Bioluminescent Creatures on the BALDRIGE
Brett Fields asks:
1. How deep do bioluminescent creatures live underwater?
Captain Nelson answers:
Most of the common occurrences of bioluminescence in the ocean are observed
right at the surface or in the surface layers (several meters to tens of
meters, within the euphotic zone). In its most familiar form,
bioluminescence, which is a biochemical reaction in certain marine organisms,
appears as a bluish-green fluorescent glow in the water as the surface is
disturbed by the bow wave or wake from a ship or by cresting or breaking
waves. Bioluminescence is quite often observed on a ship itself, as most
ships are equipped with a salt-water system for flushing toilets. If a
toilet is flushed in a dark bathroom (called a "head" on ships) the toilet
bowl will often glow because of the bioluminescent microscopic organisms in
the sea water used for flushing.
Bioluminescent displays may occasionally take on more spectacular forms, such
as appearing as parallel lines or like spiraling spokes of wheels, of
pulsating light that extend to the horizon. In the surface layers of the
ocean, the group of single-celled marine organisms called dinoflagellates
(including one microscopic organism called noctiluca) are likely one of the
primary sources of the bioluminescence observed in the ocean.
However, a variety of other, larger marine organisms, that inhabit the
abyssal depths of the oceans also display bioluminescent characteristics.
Within the deep-scattering layer (mid-ocean depths between 200 and 1000
meters) certain species of myctophids, lantern fish, euphausids (shrimp-like
crustaceans), and jellyfish all display certain forms of bioluminescence.
Even in depths exceeding the average depths of the world's ocean basins (~
4000 meters), bioluminescent organimsms have been collected and observed in such
situations.
Most of these organisms are relatively small (a few centimeters long
at most) and the bioluminescence often may appear as a line of lights along
the lateral lines of these small fish, or for example as a single flashing
light, attached to a protuberance from the fish, that dangles in front of the
fish's mouth, much as a fishing lure. Many of these organisms appear quite
ugly and grotesque under the microscope, but are quite fascinating to look
at. Bioluminescence may be a defense mechanism for some of these deep
dwelling creatures, but also may function to assist the organism in locating
and identifying sources of smaller organisms to prey upon.
2. How do you search for new species of fish?
We aren't necessarily engaged in an active search for new species of fish.
In any event, the new species of fish that we are able to collect and
identify are the small, often microscopic mid-water species (like the
myctophids and lantern fish in the deep scattering layers), not the larger
fish species that find their way to the fish markets of the world. Most, if
not all of the larger species of fish throughout the world have been
previously collected, identified, and cataloged. The most abundant species
by far, however, are the small, mid-water and deep ocean fish, that have not
been collected as extensively, so there are still new species to collect,
identify, and name.
I would have to say that the collection and identification of new species of
fish come as a beneficial by-product of our primary scientific objectives
during the GLOBEC (Global Ecosystems) studies that we are conducting in the
northern Arabian Sea. During the two GLOBEC cruises we have been using a
variety of biological and physical sampling equipment to assess the changes
in productivity in the coastal and open ocean upwelling regions off the
coasts of Somalia and Oman, as those changes are related to the shift from a
relatively weak northeast monsoon, to a very strong southwest monsoon system.
One of the primary tools that we have been using to sample the biological
organisms is a multiple opening-closing net (called a MOCNESS), that allows
us to sample the water column discretely within up to five different layers.
We usually have deployed the net to depths in excess of 1500 meters, and then
gradually retrieve the net, successively closing one net (each net is 10
square meters in area opening) and opening another at different layers in the
water column. The nets are constructed of fine mesh webbing, and the small
organisms sampled by the net are collected into a tube-like container at the
cod end of the net. Once the samples are aboard, the scientists retrieve the
cod ends, and then they will spend about the next 3-4 hours painstakingly
sorting and identifying the organisms visually, by the mark-1 eyeball if the
organisms are large enough, or under a microscope, if not. New species, if
found, are typically identified on the basis of differences in fin
characteristics, for example, or by other identifying features that are
apparent to the trained biologist's eye through a microscope, but certainly
would not be obvious to a layman.
I hope that I've answered your questions adequately. Please don't hesitate
to write again.
Regards,
Captain Craig S. Nelson, NOAA
Commanding Officer
NOAA Ship MALCOLM BALDRIGE
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