A novel approach reveals underestimation of productivity in the globally important macroalga, Ascophyllum nodosum

Abstract

Ascophyllum nodosum (L.) Le Jolis (Fucales, Fucaceae) is a modular intertidal brown alga that has the particularity of forming an air bladder once a year at the apical tip of the growing shoots. This characteristic provides a means for aging and estimating the growth of individuals. While it has long been recognized that growth can occur in older parts of the frond, this has not been properly assessed until now and has largely been overlooked when calculating the productivity of the species. Recent studies have suggested that the growth and elongation of older segments is minimal and thus has been used to infer past environmental conditions. Here we assessed the length and mass of successive internodal segments from 25 sites spread over both sides of the North Atlantic, covering a wide portion of the distribution of the species. By calculating the ratio of the mass and length of a segment divided by the segment produced the following year, we established that internodal segments continue accumulating mass for 1–5 years and increase in length for 1–3 years at most sites. Segments can almost triple their mass during their second year and more than double their length. These results indicate that previous productivity and growth estimates for A. nodosum based on apical growth alone greatly underestimate the true productivity of the species and its role in coastal carbon cycling. Furthermore, because they grow over several years, internodal segments should not be used to infer past environmental conditions or to reconstruct growth patterns over time.

A review on the chemical ecology of the Fucaceae holobionts: from fundamental knowledge to applications

“…A recent study recommended avoiding harvesting A. nodosum from the wild in Portugal because of the vulnerability and ecological importance of this southernmost population in Europe [69]. In Eastern Canada, where the commercial exploitation of A. nodosum began in the late 1950s, studies evaluating the impact of harvesting and management over 25 years concluded that A. nodosum harvesting is sustainable in this area, however it needs to be closely monitored as environmental conditions are changing [7,70,71]. In Alaska, the harvesting of Fucus distichus is also considered sustainable due to a tailored management plan which takes into account the timing of reproduction, the available biomass, and regrowth [72].…”

“…from wild populations is permitted in some countries (i.e., Ireland, France) and prohibited in others (i.e., Germany) [73]. In the future, regardless of the Fucaceae species, local harvesting and monitoring practices should be adapted to ensure sustainable management of wild resources to avoid overharvesting at a global scale [7,[69][70][71] and it may become necessary to investigate different strategies for Fucaceae cultivation in coastal and/or offshore waters [5,73].…”