October 26, 2024 was a beautiful Saturday morning at John Heinz National Wildlife Refuge, and the perfect day to gather in the Heron Room to learn and share about the Darby and Cobbs Creek Community Science Monitoring Program! 14 volunteers from the Program arrived, signed in, and enjoyed the incredible refreshments from the Buttery in Malvern while presentations began. There was a packed agenda, with welcome remarks from Aurora Dizel and Lauren McGrath, an introduction to freshwater mussels of Darby Creek by volunteer Susan Lea, and a lesson on mussel taxonomy and ecology by Dr. Erik Silldorff of the Delaware RiverKeeper Network. Afterwards, volunteers had a training on a new water chemistry test, Nitrate and Nitrite.
There is a recommended and linked list of free mussel resources at the end of the blog post!
Volunteer Susan Lea (pictured above) gave a one year update on the mussel bed that she had documented upstream from her sample site. Since the fall of 2021, Susan has been monitoring two sites, DCPS3 and DC617, in the Darby Creek headwaters in Berwyn, about 275 yards apart and bifurcated by an unnamed tributary, where sample site DCPS4 is located (see map and data, below). After noting several “fresh dead” eastern elliptio mussel shells (Elliptio complanata), meaning that the mussel may have been recently alive (Eastern elliptio mussels can live for up to 80 years), Susan discovered a small mussel bed of about a dozen live eastern elliptio mussels in August, 2022. The following year with the assistance of DCCCS staff, several more eastern elliptio mussel beds, with mussels numbering over one hundred, were identified between the two sites. Curiously, the mussel beds seemed to stop downstream from where the unnamed tributary entered Darby Creek even though their preferred sandy substrate extended further downstream.
DCCCS Data Dashboard Chloride data for DCPS3, DCPS4 and DC617.
In May, 2024, Dr. Erik Silldorff, Restoration Director & Senior Scientist at Delaware Riverkeeper Network, led a survey of these special mussel beds. Dr. Silldorff has years of experience conducting mussel surveys in the Delaware River watershed. After two days of careful inspection of the stream bed through goggles and snorkels and using clear-bottomed trays, over 850 mussels were documented in Darby Creek, a population large enough to be a remnant that survived the colonization of North America four hundred years ago. The majority of mussels found were eastern elliptio, but to the delight of all, two live Alewife floater mussels (Utterbackiana implicata) were also found in the waterway. Alewife floaters use a broad variety of habitats, including ponds and lakes, as well as streams, rivers, and tidewaters; their presence in Darby Creek suggests that there may be additional populations somewhere upstream! Truly the most exciting discovery of the survey was two juvenile mussels, less than one inch long, that were found perched on the edge of two separate fish nests. Juvenile mussels, indicative of a healthy, reproducing mussel bed, bury themselves in the sediment and are difficult to find without the use of specialized survey techniques.
Dr. Silldorff (pictured above) took the stage after Susan shared the exciting developments from the last year. His passion and excitement for freshwater mussels had everyone falling in love with these incredible bivalves. As we all learned from Dr. Silldorff's talk, freshwater mussels are not actually mussels at all, but a type of large freshwater clam! Dr. Silldorff shared about the history of freshwater mussels in the region, and highlighted the incredible diversity of mussels across the continental United States, even bringing shells that he has collected over his career to showcase the beauty of these incredible bivalves.
Dr. Silldorff also explored the fascinating world of mussel reproduction and the great risk mussels face in a changing world. Freshwater mussels require a host fish as part of their reproduction cycle, with their young larvae, called glochidia, going through a brief but critical parasitic phase. For the eastern elliptio, that host fish is the American eel (Anguilla rostrata), which is a common fish in the Darby and Cobbs Creek Watershed. Eel face significant threats, including habitat loss from large dams that prevent their migration and overfishing. Much is still unknown about the life of American eels, but we do know that where eels are absent, mussel populations decline: no young mussels are found in the Susquehanna River, where eels are no longer present upstream of the Conowingo Dam.
In order to get a host fish close enough for the larval mussels to complete their parasitic life stage by attaching to a host fish's gills, there are a number of fantastic adaptations, including the evolution of lures to attract their host:
Eastern elliptio do not have these specially adapted lures, but rather extend a mucus web that fish swim through. While less flashy, it does seem to do the trick!
The conversation on mussels wrapped up with the DCCCS's impact on the previously known population in Darby Creek. Not only documenting that these incredible creatures call Darby Creek home, but also helping to capture data that helps everyone, from biologists to municipal officials and neighbors, understand the threats that this population faces.
Recommended reading include:
North American freshwater mussels: natural history, ecology, and conservation
Author: Wendell R. Haag, published 2012
This is a free PDF!
Freshwater Mussels and the Connecticut River Watershed
Author: Ethan Jay Nedeau, published in 2008
This is a free PDF!
A huge thank you to John Heinz National Wildlife Refuge for hosting this event, to Erik for sharing his passion and endless well of knowledge, and to Susan for providing delicious light refreshments!
Thank you to all who came out for this fun day to strengthen our mussel knowledge!
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