Page 237 - NS-2 Textbook

232 NAUTICAL SCIENCES

be contended with in naval operations, in particular anti- 11,e ltmtinescence of the sea at night is one of those
submarine operations. Hydrophone reception can be seri- common, yet cmious, sights of the sea. It is a bluish-
ously hampered l as some noises are velY similar to the green, often sparkling, glow seen in waters disturbed by
sound transmitted by naval surface and underwater ves- bow waves, wakes, and cresting waves. In some areas of
sels. Such noises can also be psychologically stressful to the world this hmtinescence is very bright, to the extent
sonar operators. Therefore, the Navy began a program to that agitation of the sea by a passing vessel can briefly
record and identify biological and mechanical sounds so produce enough light on topside to read. When these or-
sonar operators could be trained to distinguish between ganisms are stimulated by waves, their rhythmic reac-
them. 11,e Navy also started a continuing research pro- tion looks like a swirling movement of light, like a pin-
gram to design equipment that could filter out as much of wheel. In calm conditions, the orbital movement of the
this biological noise as possible. seawater creates horizontal streaks where the dinoflagel-
The problem of identification is complicated by the lata tend to concenh·ate. Oceanographers are constantly
fact that the recorded sound differs according to the expanding their study of such natural bioltmtinescence
number of aninlals making noises. One croaker fish in the sea.
makes a drununing noise, but a dense shoal of croakers For the Navy, this huninosity of seawater is more
sotmds like a pnelunatic drill tearing up a pavement, than just an interesting natural wonder. Observed from
completely drowuing out the noise of any ship's pro- the air or from the bridge of a large ship, the lmuinous
peller. The tiny snapping shrimp makes a sharp snap wake of a ship or periscope traveling at even moderate
with its claw, but a large number of them sound like speed can be detected for some distance. It can clearly re-
radio static. veal the vessel's position and, roughly, its course and
In recording marine animal noises l scientists identi- speed. During World War II amphibious landings and
fied the sounds by comparing them with more familiar other navalillovements were, on several occasions, given
land animals. They learned, for example, that porpoises away by biolunlinescence in the -warm waters of the Pa-
and whales whistle, click, bark, and moan; barnacles cific. Naval oceanographers generally know where
slurp; black mussels crackle; toad fish croak, growl, and heavy luminescence regularly occurs, and can forecast
whistle; weak-fish and perch produce a rapid, raspy periods of this phenonlenon in areas where naval opera-
croak; the northern pn£fer squeaks and coughs; and the tions are planned.
sea robin makes a sound like fingernails being scraped
over a drum. FOULING AND DETERIORATION
The animals also use different means to make their
sounds. Crustaceans make percussion noises ·with their Of the many important problems with which marine bi-
claws. Fish usually make noises with their swim bladdel~ ology is concerned, none has greater econonlic signifi-
the size and species of fish determining in which way it cance to the Navy and commercial maritime interests
is vibrated. Some fish also make grinding noises with than the control of marine fouling and deterioration. The
their teeth or fins. It is still not known why these animals effects of marine growth on ships' hulls, their saltwater
make these noises, but they probably are related to intakes, valves, and piping are costly. Important also is
breeding, spawning, and defensive actions, among other the damage by marine organisms to the wood, plastics,
purposes. TIuough their study of these noises, marine bi- metal, and concrete of shore installations. For the U.S.
ologists hope to learn more about the behavior of these Navy alone, the protection and maintenance of ships,
animals. Such information could be used to help im- waterfront structures, and offshore equipment against
prove commercial fishing practices. biological deterioration and fouling costs many millions
of dollars annually More importantly, such uncontrolled
fouling and deterioration can reduce the combat readi-
BIOLUMINESCENCE
ness of naval ships and shore facilities.
Luminescence means "light created or emitted at low Constant scientific research has developed chemical
temperatures j not as a result of burning heat. II In nature, agents that have successfully protected hull surfaces for
there are at least four sources of such light: (1) mineral as long as twenty-four months. The problem is far from
phosphorus (phosphorescence), (2) radioactive minerals solved, ho'\vever. Nevv naval equipment constantly re-
that respond to or reflect certain wavelengths of light, (3) quires the development of better antifouling agents.
cool gases that can be activated by electricity (fluorescent Biological fouling impairs sonar gear by weakening
light), and (4) bioluminescence, that is, light created by in- sound transmissions. In some areas of the world, such
sects (fireflies), certain fishes of the abyss, and micro- fouling can make sonar gear unfit for use in just a few
scopic marine dinoflagellata, a single-celled phytoplank- months. The problem is complicated by the need to de-
ton. It is this fourth source of natural light that we shall velop an antifouling agent that will not itself degrade the
talk about here. acoustic qualities of the equipment.