Photo: Christopher ChanAround the world, fishermen and swimmers are running into a problem: jellyfish. The slick, stinging blobs are showing up in increasing numbers, earlier in the year, and in more places than ever before. Is there a reason for the jellyfish invasion? Unfortunately, yes—and like most reasons for ocean decline, it relates to how we are changing the environment. Data is lacking, but it’s likely that warmer waters help jellyfish grow faster and reproduce better. Also, overfishing can mean both fewer jellyfish predators and fewer competitors, which means more peace and more food for jellies. As large predatory fish …