Temperature Tolerance of Early Life History Stages of Black Mangrove Avicennia germinans: Implications for Range Expansion

Avicennia germinans (L.) L. (black mangrove) grows at its North American latitudinal limit in coastal salt marshes of Louisiana, USA. To assess low-temperature tolerance of A. germinans, we evaluated the survival and developmental progress of three early life history stages (dispersal, stranded, and seedling stages) to three temperatures (5.7A degrees C, 2.5A degrees C, and -6.5A degrees C) of four durations (2, 6, 12, and 24 h). Duration and temperature of exposure decreased mangrove survivorship, particularly 24-h exposure at -6.5A degrees C. Although there was not a significant effect of stage on survivorship overall, both survival analysis and final mortality analysis indicate that dispersal stage had the greatest survivorship. Treatments had little impact on developmental progress of surviving propagules, but propagules exposed to -6.5A degrees C were most susceptible to fungal infection. Greater cold temperature tolerance of the dispersal stage may be a mechanism for northward range expansion in Louisiana.