Friday, April 13, 2018

Name that copepod!

"Got a question for you," I told my friend, Kristina. "What copepod lives at 79 N, 4 E, 2500 m depth?"

Kristina thought for a second. Copepods are small crustaceans, related to crabs and shrimps. They are abundant all over the world, and they form an important link in the food chain. Copepods are most abundant in the surface ocean, but some live close to the seafloor. Kristina's research focuses on the distribution of copepods in the Arctic, so I thought she might be able to answer my question. Instead, she gestured across the room.

"This gentleman might now," she informed me.

AY looked up from his microscope and came over. I introduced myself, then repeated my question. He put a hand up to his chin. He thought for a second. Then he asked, "Do you have a sample?"

The amphipod specimen AY helped me identify. Two
individuals are attached to and being eaten by a carnivorous
sponge. They're the clear lumps with red eyes in the center-
top of the photo. The sponge is the pale pink stalk.
"I do!" I exclaimed. It's actually rare for me to have a physical specimen of an animal that I need help identifying. Usually, the things I need help with are rare species, ones I only see in pictures. I'll send my best photo to a taxonomist asking for help, and the most common response I get is "Do you have a sample?" Well, in this case, I did!

AY has an incredible eye for detail. I gave him two jars with copepods, and he promised to identify them over the next few days. I thought I would have to wait until next week to get an answer from him, but just a few hours later, there was an e-mail in my inbox from AY. One of the specimens I had given him was not a copepod after all but a different kind of crustacean called an amphipod. The other specimen was a juvenile copepod in the genus Xanthocalanus.

I was amazed. The specimens I had given AY were not in good shape. They were preserved in ethanol, which is not the best preservative for morphology. Both were in the process of being eaten by a carnivorous sponge. In fact, the Xanthocalanus specimen was stuck to a sponge like velcro, and the amphipod was even partially digested. I was extremely grateful for AY's taxonomist eye.

Now that I know what the small crustaceans are, I can look up information on their population dynamics. Variations in prey abundance can influence the growth and reproduction of their predators, so I want to know if there's any connection between the abundance of copepods and the recruitment of the carnivorous sponge. It's just one more avenue to pursue for my analysis of the long-term recruitment experiment from last summer. We'll see if there's any connection!

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