Towed camera imagery and benthic sled catches provide different views of seamount benthic diversity

Because benthic ecosystems of seamounts support vulnerable biota that are increasingly threatened by mining and fishing, assessments of ecological conditions and impacts are important to balance resource extraction with biological conservation. These assessments rely on ecological metrics generated from physical collections of fauna with sleds or similar gears, or by surveying the seafloor with cameras. If different gears (sled or cameras) "sample" the benthos differently, derived ecological metrics will also differ. Here, we test this hypothesis by comparing data provided by a robust benthic sled and a quantitative towed camera from colocated transects on seamounts off Tasmania (Australia). Our comparison showed these tools provide complementary but not interchangeable metrics of seamount benthic diversity and abundance. Choice of sampler(s) needs to be determined by survey objectives and consider the following trade-offs: (1) sleds will detect more species than image-based techniques; (2) specimens obtained by physical sampling (sleds) can considerably extend the scope of ecological analysis through genetic, isotopic, and other analysis of biological material not available from camera surveys; (3) image-derived data provide significantly and often considerably, higher estimates of megabenthos abundance; and (4) environmental impacts are much lower in camera surveys and therefore are arguably more ethical - an important consideration when repeat surveys are required, especially in areas of high conservation importance or heightened sensitivity. Undersampling by sleds of corals and sponges is an important aspect of gear selectivity because these taxa are consistently prominent indicators in protocols that identify benthic "vulnerable marine ecosystem" in assessments of human impacts.