Many seafloor fish communities are retaining their individuality despite human impacts

Despite widespread human impacts to wildlife diversity worldwide, many fish communities on the seafloor have maintained their uniqueness, reports a new study led by Zoë Kitchel, formerly of Rutgers University, and colleagues, published July 9 in the open-access journal PLOS Climate.

 Around the world, humans have transformed ecosystems through development, hunting and fishing, invasive species and climate change. On land and in freshwater ecosystems, these changes have typically led to a process called homogenization, where the types of organisms living in different areas become more similar over time, as native species are replaced with introduced species and species good at tolerating human activity. However, previously it was unclear whether this same trend was occurring in ocean ecosystems.

 Kitchel and a large group of collaborators looked at data from scientific fish trawling surveys to identify trends in seafloor fish diversity over time. These surveys included more than 175,000 samples composed of 2,006 fish species living on the seafloor from 34 regions and spanning six decades. The researchers saw that while almost one third of the examined regions showed homogenization, another third actually had an increase in diversity. The remaining 15 regions did not show a clear trend in homogenization over time, with some areas showing big swings in diversity between years. Further analysis showed that temperatures and the amount of fishing that occurred in the region helped explain some of the shifts in similarity across years and locations.

 Overall, the new findings show that, despite intense human impacts on the oceans, the majority of seafloor fish communities do not follow the worldwide trend of homogenization that has occurred in other environments. The research team suggested that future studies could look at terrestrial and freshwater ecosystems to see if they experience similar swings in diversity. They also concluded that, due to the differences in homogenization they observed across different locations, conservation efforts should be tailored specifically to each region to be most effective.

 The authors summarize: "Globalization and land-use change has led to widespread homogenization (or the loss of unique combinations of species) across freshwater and terrestrial ecosystems. However, until this study, we were mostly in the dark about whether the oceans were also experiencing this loss of uniqueness across space. We found that overall, communities of fish living on soft-bottom habitat on continental shelves worldwide are not uniformly homogenizing. Rather, trends in diversity are regionally specific with locations such as the western Atlantic experiencing homogenization in contrast to places such as Portugal and Greenland experiencing an opposite trend towards elevated uniqueness…[w]e found that community composition is highly dynamic through time, varying from a more homogenized to more heterogeneous state and back again over the course of a few years. This suggests that these communities of fish are resilient to environmental change." 

Dr Kitchel adds: “The long list of co-authors is indicative of the highly collaborative nature of this project. We were able to test for evidence of homogenization across diverse marine shelf ecosystems because of the contributions and knowledge of fisheries biologists from across the world through the FISHGLOB consortium. FISHGLOB is an international consortium of scientists, experts and data providers who collect, curate, standardize, share, and analyse data from scientific bottom trawl surveys (SBTS). By facilitating open and multinational science, the consortium's activities enable the understanding and prediction of fish diversity change and help to guide management actions. SBTS are one of the most widespread and long-running forms of ocean ecosystem monitoring, providing invaluable time-series of marine fish biodiversity over decades of global change."

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In your coverage please use this URL to provide access to the freely available article in PLOS Climate: https://plos.io/45YgWjf

Citation: Kitchel ZJ, Maureaud AA, Fredston A, Shackell N, Mérigot B, Thorson JT, et al. (2025) Marine communities do not follow the paradigm of increasing similarity through time. PLOS Clim 4(7): e0000659. https://doi.org/10.1371/journal.pclm.0000659

Author Countries: Canada, Chile, Croatia, Germany, France, Iceland, Italy, Malta, Namibia, Norway, Spain, United Kingdom, United States

Funding: This project was part of the FISHGLOB working group, ‘Fish biodiversity under global change: a worldwide assessment from scientific trawl surveys’, co-funded by the Centre for the Synthesis and Analysis of Biodiversity (CESAB) of the French Foundation for Research on Biodiversity (FRB), the Canadian Institute of Ecology and Evolution (CIEE), and the French embassy in Canada (to MLDP & BM). Other support was provided by U.S. National Science Foundation grants #DEB-1616821 (to ZJK & MLP), #OISE-1743711 (to ZJK & MLP), and #CBET-2137701 (MLP); the Rutgers School of Environmental and Biological Sciences (to ZJK); the Rutgers Ecology and Evolution Graduate Program (to ZJK); a Rutgers Coastal Climate Risk and Resilience Traineeship (to ZJK); the Coronavirus Response and Relief Supplemental Appropriations Act, 2021 (CRRSAA)/Higher Education Emergency Relief Fund II (HEERF II) (to ZJK); and The Natural Sciences and Engineering Research Council of Canada (NSERC) and The Social Sciences and Humanities Research Council (SSHRC) Partnership Grant (to JPA). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.