Stony coral symbioses show variable responses to future ocean conditions.

In a 2.5-year factorial future-ocean mesocosm across eight coral species, heat stress generally reduced symbiont diversity and promoted predictable symbiont restructuring in some cases.

• Why it matters: Coral reefs and their symbioses face major anthropogenic threats, but it remains unclear whether symbiont communities will be disrupted or adaptively reorganized under future ocean conditions.
• What they did: The study ran a factorial mesocosm experiment for 2.5 years, tracking symbiont community shifts within replicate fragments from the same individual coral across eight coral species.
• The result: Symbiont responses ranged from stochastic divergence to deterministic community shifts, with extreme conditions linked to stochastic diversity accumulation, supporting a host-orchestrated sorting continuum.

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