As global efforts to tackle climate change intensify, attention is turning to carbon dioxide removal (“CDR”)—strategies that draw carbon dioxide from the atmosphere and store it for long periods. The Intergovernmental Panel on Climate Change (“IPCC”) has emphasized that CDR will be necessary, alongside deep emissions reductions, to limit global warming to 1.5°C or 2°C. One emerging CDR approach involves sinking aquatic plant biomass, specifically sargassum, a free-floating brown seaweed.

Sargassum absorbs carbon dioxide through photosynthesis and, under certain conditions, sinks naturally to the ocean floor. Since 2011, massive blooms of sargassum have become a recurring issue, and begun affecting the coastlines of Florida. While offshore sargassum supports marine life, beached sargassum decomposes rapidly, releasing methane and hydrogen sulfide—posing risks to public health, ecosystems, and tourism. Sargassum, once beached, is difficult and expensive to remove  and often ends up in landfills. This growing problem has sparked interest in a potential climate win-win: intentionally sinking sargassum to both reduce beach impacts and sequester carbon in the deep sea.

Sinking sargassum could, in theory, keep the carbon stored in plant biomass sequestered in the deep ocean for long periods of time. However, there are a number of risks and uncertainties associated with sinking plant biomass, and significantly more research is required to determine whether it is a viable CDR approach. This will need to include field studies in the ocean.

A new report published by the Sabin Center aims to clarify the legal framework for sargassum removal and sinking. The report focuses on sargassum projects off the Florida coast and explores the state and federal laws that would apply to the collection of sargassum on beaches and in ocean waters, as well as its sinking.

Removing and Sinking Sargassum 101

Various methods have been proposed for collecting and sinking sargassum. This report focuses on three of the most commonly discussed options and explores their differing legal consequences. The first approach is to collect sargassum that has washed up on beaches, bale it, and then sink it in the ocean. Initial studies suggest that as the bales move down the water column, the increased pressure in the water causes the pneumatocysts (gas filled sacks) on the sargassum to pop, which removes their buoyancy and causes them to sink further to the seabed.

The second approach involves collecting sargassum in the water (i.e., before it reaches beaches) using boats and nets, trawlers with collection apparatus, or boom barriers (i.e., large floating structures that collect the sargassum together into one area). Once collected, the sargassum can be loaded onto ships, baled, and then thrown overboard, where it sinks (similarly to if the sargassum had been collected onshore).

The third approach uses novel methods, such as autonomous robots or devices, to collect and sink the sargassum. One proposal is to use robots which collect sargassum from the surface of the ocean before diving into the deep waters below to release it.

The report examines each of these approaches and their differing legal consequences.

 Legal Complexities and Pathways Forward

The legal landscape surrounding sargassum removal and sinking—especially in Florida—is complex. Permitting requirements vary depending on where and how the sargassum is collected and sunk. On beaches, removal often triggers Florida’s Coastal Construction Control Line regulations and may require permits from the Florida Department of Environmental Protection, particularly if mechanical tools are used or if the area includes protected turtle nesting grounds.

Offshore, sargassum removal in Florida waters is regulated under the Florida Aquatic Plant Management Act, and requires permits from the Florida Fish and Wildlife Conservation Commission. In federal waters, additional requirements may apply to sargassum removal, including under the Magnuson-Stevens Fishery Conservation and Management Act, which governs fishery resources and essential fish habitats like sargassum in the Atlantic. Federal permits may also be required for both onshore and offshore sargassum removal under the Rivers and Harbors Act if the removal project creates any obstacles to navigation or involves dredging activities. Additionally, federal environmental protections under the Endangered Species Act and Marine Mammal Protection Act must be considered to avoid harming vulnerable wildlife.

Sinking sargassum is regulated under an entirely different legal regime. The Marine Protection, Research, and Sanctuaries Act (“MPRSA”) regulates ocean dumping and is likely apply to many, if not all, projects that involve the sinking of sargassum. The application of the MPRSA to activities involving the offshore collection and sinking of sargassum, particularly those involving the use of autonomous underwater vehicles or robots, is an open question, however.

Ultimately, our report highlights a need for clarification of the application of existing environmental statutes to sargassum collection and sinking projects, and for improved interagency coordination and collaboration regarding their application.

for regulatory clarity regarding the treatment of sargassum collection and sinking projects. The report is part of a series of reports published by the Sabin Center on state-level regulation of marine CDR approaches. Our other reports, such as on ocean alkalinity and on seaweed cultivation, have highlighted similar needs. Taken collectively, the reports reveal opportunities for regulatory development that could help overcome barriers to research and support the responsible development of marine CDR projects, if their benefits are proven.

Read the report, “Regulation of Sargassum Removal and Sinking in Florida” here.