Phycology

Microalgae rarely grow alone. Bacteria, fungi, yeasts, other algae and animal hosts surround, attach to or enclose algal cells, and these associations control primary production, nutrient recycling, bloom dynamics and the performance of engineered cultivation systems. The interactions are still classified mostly by their outcome, as mutualism, commensalism, parasitism, amensalism, competition or neutralism. However, the same co-culture can move from mutualism to pathogenicity when growth phase, nutrient supply, light, temperature or pH change. This review proposes a classification based on the pathway that connects the organisms rather than on the outcome. Seven pathway classes are defined by what crosses the interface: metabolic exchange, growth factor provision, chemical signalling, oxidative stress modulation, algicidal and antagonistic activity, attachment and physical association, and gene transfer. Each interaction is further described by its mode of association, the obligate or facultative dependence of each organism and its context dependence. The review compares how these classes differ in their physiological effects on the alga and its symbionts in natural and engineered environments, the genes and physical structures that encode them and the magnitude of environmental effects acting on them. It then shows that pathways succeed and substitute for one another, and it discusses how mutation, gene loss, horizontal gene transfer and environmental change will redistribute pathways across algal symbioses.

This study provides a comprehensive assessment of the biomass and taxonomic and morpho-functional composition of stranded macroalgae and seagrasses on a highly productive shellfish bank in NW Iberia (Galicia), frequently affected by green tides, based on a year-long monitoring program and multivariate analyses. Macroalgal biomass showed marked seasonal and spatial variability, with the highest values recorded in spring. Chlorophyta dominated stranded biomass, particularly Ulva lacinulata, which accounted for over 63% of the total. Thin foliose morphotypes also made a major contribution to biomass across seasons and sampling locations. Linear mixed-effects modelling revealed a significant interaction between transect and intertidal level, indicating that spatial biomass patterns varied across the intertidal gradient. An interaction between season and intertidal level was also detected, although its statistical support was less consistent in sensitivity analyses. The absence of a consistent vertical zonation pattern suggests that stranded biomass distribution may be influenced by detachment, transport and deposition processes, rather than solely reflecting local macroalgal production. These findings highlight the importance of considering taxonomic and morpho-functional groups composition, spatial variability and hydrodynamic context when monitoring and managing valuable estuarine environments affected by green tides.

The freshwater red alga Riverina rivularis (Liebmann) C.W.Vieira & G.W.Saunders has historically been perceived as a rare or endangered species due to fragmented records and specific ecological requirements. However, the recent literature suggests that its distribution may be far wider than previously assumed, potentially influenced by intensified climate change. In this paper, we evaluated the current distribution of R. rivularis in Serbia, along with the key environmental factors driving its distribution and coverage. Additionally, we assessed the co-occurring benthic algal communities and the key environmental factors responsible for their occurrence. Furthermore, we predicted future species distribution under changing environmental conditions. Our results reveal that R. rivularis is far more ubiquitous in Serbian running waters than previously assumed, showing high tolerance for a wide range of environmental conditions. Hypothetical environmental change scenarios involving increases in water temperature and conductivity, both individually and combined, suggest a potential expansion of suitable habitats for R. rivularis. These findings highlight the importance of systematic monitoring and updated distribution data in freshwater conservation management, suggesting that R. rivularis should be regarded as a widespread component of Serbia’s algoflora rather than a threatened species.