Colonization of eelgrass (Zostera marina L.) by tunicates can lead to reduced plant growth and survival. Several of the tunicate species that are found on eelgrass in the northwest Atlantic are highly aggressive colonizers, and range expansions are predicted in association with climate-change induced increases in seawater temperature. In 2017, we surveyed tunicates within eelgrass meadows at 33 sites from New Jersey to Newfoundland. Eight tunicate species were identified colonizing eelgrass, of which four were non-native and one was cryptogenic. The most common species (Botrylloides violaceus and Botryllus schlosseri) occurred from New York to Atlantic Canada. Tunicate faunas attached to eelgrass were less diverse north of Cape Cod, Massachusetts. Artificial substrates in the vicinity of the eelgrass meadows generally supported more tunicate species than did the eelgrass, but fewer species co-occurred in northern sites than southern sites. The latitudinal gradient in tunicate diversity corresponded to gradients of summertime sea surface temperature and traditional biogeographical zones in the northwest Atlantic, where Cape Cod represents a transition between cold-water and warm-water invertebrate faunas. Tunicate density in the eelgrass meadows was low, ranging generally from 1-25% cover of eelgrass shoots, suggesting that space availability does not currently limit tunicate colonization of eelgrass. This survey, along with our 2013 survey, provide a baseline for identifying future changes in tunicate distribution and abundance in northwest Atlantic eelgrass meadows.

Seagrass meadows are ecologically important habitats that are declining globally at an accelerating rate due to natural and anthropogenic stressors. Their decline is a serious concern as this habitat provides many ecosystem services. Eelgrass (Zostera marina) is the dominant seagrass species in the western North Atlantic. It has recently been established that invasive tunicate species possibly threaten the health of eelgrass beds. Colonization of eelgrass leaves by tunicates can inhibit eelgrass growth and may cause shoot mortality. To document the distribution and diversity of tunicate species that attach to eelgrass in the western North Atlantic, we surveyed twenty-one eelgrass sites from New Jersey to Newfoundland. Eight species of tunicates were found to be colonizing eelgrass, of which 6 are considered invasive. Botrylloides violaceus and Botryllus schlosseri were most commonly attached to eelgrass, with B. schlosseri having the largest latitudinal range of any species. Tunicate faunas attached to eelgrass were less diverse north of Gloucester, Massachusetts, where individual survey sites exhibited two species at most and only 4 of the 8 species observed in this study. Percent tunicate cover on eelgrass tended to fall within the 1–25 range, with occasional coverage up to >75–100. Density of eelgrass was highly variable among sites, ranging from <1 to 820 shoots/m 2 . The solitary tunicate Ciona intestinalis was only found on eelgrass at the highest latitude sampled, in Newfoundland, where it is a new invader. The tunicates observed in this study, both solitary and colonial, are viable when attached to eelgrass and pose a potential threat to overgrow and weaken seagrass shoots and reduce the sustainability of seagrass meadows.

We describe an innovative method of dispersing Zostera marina L. (eelgrass) seed that has the potential to facilitate large-scale, citizen-based restoration programs. Mature reproductive shoots of eelgrass were collected during the second week of seed release and stocked into mesh pearl nets suspended from buoys set in 0.04ha plots. As the seeds ripened, they were naturally released from the nets, fell to the bottom and germinated to form a distinct arc-shaped meadow under each buoy. A survey of seedling survival indicated that recruitment was at least 6.9% based on estimated seed abundance within each net. The advantages of this method are that (1) harvest and deployment of reproductive shoots takes place on the same day, eliminating the need to store reproductive shoots in an on-shore storage facility, to obtain a sufficient number of seeds for large-scale restoration programs and (2) once trained, citizens can participate in both the collection and seeding phases, thereby, increasing awareness and value of Z. marina restoration programs. The technique presented allows for a low-cost, efficient, and simple method for successfully dispersing seed, which consequently has a significant impact on establishment of plants from seed. These attributes can also influence restoration programs for other species of aquatic plants for which the seeding of sites, historically degraded but now habitable, is possible.