Two More Things I Just Learned About Fish

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When I'm not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting, cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

1. There are salmon in Paris

"¦and they're not just on plates, but alive and kicking in the Seine. For the first time in over a century, some 1,000 Atlantic salmon (Salmo salar) used the river to pass through the City of Lights on their migration to their spawning waters.

Before the Industrial Revolution, Atlantic salmon were abundant in the Seine, but as the river became increasingly polluted the fish were killed off. By 1900 the salmon had completely disappeared and most other species of fish followed in the early 20th century. By 1995, only five species of fish "“ carp, bream, roach and eel "“ still swam in the Seine around Paris (and no people "“ summer beaches on the Right Bank had numerous signs warning people to stay out of the water).

Now, 25 years after clean-up efforts began in the river, 32 species of fish—including sea trout, herring, shad, lampreys and the Atlantic Salmon—call Paris home.

Researchers are most excited about the return of the salmon, given the species status as a bioindicator, a species used to determine and monitor the health and integrity of an environment or ecosystem. [Image credit: David Monniaux.]

2. For plankton, global warming isn't such a bad thing

The increasing water temperatures associated with global warming are a problem for all aquatic life, but the creatures that call Arctic waters home have another problem to deal with. A research team from the University of Alaska, Fairbanks has suggested that the Arctic Ocean is especially susceptible to ocean acidification "“ increasing acidity of oceans resulting from seawater absorbing carbon dioxide from the atmosphere "“ and that this will cause problems for Alaska's famous salmon and crab fisheries.

One consequence of the acidification is that increased acidity and decreased pH leaves shellfish like crabs, clams and oysters struggling to pull the minerals they need to build their shells from the water. The team found several areas in the Gulf of Alaska where concentrations of the shell-building minerals were low enough that the shellfish there wouldn't be able to build shells of normal strength. Shellfish aren't going to start disintegrating any time soon, but the change in acidity and shell composition can cause their metabolisms to slow and their stress hormones to fire up, diverting energy from growth and reproduction.

planktonOne organism already feeling the effects of acidification is the sea butterfly, also known as the flapping snail, pteropod or swimming sea snail. Sea butterflies are tiny (about the size of a lentil) mollusks that account for up to 50% of the diet of pink salmon. They're already having trouble building shells at current acidity levels and if they cannot survive, a 10% decrease in their population could mean a 20% decrease in the body weight of adult salmon. By 2050, the sea butterflies may not be able to make shells at all and go extinct, wreaking havoc on the local food web.

BUT"¦researchers at the University of North Carolina, Chapel Hill think that plankton, the base of many other marine food webs, might thrive in warming oceans. The researchers found, after warming 4-liter bottles of seawater over time, that phytoplankton grew slightly faster with every degree that the water temperature rose. Zooplankton, which feed on phytoplankton, grew even faster. This effect could work its way up the food chain, meaning more food for bigger and bigger fish. The number and growth rates of the phytoplankton would have to be sustainable, though, or top-heavy food webs would be unstable and could crash.

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September 1, 2009 - 9:48am
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