How Ancient Fish Colonized the Deep Sea
Published:14 Nov.2022    Source:ScienceDaily
The deep sea contains more than 90% of the water in our oceans, but only about a third of all fish species. Scientists have long thought the explanation for this was intuitive -- shallow ocean waters are warm and full of resources, making them a prime location for new species to evolve and thrive. But a new reports that throughout Earth's ancient history, there were several periods of time when many fish actually favored the cold, dark, barren waters of the deep sea.
It's easy to look at shallow habitats like coral reefs, which are very diverse and exciting, and assume that they've always been that way. But the deep sea is typically defined as anything below about 650 feet, the depth at which there is no longer enough sunlight for photosynthesis to occur. That means there is far less food and warmth than in the shallows, making it a difficult place to live. But by analyzing the relationships of fish using their genetic records going back 200 million years, it was able to identify a surprising evolutionary pattern: the speciation rates -- that is, how quickly new species evolved -- flip-flopped over time. There were periods lasting tens of millions of years when new species were evolving faster in the deep sea than in more shallow areas.

What we learned from this study is that deep-sea fishes tend to do well when oceans are colder, but with climate change, oceans are getting warmer. We can expect that this is really going to impact fish in the deep-sea in the coming years.