Feeding and reproduction of a tropical coastal copepod across warming and copper gradients

Tropical coastal ecosystems in Southeast Asia are facing rapid warming and increasing pollution. Shallow coastal waters now frequently exceed 34 {degrees}C during marine heatwaves, potentially pushing tropical ectotherms beyond their thermal optimum while they are simultaneously exposed to copper (Cu) contamination, especially from aquaculture and shipping activities. However, how warming alters Cu toxicity in dominant tropical zooplankton remains poorly understood. We examined the effects of Cu (0 - 40 {micro}g L-{superscript 1}) across a realistic temperature gradient (26 - 35 {degrees}C) on the calanoid copepod Pseudodiaptomus annandalei, a dominant grazer of coastal plankton communities. Adult survival, cumulative faecal pellet production (as a proxy for energy intake), and cumulative nauplii production were quantified over seven days. No significant effects of temperature or Cu on adult survival were detected, likely reflecting age-dependent variability among wild-collected individuals. In contrast, temperature strongly structured feeding and reproductive performance, which peaked at 29 - 32 {degrees}C and declined at 35 {degrees}C. Cu exposure alone had no significant effects at 26 - 32 {degrees}C due to high variability in responses. At 35 {degrees}C, however, cumulative nauplii production decreased significantly at 30 {micro}g Cu L-{superscript 1} but increased at 20 {micro}g Cu L-{superscript 1}, while faecal pellet production was reduced in Cu-exposed copepods. These findings indicate that warming can modify contaminant effects in tropical zooplankton and highlight the importance of incorporating realistic thermal regimes and natural population variability into ecological risk assessments under climate change.