Coral reef community recovery trajectories vary by depth following a moderate heat stress event at Swains Island, American Samoa Marine Biology

The 2014–2017 global coral bleaching event caused mass coral mortality and reshaped benthic communities across the Pacific. Swains Island (11.0° S, 171.1° W), a remote and uninhabited island within American Samoa, was exposed to moderate heat stress (6 °C-weeks) during this event. Temporal patterns in benthic cover and coral demography were monitored across 13 years straddling this heat stress event to assess the impacts across depth and the recovery trajectory. While Swains’s reefs retain some of the highest calcifier cover in the US Pacific Islands, successional trajectories across depth following the 2016 heat stress suggest that these reefs are experiencing a more nuanced pattern of resilience to disturbance, with early signs of recovery in shallow reefs (3–6 m), a shift to non-calcifier dominance at mid depth (6–18 m), and stability on deep reefs (18–30 m). Shallow reefs experienced the largest changes with a relative 50% decline in coral cover, which was replaced by CCA between 2015 and 2018. Shifts in shallow coral community composition were strongly driven by the loss of Pocillopora and early recovery seven years after the event evidenced by an increase in small colonies. Mid-depth reefs experienced a 33% loss in coral cover between 2015 and 2023, and corresponding increase in upright macroalgae. The degree to which increasing macroalgae represents a temporary shift or gradual decline in calcifiers remains to be seen. While Swains’s recovery bodes well for persistence of shallow reefs, its remoteness from broodstock and dominance of thermally sensitive taxa pose a threat to future climate resilience.