Benthic ecoregionalization based on echinoid fauna of the Southern Ocean supports current proposals of Antarctic Marine Protected Areas under IPCC scenarios of climate change

Abstract

The Southern Ocean (SO) is among the regions on Earth that are undergoing regionally the fastest environmental changes. The unique ecological features of its marine life make it particularly vulnerable to the multiple effects of climate change. A network of Marine Protected Areas (MPAs) has started to be implemented in the SO to protect marine ecosystems. However, considering future predictions of the Intergovernmental Panel on Climate Change (IPCC), the relevance of current, static, MPAs may be questioned under future scenarios. In this context, the ecoregionalization approach can prove promising in identifying well‐delimited regions of common species composition and environmental settings. These so‐called ecoregions are expected to show similar biotic responses to environmental changes and can be used to define priority areas for the designation of new MPAs and the update of their current delimitation. In the present work, a benthic ecoregionalization of the entire SO is proposed for the first time based on abiotic environmental parameters and the distribution of echinoid fauna, a diversified and common member of Antarctic benthic ecosystems. A novel two‐step approach was developed combining species distribution modeling with Random Forest and Gaussian Mixture modeling from species probabilities to define current ecoregions and predict future ecoregions under IPCC scenarios RCP 4.5 and 8.5. The ecological representativity of current and proposed MPAs of the SO is discussed with regard to the modeled benthic ecoregions. In all, 12 benthic ecoregions were determined under present conditions, they are representative of major biogeographic patterns already described. Our results show that the most dramatic changes can be expected along the Antarctic Peninsula, in East Antarctica and the sub‐Antarctic islands under both IPCC scenarios. Our results advocate for a dynamic definition of MPAs, they also argue for improving the representativity of Antarctic ecoregions in proposed MPAs and support current proposals of Conservation of Antarctic Marine Living Resources for the creation of Antarctic MPAs.

Physical and Biogeochemical Regionalization of the Southern Ocean and the CCAMLR Zone 48.1

“…Currently, the Ross Sea and the South Orkney Islands are the only established marine protected areas within the Southern Ocean, while three more proposal have been submitted for East Antarctica, the Antarctic Peninsula and the Weddell Sea (Sylvester and Brooks, 2020). The terrestrial ice-free area of Antarctica was divided in 16 biogeographic regions by Terauds and Lee (2016), whereas various studies of bioregionalization have been previously performed for the Southern Ocean pelagic (i.e., Grant et al, 2006;Spalding et al, 2007Spalding et al, , 2012Cabré et al, 2016) and benthic communities (Griffiths et al, 2009;Pierrat et al, 2013;Douglass et al, 2014;Hogg et al, 2016;Teschke et al, 2016;Fabri-Ruiz et al, 2020). A new physical and biogeochemical regionalization is needed to fill the existing gap in the understanding of the physical forcing on biogeochemical cycles spatial heterogeneity (Hendry et al, 2018) and to generate useful information for marine protected areas proposals and marine ecosystem modeling.…”

Individual-based model of population dynamics in a sea urchin of the Kerguelen Plateau (Southern Ocean), Abatus cordatus, under changing environmental conditions

“…Applications could be further developed to address conservation issues such as the designation of priority areas and the definition of management plan strategies. Vast areas of the French Southern Territories have recently been placed under enhanced protection of a national nature reserve based on experts' knowledge and ecoregionalisation approaches (Koubbi et al, 2010;Fabri-Ruiz et al, 2020). Most areas however could not have benefited from thorough benthic field studies, and ecological models can represent interesting tools to assess the relevance of defined protection areas for target species and ecosystems.…”

Diversity of Antarctic Echinoids and Ecoregions of the Southern Ocean

“…Environmental descriptors were selected based on data availability and ecological relevance for explaining the distribution of echinoids as recommended in former studies on the subject (Pierrat et al, 2012;Saucède et al, 2014;Fabri-Ruiz et al, 2018, 2020 and more widely, for species distribution modelling (Anderson, 2013;Franklin, 2010). They were extracted from the database compiled by Fabri-Ruiz et al (2017) and averaged for the (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) period.…”

“…Tripneusfes angulosus (Leroy et al, 2016). For correlation values exceeding 0.7, one predictor of a pair was removed based on ecological arguments that is, the most relevant predictor for modeling and interpreting echinoid distribution (Saucède et al, 2014;Fabri-Ruiz et al, 2018, 2020. Finally, 13 descriptors were used to run Random Forest models (RF) and 10 for the Generalized Dissimilarity Model (GDM) approach as categorical variables cannot be run in GDM.…”

“…The first procedure was developed to model individual species distributions as a function of environmental descriptors and then combine all ENMs into ecoregions (Dubuis et al, 2011;Calabrese et al, 2014). Following a "predict then assemble" strategy (Ferrier and Guisan, 2006), we used a novel approach combining ENM using Random Forests (Breiman, 2001) and model-based clustering with Gaussian Mixture Models (Fraley and Raftery, 2006) following the procedure recently developed by Fabri-Ruiz et al (2020). This procedure can provide the composition of species assemblages for each ecoregion but most common species only can be used as representative of the total fauna.…”