Factors associated with fish mass mortality events in North African freshwater ecosystems, Morocco as a case study

Freshwater biodiversity plays a pivotal role in maintaining ecological equilibrium and furnishing numerous ecosystem services to diverse organisms. However, these intricate ecosystems face imminent threats from various phenomena, including global warming and anthropogenic activities, leading to heightened occurrences of ecological disasters, notably mass mortality events among aquatic fauna. This study represents the first comprehensive investigation and high-frequency monitoring of the ecological disaster of fish mass mortalities in Africa. We focused on instances of fish mass mortality events (FMME) in North African freshwater ecosystems and estuaries in 2019, focusing on Morocco, as the country most endowed with aquatic ecosystems in North Africa. Seven aquatic ecosystems exhibited susceptibility, impacting a total of 10 species. Notably, 94.59% of the minimum estimated 171,064 deceased fish individuals belonged to non-native species. Lepomis macrochirus stood out as the species most profoundly impacted, representing a substantial 63.36% of the total mortalities, with Lepomis gibbosus following closely at 27.64%. Comprehensive measurements of water quality parameters, encompassing temperature, dissolved oxygen, pH, salinity, among others, were conducted, and their associations with the affected ecosystems were analyzed. Our findings suggest that the predominant cause of the majority of FMME was attributed to the critically low concentrations of dissolved oxygen, likely resulting from anthropogenic and climatic pressures. Overall, FMME can considered as a potential threat to Moroccan freshwater fish diversity and communities.