*2.2. Sampling and Taxonomic Identification*

*Trapezia* crabs were collected at three sites within IMNP (Figure 1). Each crab was obtained from a different *Pocillopora* colony at a depth of 5–7 m. Crabs were collected carefully (using metallic tweezers to extract them from the live coral colony) and immediately placed individually in 50-mL plastic tubes filled with seawater. Following collection, the crabs were preserved in 96% ethanol and transported to the laboratory. Crabs were then observed using a stereoscope (Stemi 508-Zeiss®, Oberkochen, Germany) and classified to species level following the taxonomic criteria described by Castro [16,24]; carapace shape and size, color, cheliped size and propodus color were all considered. All crabs were photo-documented using a Canon Elph PowerShot 180 camera (Canon Inc., Tokyo, Japan), and, prior to long-term storage, a sample of muscle tissue was dissected from the cephalothorax and preserved in 96% ethanol for DNA extraction. Carapace and cheliped width and length were measured individually using Image J software (Open Source, Developed at the National Institutes of Health and the Laboratory for Optical and Computational Instrumentation, University of Wisconsin, Madison, WI, USA); values are expressed per species and sex as mean mm ± standard deviation.

**Figure 1.** Study area in the Islas Marietas National Park (IMNP), Nayarit, Mexico, showing the location of sampling sites. All sampling sites have a high cover of *Pocillopora* sp. (15–33%). (**A**) Zona de Restauración (20.698860◦ N, 105.580997◦ W); (**B**) Cueva del Muerto (20.697389◦ N, 105.582806◦ W) at Isla Larga; (**C**) Plataforma Pavonas (20.700908◦ N, 105.565304◦ W) at Isla Redonda.
