Wild Slugs: Cortez Edition (Part Three)
Having slugs meant that it was time to get to work on another part of the project, determining the light sensitivity of the little gals. The I-mazes built by Glass Cages were just right, and we were able to provide a range of light intensities using full-spectrum LED lamps. We first tested using Aplysia, so we could play with parameters a bit. Having only a few Elysia meant that actual experiments would have to wait until we found more.
Another goal of the project was to get a better sense of where Elysia were distributed in the bay. We knew they could be found in front of the station, and that Bertsch had found them at Punta la Gringa, but that was about it. Based on limited experience, the preferred habitat seemed to contain turfy coralline and green algae, along with bunches of Codium, but, again, this was based on a limited sample.
For this summer, we planned two surveys in the bay. In the first, we would spend a morning sampling areas east and south of the station. The second survey would be conducted north of the station, when the students go farther out and spend the night away from the station.
For the first day, we decided to explore two islands, Cabeza de Caballo and Gemelito Esta, along with a small inlet near El Rincon at the south of the bay.
Our first site was the north end of Cabeza, along the west side. There was considerable bird life along the rocks above the water, and we thought it would be worth finding out whether the higher nutrients from the guano supported more algae for the slugs. Of course, the nutrients could also support algae that the slugs don’t like, so we should be able to learn something either way.
Once we got into the water, we could see that the bottom was different from that around the station. Below the bird cliffs, there were heavy growths of brown algae, mostly Padina and Sargassum. The presence of these species did not automatically rule out Elysia, but the possibility of finding slugs 4 cm long in a foot or more of Padina was pretty remote.
The tide also happened to be very low, so the best slug habitat may have been above or near the water line. However, exploration of the shallows did not turn up anything in the way of Codium or slugs
Farther south, things opened up a bit, and there was more bare rock among the brown algae.
There was even a little Codium. No Elysia visible, though.
The snorkel itself was awesome. Lots of different species of fish, often quite large. We were even visited by a school of Jacks, zooming by for a quick look.
After taking a few more photos for documentation, it was time to move on to the next site, Gemelito Este. As can be seen in the photo below, there is plenty of guano on the island, which suggests a lot of nutrient input.
The bottom seemed more conducive to Elysia, however. Plenty of Padina, but also significant patches of coralline and green algae.
We even found some snail or slug eggs. Not from Elysia, but a good sign that molluscs were about.
No Elysia at Gemelito Este, either. Undeterred, we continued southward to an inlet on the mainland, just north of El Rincon. The bottom looked very promising, with lots of coralline, green algae, and Codium.
Toward the end, we were hunting among the clumps of Codium and other algae, and Nancy kicked up a little Elysia. Another data point supporting our ideas about appropriate slug habitat.
Perhaps as a reward for the students’ hard work, a couple of whale sharks swam by the boat. Ricardo maneuvered the boat perfectly, to allow the students to have a quick swim with one of the sharks. Very much a high point for all.
The following day was another field trip, which included another period for snorkeling. This time, it was a small island outside the bay, Isla Pescador. No harm in looking around, right?
Unfortunately, the site is a bit more exposed to wave action, and the surge on this day made it difficult to do too much slug hunting. The bottom looked promising, though.
The following day, the Spatial Subsidy group had their field trip. They snorkeled at a different site, and brought back 11 (yes, eleven) more Elysia for us. It seemed like things were really getting started.