Monday, July 27, 2015

Pteropod catch!

I am not kidding when I tell you that Caitlin Smoot (UAF) and Jennifer Questel (UAF), our ecologists on board, caught an absolute /mess/ of pteropods in the bongo nets several times today. They were so thick in her nets that they looked like mud! Often, this is exactly how we find them: very crowded in one isolated patch. It was very cool to find them! 
Caitlin Smoot (UAF) posing with the grey cod-end of the Bongo nets, which collect all the animals that the net filters. The pteropods are the tiny black snails in the white hand-filter. There are so many they look like sand!  

This is a close-up shot of the white hand filter, showing the thousands of tiny snails. The animals themselves are dark colored, but the shells are clear. The interspersed red animals are a different kind of pteropod that grows without a shell (and really likes to eat the shelled species). You can also see some ctenophore slime-- jellfish tentacles-- threading through the pteropods!
You’ve heard us mention pteropods before: they are the small snails that are often talked about in conjunction with ocean acidification research. The snail shells are made of aragonite, a mineral variant of calcium carbonate (a more common form is chalk). In order to make these shells, pteropods use free carbonate ions naturally found in seawater. Normally it’s pretty easy, as carbonate is relatively abundant in the ocean. However, in low pH environments, free carbonate ions can be difficult to come by.

At a certain level of scarcity this means that pteropods and other carbonate shell-builders just build more slowly—sort of like you trying to conserve gas when the price of oil goes up—but eventually these shortages can get really severe. Laboratory experiments show that as pH drops, shell building slows… then stops… and then reverses. The shells pit, crack, and start flaking away as they dissolve. Research already shows that this is happening in real life: monitoring cruises just like this one off the US West Coast collected live pteropods with acidification-damaged shells.

Right now, it’s unclear whether or not dissolving pteropod shells will have a major impact on ocean ecosystems, but lots of researchers are on the job! We already know that juvenile salmon love to eat pteropods. If the young salmon can’t replace this part of their diet, they might end up going hungry. In the long term this could mean that they grow up smaller than usual, or that fewer survive to adulthood.

This could be a serious challenge for Alaska. The protein for many native Alaskan communities comes from subsistence salmon fishing, and the state’s economy is built around some shellfish and salmon fisheries that are highly vulnerable to OA. Our program works to understand OA from all these perspectives: our scientists work with shellfish hatcheries and fisheries research facilities, and even economists. For example, we’ll end up sending some of the pteropods we caught today back to the lab for a close look, and that data will end up informing the whole research chain! And it all started here on RB104, with Caitlin and Jenn.

Jennifer Questel (UAF) sorts through some of the zooplankton we collected in the Bongo nets today.
Great catch! 


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