Sunday, June 25, 2017

Arts and crafts

"I craft a lot, ok?!" Nicole exclaimed.

Nicole and Meghan, two summer interns at WHOI, helping
me make hydroid mimics.
Meghan and I burst into laughter. The three of us were crammed into my office, surrounded by plastic mesh and elastic cord. Nicole was threading the cord through the mesh in immaculate patterns - not a stray strand anywhere - almost like cross-stitch. It was impressive. The task required a lot of dexterity, and our afternoon ended up feeling like an arts and crafts class. The three of us spent hours carefully threading stretchy strings through tiny holes, making what looked like tufts of synthetic hair. Trust me, friends, it was for science.

You see, one of my sites for the succession study is dominated by hydroids. They showed up in droves and have grown to cover almost all of the available space. One of my questions for the succession study is how the first species to settle and dominate a substratum influences the development of the community, and the hydroids are obviously an important group. There is lower diversity at the hydroid-dominated site than at my other site in Eel Pond, so I want to figure out how the hydroids are affecting the organisms around them.

I expect a couple of things could be going on. First, the hydroids could be actively consuming larvae of other species and preventing them from settling or just eating all the food there is. If that's the case, I should see lower recruitment of benthic invertebrates on panels with live hydroids. However, the hyrdoids could just be passively preventing other organisms from settling by blocking their particulate food from reaching the panel or by occupying space. To see which one of these scenarios is true, I had to build structures that were exactly like hydroids but non-living.

A fouling panel with hydroid mimics (left) and
live hydroids (right)
Enter the elastic cord and plastic mesh.

Using fouling panels that had already been colonized by hydroids, Nicole and I set up an experiment this weekend. Some of the plates were "live hydroid" treatments and remained largely as-is. Other plates had their hyrdoids removed and replaced with synthetic mimics. We also had a "mesh only" treatment and a control with no inhabitants.

I'm very curious to see what recruits to the different types of panels. I suspect the hydroids have a significant effect on their community, so I should see some differences between the treatments. We'll check back later in the summer to see!

Friday, June 16, 2017

Squarepants

Friends, I hope one thing you can learn from this blog is how many diverse and fascinating creatures there are in the ocean. Even a habitat as ubiquitous and mundane as a floating dock can be covered by all sorts of captivating fauna. I have told you about the ciliates; I have impressed on you the importance of hydroids. I have shown you barnacles and spirorbids and bryozoans. I have drawn your attention to the ascidians. But there is one organism I have not yet shown you - sponges.

Halichondria panicea on one of my fouling panels, surrounded
by two spirorbids and a bryozoan. Photographed at 50x
magnification.
No, not the kind you use in your bathtub, although bath sponges were harvested from the ocean in centuries past. Marine sponges are sessile animals that filter the water for food.  If you've been reading this blog for a while or clicked on any of the links above, you'll notice that this is lifestyle is a common theme - fouling communities are by definition made up of animals that attach to a surface, and animals that live attached to surfaces tend to filter the water for their food.

There's only one species of sponge showing up on my fouling panels right now, and it only appears in Eel Pond. It's Halichondria panicea, and it's actually a non-native species. It was introduced to New England, presumably a long time ago, though nobody is quite sure when. It's been around long enough to become well-established in the fouling community.

When I first started seeing Halichondria on my panels, I didn't know what it was. It took me a little while to clue in that it was a new organism. Once I recognized its porous texture, though, I could identify it almost immediately!

Sponges are typically slow-growing but are good competitors, so they tend to dominate older communities. I anticipate that Halichondria will come to occupy larger and larger amounts of space on my fouling panels as the summer goes on. We'll see if I'm right!

The elephant

"You can eat an elephant in small bites." - Ed O'Brien

This week was an elephant. A big, heavy, brute of a week, full of data collection and field work and counting and counting and counting.

Two species of ascidians on my fouling panels:
Botryllus schlosseri (black and yellow), and Botrylloides
violaceus
(red). Photographed with a dissecting microscope
at 6.5x magnification.
To put it succinctly, my fouling panels in Eel Pond have been taken over by ascidians. Also known as sea squirts, they're squishy, gel-like, blob-shaped animals, and they have absolutely covered my fouling panels in Eel Pond!

Some of you might remember the "mystery blobs" I started finding about a month ago. At the time, I was pretty sure the blobs were ascidians, but I couldn't identify them to species. Well, now I can confidently tell you that the blobs are ascidians, but they are not one species. There are four. Four species of ascidians. All. Over. My. Panels.

As you can imagine, the copious ascidians took a lot of time to count. It was a mammoth task, but I'm no stranger to long hours at the microscope. I actually removed the ascidians from a sub-set of my panels to see if the fouling community would develop any differently in their absence, and as you might imagine, that took a ton of time too. I kept reminding myself to take it in small bits, to take breaks and pace myself. This week was a beast - an elephant I had to eat in small bites.

A species of solitary ascidian, Ascidiella aspersa (white
arrow), on my fouling panels. You'll notice Ascidiella
is much bigger than individuals in the colonial ascidian
next to it. Because it's so clear, most of the time I only
noticed Ascidiella on my panels because of its colorful
digestive tract.
Ascidians are fascinating creatures, though, and I was happy to see them recruiting to my panels. Ascidians have two different life-styles - some species are solitary, while some live in colonies of clones - but despite this difference, they all have the same basic anatomy. Each ascidian individual has a incurrent and excurrent siphon to draw water into and push water out of their body. The water gets filtered through a mesh structure inside the ascidian's body called the pharyngeal basket, which catches any particles that could be used for food. The outside of an ascidian's body is covered in a fleshy, skin-like layer called a tunic. They're actually pretty fun to dissect.

Eel Pond is notorious for its diverse and abundant ascidians, so their dominance on the panels actually fits one of my hypotheses. I think their high numbers on the Eel Pond panels shows the influence of local retention and larval supply. It will be interesting to see how the fouling communities continue to develop this summer!



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!

Friday, June 2, 2017

Bryo-zooons

When I was doing my Arctic recruitment study in Svalbard in 2015, I leaned heavily on my collaborator, P. He's a bryozoan expert, and since many of the animals on my settlement plates were bryozoans, I was constantly asking him to look over my shoulder and help me identify the organisms I was seeing. P has a unique accent, a slightly nasal voice, and a generally relaxed demeanor. He liked to draw out the "O" sound on the second syllable of "bryozoans" so it sounded more like a surfer dude speaking. Nowadays, if I ever say or think the word "bryozoans," my brain hears it in P's voice: "bryo-zooons."

I'm currently studying dock fouling communities around Woods Hole, as many of you know. I've told you about the ciliates that inhabit my fouling panels; I've told you about the barnacles. I've shown you the hydroids, the worms, and the sea squirts. Today, I'd like to focus on the bryozoans (bryo-zooons).

Like most things on my panels, bryozoans are sessile benthic invertebrates. They spend their entire adult lives attached to a surface, feeding on small particles and plankton in the water around them. They have a two-part life-cycle, though, and young bryozoans don't look like bryozoans at all. The common larval forms are cyphonautes (looks like a triangle with a red spot) and coronate larvae (looks like a fuzzy cylinder).

I actually think bryozoans are quite beautiful. The adults build colonies of clones, often with ornate calcareous shells. Check out some of the pictures below!


Microporella ciliata

Conopeum truitti

Electra pilosa

Cryptosula pallasiana

The Svalbard recruitment paper

If you've been reading this blog or a while, you'll remember I lived in Norway in 2014-2015. In fact, my move abroad was the motivation to begin sharing my experiences online. I got a research grant to study recruitment of hard-bottom benthic invertebrates in the Arctic. Using Stavanger as my home base, I went up to Svalbard to deploy and recover fouling panels in Arctic fjords. Altogether, I made three trips to Svalbard in 2014 and 2015.

I bring up my time in Norway now because the research study I did there has finally been published. The results from my fouling panel experiment appeared this week in the journal Limnology and Oceanography. Several co-authors are listed alongside me on the paper, because I received a lot of assistance with my study - my co-authors contributed their resources, ship time, taxonomic skills, and oceanographic data. I am grateful I had the chance to work with such helpful and knowledgeable scientists.

I hope you enjoy reading my paper! You can download it here: http://onlinelibrary.wiley.com/doi/10.1002/lno.10602/full