Temperature increase alters fatty acid composition and has negative effects on reproductive output of the benthic copepod Microarthridion littorale (Copepoda: Harpacticoida)

Abstract Copepods are marine invertebrates with a key role at the basis of marine food webs due to their high biomass as well as their elevated fatty acid (FA) content, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two FA which have a well demonstrated role in growth and reproduction in marine organisms. Temperature is a key driver of organisms fitness as well as ecosystem functioning and sea surface temperature is expected to rise under all CO2 emission scenarios. Thus, understanding how copepods will response to such changes is crucial given their role in marine food webs. While the majority of research has focused on planktonic copepod species, less is known for benthic species, particularly non-model species. In this study we expose Microarthridion littorale, an intertidal benthic copepod to a temperature gradient (12, 15, 18, 21 and 24 °C) including current environmental variability as well as future scenarios. Individuals were retrieved from a mudflat in the Westerschelde estuary (51°21′ 24′′ N, 3° 42′ 51′′E) and cultured at lab conditions. Survival and FA were measured after 18 days exposure. Growth rates and nauplii production were also measured for each temperature treatment. We found decreased survival, EPA and DHA content with increased temperature as well as increased growth rates and detrimental effects for nauplii production. Benthic copepods are prey for many juvenile fish, any changes in their biomass as well as their FA composition in response to temperature changes could therefore amplify to higher trophic levels with important consequences for food web functioning.