The average depth of the entire sea is about 3,800 meters. The midwater zone constitutes a huge biosphere accounting for more than 90 percent of the entire ocean's volume. Research into the midwater layers has just begun. Formerly, nets towed by ships were used to study what kinds of organisms inhabited the midwater layers. Since 40 years ago, nets capable of catching organisms in discrete depth strata have been used. However, catching live organisms was easier said than done. Besides, many deep-sea organisms have bodies so fragile, with water constituting the bulk of their mass, that their bodies collapse while they are being brought to the surface, even if they have been successfully caught. Many of them collapse so badly that their original shape is hardly recognizable. Much is owed to surveys done by such deep-sea exploratory vehicles as the SHINKAI 2000, the SHINKAI 6500, the DOLPHIN-3K, the KAIKO, and the HYPER DOLPHIN, for knowledge obtained about organisms of the midwater layers. Since it became possible to observe living organisms in their natural habitats, we have come to understand, piece by piece, their hitherto unknown morphological and ecological features. Those were impossible to study through net-caught specimens. Formerly, it was believed that in the midwater layers, crustaceans and fishes were the most common macro organisms. We now know that gelatinous organisms outnumber these hard-bodied animals. Presumably, jellyfish were destroyed when they were caught by nets. In the future, the supersensitive high-definition camera mounted on the HYPER DOLPHIN is expected to contribute greatly. The camera can obtain such clear pictures of jellyfishes' transparent body structures and their fine tentacles as will enable identification of a species without catching the organism. The inhabitants of the midwater layers play an important role in transporting nutrients produced in the surface layers to the seafloor, and they are deeply involved in the material circulation of a number of elements, notably carbon. However, the exact processes by which materials are transported from the surface layers to the deep-sea floor represent a great unknown area of science. JAMSTEC intends to employ various approaches to explore the entire biological system of this unknown area. Of those approaches, two are important: one is microscopic, focusing on individual organisms by observing them and collecting them using deep ocean exploratory vehicles; the other approach is macroscopic, grasping the state of organisms in wider areas using nets. Organisms inhabiting the midwater layers display such ecological features or functions as bioluminescence, vertical migration, transparent substance production, venom production, novel pigments and hypoxic tolerance -- al adaptations to the respective environments. Studies on these functions may lead to discoveries relating to the evolution of life and functions or substances useful to mankind. JAMSTEC has been conducting a study at Sekisei Lagoon, the largest coral reef in Japan, situated between Ishigaki-jima Island and Iriomote-jima Island, both in Okinawa Prefecture. Presently, the study aims to develop transplantation technology that may be used to restore the bleached and dead coral. Coral reefs draw attention not only as rich ecosystem resources but also as carbon sinks, to absorb carbon dioxide. Study on the ecological features of coral reefs requires continued long-range observation. However, scuba diving can permit only one hour of observation. If a submerged laboratory were established to permit researchers to stay underwater for several weeks to observe coral, it would greatly facilitate resources understanding of the ecological features of coral reefs.

Gorgonocephaid brittle star. It looks like a plant, but is actually a member of the ophiuroidea class of marine invertebrates. Suruga Bay at 900 meters deep. Photographed by the SHINKAI 2000 An aggregation of lithodid crab. Nankai Trough at 900 meters deep. Photographed by the DOLPHIN-3K.       Theragra chalcogramma. Yamato Bank, Japan Sea at 500 meters deep. Photographed by the SHINKAI 2000.   Crossota rufobrunnea. Collected in Sagami Bay at 1,100 meters deep. Photographed in a water tank on the research vessel.       The carcass of a squid on the ocean floor. Possibly died as a result of the earthquake in the central region of the Japan Sea in 1983. Photographed nine years later in 1992. Offshore Ojika Peninsula, Japan Sea at 3,300 meters deep. Photographed by the SHINKAI 6500.   Pantachogon sp. Collected at Hatoma Knoll in the Okinawa Trough at 760 meters deep. Photographed in an aquarium on the R/V NATSUSHIMA.       Ptychogastria sp. Collected off Doto, Hokkaido at 1,200 meters deep. Photographed in an aquarium on the R/V NATSUSHIMA.   Pasiphaeid shrimp. Sagami Bay. Photographed with the HDTV camera on the HYPER-DOLPHIN.       Aegina citrea. Collected in Sagami Bay at 900 meters deep. Photographed in an aquarium on the R/V NATSUSHIMA.   Calycopsis sp. Collected in the Manus Basin, Papua New Guinea at 430 meters deep. Photographed in an aquarium on the R/V NATSUSHIMA.       Ophiura sarsi. Off Sanriku at 300 meters deep. Photographed by the SHINKAI 2000.   Simultaneous mass spawning by madrepore coral. Coral spawns during the evening of the May spring tide. Photographed in the coral reef between Ishigaki Island and Iriomote Island, May 2000.