Coloration is related to habitat in Gymnothorax mordax, a kelp forest predator

Animal coloration serves a variety of functions, including communication and camouflage. We quantified hue, luminance, countershading, and pigmentation pattern of the California moray eel Gymnothorax mordax and determined whether coloration was correlated with the environmental variables of the kelp forest ecosystem. The California moray is an elongate, predatory, crevice-dwelling fish that does not rapidly change color. We photographed morays trapped at a variety of depths in 4 environmentally diverse sites around the Two Harbors isthmus on Catalina Island, California, USA. Depth, substrate type, cover type, horizontal visibility, and reef rugosity were recorded for the environment surrounding each trapped eel. We found that eels were lighter, redder, and yellower in shallow habitats with high percentages of sand, bare substrate, and seagrass. In habitats with greater substrate diversity, clearer water, and a higher percentage of boulder, morays were darker, greener, and bluer. Despite their benthic, crevice-dwelling behavior, we found that all individuals exhibited countershading, which was most extreme at the head and tail. Pigment spots became larger and more uniform in size as standard length increased, but few other size- or age-related color changes were found. We found little evidence that coloration is correlated with foraging success and instead speculate that coloration is established post-settlement in smaller size classes not examined in this study. This work shows that California morays exhibit a range of colorations and that hue and luminance are correlated with environmental variables in the Two Harbors region of Catalina Island.