Page 231 - NS-2 Textbook

226 NAUTICAL SCIENCES

nutrient fav\' materials-carbon, phosphorus, and nitro- called kelp, which may be 150 feet long. Algae are the
gen-needed to start the process of photosynthesis over most common of all plants. 111ey are a l1lm1ber of differ-
again. Since the organic material sinks, most of the decay ent colors; some float and others attach themselves to
occurs in deep ,vater. Upwelling currents eventually re- rocks. There are also some grasslike plants. In general,
turn the nutrients to the lighted zone in the upper 15-20 ho'vevel~ the sea does not have the wide variety of plants
fathoms of water where this life cycle can begin again. found on 1a:t1d or the advanced members of the plant
Though phytoplankton can live only in the lighted family like trees or flowering shrubs. Much of the sea
zone, usually in the upper 90 feet, zooplankton and and the sea floor, in fact, is barren.
larger animal life have been found in all parts of the VV-here plants exist, howevel~ there ,vill normally be
ocean, including at the bottom of the deepest part of the an abunda:t1ce of animal life. 111e smallest mumals of the
35,800-foot-deep Mariana Trench. Animals that live in zooplankton group are the one-celled protozoans. Jelly-
these great depths are generally small, ferocious carni- fishes are the largest form of zooplankton. These are beau-
vores. They have very soft, scaleless bodies ,vith a wide tiful, transparent creatures cOll1posed of many white,
variety of shapes. 111ey are often snakelike with narrow blue-green, and blue cells, but they often have stingers by
fins and very pliant bones, and most are black in color the thousa:t1ds on their lacy tentacles that can cause ex-
because of the dark environment. Many have developed treme pain, convulsions, and, if one panics, even death.
long, needle-sharp teeth and huge mouths. Others are Others in the group of tiny animals that live off phyto-
blind because they have no need for eyes in the pitch- plankton me the larvae (young forms) of oysters, snails,
black world of the abyss. Still others have large bulging and sea ,vorms. More developed aniInals are the crabs,
eyes, and many have luminescent spots and devices that shrimps, lobsters, clan1S, oysters, squid, mussels, octopi,
glow in the dark. TIUs natural luminescence (light) is be- and scallops. These animals eat the smaller species of zoo-
lieved to attract prey, their mates, or both. Much has yet plankton and graze upon phytoplankton. Starfish and sea
to be learned about these strange deep-sea animals. urchins dine on shellfish such as oysters a:t1d clams.
At the shoreline, creattues of the sea live trnder very
difficult conditions. 111ey are subject to the extremes of MARINE ANIMALS
drying, flooding, baking, and freezing if they are ex-
There are hvo ll1ajor divisions of Inarine annnals: those
posed when the tide rises and falls. Waves and currents
that do not have jaws, and those that do.
may also wash them up on the beach to die. And, of
Only two types of jawless fish exist-the hagfish and
course, there are many predators that can get them when
the lampreys. Their mouths are circular and are used to
they are exposed. Many sea a:t1in1als that live on the edge
attach to their prey. 111e hagfish feeds on dead or dying
of the sea are small, flat, or sh'eamlined, and Inany have
a:t1in1als, but lampreys attach themselves to living fish,
suction-type devices that hold them tightly to rocks.
using their rasping tongues to make open sores from
Starfish have htmdreds of such suction cups on their five
which they feed on blood and tissue. The sea lampreys in
arms. Barnacles attach to underwater slufaces and ex-
the Great Lakes have caused great damage to the lake
crete a chemical that acts as a cement to keep them in
trout and whiting fisheries, but in the oceans they are in-
place the rest of their lives.
significant. The lampreys entered the Great Lakes via the
Other marine life is found in tidal pools and hollows of
St. Lawrence Sea\va)~ illustrating hm.v hmnan endeavors
rocks and coral where they are sheltered from predators,
can in some instances upset an ecological system.
and yet have life-sustaining water around them even ·when
There are four groups of marine animals that have
the tide is out. In this category are some corals, sponges,
jaws: fish, reptiles, birds, and mammals. Fish range
sea anemones, sea cuclunbers, and sea urchins. Others live
on the beaches and bmrow into the sa:t1d for protection
when the tide is out. Able to remain in the air from one
high tide to the next, this type includes some crabs, clams,
sandworms, and sand dollars, among nlany others.
LIFE IN THE SHALLOW SEA
Most sea animals live in the relatively shallo,v V\Tater sea-
ward of the low tide level above the continental shelf.
Over much of the continental shelf, marine plant life
(phytoplankton) is able to float, or in some insta:t1ces to
Jawless fish. A sea lamprey attacking a lake trout in the Great Lakes.
attach itself to the bottom and remain within range of
Lampreys attach themselves to living fish, using their rasping
sunlight. The plants vary in size from microscopic single tongues to make open sores from which they feed on their host's
cells such as algae and diatoms to huge seaweed plants blood and tissues. Courtesy Great Lakes Fishery Commission