Quantitative Assessment of Carbon Removal Potential of Macroalgae: A Standardized Protocol for Biomass Estimation and Carbon Removal Calculation

Summary

This study presents a standardized, reproducible protocol for estimating macroalgal biomass and calculating its carbon removal potential. The workflow harmonizes sampling, calculation, and reporting to improve cross-study comparability and is demonstrated in representative kelp and sargassum communities across northern and southern China.

Abstract

Macroalgae are an important component of blue carbon systems. However, their carbon removal potential remains difficult to compare across studies because field sampling designs, biomass estimation models, and accounting workflows vary substantially. This study presents a standardized and reproducible protocol for estimating macroalgal biomass and quantifying carbon removal, integrating macroalgal biological traits, marine ecological survey methods, and carbon-cycle accounting principles into a unified workflow. The protocol specifies consistent sampling parameters, harmonized calculation steps, and standardized data recording and reporting to improve cross-study comparability and facilitate regional synthesis. We demonstrate protocol applicability using representative case studies from an offshore kelp community in northern China and a bay sargassum community in southern China, representing contrasting taxa and typical shallow coastal habitats. Using this workflow, within-team relative variability remained below 10%, and cross-team relative error remained below 15%, consistent with established variability thresholds. Overall, the protocol provides an operationally transparent framework for generating comparable macroalgal blue-carbon datasets across sites and research teams, supporting resource surveys and carbon removal assessments.

Introduction

Blue carbon refers to carbon captured and stored in marine ecosystems. It is characterized by long-term storage and high sequestration efficiency, making it an important component of the global carbon cycle and a critical natural mechanism for mitigating climate change¹. Within blue carbon systems, macroalgae are widely distributed across coastal, intertidal, and subtidal zones and fix atmospheric CO₂ into organic carbon via photosynthesis. Part of this production can be exported to deeper or offshore waters, where it may contribute to longer-term carbon storage, while another portion remains in standing biomass²

Protocol

Use this protocol to generate comparable estimates of macroalgal biomass and carbon-removal estimates across sites and research teams. An overview of the complete workflow is shown in Figure 1.

1. Protocol design basics

1. Design principles
   1. Align sampling and biomass estimation with macroalgal biological traits and local ecological context (e.g., growth form, community structure, and nutrient/seasonal dynamics) to ensure measurements reflect natural variability.
   2. Select the sampling window to match the local vigorous growth period of the target macroalgae and avoi....

Results

Case 1: Assessment of the carbon removal potential of the northern offshore kelp population

Study area and sampling periods: Field sampling was conducted in the offshore kelp aquaculture area of Qingdao, Shandong Province (water depth: 5-8 m). Measurements were collected during a vigorous growth period (May 2022) and a non-vigorous growth period (November 2022).

Sampling layout: Wit.......

Discussion

The core strength of this protocol is that it directly addresses methodological variation in existing assessments of macroalgal carbon removal potential. In practice, differences in quadrat specifications, measurement approaches, and calculation models can lead to carbon sink estimates that vary by a factor of two to three even within the same coastal system¹⁷. By standardizing the operational sequence, parameter definitions, and calculation logic, the protocol improves cross-site comparability an.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Electronic balance	METTLER TOLEDO	ML204T	For weighing samples
Elemental analyzer	Thermo Fisher	FlashSmart	For carbon content analysis
Oven	Memmert	UN55	For drying samples
GPS device	Garmin	GPSMAP 65s	For recording locations
Dissolved oxygen meter	YSI	ProODO	For measuring DO levels