Spatial Distribution and Recruitment of the Botrylloides violaceus and Botryllus schlosseri Tunicates in Barnegat Bay, New Jersey

Botrylloides violaceus and Botryllus schlosseri, colonial ascidians, are known invasive species of the North American Atlantic coast. The tunicates take residence and grow on native eelgrass (Zostera marina) blades, potentially negatively affecting eelgrass growth rate by means of smothering which reduces the plants ability to photosynthesize. Zostera marina is an important habitat, food source, and an indicator of environmental health. Invasive tunicates can decrease the amount of light that eelgrass receives which in turn, decreases the rate of growth of eelgrass. In the summer months of 2021, the relationship and abundance between the invasive tunicates B. schlosseri and B. violaceus and Z. marina were assessed in multiple locations in Barnegat Bay, New Jersey. Two collection methods were used in June and August. In June, a 2.4 meter transect (0.5m wide) was used to assess the presence of tunicate colonies on eelgrass blades in Barnegat Inlet and Oyster Creek. In August, Ham Island, Rt. 72 Bridge and Barnegat Inlet were visited. A 90 meter transect was used and all grass present within a 25cm x 25cm quadrat at each 10 meter mark was excavated for analysis of the presence of invasive tunicates as well as plant demography. Four settling plates were also placed in Barnegat Inlet between June 30th – August 12th 2021 and August 12th – September 25th 2021 to observe the recruitment of each tunicate species on an artificial environment. A regression analysis indicated a positive relationship between the number of tunicate zooids and eelgrass blade area for both tunicate species in June, but only for the B. violaceus zooids at the Rt. 72 Bridge and Barnegat Inlet sites in August. There was a negative relationship between the number of zooids and Z. marina blade area for B. violaceus tunicates in Ham Island and B. schlosseri at all three sites in August. In June, the most abundant tunicate species in Oyster Creek was B. violaceus and in Barnegat Inlet the dominant species was B. schlosseri. In August, B. violaceus tunicates were the most abundant at both Ham Island and Rt. 72 Bridge while the B. schlosseri tunicates were the most abundant at Barnegat Inlet. The tunicate abundance results from this study are consistent with results from a study conducted in the same area in 2017-2018. The abundance of B. violaceus and B. schlosseri tunicates were similar for the two study periods in Barnegat Inlet and Ham Island. A difference was found between the sites over the abundance of the B. violaceus tunicates in Ham Island in 2017-2018 and in 2021 with the tunicates covering more area in Ham Island in 2021 and in Barnegat Inlet in 2017-2018. These results suggest that compared to past studies, the invasive tunicates are still present on the Z. marina blades and could have a potential negative impact on the plant. This research is the first evaluation of the number of zooids present on eelgrass blades in Barnegat Bay, New Jersey