Jesús Rosas-Guerrero

Although there were indications of its presence in the Strait of Gibraltar in 2015, it was not until 2016 that the identity and presence of the brown seaweed was confirmed on the coast of Ceuta in northern Africa (Spain) (Altamirano et al. 2016). This species, which is native to the western Pacific, was first detected on the French Mediterranean coast in 2002. However, it did not begin to exhibit invasive behaviour until it arrived in southern Spain. Over the past ten years, it has spread to the coasts of Portugal, France, Italy, Morocco, Algeria, Spain, and the Macaronesia islands. The ecological and socio-economic impacts of this species are unprecedented, justifying its designation as a species of special concern for the Union. This makes it the first marine macroalgae species to be classified as such. This presentation will share information on these impacts, particularly on rocky seabeds and seagrass beds, where drastic biodiversity loss has occurred. It will also address the impacts on the fishing industry and local councils regarding the removal of seaweed, which results in millions of euros in losses each year. The presentation will also address key aspects of the species' invasiveness outside its native range, focusing particularly on its vegetative phenology (morpho-anatomical changes and population dynamics) (Rosas-Guerrero et al. 2025), and its reproductive phenology (Rosas-Guerrero et al. 2026). Notably, the species has an enormous capacity to produce numerous new individuals through clonal mechanisms. These individuals attach themselves not only to the seabed but also grow in the water column. It has been estimated that the pressure exerted by propagules exceeds the carrying capacity of the marine substrate, with more than half a million potential new individuals invading Posidonia oceanica per m² per year. At a physiological level, R. okamurae exhibits a high capacity to acclimatise to changing light conditions. This enables it to live at different depths and survive in darkness for extended periods without losing viability (Rosas‐Guerrero et al. 2025). For this reason, managing R. okamurae poses significant challenges at local, regional, national and international levels. Mitigating its impacts requires coordination among the relevant authorities, who must establish measures to monitor and prevent further introductions and dispersal, as well as implement strategies to manage the biomass it produces — all within the current regulatory framework. Currently, R. okamurae continues to expand its range, causing impacts wherever it arrives. If the predictive models developed for this species are accurate, it could represent the most severe invasion of the European marine environment to date, threatening the resilience of our marine habitats.

Rugulopteryx okamurae is a recently introduced brown macroalga that has expanded rapidly across the Azores (NE Atlantic). This study provides an update of the archipelago‐wide spatial spread and the first assessment of its local population dynamics. Multi‐year surveys (2019–2024) revealed a swift progression from the initial detection in São Miguel in 2019 to records in eight of the archipelago's nine islands by 2024. Early species occurrences were consistently located near main islands' harbours, indicating maritime traffic as the primary vector of introduction and inter‐island dispersal. Once established, populations persist and frequently reach high cover along extensive rocky coastlines. Monthly demographic sampling demonstrated year‐round persistence with pronounced seasonality: biomass and thallus length peaked in spring and declined sharply in summer due to widespread thallus detachment, while density fluctuated moderately, increasing in spring and again in late autumn. Asexual reproductive structures were most abundant in late winter–spring, with no record of gametangial sori. Size‐frequency analyses revealed up to seven overlapping cohorts, indicating continuous recruitment apparently maintained through both asexual reproduction and vegetative propagation. Generalised linear models detected significant negative influence of temperature and a significant positive influence of photoperiod on the species' thallus length, biomass and reproduction, suggesting that increasing daylength in winter and spring may trigger its growth, which is then halted as seawater warms up. Overall, these findings indicate that R. okamurae is now a widespread and persistent invader in the Azores, with its expansion driven primarily by maritime vectors and influenced by regional‐scale variation in environmental conditions associated with seasons.

Las invasiones biológicas son un elemento importante del cambio global y la segunda amenaza por orden de importancia para la biodiversidad del planeta, representando hoy en día un problema internacional que no entiende de fronteras políticas. A pesar de suponer entre un 10 y un 40 % de los organismos invasores a nivel mundial, diversas cuestiones relacionadas con las macroalgas aún suponen desafíos importantes. Estas cuestiones abordan el problema de la introducción de especies, los mecanismos que subyacen en el proceso invasor, las consecuencias de las invasiones y las respuestas humanas (gestión) a la amenaza y ocurrencia de las invasiones. El éxito de una especie invasora se define por su capacidad para superar todas las etapas del proceso invasivo, salvando todas las barreras ecológicas existentes y puede explicarse a partir de las condiciones ambientales favorables, los factores intrínsecos de la especie invasora (invasividad) y de la vulnerabilidad del hábitat receptor (invasivilidad). La defensa más efectiva y rentable contra las invasiones biológicas es la prevención, proponiéndose actualmente como una herramienta útil la predicción basada en modelos biológicos. El presente trabajo aborda una revisión sobre las macroalgas marinas invasoras en el Mar de Alborán actualizando la información disponible sobre sus características biológicas y ecológicas, expansión de cada una de las especies, los impactos que causan y la gestión de las invasiones.

The high variability of natural environments poses significant challenges to photosynthetic organisms, which must adapt to constant fluctuations. Mechanisms such as acclimation and adaptation are essential for mitigating stress and ensuring survival. Rugulopteryx okamurae , an invasive alien seaweed recently introduced into Mediterranean and Atlantic waters, displays a remarkable ecological success, forming dense monospecific populations throughout diverse environments. This persistence suggests highly efficient acclimation mechanisms, possibly driven by seasonal physiological performance. The aim of this study was to evaluate the seasonal physiological response of R. okamurae to seasonal environmental fluctuations within a Posidonia oceanica meadow in the Alboran Sea, to better understand the photosynthetic acclimation strategies underlying its invasiveness. Photosynthesis–irradiance curves, pigment concentrations and elemental composition were analysed in individuals sampled bimonthly from July 2021 to July 2022 at a −10 m depth. Results showed significant seasonal variation in physiological parameters, highlighting a consistent acclimation capacity and robust photosynthetic performance. Fluctuations in pigment content and photosynthetic variables reflected the species' ability to optimise metabolic activity in response to environmental changes. Light compensation and saturation parameters further indicated strong photoadaptive capacity, enabling the species to thrive under both low and high light conditions. Its tolerance to a broad range of environmental factors, combined with mechanisms that prevent photoinhibition, may explain its persistence across seasons and wide depth ranges in the Alboran Sea. Although further research along depth gradients is needed, these findings underscore the role of physiological plasticity in the ecological success of R. okamurae and highlight the value of field‐based studies in understanding invasion processes of marine macrophytes.

The success of invasive species can be measured by invasiveness, which depicts intrinsic characteristics that enable them to thrive in new environments. In invasive seaweeds, for example, the persistence of multiple overlapping cohorts throughout the year plays a key role in increasing plant cover and exerting unrelenting pressure on invaded areas. The marine brown macroalgae Rugulopteryx okamurae has recently established abundant populations in the Mediterranean Sea and Atlantic Ocean, negatively affecting both biodiversity and socioeconomic factors by unprecedently aggressive invasive behaviour. The objective of the study is to understand the invasiveness of R. okamurae through its popu lation dynamics. For this, a year-round study was conducted in a protected habitat of Posidonia oceanica in southern Spain, revealing that R. okamurae uses alternating mechanisms for population maintenance. It achieves high density of young individuals in late summer and autumn, peaking at 3285 individuals per square metre. In spring and early summer, the population shifts towards fewer – but larger – individuals, with densities dropping to 888 individuals per square metre and biomass reaching a peak of 170 g dry weight (DW) per square metre. Six overlapping cohorts were identified by Gaussian curves. They persisted throughout the year, but they were not related to environmental factors, which indicates adaptive physiological mechanisms that sustain dense monospecific populations. Additionally, the association between cohorts and different morphotypes suggests that R. okamurae phenotypic plasticity enables its persistence in introduced areas. These findings provide valuable insights into the biological traits underpinning its invasiveness in P. oceanica meadows, revealing temporal windows of invasiveness driven by different mechanisms. This knowledge is crucial for developing effective conservation and management strategies aimed at mitigating the impact of this invasive species.

Drifted material from the deep-sea species Sargassum trichocarpum was found in the provinces of Malaga and Cadiz. These finding highlights that the species is still present on the eastern Mediterranean coasts despite the threats affecting its populations, which are in a state of decline.