Density, size, and biomass of Diadema mexicanum (Echinoidea) in Eastern Tropical Pacific coral reefs

Low densities and small sizes of the sea urchin Diadema mexicanum across Eastern Tropical Pacific coral reefs, including UNESCO World Heritage Sites like the Revillagigedo Archipelago, are primarily driven by predation from macrophagous fishes. This pattern likely stems from overfishing of top predators, which has cascading effects on lower trophic levels. The study, conducted at 12 localities between 2009 and 2010, found average densities of 0.47 ± 0.15 individuals per square meter, with most urchins measuring 2 to 3 cm in test diameter and a biomass of 0.26 ± 0.33 grams per square meter. These findings highlight the ecological vulnerability of ETP coral reefs, where increased macroalgal cover due to past El Niño events has intensified bioerosion activity by sea urchins, further weakening reef frameworks.

Alvarado, J., Cortés, J., Guzman, H., & Reyes‑Bonilla, H. (2016). Density, size, and biomass of Diadema mexicanum (Echinoidea) in Eastern Tropical Pacific coral reefs. Aquatic Biology, 24(3), 151–161. https://doi.org/10.3354/ab00645