Smurfing up the stats

Things have been ridiculously busy, and my final year of undergrad is flying by like its pants are on fire. I've been tied up with class, starting applications to graduate school and contacting potential advisors, and research. The field and lab part of my research is gone till January break, but there is always plenty of the other half: organising data and analysing data and writing, writing, writing.

Scuba Smurf is a little sad about being out of the water this long (as am I) but he is keeping me company as I try to run statistical routines that I am unfamiliar with, on software that I am fairly new to. And because I am working through it slowly and over long periods of time, I came up with another work song...


The Variances Song
(To the tune of 当我们都在一起 aka 'The More We Get Together')

What's wrong with my variances, my variances, my variances
What's wrong with my variances, they are unequal
Transformations are futile
Rank-sum tests lack power
And so to fix the variances
I tried GLMs*


* and by GLM, I mean a generalised linear model, not a general linear model

Return of the petri dishes

So far this semester has been: 2.5 days Brown - 4 days Nahant - 3 days Brown - 4 days Nahant. Last Friday-Monday I was back up there running a full isopod herbivory experiment. Basically, the trial we ran the week before showed that isopods might actually graze enough to be important, so we should look at their grazing patterns in greater detail.

 Multiple-choice petri dish setup: we have 6 species in there. You can just see an isopod in front of the rubber band on the far chamber.

 

70 petri dishes, 210 isopods, 63 grams of freshly collected algae.

Here we go again...

More fun with herbivory

School started on Wednesday, which means that I had to leave Nahant and go back to Providence and actually sit in classes. My classes this Fall are fairly interesting - Conservation Biology, Methods of Applied Math, an Introduction to GIS - plus I'm auditing an experimental design class. Still, interesting classes are less exciting than actual research, especially actual research that still needs to be done. I have a very nice 3-day class schedule (Tues-Thurs) so Friday found me right back at the Marine Science Center working, again.

This summer I ran a big herbivory experiment looking at Lacuna snail preferences among different species of subtidal algae. This weekend I'm trying to figure out if other herbivores like isopods may also be important in grazing the algae.

The baltic isopod, Idotea balthica. This is a fairly large individual; the ones we find in our algae are generally around 1 cm in length.

To do this we're running a much smaller-scale pilot experiment with just a couple of algal species and only 6 replicates each. The isopods go in little modified petri dishes with a similar structural theme to the containers I used for the Lacuna experiment - identical amounts of algae in both chambers of the dish, herbivores in one chamber.

One of my petri dishes. The right chamber has herbivores; you can just see an isopod at the top-right of the tag number 08. The left chamber is herbivore-free to account for loss/gain of mass that is not due to herbivory.

The overall setup. Petri dishes are zip-tied down to the aqua mesh to keep them submerged. You can see that they are arranged nonrandomly because my arms are short and I can't reach the area in the middle right of the water table. They are interspersed, though...

Scuba Smurf did a dive to check that everything was well attached and working.

Scuba Smurf approves of this experimental setup.

The things you find in algae, part 2

Sometimes when it is 11pm and I am still in the lab and I have been sorting algae for 8 hours, I need something to remind me why I love marine science. Sometimes that thing is an itty bitty brittle star.

:)

It is 5 millimetres long. To this brittle star, the one little piece of algae I am holding in my hand is a forest.

The things you find in algae

My big herbivory experiment is done, and the summer is coming to a close - classes start in less than two weeks! There's still plenty that needs to get done - yesterday we did a trip down to Connecticut and Rhode Island to collect some algae. Similar to what I was doing at the start of the summer, we are trying to quantify the species composition of algal communities in different locations, where the invader is present.

So I am back to sorting algae out of bags, which is long and somewhat mind-numbing, but there are many happy distractions in the form of little critters hiding out in the algae.

Today is arthropod day...

A little spider crab sitting on the tip of my finger.

Itty bitty little crab - it looks like an Asian Shore Crab, which is also invasive to this region. For scale: it is sitting on a microscope slide.

A very pretty pycnogonid (sea spider) on the same microscope slide.

Egg masses

Q: What do you do when you find yourself in a large, locked room with 29 other guys/girls and an abundant but finite amount of food?

A: Make plenty of babies, of course!

(This makes perfect sense if you are a 4 mm long snail)


I took down my herbivory experiment today and re-weighed all the algae after 4 days of snail grazing. It took about 10 hours in total. But other than grazing on the algae, the Lacuna have been busy making little Lacunas. There were egg masses in all of the snail mesocosms, and most of the algae had at least one egg mass attached. (This made my job a little more difficult because I had to remove the masses before weighing the algae.)

Lacuna eggs on the edge of a sugar kelp (Saccharina latissima) blade

Eggs on the branch of an articulated coralline alga, Corallina officinalis

Also, if you're not a big fan of the algae, you can lay your eggs on your neighbour's back instead. That's what friends with hard shells are for.

:)

Intrusion intrusion

There is a fishy intruder in my seawater table. I don't know how it got there, but it certainly wasn't there when I set up the experiment yesterday. It most likely got sucked up the pipes for the seawater system, but it looks kind of big for that...

o hai.

Fun with herbivory

This blog has been awfully quiet as of late, mostly because I've been insanely busy. I've been back in Nahant for about two weeks now and am working hard to get all the planned research for my algae project done before class starts on the 7th of September and I need to be back in Providence. I've also been helping out with other projects in the lab. But I just got a big experiment up and running, so things will be a little less hectic for a couple of days - mostly simple maintenance and checking up on it.

When I last wrote about the algae project I talked about the big question of "what is it doing here?" We're trying to figure out how the invader is impacting the ecological community. In any introductory ecology class you learn that two of the main interactions between species are consumption (e.g. herbivory, predation) and competition (for space, light, food). My experiment is looking at the first interaction and asking, do the native herbivores in the community eat the invader? How much of it do they eat in comparison to other native algal species? Could this impact growth and survival of the invader relative to other species?

In this case, the herbivore is a tiny little snail, Lacuna vincta, that can occur in relatively high densities on the algae. It is found mostly at shallow subtidal depths, though I have seen it on algae in the low intertidal zone.

Here it is on a ruler. awww.

To see if it has significant preferences for the invader or for the native algae, I put a bunch of Lacuna in a little snail mesocosm (=a food container with holes drilled and mesh glue gunned on) and offer it a choice of the invader, plus five other common algal species. At the same time, I have other snails in other mesocosms that have only one species of alga, so I can compare how much of each species they eat when they have 6 choices vs. no choice over about 3 days.

Multiple-choice mesocosm. There are 6 species in each chamber, and the one on the left has 30 Lacuna snails. The one on the right is a control for any loss/gain of algal mass not due to herbivory.

I have 10 replicates of everything, so 10 x 6 species for single-choice + 10 multiple choice = 70 mesocosms. This means 240 pieces of algae which had to be collected and individually portioned/weighed and 2100 snails which had to be collected and counted. You can see why I've been busy.

Hours and hours of collecting and sorting snails...

Final experimental setup on two seawater tables at the MSC:

The W's of a species invasion

When people go beyond the typical "oh you are studying marine biology that really cool" talk (something that I should write about at some point) and want to know exactly what I am doing with my summers, I usually say that I am studying a species of seaweed that is not where it's supposed to be. Most people have never heard of the concept of introduced or invasive species before, so the conversation usually turns in that direction and only occasionally goes back to my research.

But these conversations makes me wonder how I can talk about what I do in a bit more depth, while keeping it interesting enough for people who think algae is sushi and muck on fish tanks. I am going back to a primary school English composition framework because I realised that studying a new species invasion is a bit like the compositions we were taught to write as seven year olds - you have to address the same spread of questions. Also, if you can explain your science to a seven year old then you either have a brilliant seven year old or you have achieved relatively good communication of your science. (Which is why you probably have to test it out on more than one seven year old.)

So here is a brief summary of the questions we are asking, in terms of the good old 5 W's:

1. Who

Who is the invasive? - This question is a little bit out of order, since we had to figure out what the algal species was in order to determine that it was a new invasive species. This question was answered last summer, thanks to Craig Schneider at Trinity College who first documented the presence of Heterosiphonia japonica in southern New England.

Mr. Hetsiph makes friends with a kelp stipe.

2. Where

Where is it now? - We have some idea of this from last summer and a tentative northern range limit, and there are people further south who are looking out for its spread.

Where did it come from? - Most likely from European waters, where it is also invasive, but possibly from its native region in the North Pacific. This could probably be figured out using genetic comparisons of the New England populations with potential source populations from different places, but that is out of this lab's area of expertise so it is probably a question for someone else to answer.

3. When

When did it get here? - Still unknown, but certainly sometime before summer 2009, when it was first found and identified in New England. We don't know if it was introduced only once and just spread rapidly, or if it was introduced multiple times in multiple locations.

4. What

What is it doing here? - This is where we're at now. What kind of interactions does our invasive species have with the native community of algae (competition for space and nutrients, maybe?) and the herbivores like snails and amphipods? To try and answer some of these questions, we are conducting field surveys of algal species and abundances, which will lead into field and lab experiments later on.

"What does this mean for me?"

5. Why

Why does this matter? - Probably the most important question of all. Why should anyone care? Well, invasive algae have been an issue in the western Atlantic for some time and some have significant negative impacts (e.g. Codium fragile). Coastal management agencies are interested in knowing the potential impacts of the invasion on coastal health, water quality, etc. And because of the relatively early stage of this species invasion, what we learn about Heterosiphonia could contribute to a more general understanding of what makes an invasive species successful, and how invasions spread.

That's it for now, tomorrow I shift gears completely and head for somewhere a little more exotic. I fly from Boston to Quito, Ecuador, and then take a domestic flight into Baltra in the central Galapagos archipelago on Thursday. Hopefully there will be more blogging from the land of the tortoises.

So what exactly am I doing with all this algae?

This is what I have been doing for the past week.

We've gone diving at sites in Nahant and in Rye, NH and put down 0.5m x 0.5m PVC quadrats like the one below. First, we visually identify each species of algae and record the approximate percentage of the quadrat that it takes up. Then we collect all the algae in the in the quadrat, put it in a bag and take it back to the lab. We collect about 10 bags per site.

This is a quadrat (pre-collection) from Nahant last year. I haven't yet taken my camera underwater this summer.

In the lab, we sort the algae by species and clean it - i.e. remove little critters like amphipods, isopods, little crabs, little starfish*. The result is something like in the picture - neat piles of algae on a lab tray. Then we weigh the algae by species in two ways: 'fresh weight' which is just spinning it down in a salad spinner to remove excess water and then putting it on a scale; and 'dry weight' which is putting it in an oven at about 65ºC so that it is completely dried out, and then weighing it (this destroys the algae so you can't do anything with it after).

This is all the algae from one (0.5 m x 0.5 m) quadrat from our Rye, NH collection site. I am pretty sure that if I cleaned up the algae up a bit better and arranged everything a bit more prettily, I could convince someone that it is some kind of Japanese delicacy that they should try.

This whole long process gives us estimates of two things:
1. How many species of algae are out there, and what they are
2. How much of each species is out there, in absolute terms and relative to the others. This can be measured by percentage cover of the quadrat or by weight. We are doing both to see how well the two agree (i.e. if one is an accurate proxy for the other).

These two things can then be used to tell us plenty of other things such as how diverse the algal community is, and which species we should use in lab experiments.


*This is described in one sentence, but is the longest, most tedious part of the whole process. It took us <1 hour of underwater time to collect 10 bags of algae, and a full day to clean, sort and weigh only 7 of those bags. During the process I wrote this song.

The Algae Song
(to the tune of "Daisy Bell")
Algae, Algae, give me your answers true
I've gone crazy, just from sorting you
The amphipods are too many
And Desmarestia is nasty
But soon I'll find
If Hetsiph might
Influence diversity

Off site algae collection

Today we drove slightly over an hour north to Rye, NH to revisit a site from last summer and do some algae collections there. This is a picture of our entry point into the water, and the actual site of collection is just next to/behind the big rock on the left.

The picture is deceptively warm and sunny and hides the fact that the water temperature was still 7ºC/45ºF, which is about where it is in the early winter. So we were freezing in our wetsuits for both dives and I am still cold 7 hours after exiting the water.


But on the way back we got crabcakes at a roadside place and sat in the sun and it seemed like New England summer again.