Scientists: Ocean acidification due to climate change could weaken salmon sperm - Ocean acidification cripples salmon and sea urchin reproduction, study reveals

Rising ocean acidification is threatening the reproduction of salmon and sea urchins along European coasts. New research shows that lower pH levels disrupt a key signaling process in their sperm, reducing motility and fertilisation success. Scientists warn this could lead to further population declines in already vulnerable species.

The study found that sperm movement in salmon and sea urchins depends on a molecule called cAMP, produced by an enzyme activated in higher pH conditions. When seawater becomes more acidic, this enzyme fails to trigger cAMP production, leaving sperm immobile. Without cAMP, fertilisation cannot occur.

Researchers first observed this mechanism in sea urchins before confirming it in salmon. They suspect similar pH-dependent processes may control reproduction in other marine species. Unlike mammals, where cAMP production is regulated by bicarbonate, these species rely on environmental pH to activate sperm.

Ocean acidification, caused by rising CO₂ levels, has already harmed larval development in salmon and weakened shell formation in urchins. North Atlantic and North Sea populations have declined since the early 2000s due to these effects. Both species reproduce through mass spawning, meaning even small reductions in sperm motility could severely impact fertilisation rates.

The team linked higher CO₂ concentrations to disrupted chemical balances in seawater, making it more alkaline and lowering pH. This shift interferes with the enzyme's ability to produce cAMP, directly impairing sperm function.

The findings highlight a direct link between ocean acidification and declining reproductive success in key marine species. If current trends continue, salmon and sea urchin populations could face further reductions, affecting ecosystems and fisheries. Scientists stress the need for further research into how other species may be similarly impacted.