Part III: The Physiology

Hello again!

Hello, science enthusiasts! Hello, animal lovers! Hello, conservationists! Here's your fourth stream of bubbles containing interesting information from this little corner of the California coastline. I'm Shelby, and I'm here to offer some insight on the health and function of some of the most important features of Northern California's coastal ecosystems.

In the last post I talked about the ecological principles driving the transformation of a kelp forest to an urchin barren. Now, I'd like to focus on the effects these ecological changes have on the physiology of the animals affected, specifically the key players: the purple urchins and the red abalone. Hopefully learning about how these animals are affected will make you a little more compelled to care about them.

The most important thing to remember about these marine invertebrates is that they can, in fact, survive being starved for a pretty long period of time. Its pretty common for scientists to starve invertebrates in the lab for experimental purposes, sometimes for months at a time. Of course, these animals will die if they are starved for too long, but they can definitely last a while. This doesn't mean they aren't under stress during this period; they are, after all, starving. The reason they're able to last so long is that they utilize a physiological process known as energy allocation.

Here's a simple way of looking at energy allocation. Source: https://slideplayer.com/slide/9402406/

Energy allocation is the term for how organisms divide their energy use among their essential bodily demands. The basic energy demands for survival are: maintaining homeostasis (a stable internal environment), growth and repair, movement, and reproduction. These are pretty broad umbrella terms that cover smaller functions and behaviors The amount of energy organisms can devote to meeting these demands depends on the resources available to them—food, water, etc. If there isn't enough food, the organism's metabolism changes to accommodate their metabolic needs. To compensate for the lack of energy coming in to the body, the organism usually has to sacrifice one of their functions to make it easier to cope. That way, what little energy might be coming in can be used for more important functions. The more complex an organism is, the harder it is to compensate for lack of incoming energy. That's why it's dangerous for us to go too long without food or water; too many bodily functions to manage.

Here's a slightly more detailed version of the energy allocation principle. Source: http://www.trunity.net/sam2/view/article/51cbf3867896bb431f6ad368/

Since invertebrates are less complex than vertebrates, they're very capable of coping with the loss of an inessential bodily function. For invertebrates, the first thing to go in starvation conditions is reproduction. Reproduction is considered a luxury by less complex organisms, since its not necessary for the body to function, so it's dropped pretty quickly in starvation conditions. This usually frees up enough energy for the organism to survive...not comfortably but at least efficiently. But the longer they stay in that state, the more functions have to be dropped.

So how does this effect the abalone and the urchins? They share a food source and a habitat, so they make use of the same kind of energy. But there is a distinct difference in their complexities. Purple urchins are echinoderms, making them relatives of sea stars and sea cucumbers. Red abalone are mollusks; they're essentially giant sea snails. They both crawl around on the sea floor and eat whatever smells or tastes right (usually), but their complexities are very different. Urchins are basically spiky balls with guts, tentacles, and a mouth; abalone have a whole body plan and tissues. Because of this, their metabolisms are different.

The left is a healthy urchin; the orange stuff is its intact gonad tissue. That's the stuff uni is made out of. The right is an urchin that's been starving; no gonadal tissue at all. Source: https://research.pbsci.ucsc.edu/eeb/smith/?page_id=234

Urchins are very robust; you can yank one off a rock and detach a ton of its tube feet and it'll be fine. They can harden their tests (shells) and prick up their spines. When an urchin starves, it loses its gonads and can keep functioning pretty much normally. They're not picky eaters; they'll eat whatever they can fit in their mouths: tough coralline algae, sand, rocks, dead stuff, sponges, barnacles. They can pass on this stuff fine. When they finally get their teeth into some appropriate algae, they bounce back really quickly and can grow their gonads back within a few weeks. Therefore, they can still reproduce from time to time despite living in a barren.

Starving urchins can get along pretty well on just a bit of kelp. As soon as they find just enough, they'll eat through it and be fine for a while. 

Abalone, on the other hand, are a lot more delicate. All they have for defense is their shell and the strength of their foot. When something tries to eat them, they hunker down and cling to whatever hard surface they're on. If they're successfully pried off—without care—they can bleed to death very quickly; they're hemophiliacs. They also lose their reproductive functions when starving, but unlike urchins, they also lose muscle mass, just like we would. They grow weak and shriveled, and can't grip the rocky bottom as well as they can when well fed. Abalone don't bounce back nearly as quickly either. During my time at the Bodega Marine Lab, some abalone that had been taken from the wild were kept starved, while others were fed right away, as part of a recovery experiment. When it was time for the starved abalone to be fed again, they weren't able to eat much for a week. Some more abalone someone else at the lab worked on helping some other wild abalone recover. It took them two years to grow their gonads back. 

An abalone needs a lot more kelp than an urchin does. Finding just a bit here and there with long stretches of starvation in between won't be enough to get them out of survival mode. 

This is why the abalone fishery needed to be closed. Not only are they weak from starvation, and therefore don't have enough meat on them, but they're not reproducing either. Fishing for them now would rob the populations of generations they simply can't replace. Meanwhile, any urchins who find a scrap of kelp able to grow seize on it and spawn as soon as they can. The abalone don't stand a chance.

When a red abalone is healthy, their foot covers pretty much the whole underside of the shell. When they starve, they shrivel up. Source: https://cdfwmarine.wordpress.com/2016/03/30/perfect-storm-decimates-kelp/ 

I hope understanding the physical demands these environmental changes have put these animals through can help evoke some sympathy from you, even just a little bit. These are simple animals; urchins don't have brains, abalone's brains are simple. But they still feel stress. They don't feel emotions the same way we do, but the difference being stressed verses being comfortably functioning makes a world of difference for their quality of life. The fact that they're alive and suffering should be enough, right?

Next week, I'll talk about the history and current conditions of the fisheries these animals provide, so you can get a better idea of their importance to us. If their well being as animals doesn't impact you, maybe their place in our economy will.

Stay curious.

Sources: https://slideplayer.com/slide/9402406/

 http://www.trunity.net/sam2/view/article/51cbf3867896bb431f6ad368/

 https://research.pbsci.ucsc.edu/eeb/smith/?page_id=234

 https://cdfwmarine.wordpress.com/2016/03/30/perfect-storm-decimates-kelp/