Figure - available from: Frontiers in Marine Science
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Diagram of the settlement chamber design used in this study (see also Kuffner et al., 2006 and Ritson-Williams et al., 2020) with settlement tile and larvae placed inside. The arrow demonstrates progression of swimming larvae through to settlement and metamorphosis on the substrate tile. Chamber made from PVC plastic tubing capped with mesh at either end (100 or 180 µm). One mesh cap can be removed to insert larvae and settlement tile into the chamber.
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Deoxygenation is emerging as a major threat to coral reefs where it can have catastrophic effects, including mass coral mortality. Some coral species cannot survive more than a few days of exposure to low oxygen conditions, while others can tolerate deoxygenation for weeks, suggesting that coral tolerance to lowered dissolved oxygen (DO) concentrat...
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Citations
... Furthermore, the successful completion of cnidarian early life history stages hinges upon O 2 -dependent biological processes, such as ciliary motion and cellular respiration (Ricardo et al. 4 2016; Kitchen et al. 2020) . These processes are sensitive to hypoxia in adult cnidarians (Murphy and Richmond 2016;Alva García et al. 2022;Pontes et al. 2023) , and while transcriptomic and behavioral evidence suggests that larvae are similarly harmed (Jorissen and Nugues 2021;Alderdice et al. 2022b;Mallon et al. 2023) , physiological data from a diversity of species are critically needed to better characterize these responses. In particular, comparing the effects of hypoxia on early life stages from cnidarians displaying variation in sexual system (i.e., gonochoric vs. hermaphroditic) and reproductive mode (i.e., spawner vs. brooder) is needed to better predict outcomes in future seas. ...
... Larvae of other cnidarians, including the corals Acropora cytherea and A. pulchra , and the jellyfish Aurelia aurita, also display temporary reductions in normal swimming behavior following hypoxia exposure, suggesting shared behavioral responses to hypoxia that may be associated with conserved effects on metabolism (Jorissen and Nugues 2021) . However, hypoxia does not affect larval swimming behavior in all coral species (Alderdice et al. 2022b;Mallon et al. 2023) , indicating some species-specific differences in susceptibility that may influence the taxonomic composition of future reefs. ...
... Specifically, smaller juveniles sizes are correlated with lower survival (Goodbody-Gringley et al. 2018) , poorer competitive performance for space on the benthos (Tanner 1997) , and lower fecundity upon reaching sexual maturity (Marshall and Keough 2007) in corals and other marine invertebrates. Indeed, larvae of the coral Orbicella faveolata exposed to hypoxia display reductions in juvenile survival (Mallon et al. 2023) . It was surprising that N. vectensis juveniles exposed to hypoxia during the larval stage displayed smaller sizes than controls, particularly given that most of the other metrics quantified here were unaffected in this species. ...
Seawater hypoxia is increasing globally and can drive declines in organismal performance across a wide range of marine taxa. However, the effects of hypoxia on early life stages (e.g., larvae and juveniles) are largely unknown, and it is unclear how evolutionary and life histories may influence these outcomes. Here, we addressed this question by comparing hypoxia responses across early life stages of three cnidarian species representing a range of life histories: the reef-building coral Galaxea fascicularis , a broadcast spawner with horizontal transmission of endosymbiotic algae (family Symbiodiniaceae); the reef-building coral Porites astreoides , a brooder with vertical endosymbiont transmission; and the estuarine sea anemone Nematostella vectensis , a non-symbiotic broadcast spawner. Transient exposure of larvae to hypoxia (dissolved oxygen < 2 mg L ⁻¹ for 6 h) led to decreased larval swimming and growth for all three species, which resulted in impaired settlement for the corals. Coral-specific responses also included larval swelling, depressed respiration rates, and decreases in symbiont densities and function. These results indicate both immediate and latent negative effects of hypoxia on cnidarian physiology and coral-algal mutualisms specifically. In addition, G. fascicularis and P. astreoides were sensitized to heat stress following hypoxia exposure, suggesting that the combinatorial nature of climate stressors will lead to declining performance for corals. However, sensitization to heat stress was not observed in N. vectensis exposed to hypoxia, suggesting that this species may be more resilient to combined stressors. Overall, these results emphasize the importance of reducing anthropogenic carbon emissions to limit further ocean deoxygenation and warming.
