Work

Ancient terrestrial forests reborn as modern marine ecosystems under shifting sea levels

Year: 2026

Type: article

Abstract: Sea-level rise and coastal erosion can submerge terrestrial carbon-rich landscapes, yet the ecological fate and climate significance of such relict coastal carbon deposits remain largely unknown. We report the discovery of submerged tropical peat reefs in the shallow coastal waters of the Bazaruto Archipelago, Mozambique; a legacy of ancient coastal forests now transformed into benthic marine habitats. Radiocarbon ( 14 C) dating reveals ages spanning ~ 300 to ~ 5000 years BP, indicating mid- to late-Holocene origins as coastal peat swamps and forests subsequently submerged by rising seas. Sampled peat material contains up to 40% organic carbon by dry weight, indicating an organic-rich legacy coastal peat substrate rather than a quantified habitat-scale or areal carbon stock, and δ 12 C values around − 27‰ confirm a predominantly terrestrial carbon plant origin. Peat reefs are shallower and exhibit greater variability in physicochemical, environmental, and physical properties than adjacent hard scleractinian coral reefs, influencing biological structure and habitat function. Biodiversity surveys across multiple scales (benthic quadrats, invertebrate, small fish, and megafauna transects) showed that these carbon-rich peat reefs support a biodiverse and distinctive assemblage of marine life, significantly different from nearby coral reefs. The peat substrate is colonized by diverse sessile and mobile invertebrates providing structural complexity for fish communities and as nursery habitat, with richness comparable to coral reef ecosystems. Importantly, overlapping communities highlight ecological connectivity across reef types (41 and 44 small fish/megafauna shared species), even as habitat composition differs markedly. Unlike adjacent hard coral reefs dominated by reef-building corals, peat reefs host no living corals and are instead characterized by seagrass, macroalgae and sponges using the peat as substrate, creating a carbon-rich system, and a detritus-based food web. Our findings illustrate how ancient terrestrial systems can persist and support contemporary ecological functions, and the ecological “reinvention” of Earth’s landscapes under shifting sea levels. This underscores how substrate-driven ecosystem baselines shape biodiversity, calling for the inclusion of such relict ecosystems in emerging coastal habitat mapping, conservation frameworks, and legacy coastal carbon assessments.

Source: Scientific Reports

DOI: 10.1038/s41598-026-65430-7