This story would be hilarious if it wasn't so tragic.
Humans suck at managing food webs and ecologies. We screw them up by introducing invasive species, then we make it worse by introducing other invasive species to take out those invasive species. When that goes bad, and it nearly always does, we try another tack and just as nearly make the bad situation even worse.
Such is the case on Macquarie Island, which sits between Australia and Antarctica. Cats were introduced at the end of the 19th century. The cats turned feral (who could have guessed that that would have happened). Not long after, rabbits were brought to the island by seal hunters. Again, the rabbits went wild, and as they are wont to do, mated wildly. By the 60's the rabbit population was so large that Australian authorities introduced a virus that wiped out most of the rabbits.
Unfortunately, without all the rabbits to eat, the feral cat population turned to the native birds and animals for dinner and lunch.
So they killed all the cats.
But, oops, that allowed the small rabbit population that had survived the great sickness to again grow to large enough numbers to denude large swaths of land in a frenzy of eating.
Killer bees were created by a guy mating aggressive African bees with various docile European stock to create a strain that'd make more honey in a tropical environment. Good intentions, really bad results.
Cane toads were introduced to Australia to control pests. It ate the pests, and didn't stop. It ate everything in its path on the way to becoming a national scourge. They are poisonous, wipe out native species, and a prolific breeder.
We suck at 1) preventing the spread of non-native species, 2) managing the fallout from the introduction of non-native species, 3) managing the fallout from the fallout from the introduction of non-native species, and 4) well, you get my drift.
I would put forth that our incompetence at species management extends to things like the could-be-disastrous dumping of iron in the ocean to boost the population of plankton, in the theoretical hopes that their bodies will carry sequestered CO2 to the bottom of the ocean floor.
There's nothing that could possibly go wrong with that.