Importance of wave and current exposure to fauna communities in Laminaria hyperborea kelp forests

Abstract

Hydrodynamic forces from waves and currents may have strong but different impacts on benthic diversity. In order to study the relative importance of current and wave exposure to the diversity of macrofauna associated with the kelp Laminaria hyperborea, we sampled fauna on epiphytic algae of 4 different morphological types from 27 stations in a crossed design with 3 levels of wave exposure and current speed. Fauna species number (S) was determined by morphology and amount (weight) of epiphyte and the interaction between wave exposure and current speed. Shannon-Wiener diversity H ' was determined by the epiphyte morphology and amount and degree of wave exposure. The most important factors for faunal community composition were epiphyte morphology and wave exposure, and the effect of wave exposure was different for algae of different morphology. The most diverse fauna communities were found at intermittently wave-exposed sites and on large, rough epiphytic algae. The study shows that waves and currents influence kelp fauna communities very differently. Within our study area, waves had a stronger overall effect compared to currents.

Community, trophic structure and functioning in two contrasting Laminaria hyperborea forests

“…Biomass of seaweed or consumer groups was standardised either by lamina, stipe or holdfast biomass. In order to characterize habitat features that may influence faunal distribution (Christie et al, 2007;Norderhaug et al, 2014), red, brown and green macroalgae (considered as trophic groups)…”

“…While an important dissimilarity in species composition was found among strata, a substantial connectivity exists horizontally among kelp plants and vertically among strata for several mobile taxa (Norderhaug et al, 2002;Waage-Nielsen et al, 2003). The abundance of mobile fauna in kelp epiphytes may therefore interfere with habitat complexity on the understorey and kelp size-density structure (density of adults hosting abundant epiphytes), factors interacting with wave force dissipation (Eckman et al, 1989;Norderhaug et al, 2014). In Norway, Norderhaug et al (2014) showed higher richness and abundance of mobile fauna associated to kelp epiphytes in intermediate wave-exposed sites.…”

“…The abundance of mobile fauna in kelp epiphytes may therefore interfere with habitat complexity on the understorey and kelp size-density structure (density of adults hosting abundant epiphytes), factors interacting with wave force dissipation (Eckman et al, 1989;Norderhaug et al, 2014). In Norway, Norderhaug et al (2014) showed higher richness and abundance of mobile fauna associated to kelp epiphytes in intermediate wave-exposed sites. Although seemingly at odd with our findings, this study was performed among sites displaying equivalent kelp densities in the canopy layer, therefore limiting any generalisation to heterogeneous kelp forests.…”

“…Community structure and distribution of mobile fauna has often been linked to the structural complexity of kelp individuals (Jones, 1971;Moore, 1973) and epiphytic seaweeds (Norderhaug et al, 2002;Christie et al, 2007). Within epiphytes and holdfasts, environmental factors such as turbidity and wave exposure, interacting with the complexity of seaweed forming-habitat, can also influence mobile fauna distribution (Moore, 1973;Norderhaug et al, 2012;Norderhaug et al, 2014).While these strata have been investigated with attention, understorey communities are still overlooked. The kelp canopy can provide favourable conditions to the development of functionally diverse seaweeds on the surrounding substratum (Norton et al, 1977), expected to shelter complex communities of sessile and mobile fauna.…”

Epiphytic flora on <em>Gelidium corneum</em> (Rhodophyta: Gelidiales) in relation to wave exposure and depth

“…This pattern is consistent with other studies from northwestern Spain (Galicia) (Peteiro and Freire 2013) and northern Europe (Pedersen et al 2012, Baer andStengel 2014), which found the epiphytic loads on canopyforming species to be lower on more exposed coastal stretches. Moreover, very exposed locations (NW) in our study showed lower species richness and diversity, coinciding with that found for epiphytic flora (Kersen et al 2011) and fauna growing on canopy-forming macrophytes (Norderhaug et al 2012(Norderhaug et al , 2014, according to whom lower species diversities are found under frequent or even rare ecological disturbances (e.g. wave action).…”