Extinction event, in microcosm*

It's been a little more than two years since I started my "beach critter" aquarium. I've tried to make it as home-like as possible for the animals I brought home, within the limitations of a constant water level, and limited space. They're possibly a bit safer, since I keep a close eye on predatory species and there are no interruptions in the food supply. My aim has always been to learn more about the beach environment and its residents; to recognize their individuality; to learn their habits and needs, their loves and hates. (Yes, they have those!)

Now I've learned something more, something I'd rather not have. Disaster has struck.

I should have seen it coming. Maybe I did, at some level; the last couple of weeks I've been aware that something was "off", but I couldn't put my finger on it. We reached the tipping point a couple of days ago, and then it was too late to stop the slaughter.

It's a longish story; let me go back to the point where the tank was a happy place, not all that long ago. It was full of varied life, all finding their own niches, interacting with their neighbours, teasing one another (the only way I can describe how the shrimps bounce on the crabs' carapaces, tickling their eyestalks, then dancing away when the crabs react), sometimes squabbling, sometimes co-operating. Snails tunneled through the sand or climbed the walls. Four shore crabs and a baker's dozen of hermit crabs scrambled over them or carried them on their shells. The anemones fished for bits of food; so did many barnacles. Deep in the sand, a few clams and a mid-sized polychaete worm burrowed. Too many amphipods to count swam back and forth, or hid in the sea lettuce. There were four eelgrass isopods, with eelgrass to keep them happy, tiny, brown-and-white limpets, mussels and tubeworms.

It's all gone.

I always kept a bowl of clean water with a few handfuls of sea lettuce and maybe some eelgrass, for when the crabs had eaten holes in the veggies in the tank. A hungry flatworm had been exiled there, with a snail or two, some barnacles and mussels, for prey. The bowl sat outside, in the shade. A couple of weeks ago, when I went to add fresh veggies and a change of water, I found a scum on top of the bowl. Dust in the air, I thought, and cleaned the bowl thoroughly.

(This next seemed unrelated at the time, but now I know better. The small church next door has started on a major construction project. Rather than the wood and metal of our local housing, this building uses huge, curved structures of pre-formed concrete, about three stories high. They've been working on it for about two months.

A few days ago, I walked around that side of our building, taking yard waste to the collection area. As I passed the construction, I almost choked on something wafting from it; it smelled like a combination of industrial-strength cleaner, paint thinner and maybe vinegar. I warned Laurie away, but he was already complaining about not being able to breathe. Our troubles, easily remedied by going somewhere else.)

In the aquarium, some of my critters had gone missing. I cleaned the sand, as usual, a week ago, and didn't find the polychaete. There were only eight hermits and three crabs; where were the rest? The clams had died, and the crabs had cleaned out their shells.

There was more scum on the bowl of seaweed; I drained it, and washed everything well, then put in fresh saltwater. The flatworm was gone, and there were a couple of sickly-looking polychaetes hanging out on top of the sand.

I think it was about then that I started to realize something had gone wrong.

Two days later, the scum was back, thick and oily this time. The water stunk of chemicals. The seaweed was caked with scum and I threw it out, as well as the dead polychaetes, then, with nothing left but sand and smelly water, I dumped the whole lot.

The next evening, the 29th of June, the water in the aquarium was milky and the filter pump was labouring. I could only find five hermit crabs. I took everything out and cleaned the tank and filter again. One of the crabs had molted; all well and good.

The first of July, Canada Day, was a good day. My son came to visit with his family, and later we went for a walk in the cool of the evening and met an old friend on the street. We came home to water the garden before dark. So far, so good, but after that, I checked the aquarium. The crab that molted the day before had lost both big pincers; they were floating up against the glass. Why? And the tank looked empty; there were no amphipods visible, and the anemones had contracted themselves into little plates against the glass.

When I emptied the tank again, I found three healthy hermit crabs, one dying, and one looking sick. The coonstripe shrimp were behaving oddly; trying to swim but being swept away by the current, or failing to achieve lift-off. I could smell just a whiff of that chemical smell in the water of the tank; I changed half of it, with all the fresh sea-water I had on hand.

I counted my critters: surviving were the hermits, about half a dozen amphipods (of hundreds!), most of the barnacles and mussels, the two sick shrimps, and the three crabs, including the clawless one. Looking closely at the hermits, I realized that two of them, the sick ones, had also discarded appendages; a couple of legs by one, and a pincer and a leg by the other. In the morning, those two were dead, and another looks sick now.

The snails are fine, so far. The invasive Asian mud snails seem to have multiplied; I counted about 30. The little nassas plow around as if nothing were the matter. A few periwinkles are left, but they leave the water to rest at the top of the aquarium.

Dying greenmark hermit, upside down in a "hospital" bowl. He only has three legs left at this time; a bit later, he will lose another. He can't right himself, nor walk when I set him upright.

1. I've been thinking that this is a foretaste of what will happen to our oceans as we continue to pollute our air and water.** I don't see that we are going to stop, either; not until it is far too late. I'm remembering the oilspill from last year; so many dying birds, so many dead animals. And what of the amphipods, the crabs, the beautiful anemones, the jellies and sea urchins, the shrimp, the cheerful hermits! I feel sick.
2. I think it is possible that their resistance to poisoning may be a factor in the current glut of invasive mud snails on our beaches. And, since they concentrate pollutants*** in their tissues, would they also be a factor in the reduced number of shorebirds that we see?
3. If so, maybe all life in the seas will not die out. There will always be something that can adapt, some critters that can go on as if nothing had changed. But will our shores be like my tank, now; clean sand, drowsy snails and a few hidden crabs? Nothing else?
4. As I said, I feel sick.

* Microcosm: From http://www.thefreedictionary.com/microcosm

A small, representative system having analogies to a larger system in constitution, configuration, or development:

** I found this in the morning, while I mourned my dead hermits. http://www.physorg.com/news/2011-06-scientists-massive-ocean-extinctions.html.

*** From http://www.brighthub.com/environment/science-environmental/articles/13705.aspx:

Other organisms are highly tolerant to pollution of their environments, among these are aquatic worms, leeches, and snails. As a rule, as complexity increases, tolerance to pollution decreases. Keep in mind that, even though these species may be able to survive in less than ideal environments, the species that rely on them for food may not be able to. Further, any pollutants or toxins in the prey animals or plants will be concentrated in the predators unless their systems are capable of removing the compound from their system.

Update: Another relevant article. http://www.canadaeast.com/rss/article/1420451

...the vast, empty expanses of our dying oceans.