The collection of Terra Maris contains thousands of objects. And they invariably have to do with nature in Zeeland, which is no surprise in a museum that focuses on nature and landscape. The main collections contain stuffed birds and mammals, shells, and fossil mammal bones that are found in the Delta waters. But the museum has of a lot more in its possession. For exemple, there is a sub-collection of bird- and mammal skeletons, one of dried mushrooms and one of marine invertebrates.
It is not possible to show all the objects at the same time. There is just not enough room for that. Parts can be seen in the permanent exhibition or are shown in one of the short-term exhibitions. The rest is kept in the museum's collection storage.
The collection is steadily growing bigger. Sometimes objects are purchased, or private persons donate their latest finds. And some collectors also try to secure part of their collection for the future by offering it to the museum. In this way the collection has expanded through the years, resulting in a array of distinctive organisms from the Delta area that is becoming more and more complete.