Understanding saltmarsh distribution and mangrove co-occurrence at tropical estuaries

Abstract

Saltmarshes are coastal ecosystems composed of herbaceous vegetation that provide nursery grounds for several estuarine species, coastal protection by wave attenuation, carbon sinks, and facilitate mangrove propagules establishment and survival. Saltmarshes are studied mainly in high-latitude estuarine regions of developed countries, while in tropical systems, saltmarshes are widely overlooked due to the dominance of mangrove forests. This study aimed to map the occurrence of saltmarshes in three tropical estuaries and assess mangrove propagules and seedlings within tropical Spartina spp. dominated saltmarshes. We tested the hypotheses that (1) the abundance of propagules and seedlings within saltmarshes would be higher than in non-vegetated intertidal flats and (2) mangrove propagules and seedlings abundance would be higher in denser and taller saltmarshes. Mangrove propagules and seedlings of Avicennia spp., Laguncularia racemosa, and Rhizophora mangle were mainly found within saltmarshes when compared to non-vegetated adjacent tidal flats. There was no significant effect of saltmarsh height and density on mangrove seedling abundance. The present study showed that saltmarsh facilitates mangrove colonization in mangrove-dominated regions. Future studies on tropical estuaries should assess if mangrove propagules and seedlings found on saltmarsh patches achieve the reproductive phase and promote the progradation of mangrove forests.