Why do jelly blooms happen? Are there actually more blooms now than there used to be—or are people just more aware of blooms because they can impact tourism, fishing and other coastal industries?
It’s an exciting time to be a sea jelly scientist: There’s a lot still to be learned about these beautiful animals. Researchers are working to solve the mysteries of jelly blooms and to understand how environmental issues such as climate change might affect jellies. The answers that they uncover will help to develop fisheries, tourism and marine resource management programs that reflect the most current information we have about our changing oceans.
In order to piece together the puzzle, researchers are combing through historic records, centuries-old ship logs, journals, newspapers and even fossil records to build the “historical footprint” of jelly blooms and make projections for the future.
A handful of likely suspects might play a role in jelly blooms:
As Earth’s atmosphere warms, the oceans absorb more of that heat. Over the last 50 years, surface waters have been heating up, which could help warm-water jelly species live in places they’ve never been before.
Some fishes eat jellies. Others compete with them for food. In overfished areas, jellies experience less pressure and can devour fish eggs and small fishes, which might make it hard for scarce species to recover.
Cargo ships have huge ballast tanks filled with water that help them stay stable on the ocean. At new ports, crews empty the ballasts along with any tiny aquatic animals inside, including jellies. Once they arrive, non-native jellies can thrive in the absence of natural predators, as they did in the Black Sea.
Most animals avoid the low-oxygen waters known as “dead zones,” which are heavily polluted by runoff from farms and cities. While their predators and competitors flee, jellies are adaptable enough to survive.
After drifting along marine currents, young larval jellies settle onto solid surfaces where they attach and develop into the next life stage (called polyp). Docks, oil rigs and other aquatic structures create new surfaces for polyps, which can clone themselves by the hundreds, and even thousands. Such polyp colonies can lead to a huge bloom of adult jellies that then can consume massive quantities of zooplankton, wiping out larval fish populations and outcompeting other marine wildlife for planktonic food.