How has the amount of seaweed in the Great Bay Estuary changed over time?
At intertidal sampling sites, green and red seaweeds (combined) increased from approximately 8% cover in 1980 to 19% cover in 2016. At these same sites, invasive species now dominate the red seaweed category, which comprised approximately 15% of all seaweeds in 2016.
The mean percent cover of green and red seaweeds (combined) at a limited number of sampling sites in the Great Bay Estuary was 8% in 1980 but increased to 19% by 2016 (Figure 6.1). For green seaweeds, this increase includes the presence of both native and invasive species of Ulva. It is notable that no invasive species of Gracilaria (a red seaweed) were seen in 1980, but now two major invasive Asiatic red seaweeds (Gracilaria vermiculophylla and Dasysiphonia japonica) along with a native species (Gracilaria tikvahiae) dominate the red seaweeds.36
While the seaweed data are cause for concern, it is important to note that this dataset is not comprehensive in time and space; more research is required to verify these trends. In addition, these data are restricted to intertidal areas. While important steps to establish a baseline in the subtidal area have occurred, this work needs to be followed up by additional monitoring to better assess trends.