Tracking environmental trends in the Great Bay Estuarine System: An examination of water quality and nuisance macroalgal blooms

Monitoring macroalgae populations is an effective means of detecting long term water quality changes in estuarine systems. To investigate the environmental status of New Hampshire\u27s Great Bay National Estuarine Research Reserve, this study assessed the abundance/distribution of macrophytes, particularly Gracilaria and Ulva species, relative to eutrophication patterns; compared historical (1970s-1990s) and current algal biomass/cover at several sites; and compared Ulva and Gracilaria tissue N/P content to ambient and historical levels. Nitrogen and phosphorus testing revealed that the estuarine system has become eutrophic, and Ulva and Gracilaria biomass/cover have increased significantly. The percent cover of Ulva species, at seasonal maxima, was over 90 times the value recorded in the 1970s at Lubberland Creek, and exceeded 50% cover at all sites in the upper estuary. Gracilaria cover was greater than 25% at Depot Road in the upper estuary, whereas the historical measure was 1%. Sequencing of ITS2, rbcL, and CO1 revealed the presence of previously undetected Ulva and Gracilaria species, including Gracilaria vermiculophylla (Ohmi) Papenfuss, an invasive species of Asian origin. Gracilaria vermiculophylla has surpassed G. tikvahiae as the dominant Gracilaria species in the Great Bay Estuarine System. Field collections, evaluations of historical herbarium specimens, and molecular investigations (including CO1 gene sequencing) of Gracilaria vermiculophylla were used to document its present distribution and approximate dates of introduction within New England. It was found at 18 of 24 Northwest Atlantic sites with existing native Gracilaria tikvahiae populations. Presently G. vermiculophylla is recorded from Stamford, CT to Greenland, NH. Molecular screening of historical herbarium specimens revealed that G. vermiculophylla was collected from five sites in Massachusetts during 2000, while it was first collected in the middle of the Great Bay Estuarine System (Dover Point, NH) during 2003. In Rhode Island, initial specimens were documented during 2007, while 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 to clarifying the introduction and expansion of such non-native seaweeds