Warmer Oceans from Climate Change Impact Mercury Levels in Fish

A warming ocean could cause some serious issues for our environment. It can help melt ice near the poles and can also help shift deep sea ocean currents, which can impact weather patterns. Now, scientists have discovered something else that the warming oceans might affect. It turns out that rising ocean surface temperatures caused by climate change could make fish accumulate more mercury.

Mercury in fish is nothing new. In fact, fish higher up the food chain, such as sword fish, tuna and marlin, have greater concentrations of mercury. This is mainly due to the process of bioaccumulation. Put simply, predator fish eat many smaller fish which also have concentrations of mercury. The mercury from the smaller fish is then incorporated into the predator fish in greater concentrations.

How does the mercury get there in the first place? Mercury released into the air through industrial pollution can accumulate in streams and oceans. In the water, it turns into methylmercury.

Until now, though, little has been known about how global warming might affect mercury bioaccumulation in marine life. That's why researchers decided to examine killifish under varying temperatures in the lab and in salt marsh pools in Maine.

In the marshes, the killifish ate insects, worms and other natural food sources. In the lab, though, the fish were fed mercury-enriched food. This allowed the researchers to compare fish both in the wild and under lab conditions. In the end, the scientists discovered that fish in warmer waters actually ate more. However, the fish also grew less and had higher methylmercury levels in their tissues.

These findings are important for understanding how climate change might impact our food supplies. In particular, the research reveals that increases in metabolic rate in fish actually cause increased uptake of the toxic metals. This, in particular, could greatly influence how much mercury will be found in fish in the future as our climate continues to warm and change.

The findings are published in the journal PLOS One.