You have probably heard warnings before about mercury in fish, and how you shouldn’t eat too much of it, especially if you are pregnant. Mercury is in and of itself a nuerotoxin, but it isn’t mercury that is the real danger in seafood, it is a biotoxin called methylmercury. Methylmercury is created when mercury comes into contact with water. Microscopic bacteria live in both fresh and salt water sources that can convert mercury into methylmercury inside their cells, and this is the more dangerous form of mercury that travels up the food chain or ‘bioaccumulates’ as the bacteria are eaten by zooplankton, which in turn are eaten by crustaceans and small fish, which in turn are eaten by larger fish. At each stage in this cycle, the amount of methylmercury becomes more concentrated in the bodies of the creatures eating it. This means that animals near the top of the food chain, like sharks, swordfish, and even dolphins, can have huge amounts of mercury in their bodies. Other animals that carry large amounts of mercury are tuna and even salmon. These are some of the most common seafood animals and where your body will be introduced to much of the mercury that will wind up inside you.
So how does this mercury get into the environment in the first place? Mercury today is found in much higher concentrations in the environment than it was 150 years ago. Mercury occurs naturally in most soil here on Earth, and is released both when coal is burned, and also during most mining activities. This mercury can find itself in small lakes and streams, or laying on the topsoil of the land, in which case rain often washes it into those same lakes and streams. From here it enters small bacteria that convert it into the harmful methylmercury biotoxin, and this more concentrated and dangerous mercury compound washes downstream until it reaches the ocean.
Once methylmercury enters an ocean habitat, it is absorbed by those zooplankton mentioned earlier, in whose bodies it tends to stick. These plankton are eaten and at every step up the food ladder the methylmercury becomes more concentrated until it reaches your plate. But what about fish that live in environments not near the sea floor? Fish far away from the coast have the advantage of not being near to the mouths of rivers and streams carrying higher than average amounts of mercury. Even more importantly, the things they do eat, can be controlled very carefully by seasoned fish farmers. Fish food for salmon and tuna can be tested for mercury before feeding, and since these fish can be raised in areas of the ocean that may have previously been lifeless before a seastead moved in, the risk that they come into contact with other high mercury content animals is minimal.
On seasteads, we can raise low mercury fish, or even sharks, to not only be raised sustainably, but in a more healthy way, increasing their export value and allowing us to have healthier lives.