The Southern Ocean is one of the harshest environments on the earth, yet it thrives with life. Krill is thought to be the pivotal organism in the Southern Ocean food web, as it channels the carbon produced by algae to higher trophic levels. However, mesozooplankton probably has a similar function in the Southern Ocean ecosystem. The ecosystem based management which is operated in the Southern Ocean focusses on krill and often neglects other carbon pathways. This study is set up to analyse how important mesozooplankton is in the food web of the south-eastern Weddell Sea, how its abundance and community structure is related to sea-ice and what this implies for the future management of the Southern Ocean. To answer these questions a combination of state-of-the-art research methods were used, including a size-class based approach in combination with C:N ratio analysis, bulk-stable isotope analysis, taxonomic analysis and literature studies. The biomass of mesozooplankton was found to exceed the biomass of krill in the Weddell Sea sampling area, and therefore has a higher contribution to the carrying capacity of the ecosystem. The most abundant mesozooplankton species was Calanoides acutus which corresponded with the size fraction with the highest biomass, namely 1000 μm. The undersea-ice mesozooplankton community (0-2 meter) was significantly different than in the 0-50 water depth layer. The C:N ratio was the highest in the 250 μm size fraction in the 0-2 meter. Regarding environmental variables, the interaction of chlorophyll a and sea-ice ridges best explained the species distribution of the 0-2 meter water layer. Species from the 0-2 meter depth stratum were found to be more dependent on sea-ice algae than the species in the 0-50 meter depth stratum. The health indicators of CCAMLR do not cover the whole ecosystem, as only high trophic level species are used. (Meso)zooplankton would be a good bottom-up health indicator, functioning as early warning indicator. Mesozooplankton and sea ice both fit in the WSMPA criteria and the general objectives of the WSMPA. It is concluded that mesozooplankton should be monitored and used as a health indicator for the ecosystem in the WSMPA.