Drone-Transect: a non-destructive operational protocol for drone-based conservation studies on intertidal coral reefs

With many functions attributed to drone use, different applications have been employed along the coastal environment. Most studies have focused on quantifying live and non-live cover, without measuring or quantifying species at the individual level. Thus, we proposed the Drone-Transect method, which, based on aerial images captured by drones, can identify benthic organisms on a broad spatial scale, determining abundance and spatio-temporal distribution. Using the zoanthid Palythoa caribaeorum, the method was compared to Line-Intercept Transect (LIT), aiming to verify data precision. Drone-Transect method presented little variation over consecutive days, while LIT revealed a cover variation of 51%. Taking advantage of the ortomosaic, we performed a LIT simulation with 21 repetitions. In each repetition the initial transect was placed one meter from the previous one. The result was a variation coefficient of 33% among the values obtained. In addition, the Drone-Transect method has advantages: it is non-invasive, since researchers are not located on the reefs; it does not require an in situ team which makes this method safer; and is faster, the Drone-Transect method can accomplish in 15 min with a single pilot what would take a team of six people three hours using the LIT method. Drone-Transect method is an excellent tool, both for the study of the population dynamics of a specific species and for monitoring benthic communities. It can be applied to studies focused on ecosystem conservation, through the evaluation of coral reef health, especially in conservation units.