Nutrient uptake and growth responses of three intertidal macroalgae with perennial, opportunistic and summer-annual strategies

Abstract

An important life history trait of macroalgae species is the physiological ability to cope with nutrient limiting conditions, which seasonally occur in temperate coasts while other environmental factors are adequate ( e.g., sufficient light). Nitrogen (N) and Phosphorus (P) uptake kinetics and field growth limitation were investigated in the perennial Bifucaria bifurcata, the opportunistic Ulva intestinalis, and the summer-annual Nemalion helminthoides from Asturian coasts (N Spain). We performed 4 nutrient uptake experiments (ammonium, nitrate, nitrate + ammonium, and phosphate) and monitored the growth and N content of field individuals in the presence/absence of artificial nutrient supply to assess potential growth limitations. B. bifurcata was not actively growing during summer thus low nutrient demands probably relied on stored pools and/or the low background nutrient levels in seawater, as generally observed for perennials. Corresponding N content and uptake rates in this species were the lowest. The opportunistic U. intestinalis showed kinetics suitable for assimilating N quickly at high external concentrations in order to fulfill the high nutrient demands that support its fast-growing strategy. This response is well adapted to seasons and sites of high nutrient loading but signs of nutrient starvation during summer (decreasing growth and N content) were found in the pristine studied area. N. helminthoides showed an intermediate response in terms of thallus N content and uptake affinity, together with an inducible activation of nitrate uptake. This response assured the uptake of transient nutrient pulses without the nutrient storage response of perennials, or the costly enzymatic machinery of opportunistics. This allows N. helminthoides to effectively exploit low background nutrient conditions interrupted by transient peaks during spring–summer, when most ephemerals found difficulties to survive and perennials suspend their active growth. P uptake did not differ greatly between species suggesting its secondary importance compared to N in the tested algae.