Growth and mortality of mangrove seedlings in the wettest neotropical mangrove forests during ENSO: Implications for vulnerability to climate change

Abstract

Assessing factors affecting growth and mortality of mangrove seedlings, the critical transition between propagule dispersal and recruitment to the sapling state, is crucial to understand and predict the fate of mangrove forests in our changing climate. This work aimed to understand seedling’s responses to contrasting temperature and precipitation regimes and analyze consequences for the persistence of these ecosystems under expected climate change scenarios. Growth rate and mortality of seedlings were monitored monthly in an array of mangrove forests located along a tidal and salinity gradient in the central Pacific coast of Colombia, one of the rainiest places on Earth. Seedlings were monitored from January to December 2016, coinciding with a major El Niño (EN) episode and the abrupt transition to La Niña (LN) conditions. Seedling growth rates were generally low and observed spatial patterns generally mirrored interspecific differences in the tolerance to stress induced by salinity and inundation levels. Seedlings in basin forests showed higher growth rates than those in riverine and fringe forests. Mortality was not different among species and unexpectedly low, considering the rates reported in the literature and the supposedly stressful conditions associated with the EN-LN cycle. According to our analyses the magnitude of local anomalies in air temperature and precipitation throughout the EN-LN cycle can be stronger than those expected locally for 2071–2100 in relation to global climate change. Current and expected shifts in precipitation regimes seem the main macroclimatic drivers of ecological changes in mangrove forests thriving in the Pacific coast of Colombia.