Environmental Fluctuations Are Insufficient to Explain High Coral Biodiversity: A Test of Five Storage Effect...

The storage effect is a general explanation for ecological coexistence, wherein different species specialise on different states of a fluctuating environment, for example, hot versus cold years. Despite the storage effect's prominence in theoretical ecology, we lack evidence on whether it maintains biodiversity in nature. Here, we examine five storage effect pathways in a community of 11 coral species from the Great Barrier Reef, using detailed size-structured demographic data collected over 5 years. We parameterize integral projection models, simulate coral communities, and quantify coexistence mechanisms through Modern Coexistence Theory. Fluctuations in survival and fecundity promote coexistence via the storage effect, but this stabilising mechanism is typically small compared to fitness differences. Despite exhibiting prerequisites for strong temporal niche partitioning, the storage effect cannot explain the coexistence of many species. Diversity maintenance likely requires large net contributions from other mechanisms, such as specialist natural enemies or spatial heterogeneity coupled with source-sink dynamics.