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Located in the heart of Philadelphia, Pennsylvania, Drexel University’s Academy of Natural Sciences exudes the aura of a sprawling cabinet of curiosities. Its neoclassical facade is covered in natural motifs: doors flanked by ammonites, banisters that curl into ferns, bronze doorknobs in the shape of ibis skulls. As the oldest natural science institution in the Western Hemisphere, the academy has amassed a wealth of notable specimens. Among the 19 million specimens housed here are plants acquired on the Lewis and Clark expedition, the blue marlin reeled in by Ernest Hemingway and America’s first mounted dinosaur skeleton.
Many of the academy’s more modest but impressive treasures are filed away on the second floor, in an office space filled with cabinets and enormous microscopes. Next to one of these microscopes, curator Marina Potapova opens a notebook-sized plastic container filled with glass slides. To the untrained eye, these unremarkable slides look dirty: each one appears to have been smudged by dirty fingers.
But as soon as Potapova puts one under a microscope lens, the contents of the slide dazzle. Dozens of diatoms (microscopic, single-celled algae encased in tough silica walls and found wherever there is water) are attached to the slides in a myriad of shapes.
With more than four million specimens, the diatom collection at the Academy of Natural Sciences at Drexel University in Philadelphia, Pennsylvania, is the second largest in the world. Photo by Jack Tamisiea
Some are elongated like baguettes or flattened into plates, while others stick together to resemble translucent centipedes. Others have spikes like harpoons or are shaped like plump starfish. Some even resemble ornate stained glass windows. Under a microscope, a few drops of murky pond water become a kaleidoscope of diatom diversity.
The beauty of diatoms is breathtaking. But its ecological importance is surprising. Diatoms anchor marine food webs, feeding everything from tiny zooplankton to mammoth filter feeders. (Case in point: Scientists have deduced that the increase in whales about 30 million years ago reflects an increase in diatom diversity.) Diatoms also have an outsized atmospheric impact. As one of the most prolific organisms on the planet, diatoms expel harmful gases like carbon dioxide from the air and produce massive stores of oxygen as they photosynthesize. It is estimated that about a quarter of the air we breathe is created by diatoms.
More than four million specimens of these essential algae are plastered on hundreds of thousands of slides and housed in the academy’s diatom herbarium. Only the Natural History Museum in London stores more diatom slides.
Although the academy’s diatoms no longer feed the planktonic masses or pump oxygen into the atmosphere, they do hold clues to how the aquatic world is changing. As their hard shells sink to the bottom of a body of water, they are stored in the sediment for millennia. When researchers use a sediment corer to drill through the muddy bottom of an estuary, they are collecting diatoms deposited over eons.
In addition to being abundant and hardy, diatoms are also a crucial barometer for a variety of environmental conditions. The existence of certain species of diatoms can help scientists identify everything from industrial pollution to oxygen depletion. Potapova and her colleagues recently used these time capsules of water conditions to measure how accelerating sea-level rise is endangering New Jersey’s coastal wetlands.
Diatoms, a type of phytoplankton made of silica and coming in countless shapes and forms, support marine food webs and have an outsized impact on the health of Earth’s atmosphere. Photo by Scenics & Science/Alamy Stock Photo
Thanks to a relative dearth of environmental monitoring, the historical decline of these crucial wetlands, which store carbon, provide nursery areas for fish and protect the coast from storms, has been largely obscured, making efforts by restoration are little more than conjecture.
However, the millions of diatoms stored at the academy help researchers track the decline of coastal wetlands as the ocean rises, which can help predict the coast’s future. “Diatoms are absolutely invaluable environmental archives,” says Potapova. “You can infer the future from what you are told about the past.”
Given the academy’s history, it’s no wonder the historic institution has become a hub for diatoms. With the advent of accessible microscopy in the 1850s, many of Philadelphia’s gentleman naturalists were captivated by the kingdom of tiny microbes, eventually establishing the Microscopical Society of Philadelphia in academia.
Because of their amazing beauty, diatoms took microscopic society by storm. To satiate their interest, many of these diatomists headed east to the New Jersey shore to collect samples, which they mounted on glass slides with a steady hand and a brush full of pig’s eyelashes. Fans flocked to the academy to show off their slides over gourmet lunches.
Early members of the academy were clearly enthusiastic about diatoms, but most were hobbyists and published little research on the myriad specimens they collected. Organizing the mountains of slides compiled by each collector into a cohesive collection proved quite a task for Ruth Patrick when she arrived at the academy in 1933. The daughter of an amateur diatomist who received her first microscope at age seven, Patrick gravitated. towards diatoms in his early childhood and eventually completed his PhD studying the microscopic organisms. Despite her scientific credentials, she was relegated to assembling microscopes and slides for untrained hobbyists. It took her years to even achieve membership in the male-dominated academy. But her persistence paid off and in 1937 she became curator of the nascent herbarium of diatoms.
Patrick’s first goal was to organize the merging of different collections into a unified and comprehensive source for taxonomic research. When he wasn’t setting up and organizing slides, he waded into nearby ponds and streams to collect new specimens in the field, where he gradually learned to appreciate the ecological importance of diatoms.
Ruth Patrick, the academy’s first curator of diatoms, works on the collection in the 1940s. Photo courtesy of the Archives of the Academy of Natural Sciences coll. 457
This crystallized during a 1948 expedition to Pennsylvania’s Conestoga River, a body of water heavily polluted by sewage and industrial runoff. As his team collected samples from throughout the stream, they recognized patterns in the composition of diatoms. The densities of some species exploded in areas polluted with sewage, while others thrived in places contaminated with chemicals. Patrick soon became able to use the existence of certain diatoms as a key to diagnosing pollution in lakes and rivers. This supported the idea that greater diatom diversity correlated with healthier freshwater ecosystems, a view ecologists coined Patrick’s Principle.
Patrick revolutionized the use of diatoms to control freshwater systems, but their use in coastal wetlands lagged behind. The brackish melding of freshwater and saltwater in coastal areas such as estuaries creates dynamic and complex habitats with a mix of inland and oceanic diatoms, according to Mihaela Enache, a research scientist at the New Jersey Department of Environmental Protection (NJDEP).
However, in recent decades, the sea has dominated the once dynamic coastal margin, pushing further inland as sea level rises. Over the past century, sea levels along New Jersey have risen 0.45 meters, more than double the global average of 0.18 meters. By the year 2100, the sea could rise more than a meter.
This dramatic rise in sea level has proven disastrous for the patchwork of marshes along the New Jersey coast, many of which have already succumbed to the sea. However, the full extent of the loss of these wetlands is difficult to analyze because environmental monitoring only goes back a few decades.
Without an idea of the natural conditions of a wetland, ecological restoration is daunting. Having this information is crucial, says Enache. “Without [it]you’re in the dark.” Fortunately, some of this missing data is recorded in the academy’s diatom cache.
Like most coastlines, New Jersey is familiar with sea level rise. During the Pleistocene, when New Jersey was covered in ice and home to the mastodons, sea ice absorbed the seawater reserves. About 18,000 years ago, sea levels sank more than 130 meters below their current levels, extending the New Jersey coast another 110 kilometers into the Atlantic Ocean.
The end of the last ice age led to a steady rise in sea levels. The retreat of the ice sheets caused parts of New Jersey to sink. That subsidence, combined with glacial melting, proved a powerful combination for rapid sea-level rise, according to Jennifer Walker, a sea-level researcher at Rutgers University.
In a study published last year, Walker turned to the past to put New Jersey’s current sea level rise into context. “If we can understand how temperatures, atmosphere and sea level changes are interconnected in the past, that’s what we can use to project changes in the future.”
To measure sea level fluctuation over the past 2,000 years, his team examined the shells of single-celled protists called foraminifera that are finely calibrated to specific environmental conditions. This makes them a valuable indicator for reconstructing changes in sea level. By identifying the presence of certain species of foraminifera in sediment cores collected from different points along the Jersey Shore, his team concluded that the New Jersey coast is experiencing the fastest sea level rise in 2,000 years .
The NJDEP hoped that the diatoms could…