My best friend’s wedding

Every time I return to Europe, I find myself lying in bed my first morning and enjoying the ambience. The sun rises earlier here in the summers, so there’s plenty of light coming in the window as I awaken. Sheer curtains cover the open, screenless window, and light traffic noise wafts in. There is something so bright and fresh about early mornings in European summer. The atmosphere relaxes me.

Me and Stefanie. Photo by Carl Kaiser.

I am now in Mühlhausen, Germany, the first stop on what will be a whirlwind European work/personal trip. If you’ve never heard of Mühlhausen, you’re not alone. It’s a small town in the center of Germany, not really notable for anything except for being the birthplace of Johann Röbling, the architect behind the Brooklyn Bridge. But Mühlhausen is significant to me: it is the hometown of my best friend, Stefanie.

The bride and groom emerging from the city hall.

I first visited Mühlhausen in 2011, shortly after meeting Steffi. We were both living in Bremerhaven, and she invited me for a weekend at her parents’ house. I remember the Medieval city wall and the extensive Tudor style architecture. I remember the giant Gothic cathedral in the center of town. But mostly I remember feeling welcomed, appreciated, and embraced. I’m the only German-speaking friend Stefanie has ever brought home, and my fluency alone was enough to make her parents adore me.

This weekend, I returned to Mühlhausen to witness my best friend marry the love of her life. I am so ridiculously happy for the both of them, and it was more than worth the transoceanic flight to be there.

Bride and groom sawing the log (while the bride's father
holds it in place). Photo by Carl Kaiser.

The ceremony was at Mühlhausen’s Rathaus (city hall), in the heart of the old city. We entered through an arched doorway and climbed a dark staircase to enter a large, domed hall with paintings of Renaissance-era mayors on the walls. Stefanie and André made their way to the front, where they sat sandwiched between their designated witnesses, facing the officiant. For all the time I’ve spent in this country, I’ve never attended a German wedding before, so I was curious how much it would resemble an American ceremony. There were vows, rings, and a “you may kiss the bride,” but one thing did catch me off-guard: when the officiant announced the bride and groom, she identified them each by full name, birth date, birthplace, and current address. It was a lot of personal information said aloud. I was reminded of my church back in Bremerhaven, where the pastor would announce deaths in the congregation by name and address – I guess Germans just identify each other by place of residence.

With new friends at the wedding

The other major difference was a fun one: as soon as we arrived at the reception, we found a log, about a meter long, sitting on a stand with a two-man saw leaned up against it. It’s tradition in Thüringen for newly-married couples to cut through a log together as a symbol of partnership. I must admit, it was quite amusing to watch the bride and groom don smocks over their nice clothes and set to work with a saw. They made it through in just a few minutes, and then the party began!

Stefanie is a fellow traveling scientist who’s actually lived in more countries than me. Friends came from far and wide to attend the wedding, and I was again reminded how much science is an international endeavor. I got to meet her colleagues from Canada, France, and the Netherlands, and of course re-connect with her German parents. It was an exercise in community and just a really awesome day.

Congratulations, Stefanie and André!

In print

Friends, research is a lot of work, but it is also rewarding! I always take joy in seeing my work in print, and today, another article has been published as a result of my studies.

This paper concerns the swimming behavior of oyster larvae when they are competent to settle. I've been telling you about my analysis of oyster larvae swimming behavior for over a year. When I arrived at WHOI, I was given four datasets to analyze, and to do so, I had to learn how to code. I wrote scripts to identify larvae swimming down, swimming up, and swimming in helices, calculate the proportions of each, and find their average velocities. Working with my advisor and co-authors, I picked out which results were most meaningful and whittled them down into a coherent story. My co-authors and I revised our manuscript numerous times and even started over once. Our manuscript was submitted for publication and underwent review, after which it had to be overhauled again. It took a lot of time and a lot of work, but in the end, our paper turned out very well and was accepted for publication. I'm quite proud that I was able to contribute not just to mankind's knowledge of oyster larvae swimming behavior but also to developing data analysis methods that have been implemented by other students in my lab for their own experiments.

This paper represents a lot of work by myself and my co-authors. I'm glad to finally see it in print. You can find the manuscript here, in the journal Marine Ecology Progress Series:
https://www.int-res.com/abstracts/meps/v599/p93-106/

Patriot day

Friends, it is a busy summer! I'm not sure if you're having any trouble keeping track of my projects this summer (there are several), so let's review!

There are lab experiments on oyster larvae swimming behavior;

I have an experiment hanging off the dock to see how limpets affect fouling fauna; and

I'm studying how larvae disperse among shipwrecks on Stellwagen Bank in order to stop the spread of an invasive species.

It is this latter project that brings me to the blog today. This weekend, I visited my third site on Stellwagen Bank to deploy samplers, and it was a very interesting trip!

My day began at 5:45 am. Carl and I had stayed in Beverly, MA, north of Boston, in preparation for our early morning dive. We made our way to the dock by 6:30 and discovered many of our fellow divers were already there. The regulars are all pretty hardcore morning people. We loaded our gear onto the Gauntlet and were off.

My larval traps and fouling panels adjacent to the
Patriot wreck. Photo by Heather Knowles. 

As I descended through the water, I kept one eye on Carl and one hand on the thick white mooring line. The water around me was green, but not quite soup - I could still see. The deeper I went, the dimmer it became, until the wreck began to emerge out of the darkness beneath me. I added gas to my buoyancy compensator, cleared my mask, and gave Carl the OK sign. We had arrived at the wreck of the Patriot.

My very first task on the dive was to deploy larval traps and fouling panels on the seafloor. I dropped down beside the wreck and noticed the sand was covered by sand dollars, just the like at the Josephine Marie. I pulled a larval trap out of the mesh bag I was carrying and pushed it into the seafloor, then grabbed a set of fouling panels from Carl and set about hammering it in. Carl picked up what I wanted very quickly, and within a few minutes, we had secured both sets of samplers in the sand.

Next, I pulled out a series of smaller tubes, taped together in rows of 5, and a metallic scraper. It was time to sample my target species, Didemnum albidum. However, after just a few minutes swimming around the wreck, I realized there was no Didemnum to be found. It simply wasn't there. The Patriot actually had stunningly low biodiversity compared to some of the other wrecks on Stellwagen Bank, as it was dominated only by two species (an anemone and a hydroid) and had only small numbers of sponges and sea stars. I was very surprised.

The complete absence of D. albidum from the Patriot wreck may sound like a failure for my experiment, but it's actually an answer to my scientific question all by itself. I started this experiment to figure out which direction an invasive species, D. vexillum, was most likely to invade Stellwagen Bank from, using its native sister species as a model. I thought D. vexillum could come from the north (the Patriot wreck) or the south (the Josephine Marie). Well, there are no Didemnum of either species on the Patriot, but D. albidum was all over the Josephine Marie, along with several other species. That makes the answer pretty clear to me: Didemnum is more likely to come from the south.

When I talked it over with the boat captain later, she agreed with my suspicion. She also noted that wrecks on the northern end of Stellwagen Bank are exposed to sand scour, to the point that their organisms can be blasted off by winter storms. If true, this phenomenon would explain the low biodiversity and the absence of D. albidum on the Patriot - only species that can survive the high-energy environment or recolonize quickly can survive here.

I'll return to each of my sites in August and September to collect my samplers and see what has changed on the wrecks. We'll see if my suspicions hold!

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!

To settle

Friends, as I've mentioned, there are some experiments going on in my lab at WHOI right now to examine how oyster larvae behave in different environmental conditions. Students and interns in the Mullineaux lab have been working on oyster behavior for several years now, in an effort to understand how turbulence, light, and water chemistry affect the swimming behavior of oyster larvae.

This mess of tubes is channeling compressed gas into our
flasks of seawater. 

This year, our question is how ocean acidification influences the behavior of oyster larvae when they're ready to settle and begin adult life on the seafloor. Settlement is a critical stage in the life-cycle of marine animals, and swimming larvae use a variety of physical and chemical cues to select the best place on the seafloor to attach, metamorphose, and spend the rest of their life. However, as the concentration of carbon dioxide in the atmosphere rises, more and more CO2 is becoming dissolved in the ocean, and the average pH of the surface waters is dropping. This acidification (decrease in pH) could affect how oyster larvae interpret chemical settlement cues.

We gathered larvae from a local hatchery and exposed them to filtered seawater and a chemical settlement cue (basically, seawater that adult oysters had been soaking in), at both ambient and low pH. To control the pH, we bubbled different blends of gases through the water: air for ambient pH, and air enriched with CO2  to simulate ocean acidification conditions. The bubbling process involved feeding compressed gases into the liquid solutions. We had a mess of plastic tubes stretching between gas tanks, flow controllers, and the flasks of seawater. It took about an hour for the pH in the flasks to equilibrate, and then we were off!

Example frame grab from a video recording
with larvae swimming down into
an experimental flask

With the pH-equilibrated solutions in hand, we headed over to WHOI's Shore Lab, where the experiments were to be run. We used 5 replicate flasks for each treatment. One by one, the flasks received a pipet full of larvae, and we filmed the larvae swimming for 10 minutes. We used a near-infrared camera to illuminate the flasks from behind so that the larvae were not exposed to light in the visible spectrum (light can affect their behavior). We also kept the flasks in a temperature-controlled chamber so that no convective currents would form in the flasks to disrupt swimming behavior. We were very careful to control the conditions so that the only difference between treatments was pH and the presence or absence of a settlement cue.

When entering the flasks, most of the larvae swam straight to the bottom, and then some swam back up. We'll use the videos to calculate parameters like the proportion of larvae swimming back up or staying on bottom, the proportion of larvae swimming in helices, and their average velocity. Together, these metrics will help us discern how ocean acidification affects the swimming behavior of larvae when they're ready to settle. I look forward to seeing the results!

The hatchery

Friends, while I was out diving last week, other members of my lab were undertaking their own experiments. Some of you may remember the oyster research that has been conducted in the Mullineaux lab over the past few summers. When I first started here, I was responsible for analyzing some of the data from past oyster experiments, and I submitted a manuscript for publication based on that analysis. Then last summer, one of the interns conducted her own experiments to examine how oyster larvae behave in different environmental conditions. 

Algae tanks at the Aquacultural Research Corporation. Photo
by Brooke Torjman.

Well, this year, we're at it again, exposing oyster larvae to a range of conditions in the laboratory and observing how they respond. The first step in the experimental set-up is to obtain larvae, and for that, I was sent on an expedition of sorts - a field trip to the hatchery. The oyster larvae we use in laboratory experiments are supplied by the Aquacultural Resource Corporation in Dennis, MA, about an hour's drive down-Cape from Woods Hole. I gathered up a cooler for the larvae, a flask for the algae to feed them with, and a fellow lab member for company and headed out to the hatchery. 

Oyster larvae settling on bits of adult shell at ARC. Photo by
Brooke Torjman.

Truth be told, I had never been to an actual hatchery before. It's an operation of massive proportions, with tens of millions of larvae growing at once. Giant conical tanks billow with oyster babies, while floor-to-ceiling columns bubble with algae in various shades of green and brown. 

The hatchery staff were kind enough to show us around, and we were deeply impressed by their cultures. Larval cultures in a research lab usually involve just tens or maybe a hundred individuals in a dish, so the giant tanks at ARC were on a completely different scale. 

Once the larvae are competent to settle, they are transferred into still-water tanks and allowed to attach to ground-up bits of adult oyster shells. The shell bits looked almost like sand, and the larvae looked like darker sand grains on top. You would never guess that they were living creatures when just walking by!

With a cooler of larvae and a flask of algae safely stowed in the car, we bid the ARC employees farewell and headed back to the lab. It was very neat to see the hatchery!

The voyage of the Dawn Treader: part 4

I felt a tap on my knee and opened my eyes to see Evan standing in front of me. "We're about 30 minutes out from the next site," he told me. I nodded.

I was still a bit queasy, having gotten seasick after our last dive. Slowly, I pulled myself up and walked out on deck, keeping my eyes to the horizon the whole time. I actually felt more stable than I expected. I can do this, I thought.

We rolled over the side of the boat and made our way down the line to the seafloor. The first thing I noticed were the sand dollars. Hundreds, thousands of them were scattered on the sand all around me. I swam forward, following Evan, and found the shipwreck. The Josephine Marie is a fishing boat that capsized off of Provincetown, Massachusetts. It lies upside-down on the seafloor, "turtled" as divers call it. Evan immediately began driving my samplers into the sand near the wreck, and I swam up to the hull to start scraping off adult specimens of my study species.

I'm using Didemnum albidum, a species that's native to New England, as a model to understand how its invasive sister species, Didemnum vexillum, might spread among benthic habitats. I hypothesize that shipwrecks could serve as stepping-stones to facilitate the spread of D. vexillum to the Sponge Forest on Stellwagen Bank.

It was easy for me to locate D. albidum on the wreck - it was the only white encrusting species there. I pulled out a plastic scraper and empty sample tubes from the mesh bag I was carrying and set to work. Within minutes, I had 7 D. albidum samples in my tubes, so I rolled to my left to check Evan's progress. He was right next to me, having finished deploying the seafloor samplers. I handed him a set of tubes, and we set about scraping at double time.

I was surprised how quickly we got all the samples I needed - it only took 15 minutes. I had expected it to take much longer, so I actually laughed when we finished so quickly. We had planned a total of 30 minutes on the bottom, so we used our extra time to swim around and survey other species on the wreck. Most of the hull was covered in Metridium senile, the plumose anemone, which is very common on shipwrecks in New England. There were also plentiful finger sponges, hydroids, and sea stars. I loved seeing the biodiversity.

I gave Evan a 5-minute warning and started swimming back to the anchor line. As we reached the line, I saw Evan pick up two scallop shells off of the sand. I thought he was just collecting shells, but when we got back on the boat, he handed me a scallop on the half-shell. A raw celebratory delicacy!

The second dive of the day was immensely successful, and I was overjoyed. I got all the adults that I needed and got my samplers deployed to collect later in the summer. The steam back to the marina took about 4 hours, so I took some time to relax and revel in the moment. Once we got back, I still had to preserve my collected samples in the lab and rinse my dive gear. My day actually went until 10 pm - altogether a 17-hour workday. The day had its ups and downs and I was exhausted by the end, but I was very proud that I had lead a (mostly) successful trip and gotten what I needed. My project is officially begun!