A Closer Look at a Mangrove Die-Off

Presented by Ryann E. Rossi

Ryann E. Rossi, Stephanie K. Archer, and Craig A. Layman

Mangroves are important 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 important reef and commercial marine organisms to land accretion and carbon sequestration. Unfortunately, mangrove forests have been in decline as a result of myriad of factors, particularly human activity. Although human activity is the driving cause of mangrove loss globally (e.g, deforestation and aquaculture) other natural factors such as hurricanes result in drastic mangrove loss. Here, we present a case study from Abaco, The Bahamas in which dwarf Red Mangroves (Rhizophora mangle) are dying on the Western side of Abaco in a region known as The Marls. Interestingly, humans have a low impact in this localized region. Preliminary data suggest that these dwarf R. mangle are stressed by multiple factors, one of which is a fungal plant pathogen. We used both laboratory and field observations to identify the fungal pathogen and to assess the severity across Abaco. Field observations consisted of disease incidence surveys at several sites across Abaco along 100m transects. From these surveys, a subset of leaves with lesions present were collected for isolations. Isolations involved sterilizing the leaf surface and cutting a piece of leaf at the margin of the infected area. Leaf pieces were then plated onto acidified potato dextrose agar (APDA). Upon successful growth of fungal hyphae, a subsample of hyphae was collected and processed for DNA sequencing using Polymerase Chain Reaction (PCR) with ITS primers (ITS 4 and 5). Asexual spores from fungal cultures were harvested to be used as inoculum on new, healthy R. mangle leaves. Through Koch’s postulates, we have identified a species of Pestalotiopsis as the potential pathogen causing severe leaf damage on mangroves in these die-off areas.