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...

Things that make my life easier

One of the projects I'm working on in this last month of summer is a repeat of an intertidal experiment we ran last year, with an additional control treatment. In our lab's various studies of rocky intertidal communities, a general method is to conduct regular surveys of the number and abundances of algae and invertebrates like snails.

Two of the most abundant intertidal herbivorous snails. The little snail is Littorina obtusata, the smooth periwinkle (and my favourite intertidal snail!) and the larger snail is Littorina littorea, the common periwinkle.

Survey method: 1. Place PVC quadrat on spot; 2. Record all algae and invertebrates found in quadrat

For field experiments, we set up permanent plot using bolts and washers so we can survey the same plot and track changes over time. However, the markers can be frustratingly hard to find again under all the algae, even if you know where the plot is.

One of my plot markers from last summer. When the tide comes in and out it vanishes under a canopy of algae.

So, the thing that has made my life better: pretty, eye-catching fluorescent zip-ties on the plot market bolts! They significantly reduce search time and make it possible to find and survey 40 plots in a low tide.

Bright yellow zip-tie tag on one corner of a permanent quadrat, labelled washer on the other.

They are so visible among the algae!! You can see more in the background...

Cages and friends

Over the past few days, we have been working hard to get everything ready for our big trip up to Isla Baltra, where we'll be working on multiple big experiments. I am going to be setting up my Pentaceraster cages this week, so I've been pulling together all the necessary materials and tools, and compacting them for transport.

Rolled-up cage sides and a stack of cage tops in the corner.

Someone has been busy in the week since I last worked on the caging material.

Rebar as cage anchors. I bought 6m of it at the construction store for $3.50 and asked them to cut it into 30cm pieces. They must have been very confused - I don't think they have ever cut rebar this small.

At the same time, we'll be setting up concrete bases for a large-scale sea urchin predation experiment that the lab will be running for the next couple of years. The bases will be put in the water this trip to accumulate a mat of turf algae for the urchins to graze on when the experiment actually gets going next summer. We moved them from the hardware/construction store to the loading dock yesterday. I'm excited to start putting them down using lift bags.

Jon on the station dock with his concrete bases.

The marine iguanas really liked them too.

We leave for Baltra tomorrow morning, so we loaded all our equipment into the boat today - there is a lot of it. We piled up all our stuff into a water taxi and it took two trips to get all of it on board our boat, the Pirata (probably the most adorable boat I have ever seen, complete with little pirate flag).

A very full water taxi at the loading dock. You can see: about half my cages, concrete bases, green oxygen box, GoPro camera stands, plenty of rope, quadrat, containers for Hexaplex snails. All our dive gear is in there as well, under the cages and rope.

Loading the concrete bases onto the boat. We were getting stared at by everyone in the passing boats and water taxis.

Will be hard at work for the next few days. There will eventually be photos.

More fun and cagery

When we did our first few dives at Baltra, I set up a single cage for my Pentaceraster starfish as a test to see if (1) the cage would hold up against the current/surge; and (2) if the cage would keep my Pentaceraster enclosed. We visited the site again on the final day of the research cruise, and I was very glad to see that the answer was yes on both counts (with n=1, but I'm okay with that...)

One week later: Inti from the Darwin Station examines my still-caged Pentaceraster.

Now that I know this kind of cage can work as an enclosure/exclosure, I'm going ahead and scaling up cage production in preparation for deployment next week. The test cage had a diameter of 0.5 m, which is a little small for a Pentceraster that can have an arm radius of ~20 cm. The new cages are 1 m in diameter, and I am constructing them from old caging material previously used to enclose sea urchins (yay for recycling old and fouled research gear). I have been working with wire cutters and cage wire and lots and lots of cable ties over the past 3 days.

Fun with cages. About 10 minutes after this picture was taken I switched to actually wearing work gloves.

I also made a few friends, and learnt that baby marine iguanas are small enough to fit through the holes of my cages.

This little guy came by and visited me several times.

Any kind of tedious and/or repetitive job needs a work song, so here is my cage building song:

I've Been Making Starfish Cages
(to the tune of "I've Been Working On the Railroad")
I've been making starfish cages
For hours every day
I've been making starfish cages
And the time just slips away
Hope my predator inclusions
Show me interaction strengths
Hope my starfish cages weather
The storms and surge and waves!

Kludgey science

Over the past couple of days we have been scavenging bits from Jon's piles of old research equipment at the Charles Darwin research station for use in our experiments this summer. If you've worked somewhere for 10 years I guess you accumulate lots of stuff, particularly if you're a macro-ecologist and like doing large scale things. Leslie's project aims to create a demographic model for an ecologically important predatory snail species, Hexaplex, and compare how its populations behave in areas where it is fished, versus areas where fishing is prohibited. To figure out the different parameters of the model (e.g. growth rates, mortality rates for different sizes of snail), she needs to tag a bunch of Hexaplex in their natural habitat and track them over time. So we dug into Jon's stash of barnacle recruitment plates from 2003 (complete with 8 year old barnacle tests) to find tags she can use.

Some scraping with screwdrivers and a few good rinses gave us slightly over 200 tags, all ready to be Z-sparred* onto Hexaplex shells.

Leslie is using plastic calipers for her measurements of Hexaplex, but the starfish I will be studying are a little too big for that. The bigger ones, Pentaceraster and Mithroidia, can have arms up to 17cm long. So I made my own measuring instruments out of an old transect tape, cable ties and old fishing weights. I have no idea what the weights were used for before (we pulled them out of an old box and they were all cable-tied together in fives) and I'm pretty sure that transect tape was hopelessly tangled long before I even knew what an echinoderm** was, but the cable ties were the only new component of my brand new starfish measuring tapes.

And while I had the fishing weights and cable ties on hand, I made a little upgrade to the underwater housing for my camera. The housing is positively buoyant (=it is floaty) when I dive, which is really annoying because it floats up and smacks me in the face when I'm not holding on to it. Canon makes a weight system for the housing, but it costs a whopping $26 for what is essentially a screw and a few pieces of metal. So I cable-tied a fishing weight to the bottom of the housing instead. We'll see how well that works tomorrow, when we do our first Galapagos dive (!!!)


* Z-spar is the name of an underwater epoxy. I think it is probably counted among the holy trinity of field marine ecology: PVC, cable ties and Z-spar.
** Echinoderm means "spiny-skinned" and refers to the group of animals that includes starfish (my study organisms), sea urchins and sea cucumbers.

Down to business

The general theme of our lab's research this summer is to elucidate the trophic (=feeding) structure of organisms that live in subtidal habitat in the Galapagos islands. For example, my project aims to figure out what the different starfish species are eating, and what is eating them, in order to establish their role in the food web. One of the ways we are doing this is using these little extreme-sports wearable cameras (with waterproof housings) to record video of starfish (or other study species) that are tethered within the camera's field of view. We can then analyse the video data to determine rates of predation on the starfish (or urchins, or whatever we're tethering) as well as what ate it. The GoPro cameras with extended battery packs are supposed to give us about 4 hours of continuous data.

The past couple of days has just been assembling these camera systems (and the stands) and testing them out to see how well they work, how much area/distance the cameras cover, etc. We've been snorkelling out around the dock in front of the marine research building of the Charles Darwin Station in Puerto Ayora. Here is a picture of a camera housing on its stand, weighted down by rocks. We were checking for stability and the watertight-ness of the housing on this round.

And this is me with the camera setup. I think I was sticking rocks on the base...or something. (Photos by Leslie)
On the way back from deploying the cameras, we ran into an marine iguana nomming on some Ulva (a green, sheety seaweed). I think I am starting to get used to the iguanas (hard not to when you're just about tripping over them every time you get out of the water...) but I still think they are the coolest things ever.