Movement of pulsed resource subsidies from kelp forests to deep fjords

Abstract

Resource subsidies in the form of allochthonous primary production drive secondary production in many ecosystems, often sustaining diversity and overall productivity. Despite their importance in structuring marine communities, there is little understanding of how subsidies move through juxtaposed habitats and into recipient communities. We investigated the transport of detritus from kelp forests to a deep Arctic fjord (northern Norway). We quantified the seasonal abundance and size structure of kelp detritus in shallow subtidal (0‒12 m), deep subtidal (12‒85 m), and deep fjord (400‒450 m) habitats using a combination of camera surveys, dive observations, and detritus collections over 1 year. Detritus formed dense accumulations in habitats adjacent to kelp forests, and the timing of depositions coincided with the discrete loss of whole kelp blades during spring. We tracked these blades through the deep subtidal and into the deep fjord, and showed they act as a short-term resource pulse transported over several weeks. In deep subtidal regions, detritus consisted mostly of fragments and its depth distribution was similar across seasons (50% of total observations). Tagged pieces of detritus moved slowly out of kelp forests (displaced 4‒50 m (mean 11.8 m ± 8.5 SD) in 11‒17 days, based on minimum estimates from recovered pieces), and most (75%) variability in the rate of export was related to wave exposure and substrate. Tight resource coupling between kelp forests and deep fjords indicate that changes in kelp abundance would propagate through to deep fjord ecosystems, with likely consequences for the ecosystem functioning and services they provide.

Carbon assimilation and transfer through kelp forests in the NE Atlantic is diminished under a warmer ocean climate

“…In a recent study investigating detritus transport from kelp forests to deep fjords using video cameras, Filbee‐Dexter et al. () recorded the presence of kelp laminae between 400 and 450 m, and estimated its biomass at 22.1 g of fresh weight per m −2 of seafloor. In an analysis of benthic sediment cores collected at depths of 70–262 m along the Norwegian coast, Abdullah, Fredriksen, and Christie () suggested that most of the organic matter deposited in the sediments originated from distant L. hyperborea forests, as its carbohydrate and phenolic content closely resembled that of the organic fraction.…”

Tropicalisation of temperate reefs: Implications for ecosystem functions and management actions

“…In temperate reefs (Figure a), primary productivity of species like kelp is typically very high but also very seasonal (Wernberg et al, ), and only a small proportion of this productivity (<20%) is consumed by herbivores, with over 80% ending up as detritus/dissolved organic matter (Krumhansl & Scheibling, ). Kelp detritus can be exported across distances ranging from metres to hundreds of kilometres (Filbee‐Dexter, Wernberg, Norderhaug, Ramirez‐Llodra, & Pedersen, ). This constitutes an important trophic subsidy sustaining high secondary production in habitats with no or low primary production, including reefs with no canopy seaweeds, sandy beaches and the deep sea (Filbee‐Dexter et al, ).…”

“…Kelp detritus can be exported across distances ranging from metres to hundreds of kilometres (Filbee‐Dexter, Wernberg, Norderhaug, Ramirez‐Llodra, & Pedersen, ). This constitutes an important trophic subsidy sustaining high secondary production in habitats with no or low primary production, including reefs with no canopy seaweeds, sandy beaches and the deep sea (Filbee‐Dexter et al, ). Alternatively, kelp detritus may become sequestered in adjacent “carbon sink habitats” such as seagrass meadows (Hill et al, ).…”

Coastal marine ecosystem connectivity: pelagic ocean to kelp forest subsidies

“…, Filbee‐Dexter et al. ). In these ecosystems with low endogenous productivity, the effect of subsidies on consumer–resource dynamics is often more evident, with recent studies finding the strongest consumer responses to subsidies in recipient habitats with low productivity (Sabo and Power ).…”

“…The history of subsidies work in marine systems has, not surprisingly, focused on large inputs of energy to unproductive systems such as sandy beaches (Orr et al 2005, Netto and Meneghel 2014, Liebowitz et al 2016, desert island ecosystems Hurd 1996, Spiller et al 2010), and the deep sea, in the form of whale falls (Smith and Baco 2003), or detrital subsidies to deep benthic habitats (Vanderklift and Wernberg 2008, Britton-Simmons et al 2009, Filbee-Dexter et al 2018. In these ecosystems with low endogenous productivity, the effect of subsidies on consumer-resource dynamics is often more evident, with recent studies finding the strongest consumer responses to subsidies in recipient habitats with low productivity (Sabo and Power 2002).…”