Sea lion vs. camera

Digging into the backlog of things I've meant to post, here is an excerpt of one of the videos from the fish diversity recordings featuring a curious sea lion trying to eat the camera...




As it swims off it goes right for the transect tape, which is why you see the tape move up into the camera frame. We've seen this kind of demonic intrusion before...

On Leslie matrices and ceviche

In the introductory ecology class I TA'd for last spring, the Leslie matrix is the bane of many students' lives. Many students come in expecting more saving the earth and/or charismatic megafauna and less mathematical models. About a month into the class, they are introduced to this:
which can be understood a little better by this, where each circle is one size class (1 is the smallest, 4 the biggest). P1, P2 and P3 are the probabilities of advancing (growing up) into the next class over a set time period and F1, F2, F3 and F4 are the probabilities of reproducing (making more little class 1's) for each respective size class. The number of individuals in each class after the time period is dependent on the number of individuals before the time period and all these probabilities - that relationship is described by the matrix equation.


So what does this look like in real life?

Let's say you have a snail about the size of your palm that is known to be a key predator of barnacles - this is important because barnacles act an 'entry point' of energy from the open-ocean (pelagic) to the ecological community that lives on/around the rocks and ledges (benthic). Barnacles eat plankton from the water column and use that energy to grow, making that energy available to predators like Hexaplex snails, which in turn get eaten by fish, etc. So there is a transfer of energy from the pelagic plankton to animals like fish which wouldn't happen without barnacles and their predators.

Hexaplex feeding on Megabalanus barnacles at about 8m depth.

At some sites in the Galapagos archipelago, Hexaplex is also fished to make the local dish ceviche. Presumably, the bigger snails are fished (this can be confirmed using fishing records and/or data from shell piles). How does that affect the way the population changes (grows/shrinks) at different sites? And from a bigger-picture view, how could fishing impact the flow of energy into subtidal Galapagos communities? If you can estimate the parameters of the model accurately enough, you can use the model to answer these questions. You could also model changes in the intensity of fishing to predict how the population would respond - information that can be useful if you'd like to set fishing limits or decide which population(s) are more worth protecting.

Leslie (who is very appropriately named for this research project) has been setting up to estimate class-specific Hexaplex growth rates (the P's) by measuring, tagging and releasing them at our study site. When we get back in January, we'll be looking out for these tagged snails and re-measuring them to track their growth.

Photographic record of size and shell morphology.

Newly freed Hexaplex at Isla Baltra. The bright green rock is the release point.

January is also supposed to be the reproductive season for Hexaplex, so we'll also be looking out for egg masses and laying Hexaplex in order to estimate reproductive outputs (the F's).

Hexaplex egg mass from last January, photo by JW.

Somewhat encouragingly, we recovered one of the Hexaplex that we did some preliminary tagging on in mid-June with 8-year old Z-spar epoxy. I think we only tagged 8 or 9 individuals then, so a return of one is pretty good news. We'll see what happens when we return to Baltra in 6 months.

Happy Leslie with the recaptured Hexaplex.

Terrestrial invasion

Last week we put aside our stinky wetsuits and scuba gear to explore terrestrial Galapagos for a few days. We went out into the highlands of Santa Cruz with Heinke, a postdoc at Brown, and her two Ecuadorian field assistants. Heinke studies the impacts of an tree species (Cinchona pubescens, the quinine tree) that was introduced to Galapagos from mainland Ecuador, and has been doing research here for many years.

Introduced/invasive species are a particularly big concern in island ecosystems like the Galapagos. In the Galapagos National Park, there have been huge efforts to control the spread of invasive species and protect native Galapagos species. The results of these control efforts can be clearly seen where the national park borders private/agricultural land.

National park land on the left, agricultural land on the right. The plot on the left is full of the native Galapagos miconia plant, while you can see plenty of non-native elephant grass on the right.

Miconia robinsoniana, an endemic shrub that grows at high elevations. The 'miconia zone' at ~600m is named for it.

We had a beautiful, mostly clear day at Media Luna, which is unusual - the highlands have been rainy even when the coastal areas are clear and sunny. But when they are not shrouded in clouds, the view from the highlands is incredible - 180º of ocean - and you can see all the way to Puerto Ayora!

A clear view all the way to the ocean, with Puerto Ayora and Tortuga Bay in the south.

The Cinchona trees are very conspicuous against the native shrubs of the highland 'miconia zone' - they tower over everything else. Equally conspicuous is the park management's aggressive attempts to control it - around the Media Luna crater itself, they have cut most of the Cinchonas and locally applied chemical herbicides, leaving behind bare trunks.

Cinchona trunks as far as the eye can see.

One of the big questions that people tend to ask when looking at an invasive species is: what effects does it have on the ecological community? It is a question I have been asking as well, with respect to my own algal invader. Because Cinchona is a tree in a community that previously had no trees, it has the potential to shade out other plants and limit the light available to them for photosynthesis. Heinke's experimental set-up aims to figure out exactly what the effects of Cinchona shading are, using artificial shades to control the amount of light available to the native shrubs. It will be cool to see how this affects the species diversity and composition of the plant community.

Two different shade treatments: total shade in the centre and partial shade on the left. On the right you can see a Cinchona forest that hasn't been managed by the national park - a really different-looking plant community compared to the short, shrubby one in the foreground.

For the past year, I've thought of invasive species mostly in terms of the marine algal species I study. It was interesting to look at it in a terrestrial system, particularly an island one. It gives me a slightly broader perspective on things before I return to the invasion happening in the shallow subtidal zone of New England.

The quiet beauty of mangroves

Tortuga Bay is a beautiful site about an hour's walk from town - it has a long stretch of shore that surfers go to (="the surfers beach") and a protected bay with calm water (="the swimmers beach"), as well as plenty of rocky intertidal zone, a small forest of Opuntia cactus-trees. It's a popular spot with both the tourists and locals (and with Leslie and me who do not fall into either group).

The first time we visited, it was low tide (which we planned for so we could do some intertidal exploration). But when I noticed that the swimmers' beach was surrounded by red mangroves, I was determined to come back and explore it by snorkel at high tide. So we did, and this series of photos is the result. I have gone snorkelling in mangroves before, though I have explored them above water many times back in Singapore. So this was a bit of an adventure.

Red mangroves in the foreground, Opuntias in the back. I love the Galapagos.

Above the water, the roots form a tangled network. The water is still enough to see them reflected on the surface.

Beneath the surface, the sounds of people from the beach fade away and you can almost hear the trees breathing. The visibility is poor in this soft sediment habitat but if you are still and patient (and keep your fins off the bottom!) it clears out enough to make out the somewhat eerie shapes of the submerged roots, and of the fishes hiding in this silent, flooded forest.

A tiny sergeant major emerges, dwarfed by the submerged mangrove roots.

A little bullseye pufferfish peers outward.

Mangroves are known as important 'nursery' habitat - a relatively benign place with calm water and fewer predators for juvenile fish to grow up (including commercially fished food species like snapper - see below). There is definitely a high abundance of little fish here. But there are also bigger shapes lurking in the shadows of the underwater forest. They fade in and out of the murky water and occasionally emerge from among the roots to say hello and to feed in the carbon-rich sediments of the surrounding water.

Dog snappers play hide and seek with me.

Two diamond rays lurk under the shadows of the overhanging mangrove roots. These guys dig about in the sediment and feed on invertebrates living there - check out a video of that here. In the foreground is another bullseye puffer and a young snapper.

Moving out further from the swimmers' beach, the water gets clearer and you can see just how busy the mangroves are.

A buzz of activity.

Further outside of town, El Garrapatero on the southeast side of Santa Cruz has its own mangrove thickets as well - some were growing through/on the basalt (!)

Lone tree on the rocks. There are Opuntias in the background as well.

Pneumatophore roots coming up through the muddy basalt rubble

The camera sees all: Manta ray at Baltra

Over a week after one of our early dives at Isla Baltra, I review the video from the GoPro recordings and see this. None of us knew it, but we were diving with a manta ray. I guess we should look up from working on the bottom once in a while... :)

Does fish diversity matter?

Previous work out of the Witman lab has looked at how sea urchin diversity affects processes like grazing rates in the Galapagos. Now the focus is shifting higher up the food chain to the things that eat sea urchins. More specifically, does the diversity of urchin predators affect the intensity of predation on urchins? Are there interactions between the different urchin predators that may alter predation rates? My own project aims to figure out to what extent seastars such as Pentaceraster are a part of this predation. The other obvious suspects would be predatory fishes.

Whodunit.

To get some preliminary data on the diversity of fishes (with a special interest in species that could potentially eat urchins), we've been deploying a bunch of Hero GoPro cameras at multiple sites around the central Galapagos archipelago to record 3-4 hours of continuous video data on the fish that are present. These little wearable cameras were originally made for filming high-definition extreme sports videos, but work extremely well as our underwater data-collectors - we've made little stands for them that weight them down on the rock (usually we also stick a few rocks on the stand for greater stability).

Deploying the camera system

GoPro in its natural habitat

During our 5-day research cruise, we collected fish diversity data from 11 different sites, deploying 2 cameras per site for a minimum of 1 hour continuous video data per camera. Video data are easy to collect and accumulates quickly, but it will probably take many more hours in the fall and spring to analyse fish diversity from the raw data.

Here is a one of the more exciting excerpts from Rocas Cousins, a site on the north side of Santa Cruz. How many fish species can you spot? (If you're not too distracted by the charismatic trio of ray, sealion and turtle...)

Salty sotong returns

Back from a five-day research cruise around the central Galapagos archipelago. I write about it briefly on the Brown Global Conversation blog, but more will be up here soon. In the meantime, here is my favourite photo from the trip:

My first frogfish!

Here is a picture of it from the top. It was lying in an urchin hole in the rock wall at Daphne Menor, which is just north of Santa Cruz island.

Project Pentaceraster

I wrote before that my research project here involves figuring out the basic feeding relationships of starfish in the Galapagos subtidal system. This fits into a larger framework of understanding the connections between different species in this system, including economically important species such as carnivorous fish and Leslie's Hexaplex snails, and ecologically important species such as grazing sea urchins and herbivorous fish.

A sampling of starfish species, clockwise from top left: Nidorellia armata (chocolate chip star); Phataria unfascialis (blue sea star); Pharia pyramidata (yellow spotted star); and the ever-awesome Pentaceraster cumingi (Panamic cushion star)

I am focusing my efforts on Pentaceraster for now because we have preliminary evidence that it eats sea urchins, making it a potentially important link in the food web. It is also quite abundant, so it makes up a substantial amount of standing biomass. On our dives, I have been overturning Pentaceraster along the transect to (1) take measurements of their size using my amazing starfish-measurers - I've further modified them a little by taking off a weight and adding a clip to the end; and (2) recording what they are munching on, if anything. Pentaceraster eats by everting its stomach onto its lunch, so it's easy to tell if it is feeding when I overturn it. It is not as easy to ID its lunch as it pulls its stomach back in.

Measuring the radial length (=length of one arm) of a Pentaceraster star. The transect tape is just visible in the top right.

Overturned Pentaceraster retracting its stomach. I go digging through all the bits and find out exactly what's in its mouth.

We also ran a cage trial with a recycled cage from an old experiment. Eventually I am planning to use larger cages to test the effects of including vs. excluding Pentaceraster from an area, but I need to know how well these cages will hold a starfish. We'll be back at this site next week, so I'll be able to see if Mr Pentaceraster has escaped from my setup.

Setting up the cage with Jon.

Final cage setup. One Pentaceraster and five Eucidaris sea urchins (two are clearly visible).

Subtidal again

Over the past couple of days we did our first eight research dives in the Galapagos. I was really excited to finally get back in the water (after being dry for 10 days...snorkelling doesn't really count) and start working. The water temperature here has been around 24-27ºC/75-80ºC which is the coldest I have ever seen in the tropics. But coming from 7ºC/45ºF dives in New England, it was marvelous.

Starting the day with what Jon calls "stuffing your advisor into his wetsuit"

Unlike my New England research sites, all Jon's sites in the Galapagos are only accessible by boat, so our underwater time is much more limited. So we aim to get as much out of our underwater time as possible, which means we are usually doing multiple things on each dive. Jon does his long-term monitoring of permanent wall transects and corals at each site, while Leslie and I work on our individual (starfish and Hexaplex snail) projects.

Working the permanent transect at the Guy Fawkes site.

Leslie taking shell measurements of Hexaplex snails. Plastic calipers courtesy of Sal and the Three Seas Program :)

I finally met one of the focal species of my project up close, face-to-aboral surface. Pentaceraster cumingi, the Panamic cushion star, is a large and fairly abundant seastar that hangs out mostly on the sand, rubble and rock-sand interfaces underwater. I'll be collecting observational data on its size distribution and feeding, and also running caging/tethering experiments to figure out its effects on other organisms in the ecological community. I started on this stuff yesterday - more on this in another post.

Mr. Pentaceraster says hi.

And of course, every research dive has its share of distractions. But the ones in the Galapagos are a lot more flamboyant than the ones in New England...

o hai. im in ur transectz, scaring ur fishz

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.

First look at the Galapagos

We took an early flight from Quito to Baltra airport in the central Galapagos islands on Thursday morning. If Quito by night is amazing, Quito from the air is just spectacular.


We got into Baltra airport and crossed over the canal to Santa Cruz island in a little ferry. From there it was a long drive into the town of Puerto Ayora, plenty of time to just check out the landscape. I have been on many islands, but this was like nothing I have ever seen. Capt. George Vancouver who visited the islands in 1795 described them as the most dreary barren and desolate country he ever beheld. There really aren't many tall things away from the high areas of the island, but it has its own beauty. Here are a couple of wide angle pictures from the GoPro cameras.


Towards the town of Puerto Ayora, there is more plant growth in general. And the dock area has a great intertidal zone!