In June of 1972, Hurricane Agnes inundated the Mid-Atlantic region with massive amounts of rainfall. Rivers that drain into the Chesapeake Bay collected rainwater and large amounts of sediment from erosion of the land, and sent them into the Bay. This caused salinity to reach record lows resulting in catastrophic losses to some important bay organisms. Populations of oysters and soft clams located in the upper reaches of the Bay and its tributaries suffered major losses, and some have never recovered.
Formation of the Horn Point Oyster Hatchery
In response to the devastating storm, researchers from the University of Maryland proposed to construct a production-scale oyster hatchery at Horn Point. This facility was to be used to assist in oyster rehabilitation efforts centered around the areas most severely impacted by Hurricane Agnes. Initial funding for the construction of the facility and for the first year’s operation came from a grant from the Economic Development Administration.
The original hatchery here at the lab has been in operation since 1974. The facility has been invaluable as a tool for oyster research, restoration, and education. Sadly it has started to succumb to age and the antiquated systems are now largely obsolete.
Aquaculture and Restoration Ecology Laboratory Oyster Hatchery
The Aquaculture and Restoration Ecology Laboratory (AREL) was constructed to replace the old oyster hatchery. This state-of-the-art facility has allowed us to greatly expand the capacity for oyster production here at Horn Point. It has also provided quarantine and controlled environmental facilities needed to advance oyster culture and disease research.
Since first moving into AREL, we have been able to dramatically increase oyster production and restoration efforts with billions of spat-on-shell produced and planted in the Chesapeake Bay.
Oysters are “broadcast” spawners — they release their eggs or sperm directly into the water column. The eggs are then fertilized external to the brood oyster.
In the hatchery, as oysters begin to spawn, they are sexed and separated into plastic tubs (one for males and one for females) where they are allowed to spawn out. Sexing broodstock when they begin to spawn is done in two ways. First and easiest is by observing their spawn behavior. Males spawn by expelling sperm in a continuous stream about midway along the side of the shell margin. Once a male begins to spawn, spawning may last up to an hour, usually in periods of about five minutes. The presence of spawning females may greatly enhance this activity. Females usually spawn very differently from males in that they gently open their valves and expel eggs in a “pulse” from the front of the shell. Once spawning commences in females, it too can last for an extended period of time perhaps up to an hour. As with males, the presence of gonadal material from other spawning oysters may enhance a female’s spawning activity. The second is to collect a concentrated sample of what the oyster is expelling into the water column and examining it under a microscope to see if it is eggs or sperm.
After most spawning activity has ceased, broodstock are removed from the spawning tubs and the eggs are counted. During counting, evidence of fertilization is noted and the proper amount of additional sperm is then added to insure that maximum fertilization has occurred. Spawning tubs are used to prohibit too much sperm from coming into contact with the newly spawned eggs which can result in a condition called polyspermy. Polyspermy occurs when more than one sperm attempts to fertilize the same egg, resulting in eggs that either do not hatch or in oyster larvae that are deformed. Larvae produced in this manner usually do not live more than a few days.
Production Setting System
For fertilization to occur, it is important that many oysters spawn at the same time. One oyster spawning individually would not result in any egg fertilization, therefore no young oysters would be produced. Oysters have developed the ability to sense when spawning is occurring. In nature, on a healthy oyster bar, spawning could begin with a single individual whose gonadal material (either eggs or sperm) would be released and carried by the currents to neighboring oysters. Through normal pumping and filtering activity, neighboring oysters would detect the first oyster’s spawning activity which would subsequently trigger them to spawn. If conditions are right, a chain reaction would occur where a large percentage of the oysters on that bar would spawn in synchrony. In this way, the chances of egg fertilization are greatly enhanced.
Large fiberglass tanks, located on the concrete tank pad outside the hatchery building and down near the pier, are used to produce oyster spat on cultch (shell).
Cultch is a term referring to any hard substrate used by oyster larvae to attach during settlement. In nature, this is usually other oyster shell, but almost any hard clean substrate can be used by setting oysters for cultch.