Conclusions and perspectives
There is a great concern that the hyperdiverse tropical ecosystems may
be collapsed under the cumulative impact of multiple stressors (Barlow
et al., 2018; Dinh, 2019; Worm et al., 2006). Among others, MHWs are
becoming a new but severe threat, which sometimes causes massive and
widespread mortality across taxa (Garrabou et al., 2009; 2019). However,
we know much less about how MHW may affect key grazers and intermediate
prey in the coastal marine ecosystems such as copepods, particularly in
an ecologically relevant context with biotic interactions (Truong et
al., 2020). Our results contribute to this by highlighting the severe
direct effect of MHWs on reproduction and grazing P. incisus , a
common copepods species in the tropical coastal ecosystems of Southeast
Asia. Strong mortality together with reduced reproductive success are
important mechanisms underlying the reduced copepod abundance under MHWs
(Evans, Lea, Hindell, & Swadling, 2020). Consequently, MHWs may
substantially reduce the secondary biomass production of the
zooplankton, which fuels resources and energy to the vast majority of
other marine predators such as corals, crustaceans, and fish (Arimitsu
et al., 2021; Chew et al., 2012). Most importantly, our results suggest
that P. incisus may evolve in a rapid transgenerational
acclimation to MHW, which fully ameliorated its lethal effect in the
second generation. The thermal acclimation comes with a cost of reduced
reproduction, and grazing may be a crucial and widespread mechanism for
invertebrates coping with the transient effects of heatwaves (Cavieres
et al., 2020; Dinh et al., 2020; Doan et al., 2019). Interestingly, fish
predator cues played a minor role in shaping both direct and
transgenerational effects of MHWs, highlighting the dominant MHW effects
on P. incisus . Given the widespread and severe effects of MHWs on
coastal invertebrates, the dominant effect of MHWs is likely widespread
with implications for ecological risk assessment under the rapidly
changing environment of the tropical coastal ecosystems.