Human-mediated Changes in a Natural Mangrove Seedling Recruitment and Regeneration Site at Eagle Island, Niger Delta, Nigeria

Abstract

Anthropogenic activities are major cause of mangrove decline globally, we thus postulate that human-mediated activities negatively impact natural mangrove seedling recruitment and regeneration.  The study is a post-impact assessment of a mangrove seedling recruitment site that was converted to a fishpond and other human use. Young mangrove seedlings were physically counted in eight plots established in 2020, and their species diversity was determined using Shannon diversity index.  Similarly, soil samples were collected with a soil augur and sent to the laboratory for chemical and microbial analyses. Human activities on the recruitment site were also identified and listed. The results of the study showed a decline in the number of mangrove and nypa palm seedlings (i.e., species abundance) from 1866 to 242, while the overall diversity (H) decreased from 6.186 to 2.925.  White mangroves had the highest abundance in the eight plots as opposed to the black mangroves that were the most abundant in the 2020 study.  Although, there was no significant difference in chemical composition (F_{7, 104} = 0.39; P = 0.91), there was a spike in cadmium (Cd), iron (Fe), lead (Pb), nitrate (NO₄) and zinc (Zn) concentrations between 2020 and 2023.  There was a total loss of species in four out of eight plots (plots 4-7).  The study revealed that the loss of species is attributed to four human-mediated factors, namely (i) establishment of a fishpond, (ii) bush burning (iii) physical removal of seedlings, and (iv) trampling on young seedlings by pedestrian within the recruitment site.The result of this study implies that increased human activities around deforested mangrove forest prevents natural mangrove seedling recruitment and regeneration, which negatively impacts forest recovery.