Thursday, July 6, 2017

The day the hydroids died

"Bye, bye Miss American Pie
Drove my Chevy to the levee but the levee was dry
Them good ol' boys was drinking whiskey and rye
Singing this'll be the day that I die
This'll be the day that I die"
- "American Pie" by Don McLean

Friends, ecology is full of surprises. I never thought that hydroids would dominate the fouling community at one of my study sites. I never thought that my experiment would start to look like it was covered in shag carpet from the 60s. I never thought that hydroids would hold the #1 position for so long. And I certainly never expected them to die all at once.

Dead, headless hydroids on a fouling panel being examined
under the microscope. Check out the clump at left, then
compare to live hydroids with pink heads.
It's not because of something I did (trust me, that was my first panicked thought). Almost overnight, all the hydroids have disappeared from the WHOI pier. Not just from my experiment, but from the walls of the instrument well, the lines from which instruments hang, my monitoring plates - everywhere. Dead. Headless. Nothing left but thin, rubbery stalks.

My best guess is that it's the temperature. The water around Woods Hole has been warming rapidly over the past few weeks, and considering that the hydroids started settling back in January, maybe they can't handle the summer heat.

The WHOI pier has actually started to look more like Eel Pond as the hydroids die off. Ascidians are recruiting to the empty space on the panels, and my "remove hydroids" plates are already almost covered by the squishy creatures. This shift again supports my temperature hypothesis because Eel Pond has been warmer all along. Maybe the WHOI pier is just now catching up, both in temperature and recruitment.

In case you're wondering, I am recording water temperatures at both sites. I have loggers out with my experiments, so I'll download the data at the end of the summer and compare patterns in water temperature to what I'm seeing in the recruitment. I'm glad that I have such clear patterns, both between sites and over time. This project just keeps getting more and more interesting!

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