The annotation approach used for marine imagery impacts the detection of temporal trends in seafloor biota

Image-based surveys of the marine benthos are being increasingly adopted as a monitoring tool for habitats and biota, particularly in mesophotic depths (?30–150 m) which technically difficult to survey. Many modern tools these surveys, such remotely operated vehicles autonomous underwater vehicles, can capture thousands images single deployment. Turning this into quantitative data typically involves human annotation is often time-consuming costly. Percent cover organisms one most common metrics changes abundance, may be attained through visual estimation, digitization, or point-count approaches. However, alternative abundance density (direct counts) presence-absence, well that quantify condition (e.g., bleaching) size-structure also provide information tracking change. Understanding statistical power different approaches critical designing effective image-based programs. Given differing time taken using approaches, program managers need decide where allocate resources. Here we use benthic imagery from two long-term sites south-eastern Australia annotate three example morphospecies (morphologically distinct organisms) approaches: (percent cover), full count presence-absence within imagery. Also, compare performance point bleaching our morphospecies. We spatio-temporal models trends empirical simulations detect levels temporal change sampling efforts (either 100 200 images). Additionally, examine additional insights find approach provides higher than other morphospecies, including status. Size-structure occurrence recruitment mortality events growth individuals. recommend programs should consider choice likely impact observed patterns, when focus specific indicator species rather total biodiversity.