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Climate change–induced temperature increase may influence the ecotoxicity of agricultural herbicides such as atrazine and consequently negatively impact aquatic biota. The objective of this study was to assess the effects of increased temperature on the ecotoxicity of atrazine to diatom community structure and stream periphyton load using laboratory microcosm experiments. A natural periphyton community from the Mukwadzi River, Zimbabwe, was inoculated into nine experimental systems containing clean glass substrates for periphyton colonisation. Communities were exposed to 0 µg∙L-1 (control), 15 µg∙L-1 and 200 µg∙L-1 atrazine concentrations at 3 temperature levels of 26°C, 28°C and 30°C. Periphyton dry weight and community taxonomic composition were analysed on samples collected after 1, 2 and 3 weeks of colonisation. A linear mixed-effects model was used to analyse the main and interactive effects of atrazine and temperature on dry mass, species diversity, evenness and richness. Temperature and atrazine had significant additive effects on species diversity, richness and dry mass. As temperature increased, diatom species composition shifted from heat-sensitive species such as Achnanthidium affine to heat-tolerant species such as Achnanthidium exiguum and Epithemia adnata. Increasing temperature in aquatic environments contaminated with atrazine results in sensitive and temperature-intolerant diatoms being eliminated from periphyton communities. Climate change will exacerbate effects of atrazine on periphyton dry mass and diatom community structure.

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The rapidly spreading Australian red claw cray sh Cherax quadricarinatus in the Zambezi Basin is a cause for concern considering its potential impacts. The assessment the impacts of C. quadricarinatus critical for the prioritisation of policy and management actions in Africa where literature on impacts of C. quadricarinatus is generally scant. We quanti ed the socioeconomic impacts conferred by C. quadricarinatus on artisanal gillnetting shery in Lake Kariba to validate anecdotal sher reports regarding cray sh damage to sh catch on static gillnets. From the catch assessments with registered shers, sh catch composition, catch per unit effort (CPUE), cray sh entangled on gillnets CPUE, damaged sh CPUE, and damaged areas were recorded. Basin 2 had signi cantly higher CPUE with respect to sh catch and cray sh, as well as catch damage than other basins. The damage by cray sh on sh was recorded in all the basins except in Basin 5. Damage was signi cantly correlated with the abundance of cray sh. The most frequently affected species was Oreochromis niloticus. On all sh species, eyes, guts and the tail were the frequently damaged parts. Due to C. quadricarinatus damage, shers are losing 212 tonnes per year which translates to US$ 512 352.92 in Lake Kariba. This lost amount is signi cantly high, considering the total income per household which is mainly contributed by shing. The lack of damage in Basin 5 is likely due to shers developing adaptive new techniques which are less likely to be affected by cray sh. This study is the rst in Africa to quantify the socio-economic losses due to cray sh in the eld, and the rst globally to derive observed costs for C. quadricarinatus. Data from this study have huge conservation and management implications, as cray sh threaten food security as well as incur personal losses to shers via damage-related costs.

Many small reservoirs exist throughout Southern Africa, and with adequate management have the potential to contribute significantly to food security. The fisheries and limnology of the newly created Chitsuwa Reservoir in Zimbabwe were studied with the objective of generating information to support the development, management and sustainable use of fisheries to enhance the socio‐economic status of riparian communities. Based on gill nets of various mesh sizes, it was confirmed that the reservoir is presently inhabited by a fairly diverse fish community comprising ten species belonging to five families (Clarias gariepinus; Coptodon rendalli; Labeo cylindricus; Marcusenius macrolepidotus; Micropterus salmoides; Momyrus longirostris; Oreochromis mossambicus; Oreochromis niloticus; Serranochromis microcephalus; and Tilapia sparrmanii). Oreochromis niloticus dominated the reservoir with respect to both abundance, biomass and catch. The index of relative importance revealed O. niloticus and M. macrolepidotus were the most important species. Results from the Canonical Correspondence Analysis revealed a clear division of the fish species that followed the environmental variables. Although fisheries may benefit from the invasive M. salmoides and the established O. niloticus, their presence in the reservoir is a cause for concern for conserving native congeneric species that risk extirpation through documented mechanisms. The results of the present study suggest sound management of the reservoir is required to raise its potential of supporting the livelihoods of the surrounding communities with a predicted annual fish yield of 61.5 t/year. Management of this reservoir should involve the local communities, empowering them so that they practice sustainable non‐destructive fishing methods.