Saturday, July 7, 2018

Limpet land: part 2

Friends, the summer of research continues! This week, I checked on my Crepidula fouling experiment I had begun in June. You know, the one where I put live limpets and glued shells on plastic fouling panels to see how the limpets affect recruitment of the organisms around them. After three weeks, the panels had been colonized by a variety of organisms - mostly ascidians and bryozoans - so I wanted to count them all and see if I could tell any difference between panels with limpets, panels with shells, and panels with neither.

Limpet shells overgrown by ascidians and bryozoans
It took me a whole two days to get through all 25 panels in my experiment. I was constantly running back and forth from the dock to the microscope. I pulled the panels off of their PVC backing one by one and examined them under the 'scope to identify all the organisms that were there.

I made a few interesting observations. First, the limpets were overgrown by other organisms, more so than I had expected. I saw some overgrowth last year, but only on very small individuals (I only got very small individuals on my panels last year). I wasn't sure how the larger adults would fare with overgrowth, but they seem just as susceptible to it as the younger limpets. The shells I had glued to the panels were completely covered in fauna, and the live individuals had plenty of colonists too. I was fascinated to see that they could still move around with such heavy fouling.

One of my fouling panels with live adult limpets. Notice
the large halo around the four individuals in the bottom
left corner.
Second, I noticed large halos of blank space on the panels with live limpets. I had observed this "bulldozing" last year and hypothesized it might have a significant impact on the fouling community. I still observed the halos this year, but when I counted all of the organisms on the panels, there weren't big differences in the number of organisms on panels with or without live snails. I think the amount of space left empty because of limpet bulldozing was not enough to affect the rest of the community beyond the limpet's immediate vicinity.

It may sound like my experiment disproves my hypothesis, and in the strictest sense, that is true. But like all things in biology, sometimes the result you get is a matter of scale. On the scale of a few square centimeters around the limpet, yes, the bulldozing does have a significant effect. On the scale of a whole panel, though, it does not. I'm thinking about ways to analyze my data to demonstrate this difference.

The last thing I noticed is that even though there were halos around each of the limpets, the empty space didn't stay empty for long. It was recolonized by new recruits that could eventually grow to cover the space. Limpet bulldozing may not be so much a matter of empty v. overgrown space, but rather the bulldozing allows for space to be cleared and recolonized over and over again. This turnover in the community will certainly have an effect as time goes on, especially as seasons change and new organisms become ready to recruit to empty space. I suspect limpet bulldozing may lead to more heterogenous communities.

After counting all the organisms on the panels, I reset the experiment. I replaced any limpets that had fallen off and returned all panels to their rightful places on the dock. I will return in a few more weeks to see how the community has changed!

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