Heading into Thanksgiving is tough for fair-weather boaters like me. The cold water has already chased away the rockfish, bluefish, and perch, and the Jimmy Blues are digging down into the muddy bottom to hibernate. All we have left is frozen fish and crab; better than nothing I suppose.
There is some good news for those who look deep into the river. If you’ll just grab a mask and dive to the bottom of the Severn River in about 12 feet of water, you’ll see some great sights: healthy oysters on the oyster reefs the Severn River Association (SRA) has been restoring since 2018.
Why is this happening? The magic is the cold water. Thanks to SRA’s water-quality monitoring program, we have the data to document that visibility jumps from abysmal summertime lows of one to two feet to nearly 10 feet of visibility in winter. This jump in visibility occurs because the cold water reduces the algae activity that gives our estuary system its greenness. When the water’s cold, algae activity slows to a crawl as these microscopic plants cluster on river and creek bottoms to wait out the winter.
To explain this phenomenon from an observational scientist’s POV, I employ the ‘Halden Homogeneous Hypothesis’ to help explain what’s happening down below. It’s a teaching tool we use to train students and volunteers who help SRA track water-quality conditions, especially algae booms and dead zones during warm seasons. The hypothesis simply posits that when water temperature falls below x (something less than 15 degrees Celsius or 59° Fahrenheit), visibility increases dramatically because the algae are inactive when the water’s that cold.
What’s so great about this visibility? It gives us a special opportunity to finally see and study how our oyster restoration reefs are faring. We were able to do this thanks to a new GoPro camera array created by the Smithsonian Environmental Research Center (SERC). After camera array and data recording training from SERC’s Anna Davis, SRA volunteers set out to capture these images of our bivalves on restoration reefs.
The images reveal healthy reefs. What’s special is the sunshine that reaches down to depths of 5.6 meters to create green and orange atmospheric images. Once the camera array settles on the bottom, bang! The eerie watery world of an oyster reef comes into view.
We took dramatic shots of oysters on our Traces Hollow, Wade, Weems Upper, and Chinks Point Oyster reefs, including unusual images of oysters covered with sea squirts at the Chinks Point reef. The sea squirts are like oysters, barnacles, and mussels which also show up on oyster reefs. They all help filter and clean the river water.
Learn more about water-quality and oyster programs and how you can get involved at severnriver.org.
By Tom Guay