Wild Slugs: Sea of Cortez Edition (Part One)
Has it really been that long? Well, I’ve been busy.
The preparations of the last few months have now been tested in the field. I am returning from the first two weeks of a five week field study in Bahia de los Angeles in Baja California. As I think I posted earlier (apologies if I did not), the plan for the summer was to work with Ocean Discovery Institute on fleshing out some of the details of the life history and behavior of Elysia diomedea in Bahia de los Angeles. Specifically, we want to know more about where they are found in the bay, what they eat, and how they respond to light. This information will help us to understand more about the role of kleptoplasty, along with the significance of the dramatic population fluctuations of the slugs documented previously by Hans Bertsch.
Even before we left, there were several challenges. For example, for the project to get off the ground we needed permission from CONANP, the agency that oversees the marine reserve, to collect Elysia from the bay. Months before the project began, we submitted an application for a permit to allow us to collect and study Elysia. Unfortunately, that permit was rejected because we had not been clear about the relationship between the Elysia project and ongoing research in the bay islands. Naturally, this caused us significant anxiety. After a lot of work behind the scenes by folks at Ocean Discovery and by my very good friend Drew Talley at USD, our intentions were made clear, and we were given permission to go ahead with the project.
Among the items that were absolutely necessary were aquaria for holding, observing and testing the slugs’ response to light. In April, I had started working with a local company that builds custom aquaria to build two holding/observation tanks and two “I-mazes” for testing light preference. By early June, the tanks had not materialized, and I was beginning to get nervous that missed deadlines and excuses would continue until time ran out. I decided to go with a more experienced vendor, Glass Cages, and they got the tanks into production and had them air freighted to San Diego in plenty of time. The whole process of working with them was pleasant and reassuring.
The other critical pieces for extracting and amplifying DNA are a microcentrifuge and a PCR thermal cycler. Again, thanks to the persistence of Drew Talley, we borrowed an Eppendorf centrifuge from USD, and received the loan of a demonstration model thermal cycler from Thermo Fisher Scientific.
So, after months of planning, spending a semester making sure that the methods work, arranging for care of the system in Maryland while I was gone, and enjoying a roller coaster ride obtaining permissions and equipment, it was time to get into the field.
The trip down was slightly adventurous. We traveled with the Ocean Discovery students, starting out at Hoover High School in City Heights. This year, we took the eastern route, through Mexicali and San Felipe. It was a little longer, but somewhat more scenic, and had a whole lot less traffic. The road was not great in spots, and one of the vans developed a flat tire along the way. After a little delay, we were back on our way, and arrived in the early evening.
As always, I was very happy to be there. Its hard to think of a place that I would rather be. The sea is beautiful and full of life, and the surrounding desert is spectacular in its own right. Over the course of the two weeks at the station, I tried my best to savor the views, sounds and smells.
Naturally, I was eager to get started. It was all I could do to sit still during review of procedures around the field station, because I was eager to collect slugs in order to be ready for the students’ upcoming projects. Finally, I got into the water, and began to hunt for Elysia. It was wonderful to be in the bay again, and there was lots to see. The familiar zones of Padina, Codium, Ulva, and the many other algae on the rocks outside the station reminded me of where I thought I should look. After about 1 ½ hours of unsuccessful searching, I headed back to the station to get ready for the rest of my day.
I got to meet my crew in person for the first time. The five young women were full of energy, and ready to get going with the project. The goals of the “Photobiology” group (I needed a somewhat official sounding name, sue me) will be to flesh out some basic biology of E. diomedea here in the bay. As we did for E. clarki in Maryland, we want to extract DNA from E. diomedea, and compare the sequence of rbcL in kleptoplasts with those from potential food plants. Also, we will be looking at light preferences, using “I-mazes,” which give the slugs a chance to select their favorite light intensity. We are also hoping to have a chance to explore the bay, surveying for appropriate habitat and the presence of slugs. Lots to do to get set up and get the students trained.
The hunt for Elysia continued during the morning of our first full research day. In the past, the morning hours have been the most productive in terms of slug hunting, so I had planned several mornings during the first week for collection. The crew was becoming very proficient in the water, and we hunted for about 90 minutes in the shallows in front of the station. Sadly, despite our efforts, no Elysia were to be found. After a quick cleanup, we headed for the classroom for a briefing on algal diversity, lab equipment and safety before lunch. The students had other activities in the afternoon, which gave me the opportunity to continue setting up tanks and equipment.
Our “molecular lab” is located in the garage, along with equipment for other Directed Research groups. We share the space with a group studying ways of reducing bycatch of unwanted fish species and turtles, and another group that documents the flow of energy between the rich waters of the sea and the relatively barren land of the bay islands. The space is a hive of activity at 7 am, when the other groups are rushing to get on boats. After that the space is essentially ours until lunchtime.
The other part of our “lab” consists of the observation tanks. These are in another part of the station containing the kitchen and computer lab. The 16” cube tanks sit on a sturdy table, with circulation provided by air pumps, and lighting provided by morning sunlight supplemented by desk lamps with full-spectrum LED bulbs. Once the slugs are in, the tanks hold slugs for DNA extraction and behavioral assays, with one being used solely for observation of the daily rhythms of undisturbed slugs.
Although we had not found any Elysia, at least a dozen small Aplysia rode into the tank with the plants. This will actually be handy for comparison with the responses of Elysia to light. Aplysia do not store chloroplasts, and might be expected to be repelled or indifferent to light.
Day 2 was reserved for a field trip for the students. It is supposed to be a non-work day, used to introduce the students to some aspect of the bay. It started off great, with a visit to a sea lion colony, and up close encounters with very large fin whales.
We did squeeze in a little work, because part of the trip involved time for snorkeling at Coronadito island, at the far north end of the bay, and we were not explicitly banned from looking for Elysia. Although we did not find any, it was useful to note and photograph the nature of the bottom, and the dominant algae species that were present. Lots of Sargassum, some turfy coralline algae, but not a lot of large green algae.
The days continued, with more briefings about identification of algae and molecular biology methods. The big question was whether we would actually find any Elysia. Fieldwork always requires some improvisation, but it’s a real challenge to improvise your way around the absence of your research subject. Stay tuned.