Do ecosystems need predators?

What role do sharks and other top predators play in the coral reef

ecosystem?

Some review of basic ecology ideas may help you answer the last question

An ecosystem is defined as a community of living things that interact with each other and their environment

Food webs describe the pathway for energy or elemental flow

Although a bit simplified, the basic energy flow pattern starts with the sun.

How does energy travel through coral reef systems?

To producers (algae and bacteria)

Then to consumers (animals that eat producers)

It’s more complex than that….• Producers capture

about 10% of the sun’s energy through photosynthesis

• Primary consumers range from tiny zooplankton to herbivores

• Secondary consumers are those that eat primary consumers

• Top consumers consist of apex predators

Then there’s entropy• Each level of transfer in a food web is called a trophic level

(trophic-trophikos: Greek word for nourishment)

• Only about 10% of energy is transferred to the “next” level! 90% is lost to heat, respiration, etc.

• Because of inefficient energy transfers higher trophic levels require more energy than lower trophic levels to produce the same amount of biomass

• All mass is transferred (mass is not destroyed) but is not necessarily used

Food webs also (re)cycle vital chemicals

Zooplankton

Algae

Invertebrates

Fish

Bacteria

Atmosphere

Nitrogen

Phosphorus

Carbon

Scientists are still trying to answer many questions about marine food webs!

Scientists are just beginning to better understand the role that microorganisms play

There is also much to learn about the interaction of terrestrial (land) and marine ecosystems

Can you add to or revise the first two answers on this

worksheet? Please try to do so now

Do ecosystems need predators?

What role do sharks and other top predators play in the coral reef

ecosystem?

Scientists studying the biomass of fish species in various trophic

levels in the Hawaiian Islands have collected some surprising

data!

Examining some of these findings may also assist you in determining the answers to the questions you just

considered

What can you conclude after analyzing this data? Look closely at the Main Hawaiian Islands vs. those of the

Papahānaumokuākea Marine National Monument

You may want to look at the map on the next slide and then return to this slide

Papahānaumokuākea Marine National Monument

Main Hawaiian Islands

Graphing data is a helpful analysis tool

Graphic displays are another way to represent and analyze

data

Scientists are also using geographic images and global

positioning data more frequently

Geographic pattern of apex predator biomass density (t ha -1) at the 10 emergent Northwestern Hawaiian

Island (NWHI) reefs surveyed during September/October 2000, 2001 and 2002 (DeMartini and Friedlander 2004)

The data collected to date supports a surprising

conclusion!

The protected reef ecosystems of the Papahānaumokuākea Marine National

Monument are dominated by apex predators!

Compare the fish biomass of Papahānaumokuākea Marine National Monument to the

Main Hawaiian Islands!

Apex Predators

54%

Other Secondary Consumers 18%

Herbivores 28%

Apex Predators 3%

Other Secondary Consumers 42%

Herbivores

55%

On some islands within the monument, predators account for double the biomass of fish in the

other trophic levels!

Apex Predators

Other Secondary Consumers

Herbivores

French Frigate Shoals Biomass Data

(metric tons per hectare)

Apex Predators: 1.7

Other Secondary Consumers: 0.3

Herbivores:

0.6

The reef ecosystems of the monument are thriving, containing more numbers and greater size of fish

than those of the Main Hawaiian Islands

Gardner Pinnacles – James Watt

The islands in the monument also have flourishing coral, algae and invertebrate colonies too!

French Frigate Shoals – James Watt

There is a marked difference between the reefs in the monument and those of the Main Hawaiian Islands!

Maui - NOAA

Reefs in the Main Hawaiian Islands are dominated by smaller herbivorous fish

Hanauma Bay, Oahu – Donald Miralle

Can you explain why apex-dominated reef ecosystems have:

1) more fish 2) larger fish and

3) healthier corals and benthic communities than those with fewer and smaller

predators?

Try!

Acknowledgements

• Zachary Johnson, SOEST, University of Hawaii Manoa

• George Wright, Montana State University

• James Watt

• Alan Friedlander, Ph.D