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

Abstract

The kelp Laminaria digitata growing in the low intertidal region along energetic coastlines are exposed to a range of hydrodynamic environments. Macroalgae in the intertidal zone can experience both waves and currents independently, but it is unknown how they influence growth rate. Relative growth rate of the meristematic region and the entire blade of L. digitata were measured to assess the influence of wave and current motion from three hydrodynamic environments: low current and low wave (LCLW), high current and low wave (HCLW), and high wave and low current (HWLC). Alongside hydrodynamic data, seawater nutrient concentrations and temperature were also collected and analyzed. Results suggest that differences in L. digitata relative growth rates were not attributed to the seawater nutrient concentrations or temperature, but attributed to the hydrodynamic environments. At the high current condition, kelp growth rate of the meristematic region was enhanced by 45% compared to the high wave condition. When including the entire blade growth rate, an average increase of 25% was observed between the high current and high wave condition. Potentially, the division in growth rate observed between the wave and current motion is related to the frequency and magnitude at which the hydrodynamic forces act. These findings highlight the complexity of the hydrodynamic environment and that forces associated with waves and currents may have a significant role on the productivity of kelp.

Ecological performance differs between range centre and trailing edge populations of a cold-water kelp: implications for estimating net primary productivity

“…Whilst elevated flow rates can increase productivity and overall biomass in L. digitata (e.g. Millar et al 2019), it is unlikely flow is responsible for our observed differences in regional performance as patterns run counter to our results i.e. despite lower flow rates, range centre individuals are larger and more productive.…”

“…These regional temperature differences become more apparent in summer where differences between regions are ~ 3.3 °C (Table 1). To minimise local effects of wave exposure on kelp performance and morphology (Gerard and Mann 1979;Blanchette et al 2002;Fowler-Walker et al 2006;Millar et al 2019) only fully exposed shores were selected. Wave exposure was measured using log wave fetch derived from summing fetch values calculated for 32 angular sectors surrounding each study site (see Burrows 2012).…”

“…Wave exposure was measured using log wave fetch derived from summing fetch values calculated for 32 angular sectors surrounding each study site (see Burrows 2012). Flow rates were greater at trailing edge sites but all still represented low flow sites for L. digitata (< 0.4 m s −1 ; see Millar et al 2019). Nutrients were not directly measured but UK coastlines are not characterised by major upwelling regimes and nutrients do not vary greatly with latitude (Painting et al 2013).…”

Coexistence of the native mussel, Mytilus edulis, and the invasive Pacific oyster, Crassostrea (Magallana) gigas, does not affect their growth or mortality, but reduces condition of both species

“…Previous studies around Strangford Lough have shown that differences in water motion occur within a relatively small area (Kregting & Elsäber, 2014;Kregting et al, 2016;Millar et al, 2020), which can play an important role in species morphology (Steffani & Branch, 2003;Millar et al, 2020). Our results show that the condition of M. edulis was greatest at sites with restricted water motion or unidirectional currents (KL & WS, respectively), compared to areas where waves dominate (BH; see Millar et al, 2020 for hydrodynamic characterisation of sites). Condition of C. gigas was also greatest at KL compared to both other sites, suggesting a preference for areas where little water motion occurs.…”

Length and Biomass Data for Atlantic and Pacific Seaweeds From Both Hemispheres

“…While differences among young individuals or fronds are generally small in a species, abiotic and biotic factors (temperature, competition, herbivory, etc.) often create variability in biomass accumulation patterns as individuals and fronds grow (Molis et al, 2015;Millar et al, 2020).…”