Copepods are a key trophic link in marine food web dynamics, connecting primary producers to higher trophic levels. Recent warming conditions have reduced the concentrations of essential fatty acids in phytoplankton, and it remains unknown if copepods have the adaptive capacity to cope with it. Calanoid species Temora longicornis and harpacticoid Platychelipus littoralis from the North Sea and Westerschelde mudflat were chosen to characterize the fatty acid (FA) biosynthesis response to a polyunsaturated FA (PUFA) deficient diet (Dunaliella tertiolecta) along a temperature gradient. Copepods were fed 13C-labelled D. tertiolecta to quantify de novo FA production at 11, 14, 17, 20, and 23 ˚C. At lower temperatures, T. longicornis had higher absolute FA concentrations (apart from 18:1ω11, 18:1ω9t, 20:5ω3), and de novo FA production compared to P. littoralis. T. longicornis displayed a negative relationship of de novo FA production and survival with temperature, whereas P. littoralis was eurythermic, with several moderate positive relationships (18:1ω11, 18:3ω3, 20:5ω3, 22:6ω3). Although T. longicornis had higher capabilities of bioconversion at lower temperatures, P. littoralis was stable, only increasing de novo FA production at the thermal maximum. This suggests P. littoralis has a greater potential for adaptive resilience under more extreme conditions compared to T. longicornis.
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