The Portland: part 2
Friends, I am back out at sea on the Dawn Treader to study shipwrecks in Stellwagen Bank National Marine Sanctuary! My team set aside this week for ROV dives on the wreck of the steamship Portland, sunk in 1898. It took us a while to figure out the best way to work in our study area, but we eventually smoothed out all the kinks and collected 8 hours of good footage. It was so rewarding to see the wreck!
Working in Stellwagen Bank National Marine Sanctuary is actually pretty challenging. At 450 ft (137 m) deep and ~30 nautical miles from shore, the Portland is in a weird middle ground. It's too deep for SCUBA diving but not far enough offshore to justify the use of a large regional- or ocean-class research vessel. It's not a shallow coastal habitat, but it's also not quite deep-sea either. We're filling in the gap with day-trips on a small (30 ft/9 m) boat and a small ROV, but we've had to contend with some logistical difficulties. The boat does not have a dynamic positioning system like the larger ships, so we came up with a dual-anchor system to keep it in place over the wreck. The ROV is light enough to be carried away by the strong tidal current, so we added weights in various places. It took a while for us to figure everything out, but my team has finally hit a rhythm. We are working more and more efficiently, and we reaped the benefits of beautiful footage from the shipwreck.
I was very excited to see what organisms were living on the Portland, and the wreck did not disappoint! Large plumose anemones covered the hull near the stern, and fat orange cushion stars spotted the wreck. I wasn't surprised to see plumose anemones - they have been on every wreck in the North Atlantic that I've been able to lay eyes on. I think they have a unique life-history that allows them to be successful on island-like habitats. The cushion stars were also no surprise. I spotted some individuals on the mud surrounding the wreck, so they may have migrated from the surrounding area.
What surprised me were the sponges. Large, bulbous yellow sponges were common on the hull, and a second spherical species was common too. There were even bowl-shaped white sponges similar to ones I've seen in the Arctic! I had never seen so many large sponges on a shipwreck before. Sponges are generally considered to have restricted dispersal (the larvae don't go far from their parents), so they would not be expected to reach an isolated, island-like shipwreck. I will have to figure out where the sponges came from and how they reached the wreck!
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| ROV Pixel on board the Dawn Treader |
I was very excited to see what organisms were living on the Portland, and the wreck did not disappoint! Large plumose anemones covered the hull near the stern, and fat orange cushion stars spotted the wreck. I wasn't surprised to see plumose anemones - they have been on every wreck in the North Atlantic that I've been able to lay eyes on. I think they have a unique life-history that allows them to be successful on island-like habitats. The cushion stars were also no surprise. I spotted some individuals on the mud surrounding the wreck, so they may have migrated from the surrounding area.
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| Some members of the field team. Left to right: Evan Kovacs (Operations lead, videography), Mike Skowronski (ROV pilot), Calvin Mires (archaeology), and me (biology). Photo by David Ullman (captain). |
What surprised me were the sponges. Large, bulbous yellow sponges were common on the hull, and a second spherical species was common too. There were even bowl-shaped white sponges similar to ones I've seen in the Arctic! I had never seen so many large sponges on a shipwreck before. Sponges are generally considered to have restricted dispersal (the larvae don't go far from their parents), so they would not be expected to reach an isolated, island-like shipwreck. I will have to figure out where the sponges came from and how they reached the wreck!
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