How could thermal stratification affect horizontal distribution of depth-integrated metazooplankton communities in the Gulf of Gabes (Tunisia) ?

The spatial and temporal variability of metazooplankton communities in relation to environmental and trophic factors were studied in the Gulf of Gabes during three periods of increasing thermal stratification in June, July and September. Non-metric multi-dimensional scaling (NMDS) revealed the time and space succession of three zooplankton communities in relation to the degree of thermal stratification. A co-inertia analysis showed the association between these communities and the trophic conditions (abundance and composition of microplankton) driven by stratification. Three divergent communities were evident. The first, characterized by annelid larvae and coastal copepods, was associated with shallow mixed and microplankton-rich water (June, coastal). The second, characterized by euphausiids, amphipods, doliolids and several deep-water copepods, corresponded to highly stratified microplankton-poor water (September). The third, characterized by the most ubiquitous and abundant species, was linked to intermediate water (June deep and July). Temperature and salinity conditions also explained the distribution of key species. Clausocalanus furcatus, Oithona plumifera and Triconia conifera were clearly associated with warm and highly stratified water (September). Enhanced thermal stratification led to higher surface salinity, explaining the emergence of euryhaline taxa such as Oithona plumifera