Multiscale spatial variability in epibiont assemblage structure associated with stipes of kelp Laminaria hyperborea in the northeast Atlantic

Abstract

Foundation species elevate local biodiversity and underpin critical ecological processes and functions. Kelp species are distributed along ~25% of the world’s coastlines, where they serve as foundation species in intertidal and subtidal habitats. As well as ameliorating environmental conditions and producing organic matter, they provide biogenic habitat for a vast array of associated organisms. Here, we investigated patterns of diversity and structure in assemblages associated with the stipe of the kelp Laminaria hyperborea in the NE Atlantic. Stipes were sampled at 4 study regions (with 3 sites nested within each region) in the UK, spanning ~9° of latitude. Stipe-associated communities were highly diverse (134 species) and abundant (16-4532 ind. stipe-1), with no obvious sequential shift in diversity or overall trends in abundance/biomass of assemblages with latitude. However, we observed high degrees of variability between sites from the same region and individuals within sites, indicating that processes working across smaller spatial scales were more important than those at regional scales. While we observed high between-site variability in assemblage structure, regional differences were also evident. Most notably, sites within our southernmost region (southern England) were largely devoid of amphipods that dominated all other regions. This study highlights the important role of L. hyperborea in elevating biodiversity at local to regional scales through a facilitative interaction. Moreover, given that L. hyperborea forests may be increasingly impacted by ocean warming, changes in coastal water quality and proposed exploitation, our study serves as an important benchmark against which to detect future changes.

Examining the influence of regional‐scale variability in temperature and light availability on the depth distribution of subtidal kelp forests

“…By conducting surveys across a large spatial scale, we were able to examine the influence of regional‐scale processes, such as variability in ocean climate and light availability, on local depth‐related patterns. These study sites have been the focus of an extensive field program over recent years, and latitudinal shifts in kelp forest structure, spatial variability in biodiversity, and rates of primary productivity are increasingly well understood (Smale et al 2016, 2020; Smale and Moore 2017; Pessarrodona et al 2018; Teagle et al 2018; Bué et al 2020; King et al 2021). However, as with kelp forests in many regions, patterns of vertical distribution and shifts in structure along depth gradients remain unclear.…”

Climate‐driven substitution of foundation species causes breakdown of a facilitation cascade with potential implications for higher trophic levels

“…Kelp forests support high biodiversity in coastal marine ecosystems (Steneck et al, 2002; Teagle et al, 2017). The secondary habitat provided by epiphytic algae on kelp stipes has been shown to facilitate the development of highly diverse and abundant faunal assemblages (Christie, 1995; Christie et al, 2003; King et al, 2021). Epiphyte biomass varied dramatically between species, with 90% of L. ochroleuca stipes devoid of any epiphytic material.…”

“…P. palmata is a common and abundant epiphyte on L. hyperborea stipes and densities (i.e. biomass values) were representative of naturally occurring epiphytic assemblages (King et al, 2021; Teagle & Smale, 2018). For each replicate, multiple P. palmata thalli were carefully tied together at the base, secured with tape and affixed to an open cable tie for easy attachment onto stipes in the field.…”

“…In the North East Atlantic, the cold‐adapted boreal species, Laminaria hyperborea , is a dominant habitat‐former throughout its distribution from northern Norway to northern Portugal (Figure 1a), particularly on wave‐exposed shallow subtidal reefs (Kain, 1979; Smale & Moore, 2017). Atypically among kelp species, L. hyperborea supports abundant epiphytic algal assemblages on its stipe, which serve as secondary habitat‐formers (King et al, 2021; Whittick, 1983). This habitat cascade increases living space and complexity for abundant and diverse assemblages of mobile invertebrate fauna, which represent an important food resource for higher trophic levels (King et al, 2021; Norderhaug et al, 2005).…”

“…Atypically among kelp species, L. hyperborea supports abundant epiphytic algal assemblages on its stipe, which serve as secondary habitat‐formers (King et al, 2021; Whittick, 1983). This habitat cascade increases living space and complexity for abundant and diverse assemblages of mobile invertebrate fauna, which represent an important food resource for higher trophic levels (King et al, 2021; Norderhaug et al, 2005).…”