Accounting for variation in temperature and oxygen availability when quantifying marine ecosystem metabolism

Matthew E S Bracken,Cascade J B Sorte,Luke P Miller,Sarah E Mastroni,Stephany M Lira

doi:10.1038/s41598-021-04685-8

Abstract

It is critical to understand how human modifications of Earth’s ecosystems are influencing ecosystem functioning, including net and gross community production (NCP and GCP, respectively) and community respiration (CR). These responses are often estimated by measuring oxygen production in the light (NCP) and consumption in the dark (CR), which can then be combined to estimate GCP. However, the method used to create “dark” conditions—either experimental darkening during the day or taking measurements at night—could result in different estimates of respiration and production, potentially affecting our ability to make integrative predictions. We tested this possibility by measuring oxygen concentrations under daytime ambient light conditions, in darkened tide pools during the day, and during nighttime low tides. We made measurements every 1–3 months over one year in southeastern Alaska. Daytime respiration rates were substantially higher than those measured at night, associated with higher temperature and oxygen levels during the day and leading to major differences in estimates of GCP calculated using daytime versus nighttime measurements. Our results highlight the potential importance of measuring respiration rates during both day and night to account for effects of temperature and oxygen—especially in shallow-water, constrained systems—with implications for understanding the impacts of global change on ecosystem metabolism.

Highlights

It is critical to understand how human modifications of Earth’s ecosystems are influencing ecosystem functioning, including net and gross community production (NCP and GCP, respectively) and community respiration (CR)
Key metrics of ecosystem metabolism are gross community production (GCP), which is the rate of photosynthetic carbon fixation in the community being measured; community respiration (CR), which is the rate of carbon release or oxygen consumption, and net community production (NCP), which is the rate of observed carbon fixation or oxygen accumulation in the light, including the effects of respiration on carbon or o xygen[18,19]
Repeated-measures analyses indicated that measurements conducted in the light showed that oxygen fluxes measured using the two methods were similar across dates (F1,4 = 4.7, p = 0.096) and that net community production did not change seasonally

Summary

Introduction

It is critical to understand how human modifications of Earth’s ecosystems are influencing ecosystem functioning, including net and gross community production (NCP and GCP, respectively) and community respiration (CR). Given the importance of these measurements for understanding ecosystem responses to global c hange[8,9], we evaluate the effectiveness of two of the most commonly used methods for estimating productivity—day-night measurements versus daytime light–dark incubations—highlighting differences between them and exploring the mechanisms underlying those differences These methods for measuring ecosystem metabolism are based on the long-understood fact that respiration causes CO2 release and O 2 consumption in both the dark and the light, whereas photosynthesis drives carbon fixation and oxygen generation only in the light[12,16]. Incubations of closed containers are made for 24 h (e.g., dawn-to-dawn) to encompass both night and daytime, and some containers are transparent (measuring both photosynthesis and respiration), whereas others are darkened (measuring only respiration)[15,23]

Methods

Results

Conclusion