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Living coral cover is rapidly decreasing due to global climate change and local human impacts. Response to the ongoing transformation of coral reefs requires a deep understanding of the mechanisms that regulate community assembly and sustain biodiversity in these systems. The goal of this study is to test the persistence of Devonian reef communities across 70 sea-level fluctuation cycles. Abundance data were collected for in situ coral and calcareous sponge taxa found along 164 transects across two field localities within the Canning Basin, Western Australia. The Bray-Curtis dissimilarity index was used to quantify the dissimilarity in taxonomic composition among transects. Despite the notable persistence of reef communities over numerous cycles (ranging from 22 to 29 cycles) spanning hundreds of thousands of years, significant taxonomic shifts unfolded over millions of years, primarily driven by the diversity and composition of coral assemblages. This indicates that while reef communities exhibit persistence over intermediate time scales, they undergo changes in taxonomic composition over extended periods. The observed shifts in taxonomic composition likely reflect the profound changes in Earth-surface systems that occurred during the Devonian (i.e., fluctuations in global sea-surface temperatures and sea-level). Therefore, sustained abiotic processes can act to disrupt community structure over extended time scales as the threshold for community persistence is exceeded. This study helps establish baseline community composition dynamics in systems devoid of human influence and thus deepens our understanding of naturally occurring phase shifts. Understanding the factors that contribute to the persistence of community assembly across multiple scales is crucial for conserving coral reef ecosystems in the face of ongoing environmental changes. • Understanding community dynamics is shaped by the scale at which it is studied. • Reefs were studied across 70 sea-level fluctuation cycles. • Communities were persistent for up to 29 cycles before experiencing a phase shift. • Phase shifts could reflect global environmental changes during the Devonian. [ABSTRACT FROM AUTHOR]

The monsoon system modulates surface production in the South China Sea (SCS). The winter monsoon has long been recognized as the primary factor regulating surface production in the northern SCS; however, the role of monsoon remains in debate in the southern SCS. Here, we present a long record of short-chain n -fatty acids (n -FAs) in reefal carbonates from one deep well (NK1) on an isolated coral atoll (Meiji) in order to provide new insights into the change of surface production in the southern SCS since the Late Miocene (ca. 10.5 Ma). Short-chain n -FAs indicative of total marine organic matter input are rather feasible to reflect the total production associated with mixotrophic reef-building corals that feed on various marine biotas (i.e., phytoplankton, zooplankton and bacteria). By ruling out the significant influence of diagenetic and degradation processes, short-chain n -FAs can be further applied to reconstruct paleo-production in Well NK1 coral reefs. The temporal distribution of short-chain n -FAs changes similarly with many other independent paleo-production records (i.e., Ln(Ba/Ti) and opal) in Well NK1 and adjacent ODP Site 1143, demonstrating the close coupling between coral reef production and surface water production. This occurs through the common factor of nutrients in modulating production of symbiotic autotrophic coralgae and asymbiotic phytoplankton and/or the large heterotrophic dependence of corals on phytoplankton-governed food webs in surface waters. Short-chain n -FAs inferred surface production displays a progressively decreased trend from the Late Miocene to Pliocene (ca. 10.5–2.6 Ma) followed by a substantial increase since the Pleistocene on million-year timescales, which follows the variation of terrigenous supply to the coral atoll and responds almost inversely to the sea-level change. Accordingly, we propose that long-term paleo-production in the southern SCS was associated with terrestrial nutrient input which was controlled by relative sea-level change since the Late Miocene. This study highlights the feasibility of short-chain n -FAs as appropriate production recorders in shallow-water coral reefs which are widespread in tropical-subtropical oceans, providing valuable perspectives on long-term paleo-production evolution in surface waters. • A long coral reef well (NK1) in the southern SCS was studied. • OM-poor coral reef carbonates were decalcified and extracted for biomarkers. • Short-chain n -FAs reflect paleo-production in coral reefs since the Late Miocene. • Long-term production was governed by terrestrial nutrient related to sea level. [ABSTRACT FROM AUTHOR]