Productivity and growth rate in Palmaria palmata affected by salinity, irradiance, and nutrient availability—the use of nutrient pulses and interventional cultivation

Land-based cultivation of the rhodophyte Palmaria palmata is promising for high productivity and nutrient mitigation, yet the cultivation strategy and the knowledge of the effect of various environmental factors are incomplete. In a two-phased cultivation trial, marginal proliferations were used as seedstock to test the impact of irradiance (10–280 μmol photons m⁻² s⁻¹ photosynthetically active radiation; PAR) using sequential nutrient phases of pulse additions (10% vs. 100% F/2+) on specific growth rate (SGR) and productivity (exp.1). The effect of salinity (15–35‰) and nutrient concentration (10 vs. 100% F/2+) on frond growth was investigated (exp.2). The SGR peaked at 200 μmol photons m⁻² s⁻¹ PAR in both nutrient phases with max mean SGR of 6.86 ± 0.4% day⁻¹ (mean ± SE, n = 3). Above 80 μmol photons m⁻² s⁻¹ PAR, thalli turned pale green after 3 weeks at low nutrient. Shifting to a high nutrient cultivation, thalli recovered their red color after 10 days, even at 280 μmol photons m⁻² s⁻¹ PAR and significantly upshifted SGR, dry matter (DM), nitrogen (N), phosphorous (P), and ash content by 79.3, 56.0, 27.3, and 16.4%, respectively. Peak productivity in DM (1.17 g DM m⁻² day⁻¹), carbon (C) (406.41 mg C m⁻² day⁻¹), N (20.61 mg N m⁻² day⁻¹), and P (2.06 mg P m⁻² day⁻¹) coincided with SGR. Salinity significantly affected SGR of P. palmata and peaked at 15‰. This study highlights the use of marginal proliferations seedstock, nutrient pulses, and intervention practice for biomass propagation of P. palmata while avoiding epiphytes to boost N removal.