Abundance and distribution of mesozooplankton communities on the southern and central Mozambique shelf

Abstract

Mesozooplankton are a crucial component of marine ecosystems, influencing food web dynamics by transferring energy to higher trophic levels. Their abundance and distribution provide valuable information on ecosystem health, productivity, and potential fishing areas. Previous studies using satellite chlorophyll-a data identified Angoche, Sofala Bank, and Delagoa Bight as the most productive areas on the Mozambique shelf. This study aimed to examine mesozooplankton distribution, abundance, biomass, biovolume, and community structure along the Mozambique shelf using data from two ship surveys: (i) SA Agulhas II on Sofala Bank in October 2017 and (ii) Dr. Fridtjof Nansen on Sofala Bank and southern Mozambique in February-March 2018. Semi-seasonal variations were considered, as the 2017 survey occurred in early summer (October) and the 2018 survey in late summer (February-March). Sampling grids differed too with the former focused on the Sofala Bank (central shelf region), whilst the latter was along the Sofala Bank and southern Mozambique shelf. Results showed mesozooplankton abundance and biovolume were consistently higher at nearshore stations in both years. In 2017, peaks in abundance were observed near the Zambezi River mouth and between Quelimane and Pebane on the Sofala Bank. Higher biovolume was found north of Beira and south of the Zambezi Delta. In 2018, the highest abundance and biovolume occurred along the Sofala Bank and Inhambane terrace. Multivariate analysis revealed a link between higher chlorophyll-a) and higher mesozooplankton abundance. These areas experience upwelling events and riverine influence, promoting higher productivity. Copepoda were the dominant mesozooplankton taxa in both years, followed by Appendicularia and Chaetognatha. Interannual variations in environmental drivers, particularly upwelling intensity, river discharge, and nutrient availability, likely influence the distribution and abundance of mesozooplankton communities. The southward extent of the Zambezi River plume may also influence brackish and freshwateradapted taxa. Additionally, the study identified larval stages of commercially valuable decapod crustaceans and fish larvae within the meroplankton community, highlighting the shelf role as a spawning ground and its importance for fisheries. Furthermore, the presence of uncommon/rare taxa like Monstrilloida and Facetotecta indicates a potentially richer fauna than previously documented. This underlines the need for further taxonomic exploration to understand their ecological roles and potential as indicator species.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202