No-take area status is not sufficient to protect the population of a reef-building coral in Barbados

Coral reefs are undergoing rapid degradation due to global and local anthropogenic stressors. Mitigating local stressors through the establishment of no-take areas could help coral populations withstand global ones. Here, we first assess changes over a quarter century period (1997-2023) in coral colony size-structure, density, and distribution of an important Caribbean reef builder, the massive starlet coral Siderastrea siderea, inside the only no-take area of Barbados (West Indies). We then seek to establish a 2023 population baseline for this species to assess future change, including describing coral colony size-structure as well as spatial variation in key population attributes such as colony density, size, and partial mortality. During June-Aug 2023, we counted and measured S. siderea colonies on 49 100-m2 quadrats on a fringing reef inside the Barbados Marine Reserve (0.5-7 m deep). We compared these data with similarly collected data from 1997. The 2023 data revealed a population now virtually depleted of medium-to-large (diameter>50 cm) colonies (5 % of the population) compared to 1997 (47 %). The population had also dropped in colony density by approximately 25 %. Colony size and density increased with depth, whereas colony partial mortality increased with colony size but was not related to depth. The dramatic colony size-structure shift and decrease in colony density of S. siderea, despite being in an effectively protected no-take area, raises concerns about the long-term persistence of this important coral species in Barbados.