Nutritional quality of giant kelp declines due to warming ocean temperatures

Abstract

Giant kelp Macrocystis pyrifera forms extensive forests on temperate reefs, providing habitat and food for a diversity of marine life. Kelp biomass varies in response to changing ocean temperatures, but physiological responses as reflected in the nutritional quality of kelp tissue are poorly understood. Over a 19-year period in southern California, we found that nutritional quality of giant kelp tissue declined; nitrogen content of giant kelp tissue declined by 18%, while carbon content proportionally increased. This decline in nutritional quality was associated with increasing seawater temperatures and with regional and local scale processes including upwelling as indicated by the biologically effective upwelling transport index, the El Niño-Southern oscillation and the North Pacific Gyre oscillation. Changes in kelp stoichiometry with seawater temperature have important implications for nutrition and behavior of key consumers, such as sea urchins. Our results suggest that the consequences of projected declines in kelp abundance due to climate change may be compounded by reductions in its nutritional quality.

Special issue: Questioning the roles of resources nutritional quality in ecology

“…Because all of the contributions considered at least one explicit variable to quantify the nutritional quality of the resource, none of them falls within the cluster of 'undefined food quality' (in green). Five of the articles of the Special issue(Chouvelon et al 2022, Lowman et al 2022, Mathieu-Resuge et al 2022, Sentis et al 2022, van Deurs et al 2022) fall within the cluster aquatic ecosystem/ stoichiometry-lipids/trophodynamics-fitness, a proportion that mirrors well the actual predominance of those themes within the overall research (Fig.2c). Two more articles of this Special issue (LeGall et al 2022, Zaguri et al 2022) belong to the cluster linking the nutritional geometry to physiological aspects, which is current ranked second in term of contribution to the overall research.…”

“…‐ As generally observed in ecosystem ecology, evolutionary questions are still too rarely explicitly tested in trophic ecology investigations. Despite a large array of studies have observed and discussed the evolutionary tenets at play behind the selection of consumers nutritional requirements (see for example Hudson et al 2022 in this issue), the inclusion of such research questions in the general understanding of ecosystem functioning remains limited.‐ Finally, Lowman et al (2022) illustrate that the potential nutritional quality of basal producers can be significantly altered by global warming. In the context or the current global changes and considering the multiple stressors organisms are exposed to, understanding the causes and the consequences of changes in basal resource quality in a multistressor context (concomitant changes in temperature, nutrient and water availability, presence of pollutants …) is an urgent need, as much in terms of prediction of future ecosystem trajectories as in terms of goods and services provision by nature for humanity.…”

“…Biomechanical parameters (including all physical defenses) used to be largely considered in the early 90s but the relative use of this parameter is clearly declining in the recent years. The articles published in this special issue are well representative of these trends since one third of the published articles question resources quality through the consideration of resources elemental content (Chouvelon et al 2022, Lowman et al 2022, Sentis et al 2022), while a second third focuses on resources macro‐nutrient contents, alone (Le Gall et al 2022, Zaguri et al 2022) or in association with fatty acids (van Deurs et al 2022). Finally, three articles specifically focus on fatty acids/lipids (Hudson et al 2022, Leal et al 2022, Mathieu‐Resuge et al 2022).…”

“…‐ Finally, Lowman et al (2022) illustrate that the potential nutritional quality of basal producers can be significantly altered by global warming. In the context or the current global changes and considering the multiple stressors organisms are exposed to, understanding the causes and the consequences of changes in basal resource quality in a multistressor context (concomitant changes in temperature, nutrient and water availability, presence of pollutants …) is an urgent need, as much in terms of prediction of future ecosystem trajectories as in terms of goods and services provision by nature for humanity.…”

The role of inputs of marine wrack and carrion in sandy‐beach ecosystems: a global review

“…The nutritional quality of wrack obviously plays a critical role in determining feeding choices in macroinvertebrate detritivores on beaches Duarte et al, 2010bDuarte et al, , 2011Duarte et al, , 2014Lowman et al, 2021), similar to mesograzers (macrofauna grazing on living macrophytes) in subtidal ecosystems (Duffy & Hay, 1991). The protein content of algae is considered a key trait in determining their nutritional quality as food sources (Cruz-Rivera & Hay, 2000), similar to the case for plant consumers in other systems (White, 1993), and appears selectively to influence feeding by detritivores on sandy beaches (e.g.…”