 A recent study by researchers at Scripps Institution of Oceanography
has provided a
rare glimpse into a deep-sea world 13,000 feet below the surface
of the eastern North Pacific Ocean.
Researchers David Bailey, Henry
Ruhl and Ken Smith analyzed fish and other marine animals over
a 15-year period as part of one of
the longest time-series studies of any abyssal area in the world.
The researchers discovered a nearly threefold increase in
deep-sea fish called grenadiers, or “rattails”, an upsurge that appears to have been driven by an increase
in available food.
Grenadiers eat a range of foods, from the dead bodies of fish and
whales to invertebrates such as worms and crustaceans. The most commonly
observed animals on
the seafloor include sea cucumbers, sea urchins and brittle stars,
and these appeared
to form part of the grenadiers’ diet. The growing abundance
of these animals was
followed by changes in the numbers of fish, with both groups increasing
over the
15-year study. Changes at the surface, caused by El Niños, La Niñas
and other ocean processes, apparently trickle down to the depths
some months or years later. Such oceanographic events, along with
longer-term shifting called the Pacific Decadal Oscillation, can
bring more nutrients to surface waters. While animals near the surface
can rapidly benefit,
it can be months to years later before changes reach the ocean bottom.
This finally leads to a proliferation of bottom-dwelling invertebrate
animals that make up some part of the food supply of deep-sea fishes. “This is a rare study of a large marine fish population that doesn’t
get commercially fished,” says Bailey. “Other fish populations
have their abundances, body sizes and
life histories altered by the activities of fisheries, so our study
probably gives us
some information about how fish communities work when they are not
driven
by human exploitation.”
— Mario Aguilera, ’89
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