Abstract
Megafauna play an important role in benthic ecosystem function and are sensitive indicators of environmental change. Non-invasive monitoring of benthic communities can be accomplished by seafloor imaging. However, manual quantification of megafauna in images is labor-intensive and therefore, this organism size class is often neglected in ecosystem studies. Automated image analysis has been proposed as a possible approach to such analysis, but the heterogeneity of megafaunal communities poses a non-trivial challenge for such automated techniques. Here, the potential of a generalized object detection architecture, referred to as iSIS (intelligent Screening of underwater Image Sequences), for the quantification of a heterogenous group of megafauna taxa is investigated. The iSIS system is tuned for a particular image sequence (i.e. a transect) using a small subset of the images, in which megafauna taxa positions were previously marked by an expert. To investigate the potential of iSIS and compare its results with those obtained from human experts, a group of eight different taxa from one camera transect of seafloor images taken at the Arctic deep-sea observatory HAUSGARTEN is used. The results show that inter- and intra-observer agreements of human experts exhibit considerable variation between the species, with a similar degree of variation apparent in the automatically derived results obtained by iSIS. Whilst some taxa (e. g. Bathycrinus stalks, Kolga hyalina, small white sea anemone) were well detected by iSIS (i. e. overall Sensitivity: 87%, overall Positive Predictive Value: 67%), some taxa such as the small sea cucumber Elpidia heckeri remain challenging, for both human observers and iSIS.
Highlights
Despite recent advances in technology and increased efforts to ‘‘Census the Marine life’’, the deep ocean floor remains the largest and yet least explored ecosystem on Earth [1]
In this article we describe the iSIS architecture and present its application to transect data collected at a HAUSGARTEN station
ISIS was applied to the entire images for taxa detection and the detection results were compared to our gold standard gm(k) by computing SE and Positive Predictive Value (PPV)
Summary
Despite recent advances in technology and increased efforts to ‘‘Census the Marine life’’, the deep ocean floor remains the largest and yet least explored ecosystem on Earth [1]. Megafaunal predators control the population dynamics of their prey and are important in determining benthic food webs and community structure [15,16,17,18,19] They contribute considerably to benthic respiration and affect the physical and biogeochemical micro-scale environment [20,21,22,23,24,25,26]. Small white sea anemone Small white sponge Total: Label amounts Human Gold std. The taxa with their human and gold standard label amounts. The inter- and intra-observer agreements are given by average and standard deviation pone.0038179.g001.tif(std-dev.) for the five experts. ISIS was applied to the entire images for taxa detection and the detection results were compared to our gold standard gm(k) by computing SE and PPV. The last column shows the correlation between object counts of the gold standard items and the machine detection result for the full transect. doi:10.1371/journal.pone.0038179.t002 exclude the image region covered by the OFOS forerunner weight and the camera time stamp
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