A global dataset of seaweed net primary productivity

Abstract

Net primary productivity (NPP) plays a pivotal role in the global carbon balance, but estimating the NPP of underwater habitats remains a challenging task. Seaweeds (marine macroalgae) form the largest and most productive underwater vegetated habitat on Earth. Yet, little is known about the distribution of their NPP at large spatial scales, despite more than 70 years of local-scale studies being scattered throughout the literature. We present a global dataset containing NPP records for 242 seaweed species at 419 individual sites distributed on all continents from the intertidal to 55 m depth. All records are standardized to annual aerial carbon production (g C m-2 yr-1) and are accompanied by detailed taxonomical and methodological information. The dataset presented here provides a basis for local, regional and global comparative studies of the NPP of underwater vegetation, and is pivotal for achieving a better understanding of the role seaweeds play in the global coastal carbon cycle.

Global estimates of the extent and production of macroalgal forests

“…We compiled areal NPP rates across macroalgal habitats from the literature (Figure 2, Table 2; see Pessarrodona, Filbee‐Dexter, Krumhansl, Moore, et al., 2021; Pessarrodona, Filbee‐Dexter, Krumhansl, Pedersen, et al., 2021 for details and full dataset) and multiplied the resulting average values by the estimates of the global extent of these habitats reported above (Approach 3, Table 1). Subtidal brown macroalgal and intertidal macroalgal ecosystems supported similarly large contributions to macroalgal NPP with mean values of 0.54 and 0.59 kg C/m 2 /year, respectively, and maximum reported site‐ and annual‐averaged values well exceeding 2 kg C/m 2 /year (Figure 2).…”

“…We compiled estimates of macroalgae NPP using grey literature, peer‐reviewed studies and personal unpublished data (see Pessarrodona et al., 2021 for details and Pessarrodona, Filbee‐Dexter, Krumhansl, Pedersen, et al., 2021 for the database). To be included in our compilation, studies had to fit the following criteria: first, studies had to examine macroalgae NPP on a per area basis.…”

“…brown, red or green algae) as well as their position within the water column (benthic or pelagic). These were: rhodolith beds, Halimeda bioherms, subtidal (rocky reef) brown algae, subtidal deep (rocky reef) red algae, coral reef‐associated algae, intertidal algae, floating brown algae ( Sargassum ) and floating green algae (referred to as green tides) (Pessarrodona, Filbee‐Dexter, Krumhansl, Moore, et al., 2021). Measurements were obtained from a total of 420 individual sites distributed on all continents from the intertidal to 55 m depth (Pessarrodona, Filbee‐Dexter, Krumhansl, Moore, et al., 2021), although the majority of measurements were conducted at shallow depths and in subtidal brown algae, coral‐reef associated algae, and intertidal habitats (Pessarrodona, Filbee‐Dexter, Krumhansl, Moore, et al., 2021).…”

Sea ice and substratum shape extensive kelp forests in the Canadian Arctic

“…Kelp forests in the Eastern Canadian Arctic are estimated to currently cover 312,000 km 2 of the coastal zone, in waters 30 m or shallower (Goldsmit et al, 2021), which is 9% of the estimated global distribution of kelp (1,500,000 to 2,500,000 km 2 ) (Assis et al, 2020;Duarte et al, 2021;Jayathilake and Costello, 2020). The relatively high abundance and areal extent of these primary producers compared to phytoplankton and sea ice algal production along these coasts suggests that Arctic kelp forests could be an important source of primary production for marine communities (Krumhansl and Scheibling, 2012;Pessarrodona et al, 2021;Vilas et al, 2020) and a standing stock of carbon. Based on the average biomass per area measured in our study (3.7 kg m 2 ), and assuming fresh biomass to carbon conversion ratios of 0.21 FW:DW and 0.3 DW:C (Pedersen et al, 2020;Pessarrodona et al, 2021), we estimate a total standing stock for the Eastern Canadian Arctic of 72.7 (± 8.4 SE) Tg C. This value is 4.4× more than the standing stock of kelp forests in Australia (16.6 TgC; Filbee-Dexter and Wernberg, 2020) and 10.2× than the standing stock of kelp forests in Norway (158 million tonnes WW or 7.1 TgC; Frigstad et al, 2021) (using FW:C ratios for L. hyperborea from Pedersen et al 2020).…”

“…The relatively high abundance and areal extent of these primary producers compared to phytoplankton and sea ice algal production along these coasts suggests that Arctic kelp forests could be an important source of primary production for marine communities (Krumhansl and Scheibling, 2012;Pessarrodona et al, 2021;Vilas et al, 2020) and a standing stock of carbon. Based on the average biomass per area measured in our study (3.7 kg m 2 ), and assuming fresh biomass to carbon conversion ratios of 0.21 FW:DW and 0.3 DW:C (Pedersen et al, 2020;Pessarrodona et al, 2021), we estimate a total standing stock for the Eastern Canadian Arctic of 72.7 (± 8.4 SE) Tg C. This value is 4.4× more than the standing stock of kelp forests in Australia (16.6 TgC; Filbee-Dexter and Wernberg, 2020) and 10.2× than the standing stock of kelp forests in Norway (158 million tonnes WW or 7.1 TgC; Frigstad et al, 2021) (using FW:C ratios for L. hyperborea from Pedersen et al 2020). Annual productivity rates measured for S. latissima and L. solidungula at sites around Southampton Island in 2019 ranged from 23.1 -67.8 g C m -2 y -1 (Filbee-Dexter, unpublished data) and for L. solidungula from Igloolik (Foxe Basin) in 1977 were 19.6 (± 12.1 SD) g C m -2 y -1 (Chapman and Lindley, 1980).…”