Nestled in the heart of Philadelphia, Pennsylvania, Drexel University’s Academy of Natural Sciences exudes the aura of a giant cabinet of curiosities. Its neoclassical facade is covered in natural motifs – doors framed by ammonites, railings wrapped in ferns, bronze doorknobs in the shape of ibidus skulls. As the oldest natural science institution in the Western Hemisphere, the academy has amassed a treasure trove of remarkable specimens. Among the 19 million or so specimens housed here are plants procured on the Lewis and Clark expedition, blue marlin reeled in by Ernest Hemingway and America’s first dinosaur skeleton. Many of the academy’s more unassuming but impressive treasures can be found on its second floor, in an office space filled with large cabinets and 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 unexpected slides look dirty—each one looks like it’s been smudged by dirty fingers. But once Potapova slides under the microscope lens, the contents of the slide blur. Dozens of diatoms—tiny, single-celled algae encased in sturdy walls of silica and found wherever there is water—are affixed to the slides in a myriad of shapes. With more than four million specimens, the diatom collection of 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 saucers, while others are hooked together to resemble a translucent centipede. Others are barbed like harpoons or shaped like starfish. Some even look like elaborate stained glass windows. Under a microscope, a few drops of cloudy lake water become a kaleidoscope of diatom diversity. The beauty of diatoms is impressive. But their ecological importance is staggering. Diatoms anchor marine food webs feeding on everything from tiny zooplankton to mammoth filter feeders. (Example: scientists have concluded that the rise of whales about 30 million years ago reflects a spike in diatom diversity.) Diatoms also have an outsized atmospheric effect. As one of the most productive organisms on the planet, diatoms siphon harmful gases like carbon dioxide from the air and produce vast 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 plated 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 planktonic masses or pump oxygen into the atmosphere, they 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 into the muddy bottom of an estuary, they collect diatoms deposited over centuries. In addition to being abundant and hardy, diatoms are also a critical barometer of a variety of environmental conditions. The existence of certain species of diatoms can help scientists detect everything from industrial pollution to oxygen depletion. Potapova and her colleagues recently used these water state time capsules to measure how accelerating sea-level rise is endangering New Jersey’s coastal wetlands. Diatoms, a type of phytoplankton made of silicon and of myriad shapes and forms, support marine food webs and have a major impact on the health of Earth’s atmosphere. Photo by Scenics & Science/Alamy Stock Photo Thanks to a relative lack of environmental monitoring, the historical decline of these critical marshes—which store carbon, provide fish nurseries, and protect the coast from storms—has been largely obscured, making restoration efforts little more than guesswork. 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 records,” says Potapova. “You can infer the future from what you are told about the past.” Considering the academy’s history, it’s no wonder the storied institution has become a diatom hub. With the advent of accessible microscopy in the 1850s, many of Philadelphia’s leading naturalists were captivated by the microbial kingdom, eventually founding the Microscopical Society of Philadelphia in the academy. Because of their striking beauty, diatoms overwhelmed microscopic society. To satisfy their curiosity, many of these diatoms headed east to the New Jersey shoreline to collect specimens, which they mounted on glass slides using a steady hand and a brush full of hog eyelashes. Hobbyists then gathered at the academy to show their slides over gourmet meals. The early members of the academy were clearly enthusiastic about diatoms, but most were amateurs and published little research on the myriad specimens they collected. Organizing the mountains of slides gathered by each collector into a cohesive collection proved to be too much work for Ruth Patrick when she arrived at the academy in 1933. The daughter of a diatomist who received her first microscope at age seven, Patrick to diatoms early in her childhood and eventually completed her PhD studying the microscopic organisms. Despite her scientific credentials, she was relegated to setting up microscopes and slides for untrained hobbyists. It took her years to even gain membership in the male-dominated academy. But her persistence paid off, and in 1937 she became curator of the fledgling diatom herbarium. Patrick’s first goal was to organize the merging of disparate collections into a unified and comprehensive source of taxonomic research. When he wasn’t setting up and organizing slides, he was wading into nearby lakes and streams to collect new specimens in the field, where he gradually gained an appreciation for the ecological importance of diatoms. Ruth Patrick, the academy’s first curator of diatoms, works on the collection in the 1940s. Photo courtesy of Archives of the Academy of Natural Sciences col. 457 This crystallized during a 1948 expedition to Pennsylvania’s Conestoga River—a body of water heavily polluted by sewage and industrial runoff. As her team collected samples from across the creek, she recognized patterns in diatom composition. Densities of some species exploded in sewage-contaminated areas, while others thrived in chemically contaminated spots. Patrick soon became adept at using the presence of certain diatoms as a key to diagnosing pollution in lakes and rivers. This supported the idea that greater diatom diversity was associated with healthier freshwater ecosystems—an idea ecologists coined Patrick’s Principle. Patrick revolutionized the use of diatoms to monitor freshwater systems, but their use in coastal wetlands lagged behind. The brackish fusion of freshwater and saltwater in coastal zones such as estuaries creates habitats that are dynamic and complex with a mix of inland and oceanic diatoms, according to Mihaela Enache, a researcher at the New Jersey Department of Environmental Protection (NJDEP). . However, in recent decades, the sea has dominated the once dynamic coastal margin, moving further inland as sea levels rise. In the last century, sea levels along New Jersey have risen 0.45 meters, more than double the global average of 0.18 meters. By 2100, the sea could rise more than a meter. This dramatic rise in sea level has proven devastating to the patchwork of marshes along the New Jersey coastline, several 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 dates back only a few decades. Without a sense of the natural conditions of a wetland, ecological restoration is daunting. Having this information is crucial, says Enache. “Without [it], you are in the dark.” Fortunately, some of this missing data is recorded in the academy’s diatom cache. Like most coastal fringes, New Jersey is familiar with sea level rise. During the Pleistocene, when New Jersey was covered in ice and harbored mastodons, the sea ice collected reservoirs of seawater. About 18,000 years ago, sea levels sank more than 130 meters below their current levels – extending the New Jersey coastline 110 kilometers further into the Atlantic Ocean. The end of the last ice age triggered a steady rise in sea levels. Retreating ice sheets caused parts of New Jersey to sink. That subsidence, combined with melting glaciers, proved to be a potent mix for rapid sea-level rise, according to Jennifer Walker, a sea-level researcher at Rutgers University. In a study published last year, Walker looked to the past to put New Jersey’s current season of sea level rise into context. “If we can understand how temperatures, the atmosphere and sea level changes are linked together in the past, that’s what we can use to project changes in the future.” To measure sea-level fluctuations over the past 2,000 years, her team examined the shells of single-celled protists called foraminifera, which are well calibrated to specific environmental conditions. This makes them a valuable proxy for reconstructing changes in sea levels. By detecting the presence of certain species of foraminifera in sediment cores collected from different locations along the Jersey shore, her team concluded that the New Jersey coast is experiencing the fastest sea level rise in the last 2,000 years. NJDEP hoped that diatoms could serve as similar…
