respiratory pigments with high oxygen affinity, minimal respiration, dependence on
glycolysis, intermittent migrations into oxic layers, etc. Life processes are slow,
especially under hypoxia, and there is evidence of long life-cycle times, of the order
of years for animals of modest size.
Fig. 12.1 Vertical profiles of zooplankton biomass (mg dry weight m−3) taken from
the Soviet oceanographic vessel Vityaz with nets hauled vertically over wide depth
intervals (e.g. depth = 4 km to 2 km) in subpolar (cluster of curves at right) and
subtropical (left cluster) waters. Each curve is for a separate station. Abundance falls
by two orders of magnitude between the epipelagic and 3 km.
(After Vinogradov 1968.)
Because food is scarce in mid-water, there are very low standing stocks of the
denizens of the deep. That makes it difficult to study the ecology of this zone. Very
large volumes of water must be filtered to obtain useful samples of the biota. The
usual approach is to use large nets such as the Isaacs–Kidd trawl (10 m^2 mouth area).
Much larger nets have also been tried, including Engels trawls with towing warps
from two ships, huge otter boards, and a mouth 100 m wide. Huge nets were the rage
in the early 1980s, a trend that seems to have died away. They did not catch an
Architeuthis (giant squid), and drag-forces from the nets tended to pull winches and
ships to pieces. On the whole, nothing new was learned from the effort, but upper size
ranges of some species were extended slightly. Studies with submersibles and
remotely operated vehicles have been important in recent decades, particularly for
observing and capturing gelatinous forms like the diverse and delicate deep-sea
siphonophores and ctenophores (e.g. Haddock 2004).
(^) Animal sampling has mostly been done with large trawls, so the animals studied
most closely have been fish, squid, and shrimp, the charismatic megafauna of the
mesopelagic. Most of our discussion will concern those groups. Spectacular color
pictures of those organisms taken in their natural habitat by ROV cameras can be