Transgenerational exposure to marine heatwaves ameliorates the lethal effect on tropical copepods regardless of predation stress

Marine heatwaves (MHWs) emerge as a severe stressor in marine ecosystems. Extreme warm sea surface temperatures during MHWs are often beyond the optimal thermal range and beyond one generation of tropical coastal zooplankton. However, it is relatively unknown whether transgenerational MHW effect may shape the offspring fitness, particularly in an ecologically relevant context with biotic interactions such as predation stress. We addressed these novel research questions by quantifying the reproductive success, grazing, and survival of copepod Pseudodiaptomus incisus exposed to MHW and fish predator cues (FPC) for two generations (F1 and F2). There were four F1 treatments [(control or F1-MHW) × (no FPC or F1-FPC)] and 16 F2 treatments [(control or F1-MHW) × (no F1-FPC or F1-FPC)] × [(control or F2-MHW × no F2-FPC or F2-FPC)]. In both generations, P. incisus performance was substantially lowered in MHW, but slightly higher in FPC, particularly in control temperature. F2 reproductive success and cumulative faecals were reduced by 20-30% in F1-MHW, but increased by ~2% in F1-FPC. Strikingly, direct MHW exposure strongly reduced survival, but transgenerational MHW exposure ameliorated its lethal effect and was independent of FPC. The increased survival came with a cost of reduced reproductive success, constrained by reduced grazing. The rapid transgenerational MHW acclimation and its associated costs are likely widespread and crucial mechanisms underlying the resilience of coastal tropical zooplankton to MHWs under high predation pressure in the tropical coastal marine ecosystems.