Mangroves are foundation species in coastal ecosystems providing an estimated US $1.6 billion in ecosystem services worldwide. These services range from providing essential nursey habitat for marine organisms to land accretion and carbon sequestration. Unfortunately, mangrove forests are declining as a result of myriad factors, many related to human activity. Although human activities are the driving cause of mangrove loss globally, natural factors result in mangrove loss. Here, we present a case study from Abaco, The Bahamas in which dwarf Red Mangroves (Rhizophora mangle) are dying on a large scale. Initial data suggest that prior to death these dwarf R.mangle are stressed by multiple factors, including a fungal plant pathogen, herbivory, and altered abiotic conditions (e.g., hyper-salinity). In order to determine how each of these factors contribute to the die-off we are using a series of empirical experiments. Herbivore exclusion cages were placed on live dwarf mangroves to examine effects of herbivory on mangrove health in the die-off region. Next, disease incidence surveys were completed in the die-off area and infected leaf samples were collected and sequenced for fungal DNA. A simulated grazing experiment was conducted in dwarf mangroves to determine if there is an interaction between herbivory and pathogen.
Our initial results show that there is a trend of decreased herbivory in the caged dwarf mangrove treatments, however, the experiment is ongoing. We have identified a potential fungal pathogen, a Pestalotiopsis species, on infected mangrove leaves from DNA sequencing. Though, Koch’s postulate experiments are ongoing to confirm pathogen identity and virulence. The simulated grazing experiment results show a trend of increased lesion development on cut leaves suggesting a potential interaction between grazing damage and fungal infection. Future work will incorporate how hyper-saline conditions in the presence and absence of both the plant pathogen and herbivore contribute to mangrove health.