For generations, residents lucky visitors in the right place at the right time along Alabama's Eastern Shore have rushed to the shoreline when word spreads that a jubilee has arrived.

The rare phenomenon, which brings shrimp, crabs, fish and other marine life into shallow water, has become one of South Alabama's most celebrated traditions.

According to NOAA’s National Estuarine Research Reserve System, jubilees are known to occur regularly only in two places on Earth — Mobile Bay and Tokyo Bay in Japan — and while similar events may happen elsewhere, Mobile Bay is believed to be the only body of water where they occur somewhat predictably each summer.

But behind the excitement lies an ongoing debate. While many see jubilees as evidence of the abundance produced by Mobile Bay's estuary, others point to the low-oxygen conditions that trigger them and wonder whether they signal environmental stress.

"They are essentially low dissolved oxygen events with distinct meteorological events happening in tandem," said Greg Graeber, a marine educator with the Dauphin Island Sea Lab.

Several days of hot, calm weather limit the mixing that normally replenishes oxygen in the water. During the late-night and early-morning hours, a slight east-to-west breeze can push oxygen-rich surface water away from shore, allowing oxygen-poor bottom water to move in.

"This bottom water is generally depleted of oxygen due to the bacteria working on and breaking down the bottom organic material and uptaking any available oxygen," Graeber said. "The critters — shrimp, crab, flounder, rays, etc. — go to where the only oxygen is, and that's the shore."

Those conditions create the spectacle that has made jubilees famous, but they also raise questions about what low oxygen means for the bay.

Asked whether jubilees should be viewed as a natural occurrence or an environmental warning sign, Graeber said they can be interpreted as both, though he sees them mainly as a natural phenomenon.

"Low DO drives these events," Graeber said, referring to dissolved oxygen.

While some critics point to hypoxia, or low oxygen, and anoxia, where oxygen is completely absent in parts of Mobile Bay, Graeber said those conditions fluctuate and a healthy estuary can still experience jubilees.

“We wouldn't have the biodiversity that we have in our estuary if it wasn't healthy," he said. "Do we get sewage overflows and other pollutants? Sure, but brown water means nutrients to support life. The emerald-colored water to the east, though pretty, does not support or grow nearly the biomass the northern central Gulf does."

Though he has spent nearly three decades living on Mobile Bay's western shore and has never personally witnessed a jubilee, Graeber said the events have become part of the region's culture because they bring communities together.

"My non-scientist answer is a free cooler of seafood for a while," he said. "It historically is a community thing between neighbors helping neighbors. It's got to be fun."

Graeber said he believes residents can celebrate that tradition while still recognizing the science behind it.

"Low oxygen events happen whether or not a jubilee occurs, and so for the community and neighborly event that they are, they're great."

Whether viewed as a treasured tradition, evidence of the bay's productivity or a reminder of the delicate balance within coastal ecosystems, jubilees remain one of South Alabama's most distinctive natural events.

Residents hoping to take advantage of a jubilee are still required to follow Alabama's seafood regulations. State rules limit recreational harvesters to one 5-gallon container of blue crabs per person and no more than 10 gallons per boat. Recreational shrimpers are allowed up to 5 gallons of shrimp per person, with a maximum of 10 gallons per vessel. Anyone collecting seafood during a jubilee must also observe size requirements and protected-species regulations established by the Alabama Department of Conservation and Natural Resources.

Gabriella Chavez is a Report for America corps member who writes about growth and development in Baldwin County and our natural spaces for Gulf Coast Media. Your donation to match our RFA grant helps keep her writing stories like this one; please consider making a tax-deductible gift of any amount today by visiting https://tinyurl.com/yaf8yf5n.