Environmental control of the annual erect phase of <i>Nemalion helminthoides</i> (Rhodophyta) in the field

Abstract

SUMMARY: 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.Keywords: carbon, daylength, multivariate, Nemalion helminthoides, nitrogen, phenology, phycobilins, protein, RDA, temperature.RESUMEN: Control ambiental de la fase macroscópica de NemalioN helmiNthoides (Rhodophyta) en el campo. -En las costas templadas la falta de nutrientes durante el verano, y en particular la falta de N, es la causa principal de la limitación del crecimiento de las algas. Sin embargo en la costa N de España Nemalion helminthoides (Velley) Batters aparece precisamente durante esta época del año, desde mediados de mayo a finales de julio. Por ello se asume que sus requerimientos de nutrientes son lo suficientemente bajos como para aprovechar pulsos ocasionales, y se plantea la hipó-tesis de que la condición fisiológica del talo mejora durante la ocurrencia de estos pulsos. Para comprobar esta hipótesis se midieron indicadores de la condición fisiológica tales como el contenido interno de N, C, proteínas y ficobilinas, además del crecimiento y del estado fenológico a lo largo del periodo de crecimiento estival, que se han relacionado con variaciones temporales en disponibilidad de nutrientes, irradiancia, temperatura y fotoperiodo. Los datos se analizaron utilizando una aproximación...