.
Zooplankton will have low EE (CE) when phytoplankton are sedimenting rapidly
to the bottom before they are being eaten.
If EE(CE) is high then most of the sedimentation will be in the form of fecal
pellets, which sink more rapidly than individual cells.
Zooplankton fecal pellets are good food for benthic invertebrates
Activity is energetically expensive and high Metabolic rate means
low Production efficiency
Gross PE
Endotherms
≈5% or less
≈1% some birds
Ectotherms
≈10-30% for fish
≈ 5-15% insects
Otter swim about rapidly and spend large amounts of energy looking for fish to eat
Assimilated energy ─ respiration ─ excretion = production (growth)
Net Production efficiency (NPE, %)= growth/assimilation x 100
Gross PE (%)=[assim/ingest x growth/assim] x100=growth/ingest x 100
Energy budget for herbivorous zooplantkon
NPP = rate of formation of
phytoplankton biomass
S = rate of production of
uneaten algae, mostly inedible
species (sedimentation)
F= rate of production of
fecal pellets (sedimentation)
Metabolic costs include basal metabolism, activity costs
and specific dynamic action (costs of digestion etc)
Zooplankton production is the rate at which biomass (energy)
becomes available for consumption by zooplanktivores
ZP/NPP = 0.05-0.20 but usually averages around 0.1
Pn
n 
Pn  1
In
An
Pn
Pn
EEn 
, AEn 
, NPEn 
, GPEn 
Pn  1
In
An
In
Show
n  EEn  AEn  NPEn
n  EEn  GPEn
If the productivity of a phytoplankton population is 4000 k J (kilo Joules) /yr /
m2, If sedimentation rate of dead cells to the substrate constitutes 1600
kJ/m2yr, and the phytoplankton population is dB/dt=0. If the rain of
zooplankton fecal pellets to the bottom is 1400 kJ/m2/yr. What is the
assimilation efficiency of the zooplankton trophic level (assume that they are
all feeding on phytoplankton).
1.
2.
3.
4.
5.
0.42 or 42%
0.60 or 60%
0.35 or 35%
0.25 or 25%
None of these
What is the exploitation efficiency EE (or Consumption efficiency CE) of the
zooplankton trophic level
1.
2.
3.
4.
5.
0.42 or 42%
0.60 or 60%
0.35 or 35%
0.25 or 25%
None of these
If the net production efficiency of the zooplankton trophic level is
0.40 (40%) what is the ecological efficiency () of the trophic level
1. 0.15 or 15%
2. 0.05 or 5%
3. 0.10 or 10%
4. 0.25 or 25%
5. None of these
If the zooplanktivorous fish are consuming zooplankton at the rate
of 400 kJ/yr/m2, their EE (CE) is
1. 0.40 or 40%
2. 0.60 or 60%
3. 1.00 or 100%
4. 0.25 or 25%
5. None of these
If the zooplanktivorous fish have an assimilation efficiency of 0.70
(70%) and Net production efficiency (NPE) of 0.20 (20%), the
productivity at this trophic level is
1. 40 kJ/yr/m2
2. 56 kJ/yr/m2
3. 100 kJ/yr/m2
4. 280 kJ/yr/m2
5. None of these
If in another lake with similar zooplankton productivity the
planktivore fish productivity was 2 X higher, a possible explanation
for this would be
1. the AE of the fish in that lake was 2X as high
2. the NPE of the fish in that lake was 2X as high
3. the EE (CE) in that lake was 2X as high
4. the AE*NPE in that lake was 2X as high
5. both b and d are true
6. both b and c are true
Energy budget for herbivorous zooplantkon
NPP = rate of formation of
phytoplankton biomass
S = rate of production of
uneaten algae, mostly inedible
species (sedimentation)
F= rate of production of
fecal pellets (sedimentation)
The Bioenergetic budget for
an organism
C= F + SDA + M*A+ U + G
Metabolic costs include basal metabolism, activity costs
and specific dynamic action (costs of digestion etc)
Zooplankton production is the rate at which biomass (energy)
becomes available for consumption by zooplanktivores
ZP/NPP = 0.05-0.20 but usually averages around 0.1
Textbook Chapters since the last mid-term
Chapter 17: Phosphorus concentrations and cycling
Chapter 14: Carbon and pH
Chapter 15: Dissolved oxygen
Chapter 16: Oxidation-reduction potential
Chapter 18: Nitrogen cycling
Chapter 21: The Phytoplankton—21:12-21:15
Chapter 23: The zooplankton
Chapter 26: Fish and Aquatic birds
Chapter 27:Acidification of waterways
Chapter 29: Reservoirs
Energetic losses in the food chain
Less than 1% of the incident light
energy is captured by
photosynthesis
as NPP.
Productivity declines by
about 10-fold for each
trophic level in the food
chain.
Most of the losses are
are in the form of waste
heat.
Some energy from each
trophic level winds up in
the detrital pool, and some
of this remains buried
as sediment (or soil) organic
matter (fossilized)
Yields of piscivorous fish are well correlated with primary productivity but are several orders
of magnitude lower than PP because food chains are long and Trophic efficiencies are low
•Intensive aquaculture can
produce yields that are
orders of magnitude
beyond natural
ecosystems
Figure 26-19
How to maximize energy flow to fish
Increased nutrient loading—fertilization + ammonia and anoxia tolerant species
Shortening the food chain—primary consumers (eg carps, tilapia or mullets)
Don’t rely on natural recruitment and managing the life cycle--stocking
Increasing consumption efficiency—small pens intensive feeding
Increased assimilation efficiency—feeding with easy to digest food pellets
Increased production efficiency—low activity species that don’t mind crowding,
, highly turbid water
Lepeophtheirus salmonis
Many aquaculture proponents
argue that aquaculture reduces
harvesting pressure on wild
fisheries.
Salmonid aquaculture not very trophically efficient,
food pellets made from by-catch of wild species
Major water quality issues—nutrientpollution from
cages, anti-fouling paint, antibiotics, habitat
destruction
Transmit diseases to wild salmonids—bacteria,
viruses, protozoans, fungi, “fish lice” –parasitic
copepods and other Crustacea
Genetic problems when domestic escapees
compete with or interbreed with wild fish
Argulus
Energy budget for herbivorous zooplantkon
NPP = rate of formation of
phytoplankton biomass
S = rate of production of
uneaten algae, mostly inedible
species (sedimentation)
F= rate of production of
fecal pellets (sedimentation)
The Bioenergetic budget for
an organism
C= F + SDA + M*A+ U + G
Metabolic costs include basal metabolism, activity costs
and specific dynamic action (costs of digestion etc)
Zooplankton production is the rate at which biomass (energy)
becomes available for consumption by zooplanktivores
ZP/NPP = 0.05-0.20 but usually averages around 0.1
Pelagic fish like kokanee salmon
expend a huge amount of energy
actively searching for prey--they
have high basal metabolic rates low
conversion efficiencies
The deepwater sculpin sits
on the bottom and ambushes
unsuspecting prey. They
have very low basal
metabolic rates and high
conversion efficiencies
If these two species were fed the same amount of food, the sculpin
would grow more than twice as fast as the salmon
Activity multiplier
5
4
Br3+
Mg3+
3
Mg2+
Me3+
2
Bmt2+
1
Wa2+
Me2+
Bmt3+
Wa3+
0
2.3
2.4
2.5
2.6
2.7
2.8
Log LDH activity
•The anaerobic capacity of fish muscles is closely linked to amount of energy
spent on Activity
•Lactate dehydrogenase (LDH) is an important enzyme for anerobic
respiration, and anaerobic respiration generates bursts of power--but is very
inefficient and builds up an oxygen debt.
There is a trade-off between power (the rate of energy consumption) and
efficiency.
(abs units per mg prot)
LDH activity
LDH vs body size for perch
600
500
400
300
200
100
fish
diet
inverts
zooplankton
0.1
1
10
100
1000
body size (g)
In order to keep growing carnivorous fish usually need to switch to larger and larger prey
If they do not, the activity costs escalate rapidly, and fish fail to grow (stunting)
Thus trophic position usually increases as the fish matures.
Sherwood et al. 2002, Can. J. Fish. Aquat. Sci, see my web page http://people.uleth.ca/~joseph.rasmussen/
Productivity at different levels in the food web
500 x (0.1)3 g/m /yr
2
500 x (0.1)2 g/m /yr
2
500 x 0.1
g/m2/yr
NPP around 500 g/m /yr
2
Zooplankton
Benthic & epiphytic
invertebrates
PhytoplanktonDiet shift
Benthic & epiphytic
algae plus detritus
Trophic link
Net productivity at level n = the rate of growth of biomass at that level
= [SGR +GSI] * Biomass
= NPP (TE) n-1
Classenia, a predatory stonefly, and some of the stream insect
larvae that it preys on
Stoneflies prefer prey that
are near the energetically
optimum size, when they
are given the opportunity
to select from a variety of
sizes.
Data from
Allan, JD. 1995. Stream Ecology, Chapman
and Hall. Ch. 7
Residence time and turnover of energy by trophic levels
The standing stock of energy in the
plankton is low but it is turned over
rapidly, because the organisms are
small, grow rapidly and don’t live
long
Planktonic
Herbivore
(50mg) life span
1 month
A
H1
P
Phytoplankton (0.01mg,
life span, few days
H2
Benthic Detritivore
(0.1 g) life span 1yr
Carnivorous fish
(100g) life span
5-10 yr
Turnover is slower at higher trophic levels, since larger organisms accumulate
energy over a longer life span—longer residence time and slower turnover
More definitions
net productivi ty (kJ/m 2 /yr)
Energy tur nover( / yr) 
energy stored in biomass (kJ/m 2 )
energy stored in biomass (kJ/m 2 )
Residence time (yr) 
net productivi ty (kJ/m 2 /yr)
biomass (kg/m 2 )
BAR(yr) 
rate of biomass production (kg/m 2 /yr)
BAR  Biomass accumulati on ratio
Residence time is long and BAR are high when organisms
are large and live long
Productivity at different levels in the food web
500 x (0.1)3 g/m /yr
2
500 x (0.1)2 g/m /yr
2
500 x 0.1
g/m2/yr
NPP around 500 g/m /yr
2
Zooplankton
Benthic & epiphytic
invertebrates
PhytoplanktonDiet shift
Benthic & epiphytic
algae plus detritus
Trophic link
Net productivity at level n = the rate of growth of biomass at that level
= [SGR +GSI] * Biomass
= NPP (TE) n-1
The Biomass Accumulation Ratio varies with ecosystem type
Ecosystems with largest
primary producers have
highest BAR
Aquatic systems have lower
BAR
Primary producers in
Aquatic ecosystems are
plankton and aquatic
macrophytes which are
smaller than most trees
The smallest phytoplankton
are found in the open ocean
Allochthonous energy input is important in small forested streams
Allochthonous input
makes an important
contribution to primary
consumers in small
tributaries, but much
less so farther down the
river.
Small tributaries are
usually lined with
overhanging trees
whose leaves fall into
the stream, and the
shade limits primary
production within the
stream.
Allochthonous production is energy fixed outside the system, eg leaves from the stream bank fall
into the stream, decompose and support primary consumers, or insects from the bank fall in and
feed the fish
Autochthonous energy is energy produced within the stream by benthic algae or mosses growing
on the rocks