Introduction of Gracilaria vermiculophylla (Rhodophyta, Gracilariales) to New England, USA: Estimated Arrival Times and Current Distribution

The invasive Asiatic red alga Gracilaria vermiculophylla has recently spread rapidly around the globe. In the Northwest Atlantic, it was first collected in Virginia during 1998; in New England, it was first recorded from Narragansett Bay, Rhode Island in 2007. Until now, the specific dates of its introduction and current distribution in New England have been poorly understood. We employed a combination of field collections, evaluations of historical herbarium specimens, and molecular investigations (including mt-CO1 gene sequencing) to document its present distribution and approximate dates of introduction within New England. We found G. vermiculophylla at 18 of 24 Northwest Atlantic sites growing with native Gracilaria populations. Presently, it is recorded from Stamford, CT to Greenland, NH, with no populations known from five Maine sites where the native G. tikvahiae grows. Molecular screening of historical specimens revealed that G. vermiculophylla was collected from five sites in Massachusetts during 2000, whereas it was first documented in New Hampshire from the middle of the Great Bay Estuarine System (i.e., Dover Point) during 2003. In Rhode Island, initial specimens were documented during 2007, and those in Connecticut were first confirmed during 2010. As G. vermiculophylla has gone primarily undetected in New England since at least 2000, this highlights the difficulty of documenting the arrival and spread of an invasive species that closely resembles a native congener. Hence, DNA sequencing is critical in clarifying the introduction and expansion of such non-native seaweeds.