Relationship between habitat factors, nutrient loads, and plankton community structure in varied mangrove swamps

It is widely acknowledged that mangroves regenerate and export nutrients to adjacent habitats, including marine waters. However, there are persisting claims, though less verified, that nipa palm swamps are nutrient-sapping habitats in the Niger Delta—that the palm has a poor leaf litter regime and refractory, slow-decomposing litter. This study compared variations in nutrient (nitrate and phosphate) levels and the plankton assemblages in a native red mangrove reserve and nipa palm forest in Kono Creek, a bypass of the lower reach of the Imo River in the eastern Niger Delta. Forty-eight water samples for nutrient analysis were collected for six months (January 2017–June 2017). This study provided essential baseline data on nitrate and phosphate levels in two mangrove floristic landscapes. With a composite N: P ratio of 7.2:1, relatively higher nitrate concentrations were recorded in the nipa palm forest, while phosphate values were highest in the native mangrove forest swamp. However, neither of the nutrients showed any significant difference (P > 0.05) across the sampled locations and between flood and ebb waters. Phytoplankton in the nipa palm swamp had relatively more individuals but less species richness and diversity. In contrast, zooplankton were represented by more individuals and had higher species richness and diversity in the conserved red mangrove swamp. We hypothesize that the proximity of the studied sites, tidal distribution, and skewed spatial microalgae and macroalgae nutrient consumption are among the spatial nutrient equivalence habitat drivers. It was impossible to determine whether the native red mangrove and nipa palm swamps were sinks or exporters of nitrate and phosphate. Thus, experimental investigations into the variations in the nutrient regeneration and export rates for both coastal swamp forests would provide insight into this. The implications for primary productivity and environmental monitoring in regions where native mangroves are shrinking due to human activities are discussed.