Interactive effects of marine heatwave and fish predator cues on
F1 generation
Results in the F1 generation mostly confirmed and strengthened major
findings of severe MHW impacts on P. incisus performance which
were observed in our previous study focusing on the interactive effects
of MHW and FPC on the life history traits of P. incisus for an
entire one generation (Truong et al., 2020). Indeed, MHW exposure
increased mortality, lowered hatching success, and cumulative nauplii
and faecals. MHW increased mortality, which may be a result of
physiological dysfunctions such as the collapse of ATP synthesis
(Harada, Healy, & Burton, 2019), the damage of macromolecules (Somero,
2010), the higher cellular oxygen demand than the capacity of oxygen
delivery (Pörtner, 2010). The reduced performance of P. incisuswas particularly strong for reproductive success with
~30-60% reduced the size of egg clutches, the
percentage of females produced hatched eggs, hatched nauplii from a
clutch, and cumulative nauplii under direct exposure to MHW are
widespread in tropical copepods (Doan et al., 2019; Nguyen et al.,
2020). The lower reproductive outputs are generally related to reduced
grazing, thereby energy intake. While we observed a lower cumulative
faecals of F1 P. incisus , the correlation of cumulative faecals
and nauplii was insignificant, but a positive correlation of these two
parameters was observed in F2 P. incisus .
The FPC presence caused a small increase in females with successfully
hatched eggs, the number of nauplii hatched per clutch of P.
incisus , and the FPC effect was stronger at 30°C than at 34°C, which
may be an adaptive response to predators. For example, predation can
cause 50-75% mortality in marine copepods, and increased reproductive
outputs are a general mechanism to compensate for consumptive mortality
(Hirst & Kiorboe, 2002). Importantly, the FPC-induced increase in
nauplii production only occurred at the control temperature, but not
under MHW may result from the reduced grazing as indicated by the
MHW-induced lower cumulative faecals and higher energy demand for
metabolism (Low et al., 2018). Stronger MHW-induced reductions in
cumulative nauplii and faecals were observed in FPC-exposed P.
incisus in our previous study (Truong et al., 2020), in which we could
quantify both parameters for an entire adult lifespan.