| |
Altered temperature and precipitation regimes driven by climate change are affecting the global distribution of mangroves, particularly at poleward range limits, where fewer freeze events allow mangrove migration into temperate climates. Along the west coast of Florida, black mangroves (Avicennia germinans) reach their northern range limit in the Big Bend region, where sea level rise and fewer freeze events create favorable environmental conditions for their survival. However, as black mangroves expand into temperate salt marsh, they face intense predation pressure by purple marsh crabs (Sesarma reticulatum). We conducted a field experiment investigating the relationship between crab predation and propagule density. Results showed that propagule consumption decreased with increased propagule density. On average, 27% of propagules in a 100/m2 density treatment were consumed, 55% of propagules in a 25/m2 density treatment were consumed, and 100% of propagules in a 1/m2 density treatment were consumed. We are incorporating field results into an individual-based model to quantify the relative effects of propagule predation on mangrove colonization, in concert with storm-driven dispersal and freeze events. We hypothesize that predation affects regional mangrove expansion into salt marsh by reducing overall encroachment success and that the combined effects of regional abiotic controls and local predation depend on the magnitude and frequency of abiotic disturbance, propagule density, and crab density. The individual-based model will be a useful tool for simulating spatial and temporal changes in mangrove populations on a 1-year time step under different environmental and predation scenarios. We expect the combination of field data and predictive modeling will offer new insights on patterns of mangrove coverage along a dynamic coastal region. |
