Catch and Release

The sprawling tunnels of my homeland are being invaded. There is a murky barrier all around that holds us in the bubble of its embrace. It warps and refracts the noises I chirp, but I reach my fin through as if it were no different than the water I breathe. I skim along, stirring the boundary, and choke in its wake. It is a layer of poison, buoyed by tides, and it will kill us. 

On the lowest tides I trace this boundary until there is no further path. Every day we trace the boundary, looking for an escape, and every day the boundary rises. Soon it will kill us. The barrier disconfigures all, making the stone walls of the tunnels seem twisted and undulating. And one day, beyond the veil, there is an undulating creature, whose form swirls within the poison water in time with the swimming walls. I dip my fin into the barrier and reach for them. As if my mirror, they reach back. It is a fin like my own, solid and firm—like the fin of my mother or my father, who search these tunnels as I do. Like I remember of my sister, who rests on the other side of the poison now. This fin touches me, gently, quickly, like I am hot, and it is alive, like my sister is not. And I touch it as it touches me; like it must be dead, but it is not. It feels like my own. Even as I touch them and prove them solid, their form swims in the poison current.

It reaches further, with certainty and strength, and it drags me into the poison. I thrash and I struggle and I choke. The poison burns in my gills and my veins and my nose. I grow weak and I grow faint and I think about my sister. The walls are undulating. I grow faint. They release me back across the barrier. I rest against the smooth, stable tunnel wall until the burning recedes. The undulating creature is gone. I try to navigate home, but these tunnels do not wind in their predictable patterns. It is not where I came from. It is not my home. It is so much larger. I wonder if my parents have lost another child. I wonder if I will find my sister here.

The story takes place on a hypothetical planet with large networks of underwater caves similar to those in the Yucatan peninsula in Mexico. Like the caves in the Yucatan, these caves were carved by the chemical boundary between fresh and salt water called the halocline. Salt and freshwater mixing results in a solution that is undersaturated with respect to the surrounding limestone, even if both the fresh and saltwater components are individually in equilibrium with the rock. This undersaturation results in rapid dissolution, thus carving a cave at the interface. The halocline will shift depending on the sea level and the influx of fresh water and carve a cave system.

Given that this necessitates an influx of fresh water, we can assume this planet has an atmosphere sufficient for weather and rains frequently, as well as a decent amount of exposed carbonate land mass for the fresh water to penetrate. I imagine that the cave network on this planet is even more extensive and complex than what we see on Earth. The story might take place in an area that has clusters of carbonate islands. That way, there are lots of freshwater habitats very close to each other that may or may not have passages depending the height of the halocline.

The main character in the story is a freshwater fish whose freshwater habitat is shrinking, possibly from a drought or rising sea level that is causing the halocline to rise. Channels that used to be filled with freshwater, or freshwater and saltwater, are now filled with saltwater—the supposed ‘poison’ in the story. They encounter a saltwater fish that drags them through passages that are now filled with saltwater for the purpose of relocating them to a portion of the cave system that is more extensively filled with freshwater.

There are other small touches in the story. The main character uses some method of echolocation to sense the direction of the tunnels, given that there is no light, and I think that the halocline might interfere with the reflection of the echolocation. Any waves passing through the boundary would be refracted, and it might make the halocline—and anything on the other side of it—seem warped. There are also multiple allusions throughout the story to social dynamics that arise from the environment. The freshwater fish might have to deal with habitat problems frequently, and so are familiar with mapping their tunnels to look for exit routes. The saltwater fish, on the other hand, might see themselves in an aid-giving position and try to relocate the freshwater fish to better habitats when possible, as seen in this story.