Thursday, June 8, 2017

Shag carpet

My monitoring plates on the WHOI pier.
You can't even see the plates!
Friends, I am running out of ways to describe the dense, heavy hydroids that have colonized my fouling panels at the WHOI pier. Every time I think I've reached the maximum hydroid biomass that my panels can hold, the hydroids kick it up a notch. Compare the picture at right to what I termed "hydroid city" just a few weeks ago. The pictures show the same apparatus, only this week, you can't even see the plexiglass monitoring plates underneath.

I've told you before that my dock study concerns succession in fouling communities. Since starting the study, I've actually gotten a few questions from both scientists and the general public about why subtidal hard-bottom communities on docks are termed "fouling." I think my experience with the hydroids at the WHOI pier should give you some idea. Fouling fauna make things foul. They're heavy, they're wet, they cover everything and are difficult to manage.

When I first started my dock study, I thought I would study facilitation. I thought the first organism to settle on my plates would alter the environment in such a way as to facilitate the settlement of other organisms, thus driving succession forward. I've since started to think that facilitation isn't taking place, at least not at the WHOI pier. When I look at my fouling panels under the microscope, I used to see numerous hydroids but also a variety of other organisms - bryozoans, ciliates, barnacles. My experiment on the WHOI pier has now been going for about 10 weeks, and every time I look at the panels, there are fewer non-hydroid organisms on them. I'm beginning to think that not facilitation but inhibition is at work. Inhibition means that the first organism to settle and colonize the panels takes over and inhibits anything else from settling; succession can only move forward when the first dominant organism is removed by predators.

One of the fouling panels for my experiment, photographed
in a dish of water in the lab to show all the hydroids on it.
I'm not sure if there are any hydroid predators at the WHOI pier, but the good news is that I can become the predator. I added a "remove hydroids" treatment to my study a couple weeks ago, so now a subset of my panels is cleaned of all its hydroids every other week.  If the hydroids are inhibiting the recruitment of other organisms, then the "remove hydroids" panels should be colonized by a wider diversity of organisms than the panels with hydroids. I'm very interested to see if any differences develop. Only time will tell!

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