The role of intraspecific diversity in modulating microplastic impacts on biogenic habitatsBiology & Ecophysiology

Lorenzo Cozzolino^1,2, Katy R Nicastro^2,3, Christopher D McQuaid³, Laurent Seuront^2,3,4, Sebastien Lefebvre², Camille Detree^5,6, Laura Gribouval⁷, Fernando P Lima⁸, Pierre William Froneman^3,9, Peter C Hubbard¹, Halldór P Halldórsson¹⁰, Gerardo I Zardi^3,5

¹Universidade do Algarve, Portugal - ²Univ. Lille, CNRS, Univ. Littoral Côte d’Opale, IRD, UMR 8187, LOG – Laboratoire d’Océanologie et de Géosciences, France - ³Rhodes University, South Africa - ⁴Tokyo University of Marine Science and Technology, Japan - ⁵Normandie Université, UNICAEN, Laboratoire Biologie des Organismes et Ecosystèmes Aquatiques, UMR 8067 BOREA (CNRS, MNHN, UPMC, UCBN, IRD-207), France - ⁶Office Française de la Biodiversité, France - ⁷SATMAR, France - ⁸CIBIO, Centro de Investigaccaao em Biodiversidade e Recursos Geneticos, Portugal - ⁹University of Cape Town, South Africa - ¹⁰University of Iceland, Iceland

Hard-bottom ecosystems such as rocky reefs offer structurally complex biogenic habitats that support key ecosystem functions and services. However, in recent decades, these ecosystems have been increasingly threatened by microplastic (MP) pollution, which accumulates within them and interacts with their resident species through MP ingestion and leaching chemicals. While the ecological impacts of MPs have been well documented at the species level, the role of intraspecific diversity - the genotypic and phenotypic variation within a species - remains poorly understood. Indeed, it is well acknowledged that diversity below the species level is a critical component of ecological systems, providing the foundation for species adaptation, survival and evolution while shaping ecosystem functioning and resilience. However, the role of intraspecific diversity in species responses to MP pollution remains largely overlooked. Over the past four years, we have investigated the effects of MP accumulation, ingestion, and leaching chemicals on the intraspecific diversity of keystone species, forming biogenic habitats in temperate reef systems. We demonstrated significant effects of intraspecific diversity on MP trapping by intertidal macroalgae, emphasising how phenotypic variation modulates microplastic retention in biogenic habitats. Despite detecting no effect of intraspecific diversity on microplastic ingestion in mussel and oyster reefs, we found significant intraspecific effects on the behavioral responses of the reef-forming species to MP leachates. Overall, our work emphasises the importance of integrating intraspecific diversity into MP research, particularly in biogenic habitats where its effects can have cascading impacts on the ecosystem. Understanding these interactions will help clarify the extent to which MP pollution affects hard-bottom ecosystems, ultimately improving conservation strategies for their habitats amid anthropogenic changes.