Floating Forests

In the Middlesea, you can find the Floating Forests. These are highly interdependent groves of oceanic trees that create a unique ecosystem with dozens of species. There are multiple species of floating trees, but they all tend to have a few things in common. The roots of floating trees have air bladders to provide buoyancy, and they also host masses of oysters and other sessile creatures, which serve to provide a counterweight to the trees themselves. The roots also have 'knees', similar to those found on cypress trees, which allow the roots to breathe. A particular grove will have multiple species of tree, but they all depend on the community to create a stable floating forest. One useful plant found in some floating forests is the 'spring melon', which is something like a coconut crossed with a watermelon. Sailors prize this fruit for the fresh water found inside.
Other species that live in and around the floating forests include crabs, sea birds such as gulls, auks, and fishing eagles, and sea otters. There are also species that are only found in these ecosystems - the most famous of these is the tree octopus, which hunts arboreal crabs by swinging from branch to branch and can even flatten itself out to glide short distances. Some floating forests host packs of gigantic coconut crabs which will opportunistically eat any creature that crosses there path.
The floating forests are also visited and harvested by sapient species. Some communities of Selkies have even made permanent homes in floating forests. More often, lumberjack ships will track and harvest floating forests for their timber, which is in high demand for shipbuilding. Some lumberjack companies are careful to leave the floating forest alive by preserving the root mass and some of the trees, so that the grove can regrow, but others are less conscientious and will kill the grove when they harvest it.