Going Topless with Urchins

There’s nothing so satisfying as pulling back and seeing your brand new experiment out there in the water.

It’s been a crazy week or three getting this up and running, but now my first big postdoctoral experiment is soaking in the water, with urchins grazing away.

I’m testing some ideas regarding how diversity mediates the impact of disturbance by urchin grazing, and vice-versa – how disturbance by grazing can alter diversity. In essence, I’m testing a model of a community feedback process based on a framework whipped together by Randall Hughes, myself, and a few other fabulous co-authors.

But even though your ideas may be high-up and lofty, they always meet some interesting realities on the ground. Reality point 1 – my god, we built a lot of large cages.

This is about 1/4 of the cages before deployment. The rest were in the water. Thank fod for cheerful undergrad labor (fueled by brownies made from scratch – the key is to underbake them, and use a combination of eggs and egg yolks for extra gooey-ness) They look like such simple cheap affairs – some garden fencing, some PVC, some netting around the bottom…and then there’s about 1 ton worth of chain and half a ton of rebar stuffed into them. Subtidal work: unless it’s heavy, the waves will sweep it away.

Reality 2 – sometimes, you’ve gotta do it topless. Yes, the cages have no tops. This would seem the height of insanity if you want to keep something INSIDE. However, urchins appear to not like bendy flexy things. Sure, they’ll crawl up to the tops, but then they get to that wave strip at the margin, and freak out and freeze up. I’ve watched it. It’s kinda odd. And those cages that did have a top on them? That top, even if it’s mesh, creates a LOT of lift. So, a small wave washes by, and suddenly the cage top becomes an airplane wing. Unless you’ve added a huge amount of weight to your cage (see above), you may well never be able to find your cage again.

Reality 3 – nature is variable. Well, duh. See the two cages with two very different species compositions, som providing more or less biomass. I mean, the whole premise of this experiment was to use a natural gradient in species diversity as a treatment. But sometimes adding or subtracting one species can make a huge difference. Sampling (Reality 4 – ID-ing to the species level in the field on SCUBA gets pretty tedious after one hour, let alone 4 or 5) was pretty interesting, showing that large differences were indeed generated by both position on the reef, local topography, etc, as well as whether, say, tiny sea cucumbers had colonized a plot, whether the plot was full of lush Pterygophora, or the presence of the squat thick gorgonian Muricea.

Reality 5 – hungry urchins are hungry. And devious. Upon addition of urching to plots, they zoomed over to any brown algae (particularly the aforementioned Pterygophora or any juvenile giant kelp) and began munching in earnest. Some ran for the sides of the cages (and a few managed to squeeze out – Reality 6, the best laid plans of underwater mice and men… I’ll be doing some replacements this week with larger urchins). But the instand voracious consumption was really quite impressive.

I’m pretty stoked, and deeply curious as to how this will turn out. I’m sure there will be cursing, frustration, and bizarre results in the future, but for now, SCIENCE! Love it!

the light! the heat! the feedback!

ResearchBlogging.org Sometimes, the devil IS in the details. I’ve been thinking about feedbacks between community community structure and function lately, and run into a few curious roadblocks, as well as one very very interesting story.

First, the roadblocks. Just what do we mean by structure and function, particularly in reference to a biological community? Structure seems obvious – the static properties of a biological system that we can go out, stare at, and say,”Oh, yes, hello structure!” I of course often think of things like biodiversity or biomass, but one could also reference Carbon to Nitrogen ratios, physical structure, or others.

But function – that’s more nebulous. The first thing that springs to mind is, what is the opposite of a static property. Why, a rate, of course. So, a rate process…but that’s awfully nebulous. I mean, what can’t be measured by a rate? Which leads to thinking more about the flux of matter and energy within a system. Far more tractable, but then, what gets cut out?

I am struck by the example of potential feedbacks between climate change and the nutrient content of plants. This is a lovely example drawn from a 2008 PNAS paper by Ollinger and colleagues. In it, they basically show that plants with higher nitrogen content tend to have shinier leaves. The more nitrogen in the canopy, then, the higher the albedo. Higher albedos then cool an area, or at least decrease warming as light is reflected back.

This is curious – as climate change work in the Harvard forest (or, sorry, the Hahvad Forest) have shown that warming soils can lead to faster nutrient cycling and more N availability. More N availability can change the albedo of leave in local plants, or can even cause a shift in the plant species composition to shift towards plants with more nitrogen per unit carbon.

It’s a really interesting feedback.

At the same time, even if this does something with respect to warming, CO2 is on the rise, also possibly changing C:N ratios. So, caution is warranted to thinking that Nitrogen is the solution. Indeed, considering the myriad of other changes in nutrient cycling and plant stoichiometry, the devil really IS in the details here as well, and hence caution is warranted before someone goes off, all IronEx style, and proposes fertilizing the planet to slow climate change. After all, we’re doing that already!

But it all raises an interesting question in my mind – is slowing temperature change a “function”. I would say yes – that it is the service provided by the ecosystem. It is not a flux of matter or energy, but it is still something that the system does, and hence, a function.

And functions like these are becoming more important as time goes by!

S. V. Ollinger, A. D. Richardson, M. E. Martin, D. Y. Hollinger, S. E. Frolking, P. B. Reich, L. C. Plourde, G. G. Katul, J. W. Munger, R. Oren, M.-L. Smith, K. T. Paw U, P. V. Bolstad, B. D. Cook, M. C. Day, T. A. Martin, R. K. Monson, H. P. Schmid (2008). Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks Proceedings of the National Academy of Sciences, 105 (49), 19336-19341 DOI: 10.1073/pnas.0810021105