Rapid multi-generational acclimation of coralline algal reproductive structures to ocean acidification

The future of coral reef ecosystems is under threat because vital
reef-accreting species such as coralline algae are highly susceptible to
ocean acidification. Although ocean acidification is known to reduce
coralline algal growth rates, its direct effects on the development of
coralline algal reproductive structures (conceptacles) is largely unknown.
Furthermore, the long-term, multi-generational response of coralline algae
to ocean acidification is extremely understudied. Here, we investigate how
mean pH, pH variability and the pH regime experienced in their natural
habitat affect coralline algal conceptacle abundance and
size, across six generations of exposure. We show that second
generation coralline algae exposed to ocean acidifcation treatments had
conceptacle abundances 60% lower than those kept in present day
conditions, suggesting that conceptacle development is initially highly
sensitive to ocean acidification. However, this negative effect of ocean
acidification on conceptacle abundance disappears after three generations
of exposure. Moreover, we show that this transgenerational acclimation of
conceptacle development is not facilitated by a trade-off with reduced
investment in growth, as higher conceptacle abundances are associated with
crusts with faster growth rates. These results indicate that the potential
reproductive output of coralline algae may be sustained under future ocean
acidification.