Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

Abstract

Two species of mangrove trees of IndoPacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year -1 .Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximum number of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m 2 of mangrove forest with stem densities of 24,735 ha -1 . We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year -1 . Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species.

Environmental tolerances of rare and common mangroves along light and salinity gradients

“…It was introduced to Florida at least three times during the 1960s and 1970s, when it was planted into the living collections of the Fairchild Tropical Botanic Garden, Coral Gables, FL, USA (Fourqurean et al 2010). At all three planting sites, the species reproduced prolifically, spread beyond the boundaries of the gardens, and became a naturalized invasive in the surrounding area, where it came to dominate local stands of mangroves and was estimated to have a population growth rate of 17-23 % per year (Fourqurean et al 2010). Ongoing eradication efforts have eliminated most reproductive individuals, so we collected young-of-the-year seedlings and transplanted them into treepots for use in the experiment (see below).…”

Is the Geographic Range of Mangrove Forests in the Conterminous United States Really Expanding?

“…Warmer winter air temperatures and less extreme sub-freezing winter air temperatures are likely causes of the expansion of black mangrove ( Avicennia germinans ) into salt marshes dominated by smooth cordgrass ( Spartina alterniflora ) [14,15]. Other factors such as fire, tropical storms, sea level rise, sedimentation/erosion, changing hydrology and certain management practices are also believed to be contributing to the expansion in localized areas [6,12,16,17,18,19,20]. …”

Coastal Habitats of the Gulf of Mexico

“…In south Florida, non-native mangrove species (from the Indo-Pacific) have become established in botanical gardens and these populations are reportedly expanding on the Atlantic coast (Fourqurean et al 2010). However, the mangrove habitat is considered to be difficult to invade by non-mangrove species due to the fact that flooding and high salinity exclude most other plant species unadapted to these conditions (Lugo 1998).…”