Marine organisms with shells, like mollusks and crustaceans, don't directly remove carbon dioxide from the atmosphere. However, they play a crucial role in the carbon cycle by removing carbon from the ocean, which indirectly contributes to the removal of carbon dioxide from the atmosphere.

Here's how it works:

* Carbon dioxide dissolves in seawater: The ocean absorbs a significant amount of carbon dioxide from the atmosphere.

* Photosynthesis by phytoplankton: Microscopic marine algae called phytoplankton use dissolved carbon dioxide for photosynthesis, converting it into organic compounds.

* Food web: Phytoplankton are consumed by larger organisms, including those with shells, transferring the carbon through the food web.

* Shell formation: Organisms with shells use calcium carbonate (CaCO3) to build their hard outer coverings. This calcium carbonate is formed by reacting calcium ions (Ca2+) with carbonate ions (CO32-), which are derived from dissolved carbon dioxide.

* Carbon sequestration: When these organisms die, their shells sink to the ocean floor, taking the carbon with them. Over time, these shells can become part of the ocean floor sediments, effectively sequestering the carbon for millions of years.

In summary, marine organisms with shells help remove carbon dioxide from the ocean by:

* Utilizing dissolved carbon dioxide for shell formation: This removes carbon from the ocean water.

* Contributing to the carbon cycle: The carbon sequestered in their shells is eventually deposited on the ocean floor, where it can remain for long periods.

While this process doesn't directly remove carbon dioxide from the atmosphere, it helps to regulate the amount of carbon dioxide dissolved in the ocean, which plays a critical role in mitigating climate change.