In the tropics and subtropics the red mangrove, Rhizophora mangle, provides essential habitat for other species. R. mangle prop roots support secondary foundation species such as barnacles throughout their overlapping range, sponges in the tropics, and Crassostrea virginicain subtropical/southern temperate estuaries. The relationship between primary foundation species and a secondary foundation species has largely been ignored, but may be integral for understanding ecological functions and community processes. The focus of this study is on the changing biodiversity of prop roots and the influence of secondary foundation species along the latitudinal gradient on Florida’s Atlantic coast. The hypotheses tested by structural equation modeling analysis are: A) a latitudinal gradient is present for secondary foundation species on prop roots, B) the identity of the secondary foundation species influences the occurrence of other species, C) water quality will influence both the dominate secondary foundation species and overall prop root biodiversity, D) marine geography factors will influence both the dominate secondary foundation species and overall prop root biodiversity. Water quality variables include chlorophyll a, temperature, salinity, and dissolved oxygen. Marine geography factors include tidal range, fetch, flooding, the length of the mangrove forest, and the connectivity of the mangrove forest.
Preliminary data reveal an overall trend that biodiversity on prop roots increase southward along the latitudinal gradient. The sites being studied range over 493 km from Key West to Vero Beach, Florida. The study area was split into four zones. In the study, the average prop root in the southern/tropical zone had over twenty different species present. Several species of Porifera, numerous species of Ascidiacea, and Isognomon alatus (flat tree oyster) frequently shared prop root dominance. Several species were present only in the southern/tropical zone. In the temperate 1 and temperate 2 zones, located in the northern region of the study, C. virginica averaged five species per root, dominating the prop roots in this region. Occasionally C. virginica was the only organism located on prop roots in the northern region. The transition zone, located in Miami-Dade County, contains both tropical and temperate species on prop roots. In the transition zone, there was substantially more varability in number of prop root residing species and the mean number of species on prop roots was fourteen, however C. virginica was still present, but regulated to the upper portions of the prop root.