GAINESVILLE, Florida – The US Fish and Wildlife Service has designated 190 miles of streams and rivers in Florida and Georgia as critical habitat for a rare species of freshwater mussel thought to be extinct. The new decision, which entered into force on August 2, describes the protective measures for the Suwannee moccasin, Medionidus walkeri, the number of which has been steadily decreasing in recent decades.
To determine the magnitude of this decline, biologists from the Florida Museum of Natural History, The Florida Fish and Wildlife Conservation Commission, the Georgia Department of Natural Resources, and the US Geological Survey looked at data from museum specimens to establish just how widespread the species was once.
“Museum data is essential in providing historical context for the location of these things and their abundance. Otherwise, we would have no idea what exists, ”said Jim Williams, associate researcher at the Florida Museum who participated in the study.
The critical habitat designation means that any federal agency – or state agency using federal funds – must adhere to a set of standards when working in and around mussel environments.
Many “kidneys of the river” are in danger
Freshwater mussels play an indispensable role as water purifiers in streams and rivers, filtering out organic debris and excess nutrients and providing a food source for fish, turtles and a variety of mammals. .
Although mussels can be found all over the world, North America has the greatest diversity of freshwater mussels on Earth, with over 300 species that are mostly concentrated in the Southeastern United States.
Yet their diversity belies an extinction crisis that has been building silently over the past century. Freshwater mussels are considered among the most endangered animals in the United States, with 70% of the species threatened with extinction due to the long-term effects of pollution and development.
The Suwannee Moccasin is listed as Threatened Federally under the Endangered Species Act and considered Endangered in Georgia. Based on the reconstruction of its former range from museum collections and sightings, the species was once common throughout the Suwannee River Basin, a large watershed with several rivers and tributaries that straddles the border between Florida and Georgia. But like many freshwater mussels in the region, their numbers declined for much of the 20th century.
Biologists were unable to locate even a single individual between 1994 and 2008, despite countless hours spent searching for stream beds and river channels, raising fears that the moccasin Suwannee did not pass away.
“They’re not very easy to find, and if you see more than three people per site, you’re really excited,” Williams said.
Searching for mussels in the Suwannee can be a particularly time-consuming task as many of them burrow into the sandy bottom of the river. To find them, biologists must slowly sift through the sediment by hand.
“We call it grubbing,” said Sandy Pursifull, an environmentalist with the US Fish and Wildlife Service who conducted the investigation into the status of the Suwannee moccasins. “You walk along the bottom of the stream and try to descend a few inches. Fortunately, the Suwannee River is mostly sand substrate, so you can really feel when you get the mussel. Suwannee moccasins may not look like much to a casual observer, but for mussel lovers, there are several features that set them apart. Their dark ocher oval shell gives them a fleeting resemblance to a moccasin, and a set of deeply furrowed grooves along one end make them particularly easy to distinguish. “Once you’re good at it, you can identify them just by touch,” Pursifull said.
Pursifull and biologists from the Florida Museum, the Florida Fish and Wildlife Conservation Commission, and the Georgia Department of Natural Resources conducted aquatic surveys in 2014 and 2015. They took an in-depth look at places where museum specimens had previously been collected. and the habitats where the species might be found.
After searching over 140 sites, they arrived almost empty-handed.
In Florida, researchers could not find Suwannee moccasins in many areas where they were previously found, including the lower Suwannee River and the upper Santa Fe. They were also absent from the Withlacoochee River, this which means that they may have disappeared entirely from Georgia, marking a total decline of 67% of their former range.
They are now mostly confined to a small stretch of the Suwannee River, where a network of springs helps regulate water temperature and dilute pollutants. Yet even here, state and federal biologists were only able to dredge 73 individuals scattered across 75 miles of stream bed.
Threatened by pollution, environmental changes
The decline of freshwater mussels is due to several interconnected causes. Their role as a water purifier makes them extremely sensitive to pollution. Spills of sewage from sewage treatment plants are common in the lower part of Withlacoochee, for example, where there are hardly any moccasins left. Spills can release millions of gallons of raw waste, which has a cascade of negative effects on the environment. The ammonia in human waste is particularly toxic to aquatic fish, mussels and other invertebrates, Williams said.
Excess nutrients from nearby farm fields can also trigger algal blooms that can suffocate and suffocate mussels. Even if a field is not directly adjacent to a river, over-fertilization can lead to leaching of nutrients into the water table and ultimately their path to freshwater sources.
“The Suwannee Basin has a problem with the fertilizers coming in, probably more from the springs than anything else, because the geology of this area is like Swiss cheese,” Pursifull said.
These dangers are compounded by the complex life cycle of freshwater mussels. Adult mussels are sedentary, meaning they get stuck in one place without the benefit of being able to pick them up and move around if their habitat is disturbed or polluted. The only time mussels move up or down is during their larval stage, when they depend on fish for transportation.
When a pregnant female is ready to release her larvae, she waves to nearby unsuspecting fish with an intricate lure disguised as food.
“There’s all kinds of mimicry,” Williams said. “Some of them mimic fish, and other invertebrates like snails or crayfish.” Any fish that travel to investigate, hoping to find their next meal, are instead covered in larvae that cling to their gills and travel to a new location.
While some mussels are apparently able to hide on just about any fish that comes along, others are limited to one or two species. The Suwannee Moccasin relies primarily on brown, black-banded darts for movement, fish that typically don’t travel far. This likely inhibits the ability of these mussels to easily recover from rapid environmental degradation, Williams said.
The increased runoff due to urbanization also reduces visibility in streams and rivers by adding suspended soil and lifting up sediment, making it harder for fish to find mussel lures. “If you have sediment in the water and the water is cloudy, that means all of the visual cues are gone,” Williams said.
Despite the odds, biologists hope that the protections conferred by the critical habitat designation may act as a catalyst to spur the conservation and population growth of the Suwannee Moccasin.
“Agencies will now be required to consult with us to ensure their project does not alter or destroy critical habitat,” said Pursifull.
Any project that receives federal funding or permits is subject to the rule. In and around rivers, these most often include the construction of new bridges and landscape renovations carried out by state transportation departments and dredging and backfilling permits issued by the US Army Corps of Engineers. .