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How could the loss of photosynthetic symbionts have affected marine invertebrates during the Permian extinction?

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Line graph showing the number of marine animal families from the Precambrian era to the present, with illustrations of key groups such as trilobites, ammonoids, marine reptiles, and diatoms. The graph highlights major extinction events and a rise to 1,900 living families today. — Permian extinction The diversity of marine animal families since late Precambrian time. The data for the curve comprise only those families that are reliably preserved in the fossil record; the 1,900 value for living families also includes those families rarely preserved as fossils. The several pronounced dips in the curve correspond to major mass-extinction events. The most catastrophic extinction took place at the end of the Permian Period.

During the Permian extinction, rising ocean temperatures are believed to have triggered a critical biological crisis for marine invertebrates that relied on photosynthetic symbionts.12

As seawater temperatures climbed—potentially reaching 30–32 °C (86–90 °F) near the Permian-Triassic boundary—these symbiotic organisms, which lived within the tissues of their hosts, were unable to survive the heat. Consequently, the symbionts abandoned their hosts. This loss would have been devastating for the invertebrates, as they likely depended on these symbionts for essential nutrients or metabolic support. The resulting physiological stress and loss of a vital energy source likely contributed to the widespread collapse of various marine species during this period.12