Morphological and physiological plasticity of Saccharina latissima (Phaeophyceae) in response to different hydrodynamic conditions and nutrient availability

Abstract

Morphology and physiology are two key aspects of the adaptation of kelp to varying environments. Some of these kelp responses to co-occurring highly hydrodynamic condition and high nutrient availability are well documented, but little is known about how these factors affect frond surface shape, particularly in the central frond. In this study, morphological and physiological traits of acclimatized Saccharina latissima (Phaeophyceae) (three size classes: 44.14 ± 1.15 cm, 29.60 ± 0.75 cm, and 16.07 ± 0.45 cm) were compared after 56 days under fully controlled conditions of waves or no waves, and high or low nutrient availability (i.e., LN-NW, LN-W, HN-NW, and HN-W treatments). Waves primarily increased frond biomass, elongation rate, and carbon to nitrogen ratio (C:N ratio) and induced both a greater variety in and rougher frond surface shapes. The fastest, second-fastest, and slowest growth rates were observed in the HN-W, LN-W, and LN-NW treatments, respectively. The highest C:N ratio was observed in the LN-W treatment. Together, these results seem to suggest that the thready and spring-like shapes found in the central frond (i.e., rougher frond surface) in wave-exposed conditions can at least partly compensate for low nutrient availability by enhancing nutrient and photon acquisition, particularly in low nutrient conditions. Additionally, large individuals showed significantly larger and heavier fronds compared with other size classes, and the meristematic sections of fronds had the most variance in frond surface shapes and highest C:N ratios compared with distal and mid-sections. Together, these results indicate that frond surface shapes in the newly formed central frond of S. latissima can be regarded both as possessing high morphological and physiological plasticity that enables kelp to cope with contrasting environments.