A squid’s diet

July 16, 2012

The plan for today was to launch the Midwater Respirometry System (MRS) early in the morning, but the system was not responding properly so we could not launch it. While Kim Reisenbichler and the remotely operated vehicle (ROV) pilots were trying to fix it, we adapted our schedule and decided to recover the camera system we launched yesterday afternoon. This was a short dive from 8:45 a.m. until 10:10 a.m. The retrieval went smoothly and the videos recorded overnight will now be analyzed by Henk-Jan Hoving, a postdoctoral fellow in the Midwater Ecology Lab. Here is how Henk-Jan describes his mission on this cruise:

During this cruise one of my focuses is the feeding ecology of pelagic (open ocean) cephalopods. Information on feeding will tell us where species fit in the pelagic food web of the Monterey Canyon. Also, a critical part in keeping animals alive in the lab is knowing what they feed on. Knowledge of diets will therefore also help us to improve husbandry.

We investigate the feeding ecology of pelagic cephalopods in three ways. One is by looking into the stomach contents of individuals collected with the ROV. The stomach contents of cephalopods are often hardly recognizable, because they use their sharp beak and radula (a minutely toothed ribbon-like anatomical structure) to macerate their food. Ingested food goes via the esophagus, which passes through the brain in cephalopods, to the stomach. I will be using DNA sequences to identify the stomach contents.

Squid tissue samples will be analyzed to obtain a stable isotope signature, allowing us to construct the position of squid in the food web, and to characterize trophic relationships. The analysis of fatty acids in the squid tissue will render more specific information on the group of organisms (e.g. fish or crustaceans) the squid fed on.

Another valuable way to learn more about the diet of pelagic squid is the archived ROV footage in MBARI’s Video Annotation and Reference System (VARS) database. Over the years of MBARI’s ROV observations, many squid species have been encountered with food in their arms. Yesterday, we observed a Gonatus onyx with a myctophid fish (Stenobrachius leucopsarus) in its arms. Almost all knowledge that is available in the scientific literature on squid’s diets is based on trawl-captured individuals. The stomach contents of trawl-captured squid may be biased by so-called net feeding. Induced by stress, trawl-captured squid start eating any organism that is within reach, biasing diet studies. The ROV records of squid with captured prey provide a unique natural insight into the squid’s diet.

—Henk-Jan Hoving

Gonatus squid feeding on a myctophid fish.

Gonatus squid feeding on a myctophid fish.

The second dive of the day started at 11:05 a.m. We collected different animals including several squid (Taonius and Chiroteuthis calyx). We also collected some Sergestes similis shrimp that will be used by Kim Reisenbichler for respirometry experiments.

Cockatoo squid. (Taonius)

Cockatoo squid. (Taonius)

Kim managed to fix the MRS that was then reconnected to the ROV in the evening. Everything is now ready for tomorrow morning!

MRSTrayInstall

—Geraldine Fauville