Deep ocean trenches represent a kind of aquatic dark-side-of-the-moon environment of which we know very little. In recent years, attention has been focused on thermal vents that exist in some deep water trenches and the amazing sealife that was found to be thriving in conditions that previously were believed to be hostile to any form of life. However, thermal vents are not the only source of life in the blackness of the deepest depths.
The BBC Earth News recently reported on an expedition team from the University of Aberdeen that has been investigating life in several deep ocean trenches in the southeastern Pacific Ocean off of Chile and Peru. In one particular trench that was over 26,000 feet (8,000m) deep, a new species of snailfish was discovered at 23,000 feet (7,000m).
At these depths, much of the sealife leads a scavenger existence, feeding on the remains that float down from above. In shallower areas, dead animals that come to rest on the bottom are consumed by a variety of crustaceans, bottom-feeding fish, and even sharks. At very deep depths, basically the same process occurs but with animals that have adapted to the pressure and total lack of light. It's a bleak existence with very little if any vegetation, so scavenging or feeding on the scavengers themselves is the key to survival.
The snailfish is one who feeds on the scavengers, crustaceans mainly. Although it has eyes, they are aren't of much use, so the snailfish has an extended lateral line system with sensory pores around its head which allow it to sense subtle vibrations in the water.
"When they sense movement, they suck in all the water in front of them in the hope that there are crustaceans in that water," said Dr Alan Jamieson, who lead the University's expedition.
While other animals that cruise deep open waters often utilize light-emitting organs to attract and catch prey, bottom-feeders are less attracted to those types of lures. So other sensory skills for hunting have evolved, like the snailfish's lateral line enhancement. There are over 195 species of snailfish, found in various depths in colder waters closer to the Arctic and Antarctic. They are similar to sculpin with elongated bodies, big heads, and large pectoral fins.
The University plans to conduct additional studies in the northwestern Pacific's Japan Trench. It was in the Japan Trench, in 2008, that the University, in conjunction with the University of Tokyo, discovered a species of snailfish at a depth of over 25,000 feet (7.7km), making it the deepest known fish.
The majority of the ocean exists in darkness and at great depths. While more abundant or colorful marine ecosystems in shallower waters might catch our attention, scientists know that these abyssal depths play an important role in the ocean's entire life cycle. We need to understand that role better and how it might be impacted or changing due to atmospheric and ecological changes occurring closer to the surface.
Read the BBC Earth News article.