It is well known that oyster populations today are a few percent of levels found when Europeans first entered the Bay. Over-harvesting, habitat destruction by dredging reefs, and human introduction of a disease (MSX), have devastated oysters. Artificial reefs, formed by dumping shell in piles in the water, have met with very limited success. Little spat set takes place, the shells disintegrate rapidly, and cow-nosed rays (like the one that almost killed Capt. John Smith at “Stingray Point”) wipe out many of the oysters that do manage to grow, perhaps because humans are eliminating their major predator, sharks.

Each year I pile up the shells from the oysters grown at my pier in floats and eaten. In early June, the clean shell is placed in the water in hopes of starting a “reef.” I have had no success despite there being thousands of oysters in floats nearby to provide larvae. Why doesn’t the shell attract natural “strike?” In spring of 2006 I took clean shells, drilled a hole in each one, and suspended the shells concave-side down off my pier, adding two shells every three days. The photographs (On string.jpg; Spread out.jpg) show the result. After little more than a week, the bottom two shells were densely coated, top and bottom, with “slime” or, as it is properly called, biofilms. It is well known that oysters require clean substrate for spat to attach “strike or set.” The classic book “The Oyster” by William K. Brooks, published over a century ago, clearly states this in several places. For example, on p. 99 “The first thing found out was that the floating spawn would not attach itself to or ‘set’ upon anything which had not a clean surface; smoothness did not hinder - but the surface of the object must not be slimy.” And on p. 116, in order to attract spat for commercial purposes “...it is important that the shells or other substances which are employed be perfectly clean, and that they be not put into the water until spawning has commenced.”

Dr. Jeremy Jackson, a respected scientist at the Scripps Institute of Oceanography, has advocated the “rise of slime” as one of the consequences of nutrification of the coastal ocean (www.shiftingbaselines.org.) In his 2001 paper in the Proceedings of the National Academy of Sciences (vol. 98, pp. 5411-5418) he states “Today Chesapeake Bay is a bacterially dominated ecosystem with a totally different trophic structure from a century ago.” Nutrification of coastal environments leads not only to the prolific growth of suspended algae (phytoplankton) that cloud the water, but to biofilms composed of both plants and the microbes that consume them (slime.) We have changed the Bay from an ecosystem dominated by fish, crabs, oysters and the myriad of creatures associated with healthy oyster reefs, to one dominated by bacteria.

The “rise of slime” provides a reasonable hypothesis for the behavior of the “reef balls” reported in the December 2006 Bay Journal (www.bayjournal.com.) “Before going in the water, 30 of the balls were placed in tanks filled with oyster larvae.” After a year those balls “... had become so overgrown with oysters and colonizing organisms that they had become almost unrecognizable as reef balls.” In contrast “The balls that did not have larvae before going into the water still had no oysters growing on them.” Much more success will be realized if the substrate is colonized before it can be covered in slime, which means before it is released to the environment, and this technique, commonly labeled as “spat-on-shell” is proving to be successful.

Although the practice of settling oysters on a substrate prior to placing the substrate in the environment may be useful for aquaculture, until the “rise of slime” is curtailed, natural oyster spat set (“strike”) will not improve. Not only does the slime cover hard substrates, and prevent benthic organisms like oysters from settling, it also covers the leaves of what little submerged aquatic vegetation (SAV or sea grass) remains in the Bay and further restricts the amount of light the plants can receive. The “slime” is caused by over-fertilization of the Bay because we value maximum agricultural profits, cheap food and low wastewater bills over satisfactory water quality. Until nitrate and phosphate pollution is reduced by improved agricultural fertilization practices and upgraded wastewater treatment facilities, water quality in the Bay will not improve, the ability of oyster larvae to attach naturally will not improve, and the Chesapeake Bay ecosystem will remain dominated by bacteria.

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