Echinoderm anatomy made easy

The things that randomly cross my mind when I'm should be busy with work...

This one made me happy in invertebrate zoology class back in my 3 seas days.

 

The water vascular system song

The madreporite's connected to the... stone canal

The stone canal's connected to the... ring canal

The ring canal's connected to the...radial canal

The radial canal's connected to the... ampullae

The ampullae are connected to the... tube feet

And that's the way a starfish works!
Yay!

Mr. Pentaceraster and Mr. Nidorellia would like to inform everyone that the label 'starfish' is a gross misnomer and wrongly represents their true affiliations. They would like you to know that they have nothing to do with those smelly, stuck-up, vertebrae-possessing fish, and are in fact part of the phylogenetically oppressed 97% of animal life. Mr. Eucidaris, who is lurking about in the background, would like to inform Mr. Pentaceraster and Mr. Nidorellia that they are "a pair of spine-less weenies, and should go stick their complaints up their cardiac stomachs."

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.

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!

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