Moon jellyfish clog Alabama and Mississippi coastal waters

MOBILE, Alabama
Swarms of moon jellyfish the size of dinner plates ring the barrier islands off Alabama and Mississippi.

Credit:Ben Raines

They are drifting around Fairhope, washing up on Petit Bois Island, and so plentiful in Orange Beach it looks like you could use them as stepping stones to walk from one side of Perdido Pass to the other.

While the moons don’t sting, feeling their heavy, gelatinous bodies brush against arms and legs as you swim through a cloud of them ranks among the least pleasant sensations to be had in the Gulf of Mexico. Ranging from pale pink to white, moons have short tentacles and a distinct, four-leaf clover design in the center of their bell.
August and September are typically the biggest jelly months on the coast, but it looks as if local waters are home to an especially big crop this year.
“We’ve had a lot of trouble. There were a couple of weeks before the storm where we quit shrimping over around Tensaw because we couldn’t even pick up the nets for all the jellies,” said Larry Scott, who shrimps in Mobile Bay to supply his bait shop, Scott’s Landing on the Causeway.
“It reached a point around the Battleship where we couldn’t shrimp at all. It’s not bad now — we’ve got all the freshwater from the storm. It’s pushed them all back down the bay. But for a while there, people couldn’t even fish for speckled trout.”
Scientists said it is too early to say if this was a big year for jellies all over the Gulf, but with thousands of jellies washed up on the beaches along the Mississippi Sound, the verdict for Alabama and Mississippi is in.
The area has a lot of jellies right now due in part to wind, currents and tidal action that brought large numbers of the creatures to shore this summer. While jellyfish can swim a little bit, for the most part they drift at the mercy of ocean currents.
“They tend to accumulate along the edges of the shore. It helps them in terms of reproduction to stay concentrated,” said Monty Graham, head of the marine science department at the University of Southern Mississippi.
He said the large groups seen clumped together on the surface in recent photos taken by the Press-Register are jellies at the end of their life cycle.
“When they get on the surface like that, they’ve spawned out. They are usually close to the end of their lives once they are on the surface,” Graham said. “Nothing good happens to a jelly on the surface.”
Moon Jellyfish populations fluctuate on a 10-year cycle
Graham said that scientists were slowly teasing apart the dynamics that control the Gulf’s population from year to year. A key finding, he said, is that on a grand scale, jelly numbers tend to fluctuate on a 10-year cycle, meaning a decade of high jellyfish numbers, followed by a decade of low numbers.
Right now, we are at the beginning of a decade of high numbers, he said, cautioning that predicting whether next year will be a big year remains tricky.
“The one prediction I’m comfortable with, when we enter into these eight- to 10-year cycles, we’re good at picking that up. The year-to-year numbers, so much depends on water currents,” Graham said. “But, when we enter into these eight- to 10-year phases, it seems to go every other year. Like two years ago, we had a lot, then last year, during the oil spill, we had very few. Now, this year, it looks like a lot again.”
Kelly Robinson, a graduate student studying jellyfish at the Dauphin Island Sea Lab, made a discovery in 2010 that may shed light on why some years have bigger jelly populations than others. Colder-than-average water temperatures in the spring seem to correlate with big jelly years, going back several decades, Robinson found.
Follow-up laboratory experiments suggested that jellyfish reproduce more effectively in colder water.
Robinson said the results of an ongoing federal study “will help us validate the jellyfish-climate relationships we think are happening in the Gulf.”
Robinson corresponded with the Press-Register via email from Madrid, Spain, where she is attending an international jellyfish conference organized in response to a perception “that jellies are on the rise.”
Decrying the lack of hard evidence, she said that the Sea Lab will participate in the JEDI project, an international effort to track global jelly populations more closely.
In some places around the world, close relatives of the moon jellies in Mobile Bay have been blamed for wiping out native fish populations. In July, swarms of moon jellies clogged the water intake pipes at a nuclear power plant in Scotland, forcing the plant to close for a week, according to media reports.