Challenges to the assessment of benthic populations and biodiversity as a result of rhythmic behaviour: Video solutions from cabled observatories

Abstract

All marine species studied thus far show rhythmic temporal patterns in their behavioural, physiological, and molecular functions, which are collectively known as biological rhythms. Biological rhythms are generated by biological clocks that time biological functions and are synchronized by geophysical cycles, such as the solar light-dark cycle and tidal cycle. On continental margins, behavioural rhythms can be detected by diel (i.e., 24-hour based) or seasonal periodical trawling as a consequence of massive inward and outward displacements of populations to and from the sample areas. As a result, significant errors in population/stock and biodiversity assessments performed by trawling may occur if timing of sampling is not taken into account. The increasing number of cabled and permanent multiparametric seafloor observatories now allows direct, continuous, and long-lasting monitoring of benthic ecosystems and analysis in relation to several habitat cycles. This review describes the adaptation of this technology to investigations of rhythmic behaviour by focusing on automated video imaging. Diel fluctuations in the number of video-observed individuals can be used as a measure of average population rhythmic behaviour. The potential implementation of automated video image analysis in relation to animal tracking and classification procedures based on the combined use of morphometric tools and multivariate statistics is detailed in relation to populational and community studies. Based on video cameras mounted at multiparametric cabled observatories, an integrated time-series analysis protocol using chronobiomedical procedures is proposed to place video-recorded bioinformation in an oceanographic context.