When ecologists describe paradise, they usually refer to a place that is pristine, or unspoiled by the activities of humans. The range of humans is so extensive that, in reality, a truly pristine ecosystem might no longer exist. However, there are places that come close, like Kingman Reef and Papahânaumokuâkea Marine National Monument in the Northwestern Hawaiian Islands.
These ecosystems are important natural laboratories where scientists can see how ecosystems work without the changing effects of people. This is an important step to understanding how we can restore degraded systems. Enric and his team explore coral reefs around islands that range from densely populated to uninhabited. What he has discovered is challenging one of the most basic and accepted concepts in ecology—the pyramid-shaped biomass trophic model.
Ecologists use a pyramid-shaped trophic model to describe the biomass and feeding relationships of organisms found in ecosystems, as you saw in Mission 1. In the pyramid model, the greatest biomass is represented by the producers and is at the bottom of the pyramid. First-level consumers occupy the next layer and above them are the second-level consumers. The top predators in the ecosystem usually occupy the smallest part of the pyramid, the apex. That is why those predators are called apex predators. Enric's data from Kingman Reef in the Line Islands shows the biomass of a pristine coral reef does not fit that model.
The coral reefs that Enric Sala studies are around islands uninhabited by people. Some of these he describes as being in a pristine condition. Here, Enric and other scientists found the biomass of apex predators, such as sharks, to be greater than the biomass of the prey they eat. Even in a near-pristine ecosystem, like that found on the reefs of Papahânaumokuâkea, the biomass of consumers consists mostly of apex predators. The traditional pyramid-shaped trophic model does not describe these locations. Dr. Sala's new model shows a differently shaped model at both Kingman Reef and Papahânaumokuâkea.
In these locations, some members of the reef community are able to add biomass to the ecosystem very quickly by reproducing often and producing hundreds or thousands of offspring each time they reproduce. It would be as if you had a "magic lunchbox." No matter how fast you eat or how much you eat, the box always remains full. Kingman Reef is like the "magic lunchbox." This ecosystem can support immense numbers and a high biomass of sharks because the organisms in the trophic levels below them replace their populations at such a high rate.
When scientists compared data from the remote Northwestern Hawaiian Islands with other more populated Hawaiian Islands, they saw a great contrast. In the populated islands, apex predators make up a small portion of the biomass. Why the big difference? The
over-exploitation of resources by humans has influenced the ecology of the coral reefs. People have overfished both the apex predators and their prey, causing a significant decrease in biomass at all consumer levels. In some cases, fish habitats like reefs, sea grass beds, and wetlands were destroyed. Coral reef ecosystems around the main Hawaiian Islands look more like those typical of other human-influenced areas.
Enric Sala's discovery in the Line Islands, as well as other studies, have alerted people to the sensitive ecological balance of rare pristine ecosystems. Fortunately, the United States took action in 2006, when Congress created Papahânaumokuâkea Marine National Monument—the country's largest protected area.