Application of the Visual Fast Count for the quantification of temperate epibenthic communities from video footage

Abstract

Video transects of epibenthic communities provide a valuable and non-destructive surveying methodology. The use of unstable platforms for video collection, such as divers and remotely operated vehicles, can lead to variation in the field of view, and consequently the dimensions of the surveyed area. Unless this can be accounted for, quantifying the species present can be time consuming or unworkable. Use of time-based, rather than areas-based, enumeration techniques, such as the visual fast count (VFC), can overcome this variation. Using seabed video footage from Strangford Lough, the reliability of the VFC was assessed through comparison with direct counts. Multivariate analysis of variance indicates that data derived from the VFC did not differ from that obtained from direct counts. Pairwise comparisons between locations in Strangford Lough using analysis of similarities (PRIMER) also indicated good agreement between the two methods. Use of the VFC method therefore provides: (1) a reliable alternative to direct counts for epibenthic enumeration; (2) a substantial reduction in post-survey processing time and; (3) a method capable of allowing variation in the visual field/sampled area.