Hello again: part 2

My experiment had to wait 5 years for me to return, but it was not the only patient experiment in the HAUSGARTEN this year. My friend and collaborator, Melanie, started an experiment of her own in 2015 to figure out how plastic litter impacts deep-sea sponges. After 9 years, she was finally able to finish the experiment. 

An anemone on the base of Melanie's experiment.

I volunteered to help Melanie during her ROV dive by keeping notes. The ROV team has a specialized system that automatically time-stamps and georeferences every observation during the dive. A dedicated laptop in the ROV control van and a second one in the winch control room are used for data logging. We don't want to miss anything that happens on the seafloor. 

As I watched the video feed from Melanie's dive, I started to notice something unexpected. Small white lines appeared on many of the plastic pieces in her experiment. Looking closely, I realized they were worm tubes! The worms must have settled on the plastic over the last 9 years. 

Melanie and I had discussed the possibility that something had settled on her experiment, but I didn't actually think anything would be there. It was incredibly exciting for me to see. Not only could Melanie's experiment serve its intended purposed of demonstrating plastic impacts; it could work as a settlement experiment too. 

The sponge Cladorhiza gelida and tube worms on the plastic

As soon as I noticed the worms, I started watching the feed much more intently. The ROV moved around between different bits of plastic, and I noted what species were on each one. Pink anemones on one, spiky sponges on another. The scientific names surfaced in my mind: Cladhoriza, Amphianthus. I recognized them all.

Here's the thing: all the species on Melanie's experiment were ones that I had also found on the 18-year settlement experiment. It appears that a finite set of opportunistic species take advantage of anthropogenic habitats in the Arctic deep sea. 

When the ROV dive was over and the vehicle carried the samples to the surface, I met Melanie in the lab. I carefully pulled each individual settler off of its home with forceps. One by one, I photographed, cataloged, and preserved them. My find kept flashing back to 2017, when I did the same procedure for our long-term experiment. Different plastic, different years, same animals. 

It was incredibly exciting to find the settlers on Melanie's experiment. The data I collected reinforce the results from our previous study and help us better understand the Arctic deep sea.