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.

Unexpected biotic homogenization masks the effect of a pollution gradient on local variability of community structure in a marine urban environment

“…Here we showed a spatially organized community structure in the Vieux port de Marseille similar to previous studies (Gauff et al, 2022a;Kenworthy et al, 2018b;Rondeau et al, 2022), followed by an unexpected change in the community associated to a sharp decrease in biodiversity and a decline of most species except Serpulinae, eclipsing the effects of local variation of environmental factors and thus leading to the homogenization of the biodiversity within the harbor. Urbanization and climate change have led to the worldwide homogenization of ecosystems (Clavel et al, 2011;Magurran et al, 2015;Mckinney and Lockwood, 1999;Qian and Ricklefs, 2006).…”

“…The present study aimed to describe how the sessile sciaphilic communities of the Vieux Port de Marseille are composed and how they vary in space. We hypothesized that different locations in the harbor have significantly different communities, associated to a local variation of pollution, as described in previous studies (Je et al, 2004;Kenworthy et al, 2018b;Rondeau et al, 2022;Ryu et al, 2011). In accordance with these studies, most contaminant concentrations and especially Metallic…”

“…Yet, despite the reduction of its cover between June and August, this species seems to be the least affected one since it still covers 7-44% in August. Similar experiments with settlement plates conducted in another marina have shown to have constant community differences between the entrance and the inner part of a marina over a span of more than 4 years (Gauff et al, 2022a;Rondeau et al, 2022). These differences remained constant regardless of timing of panel deployment, or length between individual assessments (Rondeau et al, 2022), i.e., regardless of successional state of the community.…”

“…Similar experiments with settlement plates conducted in another marina have shown to have constant community differences between the entrance and the inner part of a marina over a span of more than 4 years (Gauff et al, 2022a;Rondeau et al, 2022). These differences remained constant regardless of timing of panel deployment, or length between individual assessments (Rondeau et al, 2022), i.e., regardless of successional state of the community. Thus, the observed differences between June and August might not be attributed to biotic interaction among fouling species or to succession, but rather to external abiotic factors impacting the communities at all three locations.…”

An Overview of Marine Non-Indigenous Species Found in Three Contrasting Biogeographic Metropolitan French Regions: Insights on Distribution, Origins and Pathways of Introduction

“…The approach indeed has many advantages, such as its cost-efficiency, ability to examine a large number of sites and capacity to be used at a high frequency, all of which are properties required for the rapid detection of new NIS. To another extent, the image analysis tools can be used in situ for species or taxonomic groups identification or colonisation processes [124], sometimes using artificial intelligence for the automated recognition of certain species in situ, when it is possible. Image analyses and video recording in labs were also successfully implemented to study the specific behaviour of non-indigenous species [125] and to study the predation of native species on NIS communities [126].…”