Abstract
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.
Highlights
Macroalgae are the most important primary producers in temperate coastal areas (Valiela, 1995)
Despite nutrient limitation during summer, a few marine algae appear and develop in the field mainly during this period. This is the case of N. helminthoides, a red seaweed with summer-annual development that belongs to the order Nemaliales (Dixon and Irvine, 1977)
The common strategy adopted by perennial seaweeds of storing nutrient pools in winter in order to overcome the summer nutrient limitation is not possible (Wheeler and Björnsäter, 1992; Rico and Fernández, 1996; Pedersen and Borum, 1996; Pueschel and Korb, 2001; Martínez and Rico, 2002)
Summary
Macroalgae are the most important primary producers in temperate coastal areas (Valiela, 1995) In these systems, long days during summer are correlated with increasing temperature, light-dose and generally calm sea conditions. Despite nutrient limitation during summer, a few marine algae (or at least the macroscopic phases of their life cycle) appear and develop in the field mainly during this period. This is the case of N. helminthoides, a red seaweed with summer-annual development that belongs to the order Nemaliales (Dixon and Irvine, 1977). The physiological response may depend greatly on the nutrient storage capability of the species at short time scales (Vergara et al, 1995; McGlathery, 1996; Pedersen and Borum, 1996; Costanzo et al, 2000; Nielsen, 2003; Bracken, 2004; Clavier et al, 2005; Lartigue and Sherman, 2005)
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