The role of sea blight (Suaeda monoica forssk. ex gmel) in recovery of degraded mangroves at Mwache Creek, Kenya

Abstract

Given the subsequent degradation and potential encroachment of mangrove ecosystems, the slow recovery nature of these systems and huge restoration failure efforts (100% mortality after planting in some cases) of mangrove ecosystems, quantification of the role of early colonizing vegetation to mangrove systems recovery is necessary. While sea blight (Suaeda monoica) is common in the degraded sites of Mwache Creek mangrove forest in Kenya and within its growing patches a marked regeneration of mangrove seedlings, its role in mangrove forest recovery is not known. This study assessed the effects S. monoica initiates on the biotic and abiotic factors of the degraded mangrove system to enable subsequent re-entry and functional development of the system as a contribution to mangrove intertidal restoration. Using stratified systematic sampling, in sites of naturally growing Avicennia marina Forssk. (Vierh), bushes of S monoica, adjacent open canopy and adjacent bare sites as controls respectively, measurements of sediment conditions, vegetation structure, species composition, regeneration, faunal densities and diversities, soil; structure, bulk density and carbon stocks were determinants of recovery. Except for nutrients, significant differences in all sediment conditions (p<0.05) were observed amongst the four sites. Fauna densities and diversity were higher in the vegetated sites than their respective adjacent controls and their numbers significantly different in all the sites. A. marina site had the highest juvenile mangrove vegetation density and higher live biomass proportion, but there was no significant difference (p˃0.05) in these two parameters between the vegetated sites. The bare areas had the highest bulk densities and low soil organic carbon, while the two vegetated sites had higher ecosystem carbon stocks (t ha1) than their respective controls. The results suggest that S. monoica sites are functionally developing towards and becoming more akin to the natural mangrove sites. The primary mechanism proposed for improving recovery success is sediment stabilization and hydrology moderation provided by S. monoica bushes. These findings support the use of pioneer species where natural regeneration has been impeded as a tool for management in conservation and restoration of the functional integrity of degraded mangrove habitats.