Can ecosystem functioning be maintained despite climate‐driven shifts in species composition? Insights from novel marine forests

Abstract

Climate change is driving a redistribution of species and the reconfiguration of ecological communities at a global scale. Persistent warming in many regions has caused species to extend their geographical ranges into new habitats, with thermally tolerant species often becoming competitively dominant over species with colder affinities. Although these climate‐driven changes in species abundance and diversity are well documented, their ecosystem‐level implications are poorly understood, and resolving whether reconfigured communities can maintain fundamental ecosystem functions represents a pressing challenge in an increasingly warmer world. Here, we investigated how climate‐driven substitutions of foundation species influence processes associated with the cycling of organic matter (biomass production, detritus flow, herbivory, decomposition) by comparing two habitat‐forming kelp species with contrasting thermal affinities. We examined the wider ecosystem consequences of such shifts for the observed (and predicted) emergence of novel marine forest communities in the NE Atlantic, which are expected to become more dominated by range‐expanding, warm‐temperate kelp species. Warm‐temperate kelps both accumulated and released 80% more biomass than the cold‐temperate species despite being taxonomically closely related and morphologically similar. Furthermore, the warm‐temperate species accumulated biomass and released detritus year‐round, whereas the cold‐temperate species did so during short, discrete periods. The warm‐temperate kelps supported higher densities of invertebrate grazers and were a preferred food source. Finally, their detritus decomposed 6.5 times faster, despite supporting comparable numbers of detritivores. Overall, our results indicate an important shift in organic matter circulation along large sections of NE Atlantic coastline following the climate‐driven expansion of a warm‐affinity kelp, with novel forests supplying large amounts of temporally continuous—yet highly labile—organic matter. Synthesis. Collectively, our results show that, like species invasions, climate‐driven range expansions and consequent shifts in the identity of dominant species can modify a wide range of important ecosystem processes. However, alterations in overall ecosystem functioning may be relatively limited where foundation species share similar ecological and functional traits.

Climate and fishing drive regime shifts in consumer‐mediated nutrient cycling in kelp forests

“…Climate‐ and human‐driven regime shifts are common in aquatic (Daskalov, Grishin, Rodionov, & Mihneva, ; deYoung et al, ; Pessarrodona et al, ) and terrestrial (Ripple & Beschta, ; Romme et al, ) consumer communities, often resulting in alteration of important ecosystem functions via modification of top‐down and bottom‐up processes (Andersen, Carstensen, Hernández‐García, & Duarte, ). Our study is unique in that it highlights how anthropogenic defaunation can shift regimes of recycled nutrients and disrupt CND over annual or decadal scales.…”

“…Nitrate is often considered to be the major form of nitrogen that fuels this high productivity, yet its availability in many temperate reef systems varies greatly among seasons and years (Brzezinksi et al, ; Chapman & Craigie, ; Jackson, ; van Tussenbroek, ). Despite this high variability and the limited capacity for some kelps to store nitrogen for less than a few weeks (Gerard, ), measurable growth occurs year‐round in many kelp systems (Hepburn, Holborow, Wing, Frew, & Hurd, ; Kirkman, ; Pessarrodona, Foggo, & Smale, ; Reed, Rassweiler, & Arkema, ; Vadas, Beal, Wright, Nickl, & Emerson, ; van Tussenbroek, ). Such observations have prompted suggestions that recycled forms of nitrogen (e.g., ammonium and urea) are important in sustaining kelp growth during extended periods of low nitrate availability (Brzezinksi et al, ; Hepburn & Hurd, ; Smith, Brzezinski, Melack, Miller, & Reed, ; Wheeler & Druehl, ).…”

Deficits in functional trait diversity following recovery on coral reefs

“…Response diversity has stabilized functions in a range of species assemblages, including plants, sea urchins, seaweed, insects, fishes, birds and microbes [16,18,[20][21][22][23][24]. For example, tropical bird species can respond differently to agricultural practices, allowing essential functions such as seed dispersion to be © 2020 The Author(s) Published by the Royal Society.…”

Temperature, phenology, and turf macroalgae drive seascape change: Connections to mid‐trophic level species

“…However, alterations and maintenance of seascape patterns in other regions will likely depend on the complex interactions between environmental variables and life-history characteristics of the inhabitant foundation species as well as the morphology of novel species. For example, alterations in overall seascape pattern may be limited where foundation species share life-history and morphological characteristics (e.g., Pessarrodona et al 2019). These environmentally induced changes in the maintenance of species composition drive and sustain the overall increase in seascape patchiness.…”