A new piece in the puzzle: The palaeoecological significance of bryozoans over 7000 years in Daidokutsu Cave (Okinawa, Japan)

ABSTRACT Submarine caves are cryptic, climatically sensitive habitats with long‐term ecological dynamics that are poorly understood. We present the first palaeoecological analysis of bryozoans from Daidokutsu Cave (Okinawa, Japan), based on a sediment core spanning approximately the last 7000 years. We quantify temporal changes in bryozoan diversity, taxonomic and functional composition, and community turnover, comparing these with published records for ostracods, foraminifera and bivalves, as well as independent environmental proxies, that are, δ 18 O as a proxy for East Asian Winter Monsoon intensity and red soil input as a proxy for hydrodynamic energy, reflecting the winnowing of finer particles from terrigenous sediments deposited on coastal zones. The Daidokutsu bryozoan assemblage is relatively diverse, apparently highly endemic and dominated by erect colony forms. Diversity peaks mid‐record, consistent with partial cave isolation, then declines, likely towards a more specialised cave fauna, while the composition shows recurrent episodes of rapid turnover. No robust relationships emerge between bryozoan diversity and assemblage composition and the targeted environmental proxies, and detrended bryozoan diversity does not track East Asian Winter Monsoon variability as clearly as in ostracods, suggesting that bryozoans may be less sensitive to regional monsoon forcing. As the first quantitative multi‐taxon study of submarine cave evolution including bryozoans, our results show that bryozoan assemblages provide an independent perspective on long‐term ecological change, underscoring the need for further studies to assess more fully their potential as palaeoenvironmental indicators in cryptic shallow‐marine ecosystems.