About This Species
Jellyfish are among the oldest species, and are more closely related to anemones and coral than fish. There are more than 200 species of jellyfish, ranging from tiny innocuous blobs to the box jellyfish—the planet's most venomous species. Found in every ocean in the world, jellyfish come in various colors and sizes. They can have tentacles as long as 200 feet. The largest have been reported to weigh 500 pounds.
Unlike most species, jellyfish are well-suited to climate change. They can live in a range of temperatures. They can thrive in oceans where oxygen levels are depleted, and increases in temperatures can actually boost their ability to reproduce.
Jellyfish blooms come with consequences. As the species proliferate, they can have a negative impact on wild fish populations and on aquaculture facilities, like in Scotland, where in 2014 a jellyfish swarm killed 300,000 salmon at a fish farm.
In recent decades, jellyfish blooms have been on the rise. Though there can be multiple causes of blooms (for instance, overfishing of tuna or other jellyfish predators), climate change is seen as a main driver.
The blooms are happening mainly in mid-latitude waters. As temperatures rise, many other ocean species are heading toward the poles to find suitable habitats. But not jellyfish. The warmer temperatures in mid-latitudes mean longer reproductive periods for them, as well higher ingestion and growth rates.
Another effect of warmer waters: less oxygen. The saturation of dissolved oxygen decreases as water warms, and for many fish and invertebrate species this makes the water inhospitable. While jellyfish are less abundant in waters with less oxygen, they do appear to be more tolerant of it, and can end up increasing predation because their prey can't easily escape.
Jellyfish on the Rise
Reports by citizen scientists of jellyfish sightings around the Italian coastline are on the rise, according to a study recently published a group of Italian scientists.
To get an idea about how jellyfish will fare in the future, scientists look at what's happening now in the Mediterranean Sea. Because it's a "miniaturized" ocean, it responds more quickly to environmental changes. Temperatures have risen drastically in the Mediterranean since the 1980s, causing mass die-offs of species that aren't suited to the new climate. Species that prefer warmer waters are thriving. Enter jellyfish.
Not only are jellyfish on the rise, there are now species of them in the Mediterranean that weren't there a few decades ago. In August 2015, for instance, beach-goers in Israel and elsewhere along the Mediterranean were swarmed by a stinging jellyfish species that is native to the Indian Ocean, thousands of miles away. The arrival of non-native species pose a threat to indigenous species, upending the natural ecosystem.
As climate change progresses, jellyfish blooms and the emergence of tropical species are expected to increase.