Disappearance of clams a sign of dying pond?
By WILL DIXON
Ray Hartenstine.s initial survey of the south side of Warwick Pond in early July startled the Rhode Island College Library Technician. Not only was he unable to find any freshwater mussels, but he did not see a single large water insect or any other sizeable invertebrate, for that matter.
Hartenstine, who has nurtured a strong interest in malacology since studying biology and geology at URI in the late 1970s, returned later that month to investigate the north shore of the pond. This time he was accompanied by Steve Insana, Vice President of the Buckeye Brook Coalition. His organization serves as an environmental advocacy group focusing on the brook and its watershed. Using a quahog rake modified to scoop up smaller objects, the two probed the pond floor across the span of eight to 10 houses on the shore. Their catch: one live mussel.
In addition, Hartenstine again noticed very few aquatic insects or crustaceans. While they did bring up some shells, the results from this search were no less disheartening.
.Ninety-nine percent of them are dead,. said Insana. Warwick Pond is the headwater to Buckeye Brook that supports one of the state.s major herring runs.
The abundance of empty shells did serve a useful purpose, however. By studying them, Hartenstine discovered some clues to the circumstances of the mollusk disappearance. For one, all of the shells he found were fully-grown. The absence of deceased juvenile organisms means that the mussels were not necessarily being killed directly, which would leave behind the remains of younger mussels. Instead, Hartenstine realized there must be a different explanation for the disappearance.
.Something.s in the water that.s preventing the mussels from reproducing,. he said.
Thus, the mussels grow to maturity and die without leaving behind offspring. This explains why all of the dead mussels found are adults.
Hartenstine.s curiosity led him to do some research into the history of mussels in the pond. He discovered that in 1905 C. Abbot Davis printed a bulletin that mentioned five different species of mussels in Warwick Pond. The few mussels that Hartenstine did manage to find in the pond were of the Elliptio complanata, the most commonly occurring mussel on the East Coast. Therefore, in the last century four species of mussels have become extinct within the pond.
This disappearance was not necessarily a precipitous one. According to a survey by a Rhode Island state biologist, by 1990 three of the mussel species had already disappeared from the pond.
.Whatever.s happened to the mussels in the pond, it.s certainly been a long-term affair,. said Hartenstine.
Still, Hartenstine discovered that mussels grew in Warwick Pond as recently as a few years ago. From speaking with some of the people living alongside the pond, he learned that they remembered seeing live mussels only three years before. This demonstrates that though the process of extinction has been gradual, the final blow to the mollusk population came in the last several years.
.There was some sort of event that removed the oxygen,. Hartenstine speculates.
The dramatic reduction of invertebrates in Warwick Pond represents a threat to other populations. Fish, birds, aquatic mammals and other animals that eat these mollusks and insects will suffer from the loss of a source of food, and the populations the invertebrates themselves eat may begin to grow unchecked, throwing the ecosystem further out of balance.
Whatever is affecting the organisms in Warwick Pond does not seem to be present in other ponds in the city. Hartenstine said that surveys of Posneganset Pond and Little Pond both revealed mussels of different sizes, demonstrating reproduction. Spring Green Pond did not have any mussels when it was searched, but Hartenstine discovered an abundance of insects and crustaceans living there, contrary to what he found at Warwick Pond.
According to Hartenstine, the culprit behind the mollusks. deaths is likely a number of factors. One of these may be the fact that the houses surrounding the pond are not connected to the sewer system. Contamination from septic tanks could be one of the reasons for the decline of mussels. Other possibilities are industrial waste and natural factors like algae bloom. The fact that the pond is adjacent to T.F. Green Airport also raises questions as to whether chemicals from the airport are somehow contributing to the problem.
Dr. Michael Rice, Professor of Fisheries and Aquacultures at the University of Rhode Island, said that the disappearance of mussels could be linked to an event in the pond.s fish population. The larvae of the freshwater mussels in the pond live as parasites on the gills of fish until they are fully developed, at which point they drop off.
.What this basically means is that they.re dependent on the fish for their lifecycle,. said Rice.
The introduction of substances into the water that causes a loss of oxygen, such as fertilizer runoff, may kill off the fish in a pond. As a result, said Rice, the .mussels are dragged down behind them..
Insana said that for the cause of death of the pond.s invertebrates to be correctly determined, some mussels would have to be collected and dissected. This process would require the hiring of a private firm or investigation by local colleges. The examination of the shellfish hopefully would reveal just what agent is causing their death.