Acid seas threaten creatures that supply half the world's oxygen
By Martha Baskin and Mary Bruno
Ocean acidification is turning phytoplankton toxic. Bad news for the many species, that rely on them either directly or indirectly (humans), as a source of food and oxygen.
Phytoplankton are the components of the mostly single celled community that develop their own energy through photosynthesis or less commonly chemosynthesis. Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, they may appear as a green discoloration of the water due to the presence ofchlorophyllwithin their cells.
What happens when phytoplankton that make up the foundation of the marine food web are exposed to acidity? They have a harder time making certain amino acids and may have larger amounts of certain toxins.
Their toxins can concentrate in the shellfish and many other marine species (from zooplankton to baleen whales) that feed on phytoplankton. Recent research by a team of scientists aboard the RV Melville shows that ocean acidification could dangerously alter these microscopic plants, which nourish a menagerie of sea creatures and produce up to 60 percent of the earth's oxygen.
The researchers worked in carbon saturated waters off the West Coast, a living laboratory to study the effects of chemical changes in the ocean brought on by increased atmospheric carbon dioxide. A team of scientists from NOAA's Fisheries Science Center and Pacific Marine Environmental Lab, along with teams from universities in Maine, Hawaii and Canada focused on the unique "upwelled" zones of California, Oregon and Washington. In these zones, strong winds encourage mixing, which pushes deep, centuries-old CO2 to the ocean surface. Their findings could reveal what oceans of the future will look like. The picture is not rosy.
Scientists already know that ocean acidification, the term used to describe seas soured by high concentrations of carbon, causes problems for organisms that make shells. “What we don't know is the exact effects ocean acidification will have on marine phytoplankton communities,” says Dr. Bill Cochlan, the biological oceanographer from San Francisco State University oceanographer who was the project’s lead investigator. “Our hypothesis is that ocean acidification will affect the quantity and quality of certain metabolities within the phytoplankton, specifically lipids and essential fatty acids.”
Acidic waters appear to make it harder for phytoplankton to absorb nutrients. Without those nutrients they're more likely to succumb to disease and have toxic properties. Those toxins then concentrate in the zooplankton (animal plankton that feed on the plantlike phyotoplankton), shellfish and other marine species that graze on them.
Consider the dangerous diatom Pseudo-nitzschia(below). When ingested by humans, toxins from blooms of this single-celled algae can cause permanent short-term memory loss and in some cases death, according to Dr. Vera Trainer, an oceanographer with NOAA's Fisheries Marine Biotoxins Program. Laboratory studies show that when acidity (or pH) is lowered, Pseudo-nitzschiacells produce more toxin. When RV Melville researchers happened on a large bloom of Pseudo-nitzschia off the coast of Point Sur in California, where pH levels are already low, they were presented with a rare opportunity, explains Trainer, to see if their theory “holds true in the wild.”
Multiple phytoplankton populations became the subjects of deck-board experiments throughout the Melville’s 26-day cruise, which began in mid-May and finished last week.
Another worrisome substance is domoic acid, a neuro-toxin produced by a species of phytoplankton. Washington State has a long history of domoic acid outbreaks. The toxin accumulates in mussels and can wind up in humans. “Changes in the future ocean could increase the levels of domoic acid in the natural population,” says Professor Charles Trick, a biologist with Western University in Ontario, and one of the RV Melville researchers. .
During their nearly month-long cruise, researchers observed the most intense upwelling in California, which is typical for spring and early summer. Upwelling may increase off the coasts of Oregon and Washington in mid-late summer and fall. The research team took multiple measurements and water samples off all three coasts in waters of both low and high pH. Part of their hypothesis is that concentrations of essential fatty acids are lower when pH is low. They need to establish what exactly “lower'” means, but the bottom line is that fewer essential fatty acids means a less nutritional diet for fish and other organisms.
If the interaction between CO2, ocean acidity and nutrient supply to phytoplankton and other ocean-going creatures isn't something you can wrap your head around, try this: Every second breath you take is due to phytoplankton. Those single cells generate the lion’s share of the world's breathable oxygen so they are vitally important to our global ecosystem.
The RV Melville is owned by the Scripps Institute of Oceanography. The research was funded with a $1 million grant from the National Science Foundation, which underwrites approximately 24 percent of all government-supported basic research being conducted by American colleges and universities.
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