Transcript No Slide Title

The Shelf Sea Ecosystem
Dr. Mark Moore
Rm. 456/18
E-mail: cmm297
20th February 2003
•Introduction
•Primary production in shelf seas
•Secondary production and food webs
•The physics of shelf seas as a control
on food web structure
•Review and conclusions
Primary production in shelf seas
Forms of phytoplankton
Controls on growth: nutrients and light
Cell size and succession
Primary production in shelf seas 1
Smallest: cyanobacteria, mainly synechococcus in
coastal seas, <2m
Flagellates
2-20 m
Dinoflagellates
O(100 m)
Diatoms (50->1000 m)
Primary production in shelf seas 2
Photosynthesis is reduction of inorganic carbon
resulting in production of organic matter and evolution
of oxygen:
H2O + CO2 + light  organic matter + O2
Primary production and the growth of phytoplankton
can be limited by the availability of the key resources
Nutrients and Light
Growth
Photosynthesis is an
increasing function of light
and nutrients
the relative availability of
these resources can control
the growth rate
Growth
Light
Nutrients
Geider et al. 1998 Limnol. Oceanogr. 43 679-694
Primary production in shelf seas 3
Phytoplankton niche selection
after Margalef, 1979
Relationship of cell
size to succession
Red tide
Dinoflagellates
Diatoms
Nutrients
In general larger
cells (diatoms) are
found in situations
where higher
ambient nutrient
concentrations are
found
Large
Diatoms
Coccolithophores
(flagellates)
Dinoflagellates
Picoplankton
Turbulence
Light
Cullen et al. 2002 pg 297-336 in The Sea Vol
12 Wiley
Secondary production and the food web
Trophic levels
The microbial loop
Food web complexity
Loss of energy between trophic levels
Secondary production and the food web 1
Transfer of energy and organic matter through the various
trophic levels is called the food chain
Phytoplankton
Primary
producer
trophic
level
1
herbivorous zooplankton
Primary
consumer
carnivorous zooplankton
Secondary
consumer
2
But situation is more complex, e.g. fish can be
omnivorous, also the microbial loop…..
3
fish
Tertiary
consumer
4
Secondary production and the food web 2
Phytoplankton
Herbivorous zooplankton
Carnivorous zooplankton
Heterotrophic
bacteria
Bacterivorous
flagellates
Regeneration
Dissolved
organic matter
Bacteria and viruses and
micro-zooplankton
(flagellates and ciliates)
can cycle organic matter
through dissolved and
particulate pools
can act as a sink for
primary production
Kirchman Ed. (2000) Microbial ecology of the Oceans Wiley
Ciliates
Secondary production and the food web 3
Food webs are complex,
involve multiple transfers with
organisms covering wide range
of size classes
Secondary production and the food web 4
Transfer of energy between trophic levels
There is
some loss of
energy at
each level in
the food
chain (web)
Average
efficiency is
low <20%
Physics of shelf seas as a control
on ecosystem structure
Mixing, stratification and blooms at
fronts
Coastal upwelling and blooms
Nutrient inputs to coastal waters: red
tides
Physics of shelf seas as a control
on ecosystem structure 1
Temperature
Chlorophyll
Physics of shelf seas as a control
on ecosystem structure 2
Temperature
Chlorophyll
Physics of shelf seas as a control
on ecosystem structure 3
Review and conclusions:
from phytoplankton to fish
Food webs are complex
From Azam et al. 1983
Review and conclusions: from phytoplankton to fish
When nutrients are
low, favours smaller
phytoplankton grazed
by microzoo, microbial
loop and recycling
dominate
As nutrients become
more available, larger
phytoplankton can
survive, grazed by
larger zoo, less trophic
levels and hence
higher yield to top of
chain (fish)
Review and conclusions: from phytoplankton to fish
In very general (cross
system) terms,
fisheries yield can be
related to total
primary production
occurring
however the number
of trophic levels and
efficiency of these
steps governs the yield
Relationship of primary production and fish
production in three different marine habitats
Habitat
Oceanic
Coastal
Upwelling
% Ocean area
90
9.9
0.1
Mean Primary Production
(g C m-2 yr-1)
50
100
300
16.3
3.6
0.1
5
3
1.5
10%
15%
20%
Mean fish production
(mg C m-2 yr-1)
0.5
340
36000
Total fish production
(106 tonnes C yr-1)
0.2
12
12
Total plant production
(109 tonnes C yr-1)
Number of energy transfers
between trophic levels
Average ecological
efficiency