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The crown-of-thorns seastar (COTS; Acanthaster spp.) inhabits coral reefs across the Pacific Ocean. Based on studies in the Western Pacific, when densities exceed ~15 specimens per ha, coral reef degradation due to COTS predation may occur. There is little information about the role of COTS on coral reefs in the tropical eastern Pacific, although previous studies suggested it was not a concern to coral reef conservation in México. In this study, we estimated the abundance and impact of COTS on coral reefs at Espíritu Santo Archipelago National Park (Gulf of California) over a period of 12 years (2005–2016). The mean density (pooled among sites and over time) of COTS was 70 ± 5.1 ind. ha−1 (mean ± SE), with a maximum value of 143.6 ± 30.3 ind. ha−1, recorded in 2006. Densities changed significantly over time and spatially. The highest values were observed at sites located on the west side of the islands. Density was not correlated with seawater temperature or live coral cover. The absence of evidence of major live coral cover declines associated with predation by COTS, even though high densities were observed through the years in the region, lead us to conclude that this seastar does not appear to threaten coral reefs at Espíritu Santo. However, continued monitoring of COTS is required to help understand density fluctuations and to identify threshold densities needed to cause major coral damage in the region.