Relationship between Fish Fauna and Plant Communities in the Djiri River, Brazzaville, Republic of Congo

Abstract

The study of flora-fauna relationships is, of course, extremely complex, as it should consider all organisms living in the environment and incorporate fundamental knowledge of vegetation, species biology, ecological niches, diets, reproduction, and population dynamics. The disappearance of certain animals or the decline in their abundance due to poaching or habitat degradation impacts the survival of some plant species. Indeed, certain animals play a crucial role in either plant fertilization or dispersal. The overall objective of this study is to contribute to our understanding of the relationship between the surrounding flora and the fish fauna of the Djiri River. Specifically, the study focuses on (i) characterizing plant communities, (ii) cataloging the fish fauna, and (iii) assessing the relationships between plant communities and the distribution of fish fauna. The biological material consists of fish and tracheophytes recorded in the Djiri River's main channel and bed. For the flora, the classification adopted is based on APG IV (2016) for spermatophytes and PPG I (2016) for pteridophytes. The taxonomic nomenclature is in accordance with Lebrun and Stork (1991-2015). Data collection was carried out within a sampling design consisting of three contiguous stations of varying sizes, located on the lower reaches of the Djiri River (Fig. 1). The stations were delineated according to vegetation type. The floristic inventory followed a qualitative method in which only the presence of a species at each site was recorded. The choice of environmental descriptors is based on existing knowledge of the relationship between the environment and fish populations. The biological spectrum of the vascular flora of the Djiri River (Fig. 4) highlights a relative dominance of phanerophytes (39.68%) in the study area. Phanerophytes are followed by geophytes (19.05%), hemicryptophytes (14.29%), hydrophytes and therophytes (9.52% each), and chamaephytes (7.94%). Analysis of the dendrogram based on Jaccard dissimilarity (Fig. 6) revealed a strong floristic dissimilarity among the different surveyed sites. This indicates a diversity of plant communities within the study area. The study of the ichthyofauna showed that biodiversity is very high with 99 species of fish recorded, the ratio of the number of species to the number of families. the significant occurrence of spore-bearing Tracheophytes suggests a particular microclimate linked to the site's humidity. The strong floristic dissimilarity of the inventoried sites confirms the diversity of the original vegetation types. The presence of hydrophytes offers ideal living conditions for thousands of species, providing nurseries and camouflage, thus attracting numerous predators and leading to silent competition and predation in this aquatic environment.