Exploring the contrasting seasonal strategies of two crenic macroalgae

Most studies on springs assumed stability, and reduced seasonal changes in the biota. We focused on two macroalgae (the rhodophyte Hildenbrandia rivularis and the chrysophyte Hydrurus foetidus) to unveil their seasonal–development patterns in springs. H. rivularis cover remained virtually constant throughout the year, although seasonal fluctuations in ecophysiological parameters were detected. The most important determinant of seasonal changes in H. rivularis was shown to be the complex interplay between solar radiation (day length) and shading. Negative cross–correlation between Chl–a and shading was found to be significant but with a time lag. H. foetidus seasonal changes were evident both at the macroscopic level and in ecophysiological parameters. Interestingly, it occurred throughout the year in the spring whilst it completely disappeared in summer in a nearby glacial stream. Unexpectedly, variability of ecophysiological parameters (coefficients of variation) was shown to be 15–20% higher in H. rivularis than in H. foetidus.