Wednesday, May 10, 2017

Hydroid explosion!

A large colony of Obelia geniculata on one of my
fouling panels in the lab
"I might only have one match
But I can make an explosion"
- "Fight song" by Rachel Platten

Kneeling on the dock, I undid one rope, then another. I pulled up on the white thread, grabbed the edge of the PVC, and flipped my experiment up onto the dock.

And gasped in awe.

My panels were covered in hyrdoids. Big, stringy, wet colonies of Obelia. Pink buds of Tubularia all over my plates. It was a hydroid explosion!

I should have known it was coming. I mean, the hydroid colonies on my monitoring plates exploded after a few weeks. Just a few individuals can grow into a massive colony. I had thought it was already too late in the spring for hydroids to dominate the community. Guess not.

Discovering the hydroids on my experiment yesterday is an example of one of my favorite parts of ecology: the element of surprise. When I first formulated the hypotheses for my succession study, I didn't even think hydroids played a big role. I thought they might show up in small numbers with the first wave of barnacles, but that they would quickly be outcompeted by other organisms. This prediction was based on my experience with fouling panel studies in both Oregon and the Arctic. But I was wrong.

A colony of Obelia geniculata, photographed using
a dissecting microscope at 50x magnification
I actually had to adjust my experiment a little, because I hadn't been planning to consider the hydroids' role in succession. I selected a random sub-set of panels and designated them "RH" for "remove hydroids." From now on, whenever I curate my dock experiment at the WHOI pier, I'll remove all the hydroids from that sub-set of panels and see if the communities develop any differently.

I'm excited to include the hydroids as an important group in my study now. Hydroids increase habitat complexity (by forming their big, stringy colonies), so I'm curious if they have any effect on other organisms settling on the panels. I shall see! More surprises await!

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