Ocean Acidification Effects on Marine Invertebrate Reproductive Success

Ocean acidification, driven by the uptake of anthropogenic CO₂ by seawater, is lowering ocean pH and altering carbonate chemistry with profound consequences for the reproductive cycle of marine invertebrates. Successful gametogenesis, sperm motility, fertilisation and early larval development depend on tightly regulated intracellular pH, ion exchange and enzymatic pathways. Acidified conditions can reduce sperm motility, disrupt ion homeostasis and impair gamete interactions, leading to lower fertilisation rates and compromised larval viability. Responses are highly taxa-specific: echinoderms often exhibit pronounced sensitivity at fertilisation, while many molluscs show varied resilience influenced by population history and genetic variability. Interactions with other stressors, such as UV-filter pollutants or temperature anomalies, further exacerbate reproductive impairments. Understanding these effects is critical for predicting population trajectories, managing fisheries and designing conservation strategies under rapidly changing ocean conditions.

Research from Nature Portfolio

Investigations into the Mediterranean sea urchin have revealed that exposure to harmful algal-bloom toxins can trigger elevated nitric oxide production in gonadal tissues, leading to protein nitration, reduced fertilisation success and developmental anomalies in offspring that persist beyond the bloom period. This work highlights subtle yet lasting transmission of reproductive damage across generations.

Studies of male fitness landscapes under elevated pCO₂ have demonstrated that ocean acidification alters the competitive hierarchy of sperm performance in sea urchins. Males that rank highest under current conditions may lose fertilisation advantage in acidified seawater, indicating rapid shifts in selective pressures on reproductive traits.

Comparative analyses of oyster populations subject to varying salinity and pCO₂ regimes show that acidification can either offset or amplify freshening effects on sperm motility, with distinct responses between long-established and recently invaded populations. Intra- and inter-population variability suggests scope for selection and local adaptation in changing coastal environments.

Ocean Acidification Effects on Marine Invertebrate Reproductive Success publication trend

The graph below shows the total number of articles in ocean acidification effects on marine invertebrate reproductive success across all publications each year (not limited to Nature Index journals).

Technical terms

Ocean acidification: The process by which increased atmospheric CO₂ dissolves in seawater, lowering pH and altering carbonate ion availability.

Gametogenesis: The developmental process by which marine invertebrates produce mature gametes (sperm and eggs).

Fertilisation success: The proportion of gamete encounters that result in zygote formation under given environmental conditions.

Sperm motility: The capacity of sperm cells to move effectively through seawater, a key determinant of fertilisation probability.

Intracellular pH (pHi): The internal acidity of a cell, which regulates enzymatic activity and motility in gametes.

Nitric oxide (NO): A reactive signalling molecule that, in excess, can modify proteins and disrupt normal reproductive processes.

References

1. Impacts of UV-filter pollution and low pH: Sperm and adult biomarkers in the mussel Mytilus galloprovincialis in a multi-stressor context.. Journal of Hazardous Materials (2024).
2. Subtle reproductive impairment through nitric oxide-mediated mechanisms in sea urchins from an area affected by harmful algal blooms. Scientific Reports (2016).
3. Ocean acidification changes the male fitness landscape. Scientific Reports (2016).
4. Sperm motility of oysters from distinct populations differs in response to ocean acidification and freshening. Scientific Reports (2019).
5. Ocean acidification does not overlook sex: Review of understudied effects and implications of low pH on marine invertebrate sexual reproduction. Frontiers in Marine Science (2022).
6. Sperm Motility Impairment in Free Spawning Invertebrates Under Near-Future Level of Ocean Acidification: Uncovering the Mechanism. Frontiers in Marine Science (2020).