Assessing indirect biodiversity conservation benefits of fisheries closures in the Gulf of St. Lawrence, Canada

but are rather intended to provide long-term, in-situ protection for biodiversity as one out- come, also referred to as biodiversity conservation benefits (BCBs) [5]. For example, OECMs in Canada are established under the Fisheries Act and are essentially fisheries closures [6], which often do not have management plans specifically intended for biodiversity conservation benefits, but rather focus on fisheries [6, 7]. While the primary objective of OECMs is direct BCBs to specific taxa, these areas can also offer important indirect BCBs to a wider range of taxa [4, 8, 9]. In Canada, many OECMs have been established to safeguard vulnerable benthic species such as cold-water corals and sponges [9]. While these closures provide direct BCBs to these species, they may also offer indirect BCBs for other species that rely on that habitat for completion of their life cycles, including spawning and development of early life stages [4, 10]. One such area is the Gulf of St. Lawrence (henceforth, also referred to as the Gulf), a highly productive region in Atlantic Canada. The Gulf is a semi-enclosed sea whose seafloor is a mosaic of deep channels, shallow banks, sediment-covered areas, and unique ecosystems like cold-water coral reefs and sponge fields [11, 12]. Notably, the Laurentian Channel which runs through the Gulf, reaches depths of over 500 meters in some places [12]. The Magdalen Shal- lows are a notable submarine bank, which are relatively shallow compared to the surrounding waters [12]. Such banks are important fishing grounds due to the aggregation of marine spe-

cies and serve as feeding areas for many organisms [13]. The Gulf is home to cold-water coral reefs and sponge-dominated benthic habitats, particularly along the deeper parts of the Lau- rentian Channel. These ecosystems are sensitive and considered biodiversity hotspots [10, 14]. The Gulf’s high concentration of cold-water corals and sponges that create complex habitats that support a wide range of species, including those that rely on these structures for feeding, protection, and reproduction [9]. For example, the important fisheries species Atlantic halibut (Hippoglossus hippoglossus), Greenland halibut (Reinhardtius hippoglossoides), and redfish (Sebastes spp.) depend on these specific deep-water habitats for spawning and early life stages [15–17]. The overlap between OECMs in the Gulf of St. Lawrence, established to protect corals sponges and sea-pens, with potential spawning habitats of these three fish species presents an opportunity to assess the indirect BCBs provided by OECMs, specifically under current and future environmental conditions. The provision of BCBs by OECMs is essential for sustaining long-term marine biodiversity [8, 9]. However, recent studies have documented rising bottom temperatures and decreasing oxygen concentration in the region, trends that are expected to continue and intensify throughout the 21st century [18, 19]. These changes are likely to exceed the tolerance thresh- olds of the three focus species, leading to shifts in their distribution and potentially reducing

the effectiveness of OECMs in providing indirect BCBs [20, 21]. Moreover, ocean acidification is expected to further degrade the structural complexity of cold-water coral and sponge habi- tats, potentially diminishing their capacity to support marine biodiversity in the region [22]. The risk of ineffective marine biodiversity conservation through OEMCs in Canada and beyond has been discussed, both in the context of climate change and the 30x30 agenda (e.g., [6, 7, 23–26]. Research on the indirect BCBs of OECMs, particularly those protecting cold-water coral and sponge habitats in Canada, remains limited [9, 27–29]. This study contributes to filling this gap by documenting the current indirect BCBs provided by a nine, selected OECMs in the Gulf of St. Lawrence (Table 1) and examines their potential to provide these benefits under future climate scenarios. Here, we aim to evaluate the indirect BCBs of selected OECMs estab- lished in the Gulf of St. Lawrence in 2017 by adopting an integrated assessment approach. We integrate and analyse data and knowledge from multiple sources not available at the time of OECM establishment to create a comprehensive assessment of OECM outcomes in terms of indirect BCBs and potential climate change impacts on those. The implications of our findings PLOS ONE Indirect biodiversity conservation in the Gulf of St. Lawrence PLOS ONE | https://doi.org/10.1371/journal.pone.0316754 January 9, 2025 2 / 20 Funding: ABB and JADF acknowledge funding from Fisheries and Oceans Canada’s Oceans Management Contribution Program to the Fisheries

and Marine Institute’s Monitoring & Assessment of Marine Conservation Areas in Newfoundland and Labrador Project. JADF and TDE acknowledge funding from the NSERC Discovery Program and the Robert and Edith Skinner Wildlife Management Fund. Competing interests: The authors have declared that no competing interests exist.