Department of Fisheries and Ocean Sciences

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Browsing Department of Fisheries and Ocean Sciences by Subject "Abundance"

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    Spatial distribution and diversity of soft-bottom benthic invertebrates from demersal trawl surveys off the coast of Namibia
    (University of Namibia, 2022) Mateus, Ndamononghenda Lipuleni
    This study assessed the spatial distribution and diversity of soft-bottom benthic invertebrates collected during the Ministry of Fisheries and Marine Resources' annual monkfish, hake, and deep-sea red crab demersal surveys for the years 2018-2020, along the northern, central, and southern coast of Namibia. The study aimed to determine the spatial distribution and diverse composition of soft-bottom benthic invertebrates as affected by environmental factors such as depth, latitude, and temperature. 324 trawls were sampled, resulting in the identification of 130 taxa belonging to 17 classes, namely Arthropoda (44 species), Mollusca (33 species), Echinodermata (28 species), Cnidaria (23 species), Porifera (5 species), Annelida (4 species), Chordata (2 species), Sipuncula (1 species) and Bryozoa (1 species). The diversity of benthic invertebrate taxa along Namibia's coast was found to increase in a south-to-north direction. High abundances of arthropods were observed in the northern region, whilst ascidians dominated the central region, and Brissopsis lyrifera capensis and Suberites dandelenae in the south. In terms of depth, relatively high taxa richness was observed between the inner and middle shelf (101 - 400 m). Benthic invertebrate diversity distribution across regions and depths varied for each survey. For the monkfish survey, diversity was significantly different across regions (Kruskal test = 5.79; df = 2; SD = 0.44; p < 0.01) but was not significant across depths (Kruskal test = 1.23; df = 7; SD = 0.44; p = 0.36). From the hake survey, diversity was significant across both, region (Kruskal test = 35.24; df = 2; SD = 0.55; p < 0.001) and depth (Kruskal test = 17.78; df = 6; SD = 0.55; p < 0.007). The crab survey, diversity overlap across the regions (Kruskal test = 4.46; df = 3; SD = 0.33; p = 0.32) and depths (Kruskal test = 6.36; df = 3; SD = 0.33; p = 0.95). x The PERMANOVA test revealed a significant difference in the community structure across regions (Pseudo-F = 9.09, p < 0.001) and depths (Pseudo-F = 10.34, p < 0.001). DistLM of the environmental factors showed a weak correlation with the benthic invertebrate assemblage overall AICs reveal depth and latitude were strong predictor variables in the taxa assemblage. The study provides important information on taxonomic composition, spatial distribution, and abundance of benthic invertebrates along the Namibian coast. This thesis contributes a comprehensive assessment of offshore benthic invertebrate community structure and can be used to further inform marine conservation and spatial planning assessments along the Namibian coast.