Effects of temperature on carbon circulation in macroalgal food webs are mediated by herbivores

Abstract

Warming is one of the most dramatic aspects of climate change and threatens future ecosystem functioning. It may alter primary productivity and thus jeopardize carbon sequestration, a crucial ecosystem service provided by coastal environments. Fucus vesiculosus is an important canopy-forming macroalga in the Baltic Sea, and its main consumer is Idotea balthica. The objective of this study is to understand how temperature impacts a simplified food web composed of macroalgae and herbivores to quantify the effect on organic carbon storage. The organisms were exposed to a temperature gradient from 5 to 25 °C. We measured and modeled primary production, respiration, growth and epiphytic load on the surface of Fucus and respiration, growth and egestion of Idotea. The results show that temperature affects physiological responses of Fucus and Idotea separately. However, Idotea proved more sensitive to increasing temperatures than the primary producers. The lag between the collapse of the grazer and the decline of Fucus and epiphytes above 20 °C allows an increase of carbon storage of the primary productivity at higher temperatures. Therefore, along the temperature gradient, the simplified food web stores carbon in a non-monotonic way (reaching minimum at 20 °C). Our work stresses the need of considering the combined metabolic performance of all organisms for sound predictions on carbon circulation in food webs.

Climate change in the Baltic Sea region: a summary

“…The effects of warming on invertebrates are nonlinear. The respiration and growth of the isopod Idotea balthica increased up to 20 • C and then decreased at 25 • C (Ito et al, 2019). Many marine invertebrates, including isopods, will also directly and indirectly suffer from decreasing salinity (Kotta et al, 2019;Rugiu et al, 2017) and OA.…”

Climate Change in the Baltic Sea Region: A Summary

“…The effects of warming on invertebrates are non-linear. Respiration and growth of the isopod Idotea balthica increased up to 20°C, and then decreased at 25°C (Ito et al, 2019). Many marine invertebrates, including isopods, will also directly and indirectly suffer from decreasing salinity (Kotta et al, 2019;Rugiu et al, 2017), as well as ocean acidification (OA).…”

Climate change or mismanagement?

“…Such warming and the continuing influx of nutrients from agriculture are expected to lead to increasing areas of hypoxia and anoxia (Hansson et al 2019; BACC (Baltic Earth Assessment of Climate Change) II Author Team, 2015). There can be no doubt that these changes will affect ecosystems and species by triggering complex nonlinear dynamics (Reusch et al 2018;Ito et al 2019), but the resilience of commercial species will, in addition, be affected by their history of exploitation and their current stock status (Free et al 2019).…”