Ocean acidification endangers ecologically important seaweed

A team of marine biologists led by the University of Gothenburg and the KTH Royal Institute of Technology has recently predicted that ocean acidification will nearly triple by the end of this century. 

This significant environmental shift could affect vital marine life such as fleshy seaweeds, which play a crucial role in promoting biodiversity across over a third of the world’s coastlines.

Fate of seaweeds

The experts investigated the potential fate of seaweeds in oceans that are undergoing rapid acidification. They exposed a common fleshy seaweed species to the acidification levels anticipated by 2100. 

The analyses revealed that this increased acidification altered the seaweed’s chemical balance, weakened its structure and tissues, and decreased its likelihood of survival.

Unprecedented changes

“Climate change is resulting in unprecedented changes in terrestrial and aquatic ecosystems through the emission of greenhouse gases, including carbon dioxide,” the authors wrote. “Almost a third of that CO2 is taken up by the ocean, which has profound effects on seaweeds.”

Future ocean acidification

To simulate the conditions of future ocean acidification, the researchers cultivated Fucus vesiculosus, a common brown fleshy algae, in water enriched with dissolved CO2 for a span of 90 days. 

The concentration of carbon dioxide was adjusted to mirror the levels of acidification projected for the year 2100, which is almost threefold the current levels of acidification in the oceans.

Structural changes 

Throughout the experiment, both the visible growth and microscopic structural changes of the seaweed were closely observed. 

The researchers measured how well the seaweed performed photosynthesis, analyzed its chemical composition, evaluated its thallus strength, and monitored its response to mechanical stress by mimicking waves to assess its vulnerability to damage or detachment in the ocean (a metric called “drag”).

Mixed results

Comparison of these findings with data from F. vesiculosus grown in non-acidified water led to mixed results. 

The seaweed cultivated in acidified water surprisingly demonstrated greater growth, more efficient photosynthesis, and no significant rise in drag. 

However, such seaweed had reduced thallus strength, less compact tissues, a more porous overall structure, and diminished levels of calcium and magnesium – essential elements contributing to the strength and flexibility of a plant’s structure. 

As a result, seaweeds in acidified water seemed to be more susceptible to breakage and had a higher mortality rate.

Study implications 

“Negative effects of ocean acidification on the tissue structure and breaking strength of seaweeds like F. vesiculosus could have drastic effects on coastal ecosystems,” the scientists explained.

“Such changes could lead to an overall decrease in seaweed coverage, with corresponding negative effects on organisms that depend on these habitats for food and shelter.”

Further studies are needed to explore whether the repercussions of ocean acidification are consistent across all fleshy seaweed species. 

“If this proves to be a general mechanism affecting fleshy seaweeds, the expectation is that ocean acidification will have critical structuring effects on rocky-shore ecosystems given how widely distributed and fundamental brown seaweeds are across one-third of the coastlines of the world,” the authors concluded.

The study is published in the journal Current Biology.

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