The Bathypelagic Zone

The bathypelagic zone extends down from 1000m to 4000m, which is getting pretty deep. The only light is from bioluminescent organisms, and the only food is what trickles down from above, or from eating other animals. Although the water pressure at this depth is considerable, there are many different representatives of the normal marine groups: fish, molluscs, jellies, and crustaceans. Sperm whales can dive down into this zone when hunting giant squid. At these depths and below, most animals are either black or red in colour. Because only the faintest blue/green light penetrates this deep, and most bioluminescence is blue in colour, red is not reflected and looks black. Pretty tricky.

The animals shown above is one of the best known deep sea molluscs: the vampire squid. The picture on the right is a defensive posture of this animal. It completely inverts its tentacles, with their obvious webbing, up over the rest of the body. The sharp spines on the underside of the tentacles deter any potential enemies, as well as being very useful for grasping and holding onto prey. Vampire squid tend to drop down on unsuspecting victims from above and drape them in the net formed by their tentacles.

The snake dragonfish is another highly specialized fish found in the deep sea. Like the viperfish and dragonfish, this animal has large eyes, sharp teeth, a wide mouth, a glowing lure, and other light organs along the belly and near the eye. They live in the upper portion of the bathypelagic, around 1200m, and may migrate up to hunt (hence the ventral light organs for counter-illumination).

The angler fish is also a pretty famous deep water animal. There are many kinds with different looks, but all have a huge gaping mouth and a lure which is lit in deep sea species. Anglers have teeth in their throats to prevent prey from escaping. In these fish, the male has become a tiny parasite that attaches to and lives on the female, near her genitals. The range of these animals is from the surface down to the darkest depths.

This odd-looking specimen is a crustacean called an amphipod. Note that their body is red and transparent for camouflage. Swarms of these small animals scavenge whatever they can find in the deep ocean, and make up an important food source for other animals of the deep. Larger

Although not technically a pelagic (open ocean) animal, the slimestar does live in the bathyl depths, on the slopes and plains of the sea bottom. Echinoderms are very successful in the deep sea, some burrowing along the bottom sifting through the mud and sand for organic debris, and some flying above it in the abyssal zone (yes, flying). Slime stars, like other sea stars, can get quite big. This one is around 21cm long.

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