Are there any benefits of climate change for marine plants and animals?

There definitely could be. Marine plants, like land plants, need light for photosynthesis. But unlike on land, light can only penetrate into the surface of the ocean, about 100m deep. Now, marine plants, known as phytoplankton, live in the surface ocean where there is light. However, when the ocean gets cold is gets denser. That dense (heavier) water the sinks mixing phytoplankton down deeper into the ocean, sometimes so deep there isn’t any light.

In a warming climate the ocean won’t get as cold, and in turn might not mix as deep. This would give phytoplankton access to more light and could allow them to be more productive and therefore provide more food for marine animals as well.

However, there are many other factors at play. For example, phytoplankton also need nutrients which are mor common at depth, so less mixing could mean less nutrients. Their predators (zooplankton) also may be able to eat them faster in a warmer ocean. So, the net effect of climate change on marine plants is still unknown. As for the animals, more plant productivity could be a good thing, but even that would come with major shifts in the timing in location of when and where the plants grow, which could create a major ecological problem.