Scientists find underwater plants can combat ocean acidification

An underwater view of a seagrass meadow with the sunlight shining through the surface waters and illuminating the seagrass blades..
Seagrass is an underwater plant. Like land plants, seagrasses need light and carbon dioxide to perform photosynthesis. GETTY

Human-generated carbon emissions are causing the world’s oceans to become more acidic. Since the start of the industrial revolution, when mankind’s emissions began ramping up, the world’s oceans have already become about 30% more acidic. For shell-building animals in particular, like oysters and snails, ocean acidification’s impacts can be devastating.

Marine scientists have suspected for years that underwater plants and seaweeds could combat the effects of ocean acidification on marine life. Now, research recently published in the journal Global Change Biology provides the most compelling evidence yet that underwater grasslands may create safe zones for marine life vulnerable to ocean acidification’s destructive effects.

Ocean Acidification’s Toll On Marine Life

Our carbon dioxide emissions are making the oceans more acidic. As we pump carbon dioxide into the atmosphere, a portion dissolves into the world’s oceans. Once there, the carbon dioxide goes through a series of chemical changes that have an acidifying effect on seawater.

In addition to making seawater more acidic, these chemical reactions also reduce the amount of carbonate in seawater – an essential building block for the ocean’s shell-building organisms. Carbonate is similarly used by coral reefs to form their white skeletons and fish to produce their ear bones. As carbon dioxide continues to infiltrate seawater, the associated loss of carbonate makes it much more challenging for these carbonate-dependent marine animals to build their protective structures. The lack of carbonate in seawater can become so severe that it can even cause mussel shells, fish ear bones, and coral reef skeletons to dissolve.

Plants to the Rescue?

Trees absorb carbon dioxide from the air and through photosynthesis. Underwater vegetation, like seagrass meadows and kelp forests, photosynthesize like their land-based relatives. In the process, this aquatic vegetation removes some of the excess carbon dioxide in the surrounding seawater that causes ocean acidification. In theory, scientists suspect the removal of carbon dioxide by marine plants and seaweeds could make the seawater around vegetation less acidic than the rest of the ocean.

A Thorough Analysis

To test this theory, research led by scientists at UC Davis’ Bodega Marina Laboratory assessed seven seagrass beds along the Northern California coast for six years. Sensors were placed in each of the seagrass beds and in nearby, vegetation-free areas. The sensors collected information on the acidity of the seawater.

A dense seagrass bed at low tide in the foreground with a red inflatable boat and water in the background.
One of the seven Northern California seagrass beds assessed in this recent study on ocean acidification. MELISSA WARD

When the researchers compared the data from sensors within seagrass beds versus just outside them, they found a consistent trend: the seawater within seagrass meadows was less acidic than the seawater in nearby areas lacking seagrass. Overall, the seagrass meadows were consistently about 30% less acidic than seagrass-free areas.

Big Implications

For the many marine organisms that live within California’s seagrass beds, including the commercially important Dungeness Crab and Olympia oyster, seagrass’s ability to reduce the effects of ocean acidification could benefit ecosystems and the fishing industry, but only if we protect the seagrass we have and restore the seagrass we’ve lost.

Since the twentieth century, about one-third of the world’s seagrass has been lost. Seagrass’s global demise is directly related to human activities. Boats and their anchors destroy seagrass when they drag against the seafloor. Pollution and channel deepening activities make coastal waters more turbulent, reducing the amount of light that reaches the seagrass’s leaves for photosynthesis.

An anchor underwater on a sandy seafloor.
When placed in seagrass beds, anchors can rip up this important underwater vegetation. GETTY

While seagrass is challenging and expensive to restore, restoration is possible. In Virginia’s Chesapeake Bay, nearly 9,000 acres of seagrass have been restored – the largest single seagrass restoration project ever attempted. In San Francisco Bay, efforts are underway to restore seagrass beds alongside oyster reefs.

Still, retaining the seagrass we have left is vital. In addition to the underwater plant’s potential to lessen the impact of ocean acidification on marine life living within these underwater grasslands, seagrass removes carbon from the atmosphere over 30 times faster than tropical rainforests. Once stored, this carbon does not contribute to climate change unless the seagrass is destroyed. In other words, the loss of seagrass both removes an important way in which carbon dioxide can be sucked out of the atmosphere and releases the carbon the seagrass already tucked away.

With this new evidence of seagrass’s ability to reduce the effects of ocean acidification, we have yet another reason to prioritize the protection and restoration of the world’s seagrass meadows.

Liz Allen, Forbes, 12 April 2021. Article.

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