Length, strength and water flow: relative importance of wave and current exposure on morphology in kelp Laminaria hyperborea

Abstract

Water flow is a strong determinant of kelp growth, but it is also a stress factor causing breakage and dislodgement. As wave exposure and currents differ with respect to flow pattern, the 2 forces are expected to affect kelp morphology differently. We investigated how wave exposure and current speed interact and influence kelp Laminaria hyperborea morphology. We sampled thalli from 27 stations on the Midwest coast of Norway and recorded age, and length-and strength-related characters. We found that high wave exposure and current speed influenced holdfast biomass and stipe thickness. Wave exposure had, overall, a stronger effect than current speed. An increase in current speed seemed to have a considerable effect at low wave exposure levels, but the relationship weakened at high wave exposure levels. The length-related ('go with the flow') characters thallus and stipe length were influenced by wave induced water flow but not by current speed. Differences in wave exposure and current speed had very weak influences on lamina biomass and length. Thus, the proportion of the thallus being lamina was high in the most sheltered areas and decreased as the wave exposure increased. Our study suggests that the strong, orbital and stochastic mode of wave exposure has a different and stronger effect as a stressor than the more regular and bidirectional stress caused by currents.

Red sea urchins (Echinus esculentus) and water flow influence epiphytic macroalgae density

“…This might be due to the high resolution of the wave exposure model (25 m) compared to the current speed model (200 m). However, similar results were also found by other studies applying current speed models of higher resolution (Bekkby et al 2014;Norderhaug et al 2014). Consequently, we believe that the results are explained by differences in the mode of the two water forces, wave exposure being more orbital and stochastic and current speed being more regular and bidirectional, possibly allowing more light to enter the stipe-associated algae in the wave-exposed areas and resulting in more kelp canopy shading at high current speeds.…”

“…Wing & Patterson 1993), transport across boundary layers and consequently nutrient uptake (Raven 1981;Wheeler 1988), settlement, recruitment (Vadas et al 1990) and resource allocation (Raven 1988). Waves and currents have been found to interact and influence size and biomass of Laminaria hyperborea kelp (Bekkby et al 2014) and its associated species (Norderhaug et al 2014).…”

Influence of waves and currents on the growth rate of the kelp Laminaria digitata (Phaeophyceae)

“…Bekkby et al. () suggested that wave exposure had a stronger effect as a stressor on kelp compared to that of regular bidirectional stress caused by current flow. The hydrodynamic forces associated with wave environments are more frequent and potentially create additional loading and fatigue stresses on the blade/thallus than less frequent loading in current hydrodynamics with the possible result that there are trade‐offs in growth strategies.…”

Can sea urchin grazing of kelp forests in the Arctic make rocky shore systems more vulnerable to oil spills?

“…The model has been applied in several projects in Norway (e.g. Norderhaug et al 2012;Pedersen et al 2012;Bekkby et al 2014;Rinde et al 2014), Sweden (e.g. Eriksson et al 2004), Finland (Isaeus and Rygg 2005), the Danish region of the Skagerrak coast and the Russian, Latvian, Estonian, Lithuanian and German areas of the Baltic Sea (Wijkmark and Isaeus 2010).…”