Reversed trophic pyramid

In lecture, the concept of a trophic pyramid was introduced. The trophic pyramid is a diagram that quantitatively represents the number of organisms and the biomass of an ecosystem. Numbers are typically high for the lowest trophic levels (plants) and low for the highest trophic level (carnivores).

Enric Sala, a National Geographic fellow, has observed a pristine coral reef where the traditional biomass pyramid is reversed. Kingman reef, part of the Line Islands in the North Pacific Ocean, is the most undisturbed coral reef in the US. Approximately 85% of the fish biomass at Kingman is made up of reef sharks and red snappers. Kingman’s proportion of these top predators (the top tier of the traditional biomass pyramid) is greater than has been found in any other coral reef ecosystem. The only way an inverted pyramid like this can function is if there is a rapid turnover of biomass at the lower levels. In other words, the prey grows quickly and replenishes quickly (many prey species will spawn several times a year).

If the top tier of the biomass in a coral reef is overfished, there will be an increase in the population of smaller fish. The elimination of top predators also speeds the turnover rate of the reef community. Researchers aren’t sure why, but this increase in turnover rate also causes an increase in microbes, which may cause coral death.

For more information see: http://ocean.ceq.gov/pacific_assessment/pdfs/palmyrakingman_fs100808.pdf and
http://ngm.nationalgeographic.com/2008/07/kingman-reef/warne-text.

Kingman Reef is also discussed in The World Without Us by Alan Weisman.

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