Variations in Growth, Erosion, Productivity, and Morphology of Ecklonia Radiata (Alariaceae; Laminariales) Along a Fjord in Southern New Zealand1

Abstract

Spatial and temporal patterns of growth, erosion, productivity, and morphology of the dominant habitat-forming kelp Ecklonia radiata (C. Agardh) J. Agardh were studied bimonthly over 1.5 years in a southern New Zealand fjord characterized by strong gradients in light and wave exposure. Spatial differences in growth were observed with rates at two outer coast, high-light, wave-exposed sites reaching 0.42 and 0.45 cm · d , respectively, compared to 0.27 cm · d at an inner, more homogeneous site. Sporophyte productivity was similar among sites, although population productivity was greater at the outer sites due to population density being 5-fold greater than at the inner site. It was expected that the inner site would have no pronounced seasonal pattern in growth and productivity due to its homogeneity; however, all three sites displayed maximum rates in late winter/spring and minimal in autumn. Growth rates were 2-fold greater during the first growth period than the following year. This discrepancy was not correlated to inorganic nitrogen (N) levels, which remained low year-round (<4 μM), and is likely a result of an interaction between light and temperature, and the photosynthetic capability of E. radiata. Variable pigment content indicated photoacclimation at the inner site. Morphological differences were observed between sites, with E. radiata from the inner site having longer, wider, thinner blades and longer stipes. While E. radiata displayed spatial differences in growth, erosion, productivity, and morphology, populations displayed no temporal differences. These results highlight the need for greater understanding of the mechanisms influencing kelp growth and productivity in a unique marine environment.

The Abundance of Kelp Is Modified by the Combined Impact of Depth, Waves and Currents

“…2014, the discussion in Kain, 1971a and studies on other kelp species, e.g., Duggins et al, 2003;Eckman et al, 2003;Miller et al, 2011).…”

“…Water flow is also associated with wounding, breakage, dislodgement (de Bettignies et al, 2012;Graham et al, 2016) and morphological changes due to dragreducing adaptation (Armstrong, 1989). Water flow may come in the form of wave induced exposure or ocean currents, with wave exposure being more orbital than the unidirectional ocean currents, with a large tidal component (Miller et al, 2011). The effect of wave exposure on L. hyperborea distribution, growth, density, production, biomass, mortality and morphology has been documented in several studies (e.g., Svendsen and Kain, 1971;Sjøtun and Fredriksen, 1995;Sjøtun et al, 1998;Gorman et al, 2012;Pedersen et al, 2012).…”

Fiordland: the ecological basis for ecosystem management

“…This marks a distinct habitat transition in Fiordland where the composition of primary producers undergoes a dramatic shift. Wave exposure, illumination and nutrient source pools acted to structure both patterns in productivity within species (Miller et al 2006;Cornelisen et al 2007;Miller et al 2011) and the composition of the macroalgae community (Wing et al 2004). As a result, there was a distinct gradient in the relative contribution of macroalgae and phytoplankton to the basal organic matter pool along the axes of the fjords (Wing et al 2008).…”

The Influence of Physical Factors on Kelp and Sea Urchin Distribution in Previously and Still Grazed Areas in the NE Atlantic

“…Thus there is variation in the sea temperature along the coast-ocean gradient that might influence kelp growth and sea urchin survival. Local differences in current speed [23] and terrain characteristics, such as depth, curvature and slope (the two latter being proxies for substrate; steep/rugged areas implying rocky substrate and flat areas in valleys implying soft sediments), also affects kelp plants growth conditions and thereby their distribution [21], [26], [27].…”