Environmental control of the annual erect phase of Nemalion helminthoides (Rhodophyta) in the field

In temperate areas, lack of nutrients during summer, particularly N, is the main limiting factor of macroalgal growth. However, Nemalion helminthoides (Velley) Batters in northern Spain is conspicuous in the field during this time (from mid-May to late-July). Therefore, we assumed that its nutrient requirements are low enough to be sustained by transient nutrient inputs and we hypothesized that the physiological condition of the thalli was transiently improved when nutrient pulses occurred. A range of proxies for physiological condition (internal N, C, proteins and phycobilins), growth and phenological status of N. helminthoides were measured over time and related to temporal variations in nutrient availability, irradiance, temperature and daylength. Data were analyzed using a multivariate approach (redundancy analysis). Transient nutrient inputs were mainly due to freshwater runoff and wind-driven upwelling events; however, these pulses did not lead to any short-term improvement in the physiological condition of the algae because in such dominant nutrient limiting conditions plants divert transient available resources directly to growth and reproduction. Probably because of the strong endogenous nature of the N. helminthoides life-history, only daylength and temperature were found to be major environmental factors: increasing daylength was associated with growth, sexual maturation, fertilization and the increment of internal N and C, the amount of proteins and phycobilins. Decreasing daylength together with increasing temperature were correlated with spore release and senescence. This research suggests that N. helminthoides requires a high light dose to sustain growth and reproduction, and therefore it must grow and reproduce in summer even though it has to overcome nutrient deprivation during this period.