Biogeographical patterns of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39 degrees and 47 degrees north latitude (New Jersey to Newfoundland)

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Carmen, M. R., Colarusso, P. D., Neckles, H. A., Bologna, P., Caines, S., Davidson, J. D. P., Evans, N. T., Fox, S. E., Grunden, D. W., Hoffman, S., Ma, K. C. K., Matheson, K., McKenzie, C. H., Nelson, E. P., Plaisted, H., Reddington, E., Schott, S., & Wong, M. C. Biogeographical patterns of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39 degrees and 47 degrees north latitude (New Jersey to Newfoundland). Management of Biological Invasions, 10(4), (2019): 602-616, doi: 10.3391/mbi.2019.10.4.02.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.We thank Benedikte Vercaemer, Dann Blackwood, Jonathon Seaward, Dani Cleary, Sam Hartman, Kim Manzo, and Jason Havelin for field assistance. Thank you too to Alicia Grimaldi for map construction and Page Valentine for constructively reviewing the manuscript. Thank you to the Community Preservation Committee of Oak Bluffs, Massachusetts, and the USGS-WHOI Cooperative Agreement for funding (Carman). All data used in this paper are publicly available through USGS ScienceBase at https://doi.org/10.5066/P9GDBDFQ. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government