This dataset consists of one data file (Carman_Et_al_Tunicate_2017_survey_on_eelgrass_quad_data_final) and one definitions file (Carman_Et_al_Tunicate_2017_survey_on_eelgrass_quad_data_final_definitions). The data file consists of species and abundance of tunicates found growing on eelgrass (Zostera marina L.) in a survey of 33 northwest Atlantic eelgrass meadows in summer 2017. Eelgrass meadows represented in the dataset range from New Jersey to Newfoundland. Within each meadow, data were collected within individual quadrats (ranging from 0.0625 to 0.25 square meter) along transects or as general site surveys. Data include geographic coordinates for the center of each site surveyed; date surveyed; tunicate species found on eelgrass; percent cover of tunicates on eelgrass leaves; eelgrass density; eelgrass canopy height; and the name of the investigator who collected each data point.