Pattern of seedling emergence and early growth in Avicennia germinans and Rhizophora racemosa along an experimental salinity gradient

Abstract

Salinity is a major driver of emergence and early growth of mangrove propagules. The magnitude of salinity effects may vary across mangrove ecotypes. Using a randomised complete block design in a semi-controlled experiment, this study assessed the effect of salinity (low: 3–5, moderate: 15–17 and high: 34–36 Practical Salinity Unit) on the emergence and early growth of Rhizophora racemosa (G.) Meyer and Avicennia germinans (L.) L., two common mangrove species in West Africa. Per cent emergence, total height and number of leaves were recorded daily for 30 days. Data were analysed using a three-parameter log-logistic distribution and linear mixed models. For both species, results showed significant effects of salinity on per cent emergence and growth variables. There was a negative correlation between salinity and per cent emergence of A. germinans and between salinity and height and number of leaves during the early growth phase of both species. However, the per cent emergence of R. racemosa was significantly higher for moderate salinity. To avoid the risk of dieback from osmotic shock after transplantation, we recommend the use of water of low or moderate salinity in nursery, depending on whether the soil salinity is low or high where the seedlings will be transplanted.