Friday, October 26, 2012

Trickle-down Eco-nomics

Low tide yesterday wasn't particularly low, and the water was unusually murky and turbulent, but it was my last day to visit the rocky intertidal zone before heading back to the bay area to finish and fire my artworks for the exhibition.

No TPERP volunteers were at the tidepools, and I was wearing my Cabrillo volunteer shirt (even the Artist in Res has to wear one!), so I was asked a lot of questions. Especially about this.

There'd been a bit of an offshore storm (the reason for the murky water), and a dead Southern kelp crab had washed ashore. That's my foot next to him for scale, so though I didn't have a measuring device with me at the time, I can tell his carapace was nearly 5 inches across. A big male. Females of this crab are about half the size of males, and 5 inches is about the max size for the species.

That thing on his head? A barnacle. Actually several barnacles: one big one and several tiny ones. All still alive. Though not for long, probably. His corpse would eventually wash back out in the waves, break up, and degrade. Sessile creatures, unable to move once they adhere themselves to a surface as juveniles, the barnacles were stuck in a doomed situation.  

After finding him, I stayed at the tidepools much longer than I'd intended, because he drew quite a crowd. Before that, I'd mostly been pointing out the best area to watch the hermit crabs. Hundreds and hundreds of hermit crabs, housed in all kinds of different shell species, were scuttling around one particular rock shelf, just under the cliffs. Which was also the shallowest, easiest area to walk around.

Many adults asked me what species of crab this big red guy was, and my stock answer was that I didn't know the species; I could tell it was a spider crab (a family of long-legged crabs that includes those charming decorator crabs) but I didn't have a guidebook with me and wasn't sure. Now I know it's Taliepus nuttallii. Not a common find in the tidepool area. These guys are kelp forest dwellers, subtidal herbivores.

I knew it was a corpse and not just a molt, because he was quite heavy and smelled bad and attracted flies. The giant kelp these guys live on and feed on can be uprooted in heavy storms and wash ashore. Most of the time the crabs carried inshore on detached kelp would make their way back to the kelp forest, alive. I have no clue what happened to this guy. 

People also asked me if he could be eaten. Yeah, they asked if this particular crab could be eaten. This species is edible, and sometimes fished -- though more than 90 of the commercially fished crab in California is a different species: the Dungeness crab. But they made it clear they meant this crab personally. Every time some guy (it was always a man) asked me that, it could have been an opportune teaching moment, the time to let them know that collecting anything -- for consumption or any other purpose -- from a national park is prohibited. But other and more compelling teaching moments were buried in that rather bizarre question.

Eating a found, dead crab? Yuck. Marine organisms degrade very, very quickly once they die. It's almost like there's an accelerated cycle of life in the water. Like if you gave the ecosystem amphetamines, or filmed it in high speed, that would be an accurate representation, compared to land ecosystems.

And there's another factor. I've been exposed to some pretty rank things in my life: watched autopsies, been a veterinary surgical assistant, done necropsies myself on all kinds of animals when I was a zookeeper. And when I worked in a mortuary, I was exposed to even worse stuff. But the only mortal thing that ever made me barf was a dead arthropod I removed from its exhibit. The flesh had turned to liquid, and as I heaved it from the water, that liquid was exposed to the air, and literally poured out of the exoskeleton, right onto me.

Okay, I take that back. Shellfish has made me barf lots of times. I was in high school before anyone suspected that maybe I didn't get food poisoning with incredible frequency, that maybe I wasn't merely unlucky when it came to dining out. Too bad, really: crab was one of my favorites, a rare delicious treat. And rock lobster burritos? Man, I loved those when I was a kid and we vacationed in Baja. It always ended badly, and everyone concluded that I had a tender stomach, and that vacations had bad mojo for me.  

At least I'm not allergic to chitin. Chitin is the building block of all arthropod exoskeletons, land and marine. It has some almost magical properties. I'm exaggerating; there's no real magic. But its usefulness is amazing. Another teaching moment here! Commercially produced crop seed is often coated with chitin, because it can improve agricultural yields by as much as 50%. Okay, maybe it is really magic. Chitin is a common ingredient in animal feeds as well, because it aids in the digestion of whey -- another common ingredient in animal feeds, but one which herbivores like cattle otherwise cannot digest properly. And because it has wound-healing properties, it's used to make some suture materials and burn dressings, as well as many cosmetics.

The shellfish humans consume annually produces thousands upon thousands of pounds of waste shell. Rather than being dumped back in the ocean (it was, prior to the last century), chitin now powers a multi-million dollar global industry. Handily and somewhat ironically, chitin is also used in wastewater treatment and water purification technologies. (There's a wastewater treatment plant just down the road from the Cabrillo tidepools. That'll be another post.) It's a common ingredient in "diet" supplements, because it binds fat. It also binds metals and PCBS, so it's useful in toxic waste removal. But outside of this technological use, toxins a crab is exposed to stay in the animal, meat and shell. Classic food-chain concentration. Consider that fact for a moment. While also considering that crabs are regularly consumed by otters and shorebirds, among others

Shorebirds such as this egret, feeding at the tidepools while I was showing the dead kelp crab to visitors. Talk about a teaching moment!

And what about molted shells? Or shell that's discarded by predators? Well, it biodegrades...but whatever PCBs and other toxins bound to the chitin remain in the ecosystem.

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