Abstract
Reduced seawater pH and changes in carbonate chemistry associated with ocean acidification (OA) decrease the recruitment of crustose coralline algae (CCAcf.), an important coral-reef builder. However, it is unclear whether the observed decline in recruitment is driven by impairment of spore germination, or post-settlement processes (e.g. space competition). To address this, we conducted an experiment using a dominant CCA, Porolithon cf. onkodes to test the independent and combined effects of OA, warming, and irradiance on its germination success and early development. Elevated CO2 negatively affected several processes of spore germination, including formation of the germination disc, initial growth, and germling survival. The magnitude of these effects varied depending on the levels of temperature and irradiance. For example, the combination of high CO2 and high temperature reduced formation of the germination disc, but this effect was independent of irradiance levels, while spore abnormalities increased under high CO2 and high temperature particularly in combination with low irradiance intensity. This study demonstrates that spore germination of CCA is impacted by the independent and interactive effects of OA, increasing seawater temperature and irradiance intensity. For the first time, this provides a mechanism for how the sensitivity of critical early life history processes to global change may drive declines of adult populations of key marine calcifiers.
Highlights
The persistence of marine benthic populations depends on the success of reproduction and early life history processes, such as fecundity, spore/gamete release, germination, settlement, and recruitment [1,2,3]
As supply-side ecology processes are fundamental to marine populations [57], our results highlight the importance of studying adults but other stages of the life cycle to better understand the impacts of ocean acidification and warming on reef-building processes and reef resilience
Future studies should consider the relative contribution of space competition by filamentous algae and spore germination on Crustose coralline algae (CCA) recruitment, preferably in natural habitats where the natural variability in ecological processes can be considered, variability that cannot be incorporated in laboratory experiments
Summary
The persistence of marine benthic populations depends on the success of reproduction and early life history processes, such as fecundity, spore/gamete release, germination, settlement, and recruitment [1,2,3]. Understanding how global climate change affects marine populations requires consideration of the ecology of early stage processes. Coralline algae germination and climate change they attach to the substrate and germinate. Subsequent cell division occurs, a germination disk is formed, and in the case of calcifying red algae, calcification takes place further cementing the crusts to the substrate, completing the settlement process [5,6,7]. Despite the fundamental importance of early life stages to most marine organisms, there is a critical knowledge gap of the interactive effects of climate change stressors (ocean acidification and warming) with other environmental factors on the development of marine algae Despite the fundamental importance of early life stages to most marine organisms, there is a critical knowledge gap of the interactive effects of climate change stressors (ocean acidification and warming) with other environmental factors on the development of marine algae (e.g. [9]), on tropical populations
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