Tomorrow is a day internationally dedicated to celebrating one of the most important ecosystems on our planet. And for once, I don’t mean forests. Tomorrow is the UN-designated World Oceans Day. But don’t worry, this doesn’t mean we won’t be talking about forests. After all, you can’t have one without the other.

This nautilus needs calcium carbonate to form its shell. Credit: Pacificklaus Photography, 2009

Yesterday, Michelle wrote about an important way that forests and oceans are connected: Forests prevent erosion into rivers and streams, keeping large quantities of sediment from washing into oceans. But that’s not the only way that forests help oceans out. Oceans and forests are Earth’s carbon sequestration dream team. Together, they regulate our planet’s climate. And when one of them is on the bench, the other one has to pick up the slack.

So, when deforestation prevents forests from sequestering their fair share of CO2, the oceans end up absorbing more, leading to ocean acidification. This is bad news for calcifying marine organisms — those organisms whose skeletons are formed from calcium carbonate, like corals and mollusks. As the water becomes more acidic, fewer carbonate ions are available to form their shells, leading to thinner shells and less protection for the organisms. If the ocean continues to acidify, shells and coral could dissolve. The changing chemistry of the ocean may have other effects that we aren’t aware of yet, as well.

In this way, deforestation sets off chain reactions that affect the whole planet. That’s why we’re working hard to restore forests where we can and protect healthy ones from deforestation. This World Oceans Day, consider helping our forests help our oceans. There’s no such thing as a team of one, and the oceans need their partner.