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mogurnda

Solar Sea Slugs: my new project

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After many years of doing expensive research to - hopefully - benefit human health, I have decided to try a different approach.  I wanted a relatively cheap project that answered a fundamental biological question, but wanted it to be fun, and to have my students in Mexico and my undergraduates here take part in it.  I decided to try to understand how kleptoplastic organisms, those that steal chloroplasts from their food plants and use them to perform photosynthesis, regulate their exposure to sunlight.

 

 

As many of you may know, Elysia crispata, the Caribbean lettuce sea slug that some of us have tried to use for algae control, sucks the juice from its food plants and uses the chloroplasts.  They continue to eat, but can get by for months just living off sunlight. Here is one on a reef in Bonaire, from a few years ago.  

 

 

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People have studied the symbiosis in other species of Elysia, including E. chlorotica, which lives in the Chesapeake.  What is getting the most attention is that the slugs need algal proteins to maintain the chloroplasts, and there is evidence that the slugs are expressing genes from algal DNA.  After that, it gets a bit controversial, with some saying that the slugs have actually incorporated algal DNA into their genomes (“horizontal transfer”) and others saying that it is not present in unfed juveniles.  Very interesting question, but not mine.

 

 

I want to know how a slug knows when it has had enough sunlight.  There are hazards to being in the sun too long (predation, radiation damage, free radicals), but you want to get as much energy as you can.  How do the slugs sense the intensity of light (eyes?  photosynthetic byproducts?), and how does it count the amount of time it has been exposed?  With a very simple nervous system, which has really big neurons, the slug should be able to reveal its secrets.

 

 

The first step was finding them.  I had found Elysia diomedea at the marine station at Bahia de los Angeles when I had worked there in the past, but it took a week to figure out that they are out in the morning, and not the afternoon.  I was working on another project most mornings, but managed to find them on a day off when I had all but lost hope.  This one is near some Codium, a possible food plant (still not known).

 

 

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To be continued…

 

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Interesting thread. Tagging along

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Great thread.  You have my attention.... wow me ;)

 

I hope I have not oversold the story.  We are just starting out, but will add some tidbits in a moment.

 

I wrote an article about them a number of years ago.  Very cool creatures.

http://breedersregistry.org/maquaculture/elysia-crispata-sea-slug-spawning-in-a-100-gallon-reef-aquarium/

Why am I not surprised  :cool:

 

There is a publication somewhere in my files about food preferences among Elysia species.  Most have a single food plant.  For E. chlorotica (the one found near here), it is the hair algae Vaucheria.  E. crispata is known to feed on a few species, but I'll be danged if I can remember which ones (Bryopsis?)  or where the paper is.  Will look a little harder.

 

It is not known for E. diomedea, but some suspect the brown alga Padina (probably wrong), and I suspect either the native species of Codium or the turf algae that they spend much of their time on.  I had a brilliant experiment to look at that, but lost a week finding the little buggers.

Edited by mogurnda

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Before I get into the data, let me set the stage.  I have been working with a group at Bahia de los Angeles in the Sea of Cortez that looks at how to reduce turtle bycatch and how the nutrient-rich sea can support life on the desert islands.  Long story about how I ended up doing this, but I have been working with the people on the island questions.

 

To give you a sense of the contrast, here are some of the students on on of the larger islands, setting pitfall traps.

 

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The area is totally amazing.  On one morning, we saw about 5 whale sharks, a huge pod of dolphin, and a few fin whales on the way to the first island.

 

Once again, photobucket is misbehaving, so I will need to pause.

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For those that dont know the sea of cortez is the gulf of California.

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For those that dont know the sea of cortez is the gulf of California.

Good catch.  I always think that people are more familiar with Sea of Cortez, which has its problems.

 

Before I get back to the science, a little marine eye candy.

 

The area between the islands we worked on and the huge Angel de la Guarda island to the east is called the Canal de las Ballenas, or Channel of the whales.  Kind of a no-brainer, because there are tons of whales.  Mostly fin whales, like this one, but also Bryde's whale, and the occasional sperm whale or blue whale.

 

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Also sea lions, and an unusually large number of whale sharks. No chance to snorkel with them this year.

 

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One other cool thing was the reappearance of huge numbers of Humboldt squid.  These guys are about 3 feet long and aggressive.  For anyone who studies neuroscience, they have enormous axons.

 

IMG_1385adj_zpsa76c7102.jpg

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I am already wowed just looking at the pictures.  I can see why you are studying how to develop a local economy, those islands look pretty barren in the pictures.  

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how many slugs can you catch in those pitfall traps?

Exactly none.  For some reason, they have no interest in crawling out of the nice, wet ocean to fall into the traps on the scorching rocks.

 

The traps were to survey scavenging beetles, continuing a project that has been going on for >30 years.  The idea is that there is actually a higher population of land animals (beetles, centipedes, scorpions) on the islands than on the mainland, due to "spatial subsidy" of energy from the ocean to the island.  The input comes in the form of wrack, guano, carrion that washes up, and can include dead baby birds on nesting islands. Normally, that part of the project is run by an old friend of mine, but I had to take over this year because he was ill.

 

Here is a scorpion, fluorescing under a blacklight.

 

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Having to do both jobs was a bit of a problem, actually.  

 

My original plan was to devote most of my energy to the slugs, and help out with the islands when needed.  When things changed and I had to supervise the island work, I needed to be on the boats every day from 6am - 12:30pm.  After searching without success for many afternoons, I discovered on a day off that the slugs were easy to find in the morning but disappear after midday.  Cost me a week.

 

I did find them, though, and got a chance to do some simple phototaxis experiments, trying to figure out which part of the spectrum was of interest to them.

 

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I brought an LED controller and some LEDS down from the lab, and had a look at which wavelength they preferred.  It was a simple, first pass at figuring out what signals they use for figuring out light levels.  

 

Their eyes, assuming they resemble their relatives, should be most sensitive to green or orange.

 

If they were monitoring photosynthesis, then they should respond most strongly to blue or maybe UV.  

 

So which did they care about?

 

I gave them a choice of orange (591 nm), green (525 nm), blue (470 nm) and UV (370 nm).  

 

They explored the whole tub, but spent most of their time near, or sitting on top of the orange and green.  They did do funny wiggles when I shined the blue on them, but I am not sure what that means.

 

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Conclusive?  No.  But it looks like they are using their little eyes to monitor light levels.  There could be photoreceptors, in addition to their eyes, that respond to long wavelengths.  Plus, under the conditions in the station in Mexico, I could not control a lot of the variables that I would normally deal with in the lab here.  

 

So, did I solve anything?  No, but I did not expect to.  I have pages and pages of notes about the behavior and physiology of the guys, and the rest of the summer should be more productive in terms of experiments and thinking about proposals.  Because this is all on my own time, it is not costing anyone else a cent, so I can be as dumb as I want.  Plus, looking for them got me out snorkeling every day for an hour or two.  

Edited by mogurnda

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Beautiful stuff, Dave. I love the desert in Baja. It looks really serene where you're at. How's the local situation?

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Absolutely serene.  There is no reason for trouble to visit the little town, which is not really on the way to anywhere.  The big excitement this year was that one of the locals opened up a new restaurant with fantastic smoked fish.

 

There were the usual military checkpoints along the road, but it's not a big deal once you get past the idea of a 17 year-old with an AK-47.

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A few more underwater photos for the moment.  Photography while snorkeling is definitely a challenge.  I am used to being neutrally buoyant and having a source of air at the bottom, but it is different trying to snap off a shot or two while holding one's breath.  Even wore weights, which helped a little.

 

A cerianthid anemone, maybe Pachycerianthus.  These guys are out in broad daylight, which is very different from the Caribbean.

 

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Pseudosuberites is a common barrel sponge in the subtidal.

 

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Note sure of the species on this urchin

 

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I really like this photo of one of the more common sea stars, Phataria unifascialis

 

IMG_1363_adj_zps01ec129a.jpg

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Hey, those zoas are about the color of the Baja Mountain Dew flavor, which is appropriate.

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I love those zoas. Looks nice that way. Living the dream!

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Hey, those zoas are about the color of the Baja Mountain Dew flavor, which is appropriate.

Now I wish i'd collected them.  That would be a perfect name!

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Except that we would totally lose our permits.  The Mexicans have some pretty strong laws about working and collecting in protected areas.  Gives me hope that the place will stay in good shape.

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Great to hear that the Mexican government has effective enforcement of marine sanctuaries.  Much of their enforcement has a different reputation in the DF, or capital city.  Did you ever see the blue spot gobies/jawfish while snorkeling?  It would be a real treat seeing them in a natural setting.  They don't get imported much because they succumb to infections from shipping and handling.

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Did you ever see the blue spot gobies/jawfish while snorkeling?  It would be a real treat seeing them in a natural setting.  They don't get imported much because they succumb to infections from shipping and handling.

I wish!  My understanding is that they tend to stay deeper than normal snorkeling depth, and are more around the islands than onshore.  There is a dive shop in town, and I hope to get a chance to go out with him next time I am down.

 

There were lots of other fish, though.  Cortez and king angels, wrasse, triggers, puffers, barracuda and more.  

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The story continues...

 

Now that I am home, I was hoping to get started with experiments on our own Elysia chlorotica.  Unfortunately, at least as far as I can tell, they don't become common until later in  the season.  Never fear, many suppliers have Elysia crispata available right now.  I got really excited when I saw that LiveAquaria had a photo of E. diomedea (my Baja species) for their "lettuce sea slugs."  After talking to them, it was pretty clear they were just cluelessly using a photo that someone had pulled down from the web.  

 

I ordered from Carolina Biological, because they deliver to us regularly and the price was good.  I also ordered Halimeda and Penicillus (shaving brush) macroalgae from Gulf Coast Ecosystems, because there is a nice study that showed pretty clearly that they actually eat those plants.

 

Here is the start, a 20 long in my already too-cluttered office. 

 

3aaf35b4-2c08-4c65-9949-d186586717fd_zps

 

 

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