Rocky intertidal systems are useful to study the influence of measurement scale on spatial biological variation in community structure. Vertical biological variation across elevations (triggered by tides) has typically been found higher than horizontal (alongshore) variation at local scales but lower than horizontal variation at regional scales. In those studies, alongshore environmental variation increased with scale. We surveyed the Canadian and Chilean coasts at those scales but with a limited underlying alongshore environmental variation and found that horizontal biological variation was never higher than vertical biological variation. Predicting spatial scales of biological variation should thus consider the underlying environmental variation. These photographs illustrate the article “Interhemispheric comparison of scale-dependent spatial variation in the structure of intertidal rocky-shore communities” by Alexis M. Catalán, Nelson Valdivia, and Ricardo A. Scrosati published in Ecosphere. https://doi.org/10.1002/ecs2.3068.