Persistent dominance of non-indigenous species in the inner part of a marina highlighted by multi-year photographic monitoring

Abstract : As a result of urbanization, coastal environments are being disturbed by various anthropogenic pressures. These are concentrated in harbor areas where the addition of artificial structures and the presence of pollutants seems to favor the settlement of non-indigenous species. Most studies on these organisms are often carried out in a single time window without integrating temporal variability. Here, we analyzed multi-year photographic data of marina communities taken from 3 experiments conducted between 2016 and 2019 in the same marina. These photographs were of recruitment plates placed at the inner, middle and entrance locations of the marina, permitting us to discern the community differences and the distribution of non-indigenous taxa between these 3 locations. Over the entire study period, the communities that grew at the entrance and the inner locations of the marina were always different. Non-indigenous taxa also appeared to be more prevalent in the inner location of the marina. Our results suggest that the presence of different environmental filters between the entrance and the inner location could explain these observations. We suggest this could be due to a pollution gradient, with high pollution at the inner location of the marina, and to competitive pressure exerted by the tunicate Ciona intestinalis at the marina entrance.