Leg 3—March 16
We are now even closer to La Paz and are heading down to 1,600 meters with the ROV for one last look in the deep waters of the Gulf of California. The divers have dried their gear and packed it away as there will be no blue-water dive today due to time constraints. During this leg, our six divers collected a diverse assemblage of ctenophores, siphonophores, hydromedusae, salps, pteropods, amphipods, copepods, polychaetes, arrow worms, and larvae. These specimens provided an important source of experimental replicates for the scientists on board.
Among the highlights from this cruise were:
- collecting two specimens of a new family of siphonophores that we have only ever collected once off the coast of California
- observing likely new species of siphonophores and undescribed ctenophores which are rare at Monterey latitudes
- recording for the first time, color 4k resolution video of natural bioluminescence from many species
- comparing extensively physiological data from deep and surface gelatinous organisms
- discovering new symbiotic associations between crustaceans and jellies
- observing a new developmental structure in a siphonophore species we are describing
- conducting chemical studies on the generation of bioluminescence in the thick layers of ostracod shrimp
- observing a squid brooding its gigantic eggs
- having a freezer stocked with locally-made palatas (Mexican popsicles).
It is a testament to the excellent crew of the ship and ROV pilots that we were able to conduct a full set of dive days for both ROV and SCUBA operations, with no major weather issues and only one dive where the ROV had to be pulled early due to a hydraulic issue. TheDoc Ricketts is outfitted with 12 suction samplers and 12 D-samplers for midwater work, and we came up with a full load of samples almost every dive.
While we are accustomed to the layers in Monterey Bay (shallow waters where photosynthesis occurs and midwater zone with its oxygen minimum layer), in the Gulf of California, these transition zones are compressed into much shorter vertical scales, and they occur at much shallower depths. The set of species that can tolerate these extremes also seem to be limited, because in the Gulf we tend to see lots of a particular species at a time. Which subset we see changes day-by-day and depth-by-depth.
When reviewing the records from our 2003 and 2012 expeditions, we found nearly all of the same species were noted, but species that were dominant in one year would be rare or even absent in others. George never did see the thick layers of giant larvaceans he was hoping to revisit. While blue-water divers were stung mercilessly by Rhizophysa in past years (it is a relative of the Portuguese Man o’ War), on this expedition the tiny specimen that Cat sampled on March 11 turned out to be the only one we saw. However, we did find three strange floating clusters down near the bottom that turned out to be Rhizophysa egg masses!
How much of this variation is seasonality, and how much is indicating a change on longer time scales? Answering these temporal questions would require additional visits to the Gulf. Unfortunately, given the logistical and bureaucratic roadblocks, we may not have such an opportunity in the future. On the bright side, we do have sufficient data to publish a thorough review of the diversity and ecological interactions of the Gulf’s typical inhabitants. Like the premise of many movies, the Gulf has an intriguing cast of quirky characters who have adapted to thrive in a challenging and fascinating environment.
Until next time…
—Kyra Schlining and Steve Haddock