CRABS

The biocontrol we need? Or the debacle we deserve?

I don’t know about you but I would not survive without lists. I keep lists of everything. Weekly lists of things to do that week, lists of books to read, shows to watch, dog sweaters to crochet. I keep daily lists of things I need to get done by the end of the day (one hopes). And I keep lists of ideas.

Unfortunately I don’t always write down the context of said idea. Which is why I saw I had “CRABS” in all caps on my list and could not for the life of me remember why.

Luckily for us all, I did.

CRABS. By Nhobgood (talk) Nick Hobgood - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11449055

Send in the crabs

I came across this story on Vox last week:

Scientists will unleash an army of crabs to help save Florida’s dying reef

Not all heroes wear capes. Some are crabs.

Ok first off, A+ dek (that’s the little tag line under the headline). Super memorable and kind of makes you smile, it’s great. The article itself is a fun read about a lab that is trying to solve an issue with coral reefs in the Caribbean.

Reefs are facing a ton of pressures right now. Heatwaves that increase bleaching (which makes the algae that live inside coral flee in panic), ocean acidification that renders coral skeletons fragile, overfishing, you name it corals are suffering from it. One of those problems is release of lots of nutrients into the water from the shore (from, well, us). Nutrients are great, they make things grow! But in this case, the stuff that grows is algae.

And algae (which can be the algae you’re thinking about, but can also be seaweed) is bad for reefs. It smothers baby corals and stops sunlight from getting to the ones that remain. Algae, of course, has always existed and reefs have always had it, but the number of things on the reef that eat the algae has gone down. Specifically, the long-spined sea urchin had a bad disease outbreak and was extirpated. So, how to save the reefs?

Enter the crabs.* The idea of the story (and the paper on which it is based), is that Caribbean king crabs, which are also native to the area, can be bred up and released. These crabs eat algae, and they do it FAST. The study notes that adding crabs to test patches of reef reduces algae cover by 50-80% (!) over two years, and increases recruitment of new baby corals and more fish species, compared to no crabs or scrubbing the algae away (which is something that some groups do now).

The lab is breeding up a few hundred of the crabs and due to release them, and there’s a cute anecdote at the end about how you need to make sure the crabs are afraid of predators, so they use hilarious gloves dressed up to look like squid, with googly eyes, and they poke the crabs to make them scared.

It’s a nice story, and is of a type called solutions journalism, which is esp needed in the climate crisis because otherwise it’s just too depressing, you know?

But maybe we should pause before we send in the crabs.

Where are the crabs?

I’ve got some questions about this article, and the paper on which it is based. These are questions that I think the article could have answered. Why they didn’t? I dunno, maybe editors cut the answers because they were boring or they just didn’t come up. We journalists are human, just like you. We are not smarter or better. We just know and do different things. And based on what I know and do (which is writing about animals that we come to hate), some things about the article and the paper stuck out to me.

My concerns and questions:

1. This is basically a profile of one scientist. Which is fine. But it’s also promotion of a form of biocontrol (releasing one living thing in the hope it will control another), and there’s no outside comment, there’s no other scientist saying “yeah you know this looks like a great idea!” Or “Yeah, no this looks like a bad idea.” If a guy is going to dump hundreds of crabs in the sea I’d really like to know what other crab people and coral reef humans think of this.

2. The paper (open access! We love it) says one of the problems was the near extirpation of the long spined sea urchin, another native species that eats algae. The paper notes that results of trying to reintroduce these have been mixed. Why is that? What happened? Are there any lessons that could transferred to the crabs?

3. Speaking of, where are the crabs normally? Are they just getting super fat and doing super well with all this algae? If not, if their numbers are changing or even going down, why?

4. The paper notes that under natural conditions, the concentration of these crabs is low. Possibly this is due to high predation of juvenile crabs. They confirmed these crabs need to be large, as predation was indeed high for the smaller crabs. It looks like larger ones survive, but they also show some experiments where it looks like the number of crabs dropped by up to 80% over a year. The study itself used between 3 and 20 square meter test plots, dropping in 84 crabs per plot. So how many crabs will you need? Will you need to restock them?

5. The crabs are being predated but by what? Will numbers of those predators increase? What effects could that have?

6. The article finally states that the scientist is going to start just dropping these hundreds of crabs into the ocean at the end of the year. Which…what? Who has approved this? Anyone? Where will they do it? This is not Australia in the 1930s, you can’t just dump crabs in the ocean. Unless…unless you can?

7. One of the pressures reefs are under is ocean warming, are the crabs immune to this? How do they deal if the ocean is literally the temp of a hot tub (which has indeed happened).

8. The paper and the article both confidently state that the Caribbean king crab is herbivorous. But…is it? Is it really? One of the first real descriptions of the crab in the late 1980s says that it is not. That it, like, honestly many species of crab, is a generalist scavenger and will eat basically anything. If there’s algae? Sure, eat algae. If there’s dead fish? Eat dead fish. If there’s something else? I’d be interested to see what happens if the algae is gone and the crabs persist.

Don’t bother, they’re here.

These concerns might seem small, and I swear I’m not trying to be a jerk on the internet (though I am that I suppose). I’d love for us to solve the problem with crabs, it’d be boss if it worked.

But this is biocontrol. And biocontrol can go either very well, or very badly. If it’s going to go well, it needs to fulfill some very, very specific criteria:

1. The thing you release should dine on one thing, and one thing only. That thing needs to be the thing you want to get rid of.

2. The thing you release needs to have something to limit it. This could be the fact that it eats one thing. It could be that it cannot go past certain temperature limits, or over certain terrain. It could be that they carry a gene or disease that keeps numbers down. It could be a predator that eats them.

If you DO have those things, you can have drastic, impressive success. Like the prickly pear cactus in Australia, which was controlled by import of an insect that eats cactus, and only cactus. Or the bugs to control St. John’s wort on US range land.

But if you don’t have those things, the situation can go south quick. Consider the cane toad (Bufo marinus).

Every cane toad picture looks to me like they’re saying “WHATCHU LOOKIN AT”. Cane Toad (Bufo Marinus) in Tampa, Florida image by: Bill Waller. Wikipedia, CC BY-SA 3.0

The cane toad was introduced to Australia in the 1930s to fight a cane beetle, which was causing cane sugar problems (lotta cane references in that sentence). It made sense, when presented with cane beetles, cane toads did indeed eat them. Cane is in the cane toad name! It’s in the beetle name! Obviously a match made in heaven.

But, as I note in my book (yeah yeah, I have to self promote ok I have to eat), cane beetles dig as grubs under the soil, and fly as adults. Cane toads do neither of those things. When the cane toads arrived, they thrived, but not on cane beetles. Instead, they thrived on everything else, and became a slow motion hopping march across Australia that is still ongoing. They have caused major deaths among many predators as well, due to their giant poison sacs on either shoulder. It’s a potent lesson in how biocontrol can go wrong.

There are a couple of things that made the cane toad such a catastoadphe.

1. No one studied them over a long period to see how well they might breed and spread. No one looked at whether their populations would be limited or how.

2. Cane toads are generalists. They’ll eat lots of things.

And this is what I’m worried about with the crabs. The scientists are studying them, and that’s good. But lots of questions remain. How will they breed and spread? Will the populations be limited? What happens if they’re not?

And what DO these crabs EAT? Even eating “algae”, well, algae is a vast category of things. It’s the green slime you’re thinking about. It’s seaweed. It’s the tiny symbionts inside coral itself!

The article at Vox could have asked some of the questions, at least had another scientist say if it looked good or not, and tell us who was approving releasing crabs into the sea and where. It didn’t. And I worry that people are gonna get all hype for crabs, like we were all hype over big plastic booms to remove ocean plastic (in a strange coincidence, that piece was written by the same reporter), only to be let down.

Where have you been?

Is it reading about the snake with the biggest gape for its size? This snake crushes whole eggs inside its body with its own spine, and can swallow an egg several times larger than its head. I love that this particular scientist is basically just, all about snake jaws all the time.

Maybe it’s reading Michele Bank’s newsletter, about how people assume she’s a scientist. She’s not. And you know what? That’s ok. We can all love and be inspired by science, just as we can all love and be inspired by art! We don’t need to all be scientists or artists!

Where have I been?

On the podcast, I’m talking with my colleague and friend Richard Fisher about his book The Long View. We talk about how humanity has ended up so very short sighted, and also get into a fun argument about art. I still kind of hate most long term art projects but he sold me on a couple of them.

I also wrote about frog microbiomes for Science News. Because it turns out that the frog microbiome can make a major difference in how well a tadpole responds to heat! A big deal as we’re getting more heatwaves, but also no reason to be up and giving microbe transplants to a bunch of ponds. Just….hold your horses. Or frogs. Or whatever.

And I WILL be giving a talk in Washington DC on November 4! I’m in conversation with Erin Spencer and John Swaddle, talking about humans, wildlife, and writing about where they meet. There will even be book buying and signing opportunities so if you want in on that, get on it!

*This article is also weird about crabs being…creepy? “If you find crustaceans icky, Jason Spadaro’s lab is not a place you want to visit.” Like ewww crustaceans they are like spiders? But…crabs are kind of cool and most people don’t find them offputting. Why not say, “if you find crab legs delicious, a visit to Spadaro’s lab would make you very hungry?” Or I dunno “what do crabs eat? Why do we never think about what crabs eat?” Anyway, that stuck out for some reason.