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Midwater Ecology Expedition Fall 2019 – Log 4

Astrid taking a careful look while dissecting an ocean sunfish to look for parasites.

Midwater Ecology Expedition Fall 2019 – Log 4

The word from Captain George Gunther was that we might have a short dive Tuesday due to deteriorating weather. This was seconded by the modern sailor’s favorite tool, But first thing in the morning, the winds were light and we began our dive at 6:30 a.m., as always, feeling optimistic and excited about what the day would bring.  By 10:30 a.m. that optimism had turned like the weather. Winds gusting to 28 knots meant recovering the ROV in order to beat a hasty retreat into the relatively calm waters outside of Monterey harbor. What to do when the planned ROV dive is scrubbed due to high winds? Any number of things as it turns out.

Our colleagues from GEOMAR, Henk-Jan Hoving and Stella Scheer, noticed the surface waters full of Chrysaora fusescens, medusae commonly called “sea nettles.” If you’ve visited the Monterey Bay Aquarium, you may have seen these beautiful brownish-red medusae swimming gracefully with their tentacles and mouthparts streaming meters behind them. At this time of year these jellies are so common in Monterey Bay and along the California coast that leatherback turtles travel all the way from waters off Japan, crossing the vastness of the Pacific Ocean, just to feed on them and on Aurelia aurita, the moon jelly, also common here.

They aren’t the only ones. We have been encountering dead or dying Chrysaora hundreds of meters deep; usually with seastars, like Rathbunaster, eating them. Henk-Jan and Stella are interested in foodfalls and the animals attracted to them and made good use of the opportunity to collect some sea nettles they saw floating on the surface. The jellies will be frozen in order to make an artificial foodfall that we can later take down with the ROV to monitor.

While scanning the surface for Chrysaora, MBARI Postdoctoral Fellow Astrid Leitner and Kat Bolstad, a cephalopod researcher from New Zealand, spotted several dead Mola mola (ocean sunfish) floating at the surface as well. Since they were small, less than two feet in diameter and dead, it was easy to scoop them up in a net. All were missing their fins—a sign that sea lions had killed them. Not to eat, but because sea lions often grab small ocean sunfish by their prominent dorsal or ventral fins and then fling them like frisbees through the air! Fun for the sea lions, maybe, but not so much for the hapless sunfish. Like leatherbacks, the largest turtles, Mola mola eat jellies and grow to be among the largest of all bony fishes (hmm, must be something to this jelly diet).

Writhing mass of tapeworms from the gut of a Mola mola!

Along the way these slow-swimmers are parasitized by many different animals, from copepods to sea lice, roundworms, and tapeworms. And this is what had Kat excited (well, in a kinda’ gross, I’d-rather-be-dissecting-squid sort of way) as she and Astrid expertly dissected the Molas, and found and filled a bowl full of writhing tapeworms (cestodes) to pass along to colleagues who study these parasites. What remains from the Molas will be used for—you guessed it—foodfalls.

Bruce continues work on a manuscript while he watches the wind, Kim monitors his in-lab respirometers to make sure his Poeobius (butt worms) are still performing, George is currently keying out coronate medusae collected yesterday and me, well, seeing as we have some time, maybe I’ll write up a blog.

And so it goes, full circle back to where we started and, hopefully, tomorrow, back in the water first thing!