Marine Food Chains/Webs
• Energy from primary production is
transferred up the trophic chain
• Each step is inefficient (~90% energy is lost)
• Shorter chains are more efficient at
producing apex predators
It’s a web,
not a chain
Marine Food Chains/Webs
• Energy from primary production is
transferred up the trophic chain
• Each step is inefficient (~90% energy is lost)
• Shorter chains are more efficient at
producing apex predators (harvestable fish)
Bottom Up Estimates
of Fish Production
• Fish production is equal to the PP multiplied by
the efficiency of exchange for each trophic level
• Ex: 3 trophic level system
Fish Prod = TotPP * eff1 * eff2
• Ex: 6 trophic level system
Fish Prod = TotPP * eff1 * eff2 * eff3 * eff4 * eff5
• Efficiencies are small (~10%) so most PP is lost
CalCoFI Primary Production
• Estimated PP from ocean
color imagery
• Used a bio-optical
algorithm (VGPM)
• Compared results to PP
observations from CalCoFI
• Kahru & Mitchell [2002]
CalCoFI Primary Production
r2 = 0.59
0-100 km
Total nearshore PP
2.7+1.4+1.5+2.5
= 8x1012 gC mo-1
~1x1014 gC y-1
CalCoFI Primary Production
• Satellite estimates of PP show fair validity
to observations
• Seasonal cycle is obvious
• Total nearshore PP ~ 8x1012 gC month-1
~ 1x1014 gC year-1
• How many tons of fish are produced?
Bottom Up Estimates
of Fish Production
• Fish production is equal to the PP multiplied by
the efficiency of exchange for each trophic level
• Ex: 3 trophic level system
Fish Prod = TotPP * eff1 * eff2
• Ex: 6 trophic level system
Fish Prod = TotPP * eff1 * eff2 * eff3 * eff4 * eff5
• Efficiencies are small (~10%) so most PP is lost
Bottom Up Estimates of CA
Current Sardine Production
• So Cal Bight – Int PP ~ 1x1014 gC year-1
• Focus on clupeid fish (cf., sardines)
• This food chain PP energy goes to fish in 2 steps
Bottom Up Estimates of CA
Current Sardine Production
• Clupeid Fish Prod = Tot_PP * Eff1 * Eff2
= (1x1014 gC year-1) (0.1) (0.1)
= 1x1012 gC y-1
• Fish are not made of just carbon
– Wet weight is ~10% carbon
• Annual Clupeid Fish Prod = 1x1013 g Fish
= 10x106 Mt
1,000,000 Mt/y
Spawning biomass is
roughly the same as
our fish production
guestimate
Sardine Stock
Assessment from CFG
Sardine biomass is
10% of possible
fish production
10,000,000 Mt/y
100,000 Mt/y
Sardine landings ~ 1% Total Clupeid Fish Production
Bottom Up Estimates of Fish
Production
• Open ocean total PP ~ 50x1015 gC year-1
• Focus on tuna in an open ocean food chain
• This food chain PP energy goes to tuna in 5 steps
Bottom Up Estimates of
Global Tuna Production
• Global Tuna Production =
= Tot_PP * Eff1 * Eff2 * Eff3 * Eff4 * Eff5
= (50x1015 gC year-1) (0.1)5
= 5x1011 gC y-1
• Taking into account wet weight
• Annual Maximum Tuna Production = 5x1012 g Fish =
5,000,000 Mt/y
• Global catch for “tunas” is ~6x106 Mt/y (FAO)
WARM
Switching
between
Sardine &
Anchovy
COOL
Varved Sediments in Santa
Barbara Basin
Varved Sediments in Santa
Barbara Basin
• The Santa Barbara Basin is nearly anoxic
Sill depth
Varved Sediments in Santa
Barbara Basin
• Sediments form in annual varves
• Low O2 – little bioturbation – require C inputs
Respiration &
Remineralization
hn
CO2
NUTS
O2
remineralizers
sinking
organic
matter
Biological processes consume plants & O2 to
make CO2 & nutrients
Varve Formation
Varve formation requires high inputs of
sinking carbon to suck up O2
Example from Santa Monica Basin
Fish Abundance from Varves
• Fish scales are ID’ed & counted
• Annual varves are dated
• Results in fish scale deposition rate
• Correlated to fishery biomass records to
produce a 1700 year biomass time series
Epochs of sardine dominance…
Fish Abundance from Varves
• Switching between anchovy & sardine is
seen – on 20 to 50 year time scales
• Policy implications are important
– Fishery collapses are not JUST due to fishing
– Climate control of fish abundances
Fish Production in CA Current
• Bottom up controls of fish production
• Some consistency with fishery statistics
• Hard to use alone to predict harvest quotas
– BUT sets an UPPER bound
• Switching of stocks & climate control
– Only one clupeid fish fills niche (sardine OR anchovy)
– Who it is is controlled by climate (PDO; cool/warm)