1. The Trophic Structure of Hawaiian Reefs
Part 1

2. Food Chains
Artificial devices to illustrate energy flow from one trophic level to another
Trophic Levels: groups of organisms that obtain their energy in a similar manner
Food Chains
Although the term 'food chain' has entered into common usage, in most ecosystems food chains do not occur. The idea that energy flows along a chain of consecutive links made up of various consumers is unrealistic. As we will see shortly, trophic interactions are considerably more complex than a series of linear steps. Food chains are a useful beginning to illustrate the concept of trophic levels.
Trophic levels are a way of identifying what kinds of food an organism uses.
Primary producers obtain their energy from the sun or chemical sources and utilize inorganic compounds from the environment to make organic compounds.
Herbivores feed on primary producers that utilize the sun for energy
Carnivores feed on herbivores and other heterotrophic organisms.

3. Food Chains
Total number of levels in a food chain depends upon locality and number of species
Highest trophic levels occupied by adult animals with no predators of their own
Secondary Production: total amount of biomass produced in all higher trophic levels
Food Chains
In food chains, the total number of trophic levels depends upon the location and number of different species.
In general, the highest trophic level is occupied by adult animals with no predators of their own. For example, killer whales would occupy the highest trophic level in an antarctic food chain.
Secondary production refers to the total amount of animal biomass produced in all trophic levels above the primary producers. That is, it reflects all heterotrophic production.

4. Nutrients
Inorganic nutrients incorporated into cells during photosynthesis
- e.g. N, P, C, S
Cyclic flow in food chains
Decomposers release inorganic forms that become available to autotrophs again
Nutrients
Inorganic nutrients are incorporated into cells during photosynthesis and chemosynthesis.
Examples of important nutrients are nitrogen, phosphorus, carbon and sulfur.
The flow of nutrients in a food chain is cyclical. A pool of nutrients resides in a trophic level until animals die or excrete it. Then decomposers can release it in a form that is utilizable by autotrophic organisms.

5. Energy Non-cyclic, unidirectional flow
Losses at each transfer from one trophic level to another
- Losses as heat from respiration
- Inefficiencies in processing
Total energy declines from one transfer to another
- Limits number of trophic levels
Energy
Unlike nutrients, the flow of energy is not cyclical but rather is unidirectional. Energy is captured by primary producers and transferred to higher trophic levels. At each transfer, only a fraction of the energy is passed on and much is lost.
These losses are in the form of heat and inefficiencies in processing and assimilating energy.
Thus, the total available energy declines as one moves up trophic levels in a food chain.
This places a limit on the number of trophic levels that can exist. At some point, there is too little energy available to sustain further transfers.

6. Energy Flow

7. Energy Flow through an Ecosystem
Food Chain
Tertiary Consumer
Producer
Primary Consumer
Secondary Consumer
grasshopper
snake
grass
hawk
heat
Example Food Chain
This simplified food chain illustrates links in a food chain. The chain begins with diatoms which are consumed by herbivorous copepods. The copepods are consumed by carnivorous zooplankton (in this case, chaetognaths) and the chaetognaths are consumed by planktivorous fishes.
In a food chain, energy moves in a linear fashion from producers through consumers.
heat
heat
Nutrients
fungi
Decomposer

8. Transfer Efficiencies
Efficiency of energy transfer called transfer efficiency
Units are energy or biomass
Pt = annual production at level t
Pt-1 = annual production at t-1
Et = Pt
Pt-1
Transfer Efficiencies
Only a portion of the energy in one trophic level makes its way to the next. This is called the transfer efficiency. The currency may be energy or biomass.

9. Transfer Efficiency Example
Net primary production = 150 g C/m2/yr
Herbivorous copepod production = 25 g C/m2/yr
= Pcopepods
Et = Pt
Pt-1
= 25 = 0.17
Pphytoplankton
150
Transfer Efficiency Example
Let's assume that we wish to calculate the transfer efficiency between primary producers and herbivorous copepods.
Our currency will be grams of carbon.
The annual production of primary producers is 150gC per square meter per year.
The annual production of copepods is 25 gC per square meter per year.
The transfer efficiency is then 25/150 or about 17%.
Typical transfer efficiencies from primary producers to herbivores are about 20% while efficiencies between higher levels are about 10%.
Typical transfer efficiency ranges
*Level 1-2 ~20%
*Levels 2-3, …: ~10%

10. Energy and Biomass Pyramids
Kaneohe Bay
10 J
Tertiary consumers
100 J
Secondary consumers
1000 J
Primary consumers
10,000 J Limu
Primary producers
1,000,000 J of sunlight

11. Energy Use By An Herbivore
Algae eaten by Uhu
Cellular Respiration
Feces
Growth

12. Food Webs Food chains don’t exist in real ecosystems
Almost all organisms are eaten by more than one predator
Food webs reflect these multiple and shifting interactions
Food Webs
Remember that food chains are an artificiality that don't really exist. In reality, the trophic linkages between organisms are much more complicated. Most organisms have more than one predator and the diets of animals shift as they develop.
Food webs reflect the complexity of trophic interactions.

13. Antarctic Food Web

14. Some Feeding Types Many species don’t fit into convenient categories
Algal Grazers and Browsers
Suspension Feeding
Filter Feeding
Deposit Feeding
Benthic Animal Predators
Plankton Pickers
Corallivores
Piscivores
Omnivores
Detritivores
Scavengers
Parasites
Cannibals
Ontogenetic dietary shifts
Food Webs ...
There are many trophic categories that are too complicated to fit into the simple concept of a food chain.
Many animals are omnivorous. That means that they consume a wide variety of prey. An omnivore might consume diatoms and crustacean larvae. Thus, it's feeding at trophic levels one and two.
Detritivores feed on dead organic matter that can be derived from a wide range of sources at varying trophic levels.
During development (ontogeny) animals often shift their diet as they grow larger. Consider a tuna which may begin by feeding on copepods and zooplankton but which progresses to large fish at adulthood.
Parasites complicate the picture because they may have a number of different hosts of different trophic status.

15. Food Webs…
Competitive relationships in food webs can reduce productivity at top levels
Phytoplankton
(100 units)
Phytoplankton
(100 units)
Herbivorous
Zooplankton
(20 units)
Herbivorous
Zooplankton
(20 units)
Food Webs ...
The presence of two competitors feeding on the same prey items may alter the availability of energy to higher trophic levels. Consider the example on the left where carnivorous zooplankton of species A feed on herbivorous zooplankton and are themselves consumed by fishes.
Let's introduce a second species of carnivorous zooplankton. Species B isn't consumed by fish but shares the supply of herbivorous zooplankton with species A.
The result is that the availability of energy to fishes is diminished.
Food webs contain many of these sorts of competitive relationships and prey preference.
Carnivorous
Zooplankton A
(2 units)
Carnivorous
Zooplankton A
(1 units)
Carnivorous
Zooplankton B
(1 units)
Fish (0.2 units)
Fish (0.1 units)

16. Primary Producers zooxanthellae in corals
filamentous algal scum (turf algae)
coralline (calcareous) algae
non-coralline seaweed
filamentous algae growing through the upper layers of the porous reef rock (endolithic algae)
benthic and interstitial diatoms
phytoplankton

17. zooxanthellae

18. turf algae

19. coralline red algae

20. crustose coralline red algae

21. benthic seaweeds

22. benthic diatoms

23. phytoplankton

24. Herbivores herbivorous fish herbivorous snails and sea hares
most parrotfish
surgeonfish (e.g., manini, palani, pualu, kala)
Pacific Gregory (Stegastes fasciolatus)
tidepool blennies
herbivorous snails and sea hares
most sea urchins
herbivorous crabs
green sea turtles

25. parrotfish
Eat coral, make sand!!

26. surgeonfishes

27. Pacific Gregory

28. tidepool blenny

29. tiger cowrie

30. chiton

31. Carnivores Sharks – eat larger fish and crabs
Groupers – eat small fish
Eels – eat small fish, crustaceans
Stingrays – eat crabs
Octopus – eats crustaceans