Environmental factors influencing primary productivity of the forest-forming kelp Laminaria hyperborea in the northeast Atlantic

Abstract

Rates and drivers of primary productivity are well understood for many terrestrial ecosystems, but remain poorly resolved for many marine ecosystems, particularly those within in coastal benthic environments. We quantified net primary productivity (NPP) using two methods as well as carbon standing stock within kelp forests (Laminaria hyperborea) at multiple subtidal habitats in the United Kingdom (UK). Study sites spanned 9° in latitude and encompassed a gradient in average temperature of ~ 2.5 °C. In addition to temperature, we measured other factors (e.g. light intensity, water motion, nutrients, sea urchin density) that may influence productivity. Although estimates of NPP were highly variable between sites, ranging from 166 to 738 g C m-2 yr-1 , our study-wide average of 340 g C m-2 yr-1 indicated that L. hyperborea forests are highly productive. We observed clear differences between NPP and carbon standing stock between our cold northernmost sites and our warm southernmost sites, with NPP and standing stock being around 1.5 and 2.5 times greater in the northern sites, respectively. Ocean temperature was identified as a likely driver of productivity, with reduced NPP and standing stock observed in warmer waters. Light availability was also strongly linked with carbon accumulation and storage, with increased light levels positively correlated with NPP and standing stock. Across its geographical range, total NPP from L. hyperborea is estimated at ~ 7.61 Tg C yr-1. This biomass production is likely to be important for local food webs, as a trophic subsidy to distant habitats and for inshore carbon cycling and (potentially) carbon sequestration. However, given the strong links with temperature, continued ocean warming in the northeast Atlantic may reduce primary productivity of this foundation species, as optimal temperatures for growth and performance are surpassed. Primary productivity underpins most food webs and ecosystems on Earth, and as such, understanding rates, trends and drivers of primary production by autotrophs is a fundamental goal of ecology 1,2. Net primary productivity (NPP; gross primary productivity minus energy required for respiration and maintenance) is as important in the marine realm as it is on land, yet current understanding of rates of NPP is comparatively poor for many marine ecosystems and habitats 3,4. Even so, the most reliable available estimates suggest that ocean-based NPP is significant, accounting for ~ 50% of NPP on Earth 5 , with approximately 90% of that contribution attributed to open ocean phytoplankton, 10% attributed to coastal macrophytes (e.g. seagrass meadows, macroalgal beds)

Ocean warming and species range shifts affect rates of ecosystem functioning by altering consumer–resource interactions

“…All rights reserved Ireland. Rather, they were selected from a limited set of kelp-consumers that are likely to co-exist with range-expanding warm-temperate kelps such as L. ochroleuca and S. polyschides, thus creating novel consumer-resource interactions (Smale et al, 2015;Smale et al, 2016;Pessarrodona, et al, 2018a;Smale et al, 2020). In addition, species such as E. esculentus are key components in structuring kelp-dominated systems in other regions and it is possible that their importance in the UK and Ireland will increase under future ocean warming and community reconfiguration (Sjøtun et al, 2006;Norderhaug & Christie, 2009;Rinde et al, 2014;Filbee-Dexter & Scheibling, 2014;Leclerc et al, 2015).…”

Priming of Marine Macrophytes for Enhanced Restoration Success and Food Security in Future Oceans

“…Modeling studies, based on projected carbon emission scenarios, predict that poleward range shifts will intensify (Jueterbock et al, 2013;Valle et al, 2014;Assis et al, 2016Assis et al, , 2017Chefaoui et al, 2018;Wilson and Lotze, 2019). Even if rising sea temperatures remain below lethal limits, they reduce macroalgal growth and performance (Nepper-Davidsen et al, 2019;Hereward et al, 2020;Smale et al, 2020), increase disease outbreaks and biofouling (Harley et al, 2012;Nepper-Davidsen et al, 2019;Qiu et al, 2019;Smale et al, 2020), and radically alter ecological interactions that determine persistence (Provost et al, 2017;Vergés et al, 2019)-thus compromising future sustainability of natural habitats, and production security of associated industries.…”

A global dataset of seaweed net primary productivity

“…12,24 ) or focused on specific taxa (e.g. 25,26 ). These limitations have precluded a global understanding of the patterns and determinants of NPP across seaweed taxa, which is in urgent need to inform on the promising potential of seaweeds.…”