(Note: This meeting and presentation took place online, via Zoom platform technology, due to social-distancing protocols prompted by the ongoing COVID-19 pandemic.)
At 7:00 pm, President Rochelle Thomas called the meeting of the Society to order. After introducing herself, she thanked the attendees for joining, noting that this was the last meeting of the season. Rochelle hopes to have more information about resuming in-person meetings at the American Museum of Natural History at our September meeting.
President Thomas announced the results of a new-member vote, which passed with 127 votes of approval and 0 of disapproval. She welcomed the following ten new members:
- Aaron Stern, sponsored by Mindy Kaufman
- Frederica Miller, sponsored by Ken Chaya
- Leila Javitch, sponsored by Maggie Bradley
- Christina Tsakos, sponsored by Maggie Bradley
- Andy Shawhan, sponsored by Miriam Rakowski
- Carmen M. Ramis, sponsored by Maggie Bradley
- Jared Meek, Associate, Rochelle Thomas
- Ashley Toth, sponsored by Rochelle Thomas
- Jim Toth, sponsored by Rochelle Thomas
- Yao Tseng Chen, sponsored by Will Papp
President Thomas then announced the result of the online vote to approve the minutes of the March 2022 members’ meeting. The vote passed with 126 votes of approval and 1 of disapproval.
Over the summer, members will receive a renewal package in the mail. The package is scaled back to reduce paper waste, and members are encouraged to use the website for in-depth information about the field trips. The Linnaean Society’s annual Homecoming Picnic will resume this year after a hiatus due to COVID19 restrictions. Additionally, the Society will have hats available for purchase in the fall.
At 7:10 pm, President Thomas introduced the evening’s speaker, Dr. Melanie Stiassny.
Dr. Stiassny is the Axelrod Research Curator in the Department of Ichthyology at the American Museum of Natural History and an adjunct professor at Columbia University, where she teaches both graduate and undergraduate courses. Before coming to New York, Dr. Stiassny was an assistant professor of biology at Harvard University, where she taught for five years. After earning her Ph.D. at the University of London, she spent three years of postdoctoral research in the Netherlands before joining the faculty at Harvard University. She has conducted extensive research throughout the world’s tropical waters, studying fishes’ evolution, behavior, and conservation.
Based on her many years of collecting, documenting, and studying the fish in the lower Congo River, Dr. Stiassny explained the river’s unique hydrological and geographical characteristics and their role in driving the evolution and diversification of its exceptional fish fauna.
The Congo River is the freshwater heart of central Africa, with its basin covering 3.7 million square acres and running for 2,500 miles. It is the deepest major river in the world, both at the lowest point and on average, sometimes exceeding 220 meters (720 feet) in depth. The river has always played an essential role in structuring biodiversity on the African continent. Notably, our two closest living relatives live on opposite sides of the river: the chimpanzee in the area north of the river and the bonobo to the south.
The lower Congo, near the twin Congolese capitals of Kinshasa and Brazzaville, was established between 2-5 million years ago, making the region relatively young. The region is a hotspot of biological diversity for several reasons. Although it constitutes less than two percent of the entire Congo river, some of the most spectacular cataracts, falls, and gorges on Earth are located in this area. The annual water discharge is over 46 thousand cubic meters a second, three times that of the Mississippi River. The water flows down a very narrow bedrock-constrained gorge and drops over 280 meters on its way to the Atlantic Ocean, resulting in a series of high-power rapids. In some areas, the water is deep and calm; in others, there are white water rapids. The bank habitats are unique and varied, even from one side of the river to the other. Dr. Stiassny believes this region to be the most unique place on the planet.
The river is exceptional not only because of its geographical uniqueness but because of the incredible assortment of fishes it harbors. This stretch of the river is home to over 300 species of fish, many with unique adaptations—including bizarre morphologies—that enable them to survive in an environment with intense rapids. There are at least 90 endemic species.
Dr. Stiassny leads The Congo Project, a partnership between the University of Marien Ngouabi in the Republic of Congo, the University of Kinshasa in the D.R.C., and the A.M.N.H. that studies the unique fish and geography of the lower river. She and her team work closely with local scientists, fishermen, and volunteers to ensure local knowledge is incorporated into the project and that new scientific findings are shared with the community and government, which is crucial to advocating for environmental protection for the river.
Initially, the project’s focus was to identify and assess barriers along the river, assuming they would be the changing points–the promoters of species diversification–both in the past and ongoing today. However, the team discovered something extraordinary. Substantial divergence existed even in areas with no rapids, and fish geographically next to each other were not interbreeding. Over time, this situation results in a lot of speciation and presents a major problem to researchers, because the fishes are so different from each other that it’s like comparing a kiwi to a parrot.
Dr. Stiassny noted that it is easier to get to the bottom of the Marianna Trench than to the bottom of the Congo River because of the extremely fast-moving jets of water. The research team partnered with the National Geographic Society and the U.S. Geological Survey to map the bottom of the river and the water flow. Using kayaks equipped with echo-sounders and depth measurement equipment, they found that the river was close to 800 feet deep in some pockets, making it the deepest river ever recorded. Other areas have flow separation, essentially rivers within rivers. The complexity and power of the currents are the keys to the evolutionary richness of the lower Congo. In some places, the banks are only half a kilometer apart, but the fish from one side could never swim across to the other bank and live. The hostile environment forces the separation of populations of breeding fish, resulting in the evolution of new species.
Because of the water’s depth, many fish are blind and de-pigmented. They have very different shapes and sizes, but a similar phenotype (body type) is shared across many distantly related fish families, all found within a single area. Because of its geology, this is a challenging place to gather species. Often after a new species is found once, it can’t be re-found again. Therefore, the team must be very resourceful in determining how to conduct their research.
One key species the team studied is the Blind Cichlid. Curiously, this fish is only found dead or dying at the surface in one small region of the lower Congo. The team determined that these fish were suffering from something akin to the bends. The hypothesis is that some fish get caught in the fast water jets and are thrust to the surface, causing catastrophic decompression and death.
These fish have no pigmentation and have lost many of the genes that typically serve to repair UV damage because they are never exposed to ultraviolet light. Their eyes are recessed, and they can distinguish between light and dark but can’t form actual images. They also have some physical abnormalities that improve their maneuverability in the water.
The extreme hydrology of the river provides this treasure trove of diversification and adaptation, which has only begun to be studied and understood. Unfortunately, the region is under dire threat because the government is keen to harness the river’s power for financial gain. There are plans to develop a dam that would generate 40 gigawatts of energy, twice the output of the Three Gorges Dam, currently the largest dam on the planet. If this dam were put in place, it would devastate the lower Congo system, cutting off the sediment load into the ocean, extending the river’s waters over three thousand square kilometers of land, destroying the lives of the people in the area, and killing the barely explored wildlife in this unique ecosystem. Dr. Stiassny, her team, and many others are working to urge the president of Congo to understand these issues.
The evening ended with Dr. Stiassny answering several questions from members and receiving a huge thanks from the Linnaean Society for discussing this fascinating and essential body of work.