Ocean Acidification: Algae Floppy in Higher Carbon Dioxide Water

More acidic ocean water can upset the balance, as we've learned. New research from the University of Washington has found that a more acidic ocean can weaken the outer shell of a slender alga with the whimsical name of the mermaid's wineglass. 

The team's findings, which are pertinent at a time when climate change may increase acidification in the ocean, were recently published in the journal Biology Letters.

Mermaid's wineglass, or Acetabularia acetabulum, is often umbrella-like and has a ring of branches that can be separate or forming a fused cap. It reaches a few inches and lives on shallow seafloors, collecting sunlight for photosynthesis. It has a protective skeleton of calcium carbonate, as a release noted.

Following news from a colleague (Jason Hall-Spencer from Plymouth University) that mermaid's wineglass looks different in some parts of the Mediterranean Sea, UW biology doctoral student Laura Newcomb began research on the effects of acidity on calcium carbonate levels but on the mermaid's wineglass in particular, the release noted.

Hall-Spencer, who had been researching underwater seeps of carbon dioxide in Europe, told the UW researchers that "The algae far from the seeps appeared whiter -- probably because of their well-developed skeletons," said Newcomb, according to the release. "But ones found closer to the vents are more brown and green."

The CO2 seeps in question were created by underwater volcanic activity. In Italy, Newcomb collected fresh samples of the algae from near and far from the seeps, and did a reading of carbon dioxide in the water in each location. Nearer to the seeps, carbon dioxide levels were much higher -- five times higher than in water at a greater distance from the volcanic activity, as the release noted.

The mermaid's wineglass skeletons were more floppy and had different composition when in higher CO2 levels. They contained 32 percent less calcium carbonate near the seeps. The algae's normally stiff, straw-like stems were 40 percent more droopy than stems of counterpart organisms from more normal water, the release said.

Newcomb and UW biology professor Emily Carrington developed a hypothesis that the less structured mermaid's wineglass might be more easily damaged from sea currents and marine-animal grazing. Also, having less foundation may make it harder for the algae to disperse offspring. That said, less substantial skeletons might be able to transmit more sunlight for photosynthesizing food. Also, ithe algae's new structure is possibly less appealing to snails, which commonly eat the wineglass; the scientists did not see them near the algae in the seeps, the release noted. 

The team expects to return to the seeps to test their theories later, according to the release.

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