Sunday, June 24, 2018

The voyage of the Dawn Treader: part 4

I felt a tap on my knee and opened my eyes to see Evan standing in front of me. "We're about 30 minutes out from the next site," he told me. I nodded.

I was still a bit queasy, having gotten seasick after our last dive. Slowly, I pulled myself up and walked out on deck, keeping my eyes to the horizon the whole time. I actually felt more stable than I expected. I can do this, I thought.

We rolled over the side of the boat and made our way down the line to the seafloor. The first thing I noticed were the sand dollars. Hundreds, thousands of them were scattered on the sand all around me. I swam forward, following Evan, and found the shipwreck. The Josephine Marie is a fishing boat that capsized off of Provincetown, Massachusetts. It lies upside-down on the seafloor, "turtled" as divers call it. Evan immediately began driving my samplers into the sand near the wreck, and I swam up to the hull to start scraping off adult specimens of my study species.

I'm using Didemnum albidum, a species that's native to New England, as a model to understand how its invasive sister species, Didemnum vexillum, might spread among benthic habitats. I hypothesize that shipwrecks could serve as stepping-stones to facilitate the spread of D. vexillum to the Sponge Forest on Stellwagen Bank.

It was easy for me to locate D. albidum on the wreck - it was the only white encrusting species there. I pulled out a plastic scraper and empty sample tubes from the mesh bag I was carrying and set to work. Within minutes, I had 7 D. albidum samples in my tubes, so I rolled to my left to check Evan's progress. He was right next to me, having finished deploying the seafloor samplers. I handed him a set of tubes, and we set about scraping at double time.

I was surprised how quickly we got all the samples I needed - it only took 15 minutes. I had expected it to take much longer, so I actually laughed when we finished so quickly. We had planned a total of 30 minutes on the bottom, so we used our extra time to swim around and survey other species on the wreck. Most of the hull was covered in Metridium senile, the plumose anemone, which is very common on shipwrecks in New England. There were also plentiful finger sponges, hydroids, and sea stars. I loved seeing the biodiversity.

I gave Evan a 5-minute warning and started swimming back to the anchor line. As we reached the line, I saw Evan pick up two scallop shells off of the sand. I thought he was just collecting shells, but when we got back on the boat, he handed me a scallop on the half-shell. A raw celebratory delicacy!

The second dive of the day was immensely successful, and I was overjoyed. I got all the adults that I needed and got my samplers deployed to collect later in the summer. The steam back to the marina took about 4 hours, so I took some time to relax and revel in the moment. Once we got back, I still had to preserve my collected samples in the lab and rinse my dive gear. My day actually went until 10 pm - altogether a 17-hour workday. The day had its ups and downs and I was exhausted by the end, but I was very proud that I had lead a (mostly) successful trip and gotten what I needed. My project is officially begun!

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