Mangrove population dynamics in relation to disturbance and recruitment within South African estuaries
Mangroves uniquely regulate their changing environment; however, as they complete their life cycle in this dynamic ecosystem, continuous monitoring is essential to determine if they are selfsustaining, regenerating sufficiently, and managing threats. This study evaluated the status of four mangrove sites on the eastern coast of South Africa. Observational quantitative data was used for disturbances, disease indicators and the population structure and recruitment status of the forests and respective species. Disturbance was quantified by ranking it on a scale from 0 to 4 (four being the highest) for each site. The presence was noted for disturbances (per estuary), disease indicators (canker, fungi, and gummosis) and reproductive structures (flowers, propagules, and calyxes) for each individual within our sampling sites. To quantify and assess the population structure of each estuary, various indices were used to establish the importance of different species, while also looking at different regeneration classes (RC) to evaluate their stocking densities and recruitment. The disturbance levels in the Eastern Cape are moderate (17-25 out of a possible 48), with specific emphasis on resource use as the source of disturbances. Of the disease indicators, fungal growth was present on the majority of all trees (> 90%), while gummosis showed the least incidences. Of the three prevalent species in South Africa, Avicennia marina was the most affected by both gummosis and canker, while B. gymnorrhiza and R. mucronata displayed reduced incidences. The likelihood of canker also increased with the age (DBH) of trees. This study shows that A. marina has the lowest reproductively active population, while the less abundant R. mucronata has the highest.
Mangrove population dynamics, Disturbance, Disease indicators, South African estuaries, Recruitment
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