Do ecosystems need predators?

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

Some review of basic ecology 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 Atmosphere Algae Phosphorus Fish Zooplankton Nitrogen Carbon Invertebrates Bacteria

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

Do ecosystems need predators? Can you add to or revise the first two answers on your 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 answering the questions you just considered

What can you conclude after analyzing this data 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 now using geographic images and global positioning data more frequently to help analyze data

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!

Other Secondary Consumers 18% Other Secondary Consumers 42% Compare the fish biomass of Papahānaumokuākea Marine National Monument to the Main Hawaiian Islands! Apex Predators 54% Apex Predators 3% Other Secondary Consumers 18% Other Secondary Consumers 42% Herbivores 28% Herbivores 55%

On some islands within the monument, predators account for double the biomass of fish in the other trophic levels! French Frigate Shoals Biomass Data (metric tons per hectare) Apex Predators: 1.7 Other Secondary Consumers: 0.3 Herbivores: 0.6 Apex Predators Other Secondary Consumers Herbivores

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! 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