Marianela Zanolla

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 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.

As the commercial use of seaweed for natural product extraction calls for abundant, uniform biomass, this study focused on the production and the variability of the harvested biomass of valuable compounds produced by a commercially relevant red algal species, Asparagopsis armata. Its tetrasporophyte stage was retrieved from two Irish localities and grown for over 2 years in indoor cultures at 13 °C and 17 °C, and bromoform, mycosporine-like amino acids and phycobiliprotein contents were monitored over time. Growth rates at different temperatures were specific to isolates, and one isolate failed to grow at 17 °C. All compounds of interest were detected by the end of the 2-year cultivation period, and most of them were produced at an exponential rate at 13 °C but not at the higher temperature. At 13 °C, bromoform reached concentrations of 10.00 ± 0.55 mg g⁻¹, total mycosporine-like amino acids of 2.65 ± 0.10 mg g⁻¹, phycoerythrin of 11.46 ± 0.35 mg g⁻¹ and phycocyanin of 72.13 ± 1.74 mg g⁻¹ in Irish isolates. The observed variability in compound content was statistically significant but not large enough to impede commercial utilization. Bromoform content in cultivated samples was almost 6-fold higher than in field-collected samples though natural bromoform variability remains to be elucidated. Our findings suggest that the tetrasporophytic phase of A. armata is a suitable candidate for indoor cultivation; abundant and homogeneous biomass composition can be obtained which can be further optimized by growth temperature.

Can the reproductive traits of