(Some of) the Science of Service

Sunrise over the Chesapeake Bay, and the Philip Merrill Center.

Over the course of the week, we’ve had our hands in a few different projects.  But the two that we’ve had the most experience with are oyster restoration and tree planting. Why are these two projects on the top of the Chesapeake Bay Foundation’s “to do” list, and why do they need your help?  Well, hopefully I’ll be able to give you a bit of an idea as to why the work that they are doing is essential for helping to protect the Chesapeake Bay watershed.

The Chesapeake Bay is home to a wonderful variety of plants and animals. One of the invertebrates that makes a home here is the Eastern oyster, Crassostrea virginica. In fact, the name Chesapeake is derived from an Algonquin word meaning "great shellfish bay". This bivalve mollusk, which was once abundant in the Bay, has faced many hardships in the recent past. Over-harvesting, poor water quality from over nitrification and pollution, and in increase in sedimentation from runoff has caused populations to decline to less than 2% of their historical numbers. This is a problem for the oysters, and other denizens of the Bay.

Crassostrea virginica (Eastern oyster) spat attached to reclaimed shell in an oyster float.

When oysters breed, the larvae float in the water column until they find a hard substrate to latch onto. Often, this substrate is the shell of other oysters. But with less oysters in the Bay, it is becoming harder and harder for the larvae to find a place to call home. The once abundant oyster bars (or reefs) are no more, which means that other fish and invertebrates also no longer have a place to make their homes. If a lucky oyster can find a resting place, it latches on, and starts to secret a shell around it. These juveniles, known as spat, are hermaphroditic, only becoming male or female later in life. Once they reach reproductive age, they release eggs and sperm into the water, and the cycle starts again.

As if hunting for real estate at such a young age doesn't pose enough of a problem, C. virginica also has trouble finding a proper meal. The Eastern oyster is a shallow water filter feeder. Large individuals are said to be able to filter over 40 gallons of water a day. In fact, the not so distant past, it would take all the oysters in the Bay between three and five days to filter the entire volume of the Chesapeake.  Now it takes them more than a year to accomplish the same goal. But they now face a new challenge in addition to decreased numbers. The sediment from runoff that clogs the Bay, also clogs their gills as they pump water through their shells. When they should be filtering out the plankton and other nutritious particulates, they are filtering dirt and polluted water, which effectively chokes them to death. This, in combination with the other factors mentioned above, makes the situation for oysters in the Bay rather grim.

Callinectes sapidus, the Chesapeake Bay blue crab, on a reef of live Eastern oysters.

It's also no secret that the water in the Chesapeake Bay is not as clean and healthy as it once was.  The reduction in oyster population is part of the problem, but there are other anthropogenic factors involved as well.  One of the biggest is changes in the way the land in the Chesapeake Bay watershed has been used in the last 100 years.  Many of the traditionally forested areas have been turned into agricultural, urban, or suburban areas.  This may seem like a good idea, as people need food and places to live.  But it has had some serious side effects on the Bay.  Trees play a crucial role in the watershed.  They literally hold onto the soil with their roots, preventing sediment and runoff from eroding into the streams, creeks, and tributaries that lead to the Bay.  They also absorb nutrients from the soil in order to survive and grow.  But today, these excess nutrients flow into the Bay, and are one of the major pollutant offenders.

These nutrients aren't only good for trees, but for another group of photosynthesizing organisms as well: algae.  And if the nutrients aren't absorbed by the trees, they make it into the Bay, where they cause algae blooms to flourish.  This is also not a good thing.  Algae live fast, and die hard, ad as their bodies decompose, dissolved oxygen in the water is used up, causing hypoxic conditions.  Low oxygen levels in the water means that the critters that live in the Bay - oysters included - have one more agent working against them.  The stress from poor water quality, over sedimentation, and excess nutrients, also makes them more susceptible to a number of diseases that hurt their populations.

A field of recently planted oak, redbud, sycamore, and shrubs that will one  day turn this farmland into a forest.

It's a vicious cycle.  Too many oysters are harvested, so the young don't have a place to attach and grown, and water quality begins to degrade.  Changes in land use release more sediments and unwanted nutrients into the Bay, which only makes the situation worse.  Disease takes a foothold.  Less oysters survive into adulthood, even in protected areas, and it takes longer for the Bay to bounce back.  The Eastern oyster serves a crucial role in the bay, providing a habitat for other species of plants and animals, and as the primary filtering agent. And it's easy to point to them and show their importance in protecting the fragile ecosystem of the Bay.  But like any ecosystem, the Chesapeake Bay is a complex environment, composed of many living and non-living factors, and the interactions between them.  Trees might not seem all that connected, because when one thinks of the Bay, they think of blue crabs, osprey, and diamondback terrapins. But trees also play a vital role, as do the people working to restore many of the traditionally forested areas in the Chesapeake Bay watershed.

Luckily there are both organizations and individuals working to help “save the Bay”.  Certain areas of the Bay are now protected from harvesting, so that oysters can live and reproduce with minimal human interference. Sustainable practices keep unprotected areas from becoming over harvested. And shells from harvested oysters are collected and placed back into the Bay, in the hopes that they will provide a home for spat that are "seeded" on these natural, man-made bars. Trees and forests are being replanted and monitored.  Pasture that was once set aside for growing corn is being converted back into grass land for livestock to graze on.  Underwater grasses are being restored to provide habitat and food for other species, as well as tackle the pollution problem.  After 100 plus years of changing the face of the Bay, humans are finally realizing the importance of these key plants and animals, and making a concerted effort to help them regain their former glory.

Pandion haliaetus (osprey) in flight over the Bay.

We’ve had the pleasure of working with the Chesapeake Bay Foundation on some of their ongoing projects over the course of the week, and we look forward to joining them again in the future.  Every tree planted; every oyster spat that grows to maturity makes a difference. And you can be a part of the action as well.  Whether it's picking up a piece of litter you find on the ground and preventing it from going down a storm drain, donating a few dollars or your time to a non-profit organization, buying local food, advocating for the cause, or just fixing a dripping faucet, each one of us has the potential to make a huge positive impact on the health of the Bay, or your local watershed.  So do what you can, when you can, and be a part of the process that will help preserve this beautiful place for generations to come.  The seafood lovers and beach goers of the future thank you!

-David Tana-