The midwater zone, or mesopelagic zone, is a region where sunlight is too weak to drive photosynthesis, yet penetrates sufficiently to affect the behavior of the animals in the region.  This is attested to by the diel migrations of many of the organisms of this zone and even by acclimated human eyes.  The mesopelagic zone is often defined as being between 200 and 1000 meters deep, although this is a somewhat arbitrary delineation.  The midwater zone is a huge area, containing about one quarter of the entire ocean and the bulk of the ocean's biomass.

Up until the 1960’s, research into the mesopelagic zone was limited to net sampling.  Although tremendous amounts of information can be obtained on many midwater taxa with the use of nets, the gelatinous organisms are consistently under-sampled due to the fragile nature of their soft bodies.  It was not until the advent of blue water diving techniques, specialized nets, submersibles, and remotely operated vehicles (ROVs) that the gelatinous organisms role in the mesopelagic ecosystem was appreciated.  Consequently, gelatinous organisms have not been given their justified position in the midwater food web.  Gelatinous predators may fill the same ecological role as fish and yet they have been hypothesized to be a trophic dead-end.  Much more research needs to be done to elucidate these issues.

by Kevin Raskoff