Chesapeake Now! Maryland's Most Iconic Bivalve
Oct 14, 2014 02:33PM ● Published by Cate Reynolds
Photo by Sarah Walker, ORP
Maryland’s Most Iconic Bivalve
The Importance of Oyster Restoration in the Chesapeake Bay
By Lisa A. Lewis
Unlike coral reefs, which are some of the most colorful and beautiful ecosystems in the world, oyster reefs aren’t especially pleasing to the eye. Formed when individual oysters attach to one another, these dense reefs often resemble a pile of rocks. But what they lack in beauty, oyster reefs more than make up for in function. Indeed, oysters are critical to the Chesapeake Bay because they improve water clarity and provide habitat for aquatic life. In fact, oysters play such a vital role in the ecosystem that their population is monitored via annual field surveys, and oyster restoration is one of Maryland’s top priorities.
According to Oyster Recovery Partnership (ORP), the Chesapeake Bay oyster industry was the “envy of the world” until the population plummeted nearly 50 years ago and has never recovered. So scientists—and perhaps the entire state of Maryland—were excited to hear some good news this year. A press release issued by the Maryland Department of Natural Resources (DNR) in May 2014, which reported the results of Maryland’s 2013 Fall Oyster Survey, indicated that the oyster biomass index (a combined measure of oyster abundance and size) has more than doubled since 2010, reaching its highest point since 1985.
“These survey results indicate that our multi-pronged strategy to restore our native oyster population is paying off,” said Governor Martin O’Malley in the press release. “While this progress is noteworthy, it underscores the need to stay the course, reinforcing our commitment to protect our investment and rebuild this essential, iconic species.”
The increase was attributed to high oyster survival over the past few years and strong reproduction in 2010 and 2012, which, in turn, resulted in an increase in harvests.
“Preliminary harvest reports for the past season have already surpassed 400,000 bushels—with a dockside value in excess of $13 million—the highest in at least 15 years,” said DNR Secretary Joe Gill in the press release. “Coupled with the survey results, we have reason to be cautiously optimistic a sustainable oyster population can once again play a vital role in the Bay’s ecosystem and Maryland’s economy.”
Naturally, the population increase is encouraging, but it’s important to put the survey results into perspective. Mike Naylor, DNR shellfish program director, says enthusiasm about the increase of oysters in their remaining habitats should be tempered by the recognition that most of the Bay’s oyster habitat has been lost. “We hope our strategies are helping, and there is some reason to believe this,” he says. “But this increase was predominately a natural event, resulting from low disease-related mortality and good reproduction.”
Importance of Oysters
A symbol of Chesapeake Bay heritage, oysters play a vital role in the ecosystem. Since they are filter feeders, oysters feed by pumping water through their systems, trapping food particles as well as filtering silt, sediment, and nitrates from the water. Oyster reefs also provide habitat for a variety of marine organisms. And, of course, oysters comprise one of the Bay’s most important commercial fisheries, contributing millions of dollars to the economy each year.
Harvest data collected since the 1800s shows that 125 years ago, bushels exceeded 10 million a year. But historical over-harvesting, disease, habitat loss, and degraded water quality caused a serious decline in the oyster population, making oyster reefs one of the most endangered marine habitats in the world. The severity of this decline is evident by the fact that it now takes oysters much longer to filter the entire Bay than it did in the past.
Jump-starting Mother Nature
The fact that the 2013 oyster population increase was primarily a natural event is good news. But sometimes Mother Nature needs help, which is why oyster restoration is so important.
“We can never replace Mother Nature,” says Stephan Abel, executive director of ORP. “But oyster restoration is a way to ‘jump-start’ Mother Nature. We hope we can learn from our efforts and replicate the process going forward.”
ORP works with state and federal agencies, scientists, industry leaders, and conservation organizations toward the goal of oyster restoration, including their major restoration partners: the University of Maryland Center for Environmental Science (UMCES) Horn Point Laboratory, the DNR, the National Oceanic and Atmospheric Administration (NOAA), the Chesapeake Bay Foundation (CBF), the U.S. Army Corps of Engineers, and the Nature Conservancy.
In order to understand the restoration process, it’s important to understand how oysters reproduce. Oysters spawn in the summer when water temperatures rise. Adults release eggs and sperm into the water, and fertilized eggs develop into free-swimming larvae. The larvae are carried by the Bay’s currents for several weeks and then settle to the bottom of the Bay and attach to a hard surface, or substrate. Once they attach to a substrate, they are called spat. Interestingly, many oysters change sex over the course of their lifetime. Oysters less than one year old are typically male; older oysters are usually female.
Restoring an oyster reef can be likened to a construction project. Restoration partners evaluate a site to determine what type of work it requires to make it suitable for accepting oysters. Since oysters require hard substrate to survive, ideal areas are those least affected by silt and sediment. Once a reef is selected, it is rehabilitated and prepared to receive hatchery-produced spat on shell. This process may involve planting clean shell to create a suitable bed for oysters. Hatchery crews produce spat on shell, which is transported to the newly prepared reef and washed overboard, where it is allowed to grow. (Prior to depositing spat on shell, divers survey the reef to ensure that it is suitable to plant spat on shell.) Once the oysters are deposited onto the reef, scientists monitor the site’s progress, so they can make improvements for future restoration projects.
“Restoring significant amounts of healthy oyster reefs to the Bay is [an] enormous [job] that will be expensive and take a long time to complete,” says Dr. Don “Mutt” Meritt, director of Horn Point Laboratory Oyster Hatchery. “Much of our once-productive oyster reefs have been destroyed. Some require spat to be placed on them because natural spat events are rare and/or very light. So spat needs to be produced in other regions or in a hatchery.”
The new Bay Agreement has set a goal of restoring 10 Bay tributaries by 2025. Harris Creek, a tributary of the Choptank River on Maryland’s Eastern Shore, was the first location chosen for restoration and is the largest oyster restoration effort ever conducted in the Chesapeake Bay and on the East Coast. Restoration work is also underway in the Little Choptank River.
“Early efforts with hatchery-based oyster restoration were spread out and covered many smaller plots in multiple tributaries of the Chesapeake Bay,” says Meritt. “A decision was made a few years ago to try to concentrate much of the effort in one or two ‘target’ estuaries to test the theory that by significantly increasing the biomass of oysters in a small tributary, we could start to see some major changes in the ecology of the system. Harris Creek was the first targeted tributary because of its size, the availability of good oyster bottom, and the fact that it used to see decent natural sets. Not enough time has elapsed to evaluate this theory, but we have certainly demonstrated that in the short term (one to four years), it’s possible to restore very significant levels of healthy populations of oysters through our cooperative program.”
Governor O’Malley has made oyster restoration a priority of his administration. Under his Oyster Restoration and Aquaculture Development Plan, Maryland is making significant progress toward its goal of large-scale restoration.
“We know our strategies can be successful, and we have direct evidence of the effects of our directed restoration activities,” says Naylor. “Some of the largest oyster restoration activities ever undertaken are underway right now in Harris Creek and the Little Choptank River. Early results are very encouraging, and the hope is to fully restore five Maryland tributaries by 2025.”
“Oyster restoration is fascinating,” adds Abel. “It’s a huge undertaking that involves the cooperation of several agencies working together for a common cause. But it’s a very positive experience because it shows what we can accomplish when we all work together.”