Natural populations of eastern oysters (Crassostrea virginica ) have been decimated because of disease and overharvesting. In response, restoration programs have been initiated to rebuild substrate and reintroduce breeding oysters to reestablish reefs, thereby restoring ecosystem services. Since 2009, The Nature Conservancy (TNC) has teamed up with several agencies to restore degraded oyster reefs in New Hampshire’s Great Bay estuary. Recently, the TNC Supporting Oyster Aquaculture and Restoration (SOAR) program was established to buy up to 5 million eastern oysters from farms in multiple northeastern states and move them to nearby restoration grounds. The intention was to support oyster farmers who have had difficulty selling oysters during the COVID-19 pandemic. Unlike other states in the program, there are no restoration grounds in Maine to serve as “nearby” reefs. Instead, SOAR sought to move oysters from Maine farms to the Great Bay estuary.
Given biosecurity considerations and the recent growth of oyster aquaculture in the Great Bay estuary, there was concern regarding the planting of oysters from distant farms on the restoration reefs and the likelihood those oysters would introduce new pest species. Despite the routine movement of seed from Maine to New Hampshire farms , New Hampshire oyster farmers were worried about introduction of novel species of blister worms, in the polychaete genus Polydora . To support the SOAR program and Maine oyster farmers, samples of oysters from each participating Maine farm were inspected for shell-boring polychaete infestations. Polydora websteri , a common shell-boring species with a worldwide distribution, was in high abundance in reference samples from oyster farms in Great Bay and in samples from the restoration reefs. A second shell-boring species, provisionally identified as P. onagawaensis , is also present on oyster farms in Maine but has not been observed previously in Great Bay. We used burrow shape, microscopic analysis of morphological features, and molecular analysis of the mitochondrial CO1 (mtCO1) gene to identify worms extracted from the oyster samples from Maine farms to species . We found that the abundance of shell-boring polychaetes was variable along the coast of Maine, with farms in close geographical proximity having very different pest loads. Both P. websteri and P. onagawaensis were identified by molecular analysis on some Maine farms while only P. websteri was found in the samples from New Hampshire farms and restoration sites. The resulting data were used to reduce the likelihood that P. onagawaensis was introduced to New Hampshire waters. This project represents a successful collaboration between The Nature Conservancy and University of Maine undergraduate students to prevent the transfer of non-native species from oyster farms to the reefs, which in turn would have increased the likelihood of the pest species recruiting to Great Bay oyster farms.