While not nearly as serious and alarming as the proposed iron fertilization experiment, human meddling with the ecosystem on Macquarie Island in the Southern Ocean has caused some problems that are proving difficult to fix. First rabbits were brought to the island to serve as a food source for sealers. Then cats were brought to the island to control the rabbits. Next, humans introduced a virus to kill off the remaining rabbits. Finally, humans got rid of the cats, who had started eating seabirds when the rabbit numbers declined. Without the cats, rabbit populations rebounded and destroyed seabird habitat. Sound like a mess? It is, and an expensive one that will cost the Australian government $16 million dollars to fix.
Mostly, though, it demonstrates the need for comprehensive evaluation of any human attempts to reshape the environment or ecosystems to fix environmental problems or suit our needs better. We know more now about ecosystems than we did when rabbits were introduced on Macquarie in the 19th century, and can recognize that cats and rabbits should have been eradicated simultaneously, but our knowledge is far from complete. We're far better at analyzing why these projects went wrong than figuring out how to carry them out successfully. When it comes to altering the environment to accomplish a particular goal, extreme caution should always be the rule. Finding less intrusive ways to accomplish the same results (i.e., stopping pollution into bodies of water instead of introducing filter feeders to clean up runoff) should be standard operating procedure.