The importance of oysters

By Peter Sun/ Special To The Tab

 

 

Oysters have been a popular food since ancient times. Roman emperors paid for them by their weight in gold. The Romans were so enthusiastic about these marvelous mollusks that they marched thousands of slaves through rugged terrain all the way to the English Channel to gather them. While oysters have had a reputation as a delicacy for many centuries, we have only more recently begun to appreciate their environmental benefits. Scientific research has shown that oysters are voracious filter feeders. They consume large quantities of algae and excess nutrients - up to 5 liters per hour. They play a major role in maintaining the ecological balance in the waters where they grow.

Take the Chesapeake Bay, for example. Today, the water is often turbid, carrying large amounts of sediment and phytoplankton (microscopic organisms), which limits the biodiversity of the bay. However, if we go back approximately 40 years, <!--[if gte vml 1]>

NNHS Biology students Alissa Becker, left, Peter Sun and Joy Huang, right, at Whole Foods Market with their subject.

<![endif]-->we know that nature provided 3-4 million bushels of oysters annually in the bay, which was in great shape ecologically. These oysters filtered all of the bay’s water in a mere 4 to 5 days. During this filtering process the oysters use their cilia to strain out microscopic plants and to wrap whatever they cannot digest in mucus, which they then transport to the mouth. The mouth then does the job of breaking down the material, which moves to the stomach and is eventually expelled as feces or pseudofeces (material excreted, but not through the gut) that contribute to the sediment of the bay. Oysters consume phytoplankton so rapidly that several large oysters can clear an aquarium filled with green water within hours. When oysters strain out microscopic plants in the bay, they create room for other organisms to survive, thus maintaining the ecological balance that fosters species diversity in the bay.

Sadly, the ecology of Chesapeake Bay is now very unhealthy. Oysters are nearly absent from the bay. They have been reduced to one percent of their population of 40 years ago. This is because enormous quantities of nitrogen and phosphorus (over 300 million pounds) are deposited in Chesapeake Bay each year in the form of man-made fertilizers. These provide a tremendous source of nutrients for phytoplankton and algae. When these phytoplankton and algae are overabundant they gather to form large green masses that block the light that would normally filter to the bottom and allow healthy aquatic vegetation like seaweed and ell grass to grow. The excessive phytoplankton absorbs enormous amounts of oxygen very rapidly in a given location, causing anoxia, which means that no oxygen is left to circulate in the water. The result is devastating; it kills off many animals that require oxygen to live. During the summer, when the temperatures are high and there is little vertical mixing of water in the bay, the warmer water remains afloat because it becomes less dense, while the cooler, denser water remains at the bottom. The water at the bottom can be anoxic for many weeks. This destroys many or even most of the living organisms, such as fish, leaving acres of the bay’

s bottom barren.

How did such a healthy bay change so dramatically in just 40 years? There are many answers to this question, but they all boil down to this: humans have been over-harvesting a most precious natural resource. There is historical evidence that the over-harvesting of Chesapeake Bay goes back 140 years, to about 1865. Oyster harvest dropped precipitously between 1890 and 1905; even so, 12-15 million bushels of oysters were still harvested during that time period. Since 1905, the oyster harvest has declined from 5 million bushels annually to a meager 100,000 bushels in 1993. There is clear evidence that it is the drastic decline in oysters that is responsible for the drastic decline in the water quality of Chesapeake Bay.

Fortunately local governments have recognized the nature and the severity of the problem. Laws have been passed to limit the over-harvesting of oysters. For example, the 1927 10 Percent Shell Tax Law required oyster processors to make 10 percent of their shucked shell available for state use in planting, a method to create new oyster beds. The 1953 55 Percent Shell Tax, increasing the tax on oyster processors by 50 percent, was passed to slow the market demand for oysters. The 1972 Moratorium on New Leases suspended awards of new leases of oyster grounds so that the over-harvested oyster grounds could recover. Although these steps taken by governments were inadequate, they were milestones that acknowledged past mistakes and attempted to rectify them. Such laws, when combined with efforts to raise public awareness of the problem, are ways to help bring back the oysters that are so essential to the heath of the environment.

Oysters are much more than a human delicacy. They perform amazing environmental services, not only in Chesapeake Bay but also in many coastal areas all over the world. We humans should do whatever we can to preserve this delicate and delectable creature that quietly works environmental wonders.

Peter Sun was assisted by NNHS classmates Alissa Becker and Joy Huang in writing this article as part of an Environmental Service Project in Zachary Snow’

s Biology class.

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