Eco-Functional Benthic Biodiversity Assemblage Patterns In The Guinea Current Large Marine Ecosystem
Functional diversity, an important component of biodiversity, has in recent years engaged global attention. This is in great part due to the mechanistic understanding achieved from functional diversity studies in the face of accelerated global biodiversity changes ascribed primarily to anthropogenic drivers. The exigency of the situation has stimulated biodiversity-ecosystem functions (B-EF) studies to elucidate ecosystem processes and services that are at threat notably in the marine ecosystem. The marine benthos is the largest ecosystem on earth and supports the highest phylogenetic diversity but has rather witnessed comparatively low attention in the B-EF studies than the terrestrial counterpart. This thesis is aimed at i) quantifying benthic functional diversity (using biological trait analysis) and assemblages along abiotic gradients in the Guinea Current Large Marine Ecosystem (GCLME); and ii) examining the impact of bottom trawling for demersal fishes on the functional structure of epibenthic fauna along bathymetric gradients. In achieving the above-mentioned objectives, epibenthic fauna of bottom trawl samples were collected from Ghana to western Nigeria‘s continental shelf in 2003. Further, macrobenthic infauna and abiotic samples were collected from coastal waters of Guinea Bissau to Gabon in 2007. Each processed dataset was treated as a stand-alone in the thesis. In decomposing the assemblage patterns, suites of univariate and multivariate statistics were employed. The results indicated 381 macobenthic species comprising polychaetes (61.15% richness and 55.15% abundance), crustaceans (18.64% richness and 28.02% abundance), molluscs (9.19% richness and 2.23% abundance), echinoderms (2.63% richness and 1.84% abundance) and =others‘(8.39% richness and 12.76% abundance). Functional diversity analysis indicated spatial differences in eco-functional traits namely small body size, solitary lifestyle, burrowing and deposit-feeding, and these traits dominated the assemblage especially from Ghana to Benin. The results suggest that these areas are potential surrogates of allochthonous organic material possibly driving pelagic productivity that is translated to the benthos. Significant (p<0.05) relationship was found between functional traits (also species diversity) and sediment parameters (i.e., nitrate, calcium, magnesium, organic carbon, silt & clay). These abiotic variables largely implicate productivity and climate change models as principal community drivers, and are likely to impact ecosystem functions directly by altering B-EF relationship. Inferentially, the results indicated an unstable, dynamic, productive and low biomass-supported ecosystem Guinea Current Large Marine Ecosystem (GCLME), reflecting in the small body size solitary burrow- dwelling deposit-feeding organisms, which potentially exert the strongest influence on ecosystem processes (e.g., nutrient remineralization). These species used multiple adaptative strategies including trophic, lifestyle, anatomical and morphological in the prevailing environment. Bottom trawled epibenthic sample analysis showed significant difference (p=0.002; ANOSIM) of assemblages along bathymetric gradient, notably between shallow- depth (11-30m) and deep-depth (51-70m). Functional analyses showed dominance of carnivores (28% contribution), opportunistic/scavenging (9%) and herbivore (9%) in shallow waters, while filter-feeders (18%) dominated deep waters suggesting gradient in structuring forces. The high abundance of motile epibenthic fauna (64%) is suggestive of an unstable substrate and turbulent system supporting motile carnivores and filter-feeding organisms. The evidence of trophic interactions between demersal fishes and epibenthic fauna occurred ideally in most tolerable and favorable zone (i.e. mid-depth). Abundance-Biomass Comparison (ABC) analyses indicated an ecosystem which is stressed (66.56%) with the degree of stress inversely related to increasing water depth. The findings of this thesis have important implications for marine biodiversity conservation and resource management approach in the GCLME.
