BACKGROUND: Subtle ecological and behavioral mechanisms that enhance reproduction such as nest building by animals may provide useful information of population level processes. Variation in behavioral traits may be observed as phenotypic traits that are shaped by sexual and natural selection. Using ecological sampling of benthic substrata and underwater video recordings, we assessed nest-building behavior through habitat modifications, and size of individuals performing parental care behavior and egg/hatching traits of an abundant temperate reef fish, Chromis crusma. RESULTS: We identified that only male individuals performed nest building and uniparental care. We noted that nests containing filamentous green or red algae had the highest percent cover of eggs. Using video recordings, we provided evidence of parental care. Male individuals spent nearly 80% of their time inside the nest, aerating the eggs with their fins and mouth, removing unwanted materials, and defending the nest against conspecific, heterospecific, and other predators. The field-collected eggs, characterized by an oil globule and adhesive filaments, hatched after 7 days in the laboratory. The nest-building and parental care behavior of C. crusma lasted for 3 months, and several nests can be constructed throughout the season. CONCLUSION: The behavior of building and defending the nests, which is a characteristic of the family members, is a key aspect for the success of the C. crusma; this fish is abundant in kelp ecosystems of the southeastern Pacific.