Southeastern Naturalist A.Williams, S. Eastman, W. Eash-Loucks, M. Kimball, M. Lehmann, and J. Parker 2014 Vol. 13, No. 1 56 SOUTHEASTERN NATURALIST 2014 13(1):56–63 Record Northernmost Endemic Mangroves on the United States Atlantic Coast with a Note on Latitudinal Migration Asher A. Williams 1,2,3,* , Scott F. Eastman 1,2 , Wendy E. Eash-Loucks 1,4 , Matthew E. Kimball 1,2,5 , Michael L. Lehmann 6 , and John D. Parker 7 Abstract - The northern limits of three mangrove species—Avicennia germinans (Black Mangrove), Rhizophora mangle (Red Mangrove), Laguncularia racemosa (White Man- grove)—on the United States Atlantic coast are vouchered and described in comparison to rtgxkqwu dqwpfctkgu fgÝpgf kp nkvgtcvwtg cpf jgtdctkwo eqnngevkqpu0 Vjg nqecvkqp cpf igp- eral status of individual trees were used to delineate northern maxima and show that present ranges extend beyond historic records. The gradient structure of the ecotone within an area of uniform climate is interpreted as ongoing latitudinal movement. Introduction Mangroves represent multiple taxa of tropical macrophytes that occupy coastal margins and reproduce viviparously. Unique among wetland trees, mangroves fac- ultatively resist toxic osmotic gradients in saline soils by excluding and or excreting excess salts (Snedaker and Snedaker 1984). Mangroves are further adaptive in aquatic environments by dispersing viviparous propagules, rather than seeds, via surface waters (e.g., tides, wind, currents) (Odum and McIvor 1990). Hydrologic conditions *ycxg gpgti{. htgujycvgt kpÞwz. vkfcn rtkuo. gve0+ nkokv nqecn jcdkvcv xkcdknkv{ *Qfwo and McIvor 1990), although thermal requirements generally restrict mangroves to vtqrkecn cpf uwdvtqrkecn ¦qpgu *Yckugn 3;94+0 Vyq dkqigqitcrjke rcvvgtpu tgÞgev fundamental ecology and adaptation in these organisms: decreased abundance along latitudinal axes (Ellison et al. 1999), and lower species richness in the Americas as eqorctgf ykvj vjg Kpfq/RcekÝe *Ocepcg 3;8:+0 Rtqfwevkxkv{ kp ocpitqxg uycoru. poised at the interface of the ocean, plays a disproportionately large role in global carbon budgets (Bouillon et al. 2008). Furthermore, mangrove shorelines decrease pwvtkgpv ghÞwz htqo guvwctkgu *Tkxgtc/Oqptq{ gv cn0 3;;;+. uvkowncvg hqqf ygdu. cpf rtqxkfg jcdkvcv vjcv gpjcpegu Ýujgtkgu *Dctdkgt 4222+0 Ocpitqxgu cnuq hqto c rj{uk- ecn dcttkgt vjcv fcorgpu ycxg gpgti{. fktgevn{ dgpgÝvvkpi jwocp eqcuvcn fgxgnqrogpv (Vermaat and Thampanya 2006, Zhang et al. 2012). 1 Guana Tolomato Matanzas National Estuarine Research Reserve, 505 Guana River Road, Ponte Vedra Beach, FL 32082. 2 Department of Biological Sciences, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224. 3 Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803. 4 King County Department of Natural Resources and Parks, 201 S Jackson Street, Seattle, WA 98104. 5 Baruch Marine Field Laboratory, University of South Carolina, PO Box 1630, Georgetown, SC 29442. 6 Smithsonian Marine Station, 701 Seaway Drive, Fort Pierce, FL 34949. 7 Smithsonian En- vironmental Research Center, PO Box 28, Edgewater, MD 21037. * Corresponding author - awil336@tigers.lsu.edu. Manuscript Editor: Joey Shaw