Short Papers and Notes

RANGE EXPANSION OF BLACK MANGROVES (AVICENNIA GERMINANS) TO THE MISSISSIPPI BARRIER ISLANDS.—The expansion of the black mangrove (Avicennia germinans) into Gulf of Mexico salt marshes is among the many climateinduced poleward range shifts of tropically associated marine plants and animals that have been documented in recent decades (Perry et al., 2005; Lasram and Mouillot, 2009; Fodrie et al., 2010; Comeaux et al., 2012). Gulf of Mexico salt marshes are normally dominated by salt marsh cordgrass (Spartina alterniflora) and black needlerush (Juncus roemerianus). Some research suggests salt marsh vegetation may actually facilitate black mangrove seedling growth, with the marsh influence becoming neutral as mangrove seedlings mature (Guo et al., 2013). While the distribution of black mangroves is limited by freezing temperatures in the north, in warmer climates competition with mangrove species may limit salt marsh distribution (Kangas and Lugo, 1990). Warmer winter temperatures and infrequent and less extreme frosts are likely causes of the expansion of black mangroves in the Gulf of Mexico (Sherrod and McMillan, 1985; Pickens and Hester, 2010; Cavanaugh et al., 2014), and recent studies suggest there is a temperature threshold for mangrove dominance (Osland et al., 2013; Cavanaugh et al., 2014). In the absence of freezes, mangroves have been shown to channel large amounts of energy into production and outcompete salt marshes by shading them (Stevens et al., 2006). Although some studies in the Gulf of Mexico have examined the effects of black mangroves on nutrient cycling, decomposition rates, and sediment accretion within recently colonized salt marshes (McKee and Rooth, 2008; Perry and Mendelssohn, 2009; Comeaux et al., 2012), there is a lack of information on the broader ecological changes these mangrove expansions may have for species that inhabit salt marshes. Recently, we have located black mangroves on Horn and Cat Islands, which are part of the Mississippi barrier island chain in the northern Gulf of Mexico and, to the best of our knowledge, are the northernmost populations (Fig. 1). We have located fewer than 10 black mangroves on Horn Island and one tree on the northern shore of Cat Island (Fig. 2). The mangroves on Horn Island are the focus of a study to define the effects that black mangroves have on the abundance and secondary productivity of salt marsh-associated taxa, such as penaeid shrimps, blue crabs, smaller crustaceans, and juvenile fishes. These macrofaunal species typically rely on salt marshes of the northern Gulf as nursery and foraging grounds. Because Spartina alterniflora exists lower in the intertidal zone and is flooded more frequently and for longer durations than the black mangrove habitat, faunal