The use of coastal cabled video-observatories to monitor seasonal changes in shallow water fish community

Abstract-Seasonality in marine fish communities is usually studied by using different sampling techniques (e.g. visual census in shallow water or trawling in deeper areas) that are hard to perform over long periods with a high frequency of data recording. Furthermore, the coupling with fluctuations in key habitat parameters (e.g. light, temperature, salinity, and turbidity) is not a simple task to accomplish. Cabled video-observatories implemented with multiparametric sensors for habitat monitoring are allowing for the first time the continuous and long term recording of marine communities' dynamic (e.g. day-night, seasonal, and predator-prey fluctuations). In this scenario, the OBSEA video-cabled observatory has been recently deployed (2009) within a coastal area in the western Mediterranean Sea (Vilanova i la Geltru - Spain) at a depth of 20 m. It is endowed with a video camera and a CTD. The OBSEA is located in a sandy area in which are placed numerous artificial reefs that protect the ground from trawling. The OBSEA is placed in front of one of these reefs. Accordingly, we report here only the preliminary results of this study consisting of one month video-monitoring at 30 min frequency of the local fish community in association with environmental fluctuations. In the future this analysis will cover an entire year. Waveform analysis was carried out in order to detect the occurrence of significant daily periodicity in species abundance, while time series of community fluctuations were related to environmental parameters (temperature and pressure at the sea bottom). In both cases particular attention was directed to interacting species such as predators and preys. Preliminary results highlight how cabled observatories could contribute to study community's dynamic. Finally, the analysis of the entire year observations will allow to study changes of the artificial reef community among different seasons. Moreover, the long term data from OBSEA could permit to evaluate possible climate changes effects on the local fish community