Ecological traits, genetic diversity and regional distribution of the macroalga Treptacantha elegans along the Catalan coast (NW Mediterranean Sea)

Este artículo contiene 10 páginas, 4 tablas, 5 figuras.The widespread decline of canopy-forming macroalgal assemblages has been documented in many regions during the last decades. This pattern is often followed by the replacement of structurally complex algal canopies by more simplified habitats (e.g., turfs or sea urchin barren grounds). Against all odds, the fucoid Treptacantha elegans, a large Mediterranean brown macroalga, broadened its depth range to deeper and exposed environments and displayed an unexpected range expansion along the northern coast of Catalonia over the last two decades. Here, we reconstruct the spread of T. elegans in time and space and unravel ecological and demographic traits such as population dynamics and genetic patterns to provide a comprehensive and integrated view of the current status and geographical expansion for this species. Fast-growing dynamics, early fertile maturity, and high turnover rate are the main competitive advantages that allow the exposed populations of T. elegans to colonize available substrata and maintain dense and patchy populations. We also provided evidence that the deeper and exposed populations of T. elegans constitute a single group across the Catalan coast, with little genetic differentiation among populations. This seems to support the hypothesis of a unique source of spread in the last decades from the Medes Islands No-Take Zone towards both southern and northern waters.This work was partially funded by the long-term monitoring programme of the Natural Park of Cap de Creus and the Natural Park of Montgrí, Medes Islands, and Baix Ter protected areas (Public Agreement PTOP- 2017-130, Departament de Territori i Sostenibilitat of the Generalitat de Catalunya) and the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement No 689518 (MERCES) and the Grant Agreement No 730984, ASSEMBLE Plus to the Portuguese node of EMBRC-ERIC (EMBRC.PT ALG-01-0145-FEDER-022121). Cristina Linares gratefully acknowledges the financial support by ICREA under the ICREA Academia programme. Simone Mariani was supported by the Spanish INTRAMURAL CSIC PIE201730E033. Work at CCMAR was funded by FCT—Foundation for Science and Technology (Portugal) UID/Multi/04326/2019, PTDC/MAR-EST/6053/2014, Biodiversa/0004/2015, SFRH/BPD/88935/2012 (DL 57/2016/CP1361/CT0010), SFRH/BSAB/150485/2019, and a Pew Marine Fellowship.Peer reviewe