The first family of predators we shall<br >i consider are those which most ob~en，ers are armed with chemically activated， springloaded<br > never suspect of predation， stinging cells， called cnidocytes， which are tipped with structure ~mallcr th m ，..，， ，<br > Nowba~k，qf ~ ，~r I ，，: ，<br >:he sunlit shallows of the tropical world are neurotoxins. While the poison darts， called then hundred~ .m，i th.，u，~，~ ~ ，. ~，. .<br > nematocysts， in these stinging cells Usual v cannot<br >:m to us gardens of coral. As we look at these penetrate human skin ( f they do， the pain is you see.<br >our percepnon of their life is unavoidably<br >~ d by our experience on land~ To the mind of temporary)， they are highly lethal to marine organisms Then lina，gine ~-tmtles， ，， ，r.xi h ，，，<br > the vast rock bulk beneath the rt r<br >tl man， a bed of corals has as its closest fishes. The tentacles capture food that is carried along would take the loquaciou， ，， ~-it~h， <，~，E，，， ，i<br > SUCh as zooplankton or， in the case of anemones， to The number of polvp~ > ，Inlt.h ~ <br >a flower garden~ Both are beautiful， both are in the current-drlven waters and pass the food to the<br >"ized by a profusion of color and form， both central mouth to be ingested by the coral.<br >ted" in the ground~ Naturally， then， a bed of<br > Asimov or a Carl Sagan t ， v，，k~- d~:m l，. ， -~<br > Many corals also have a complete back-ur) s "ste "<br >~ colored corals just beneath the surface of ~ smlply stand in awe.<br >~ evokes the flower-garden image， and many survive even a complete absence -g ; 5" m to Corals reproduce both s~xuaJlv an，/ *，c，q ~l]，<br > . * current-tmrne<br > method performs a valuable， funcri~，.. A v，~，<br > food. Embedded in the tissue of coral polyps are reproduction (or budd.ngi occur~ whet， ~r， m，i~<br >u write about the sea s creatures further this microscopic algae cells called zooxanthellae. These tiny polyp develops a bud which gr-m， r3~ht ，.~~- ，，<br >.n by referring to these communities of coral " ， "<br >gardens." plant cells gather sunlight and the coral s waste， and " "<br > This is invaluable to the dome .~r rcct-bu，/dm< ，<br >Ith about corals and other sessile (rooted) sea photosynthesize food and oxygen. Thus， the coral and If you were to draw on a b-，lloon a nun，b~，r ，t ，<br > zooxanthellae nourish each other even without other poiyps， then inflate the balloo~，， rot， mm~ed， ，t~l<br >is far more intricate and complex， food. It is， in fact， the zooxantheflae which Usually that the<br >in with， we must recall that the sea is like a give color to the coral; coral polyps themseh，es are role of budding is to fill in d~e ::at.， ~， r<br > n at its clearest， seawater contains quantities colorless， dome grows larger， <br >，lankton and zooplankton~ Phytoplankton are Another profoundly important chemical activity of open water. The resulting pelagic lap，~，， crmbk， ，，<br > Sexual reproduction releases eggs md ，pctm J，<br >Iplex communities of single- and multi- the coral polyp is the secretion of limestone (calcium to colonize new regions far downstream， ，，r ro<br >e-floating creatures which collect sunlight<br >t their nourishment via photosynthesis， carbonate) in the form of a protective cup about its repopulate areas of natural destruction.<br >ttlike cells are a principal source of our body. When a coral is not extending its tentacles to<br > feed， its body is withdrawn into and protected by the Interestingly， in certain areas wt ere men h ~ ，<br >(ygen supply. Most zooplankton， on the stony cup. dynamited cora reefs for fis a or con，truer.on， ，，<br >I. are often troy creatures who ingest The cup each coral polyp secretes is extended by the in the moon-barren craters~" " ~ " "~<br >kton and other zooplankton for their food. polyp over the years. The cumulative lengthening of corals seem to have difficu tv estxbl s n ~ h~ rn-<br >~ for ~uch sessile creatures as corals， Tridacna<br >uges， and tunicates (sea squirtsl to have thousands of cups by succeeding generations of corals Among the 2，500 species of coral there .~ .m<br > astonishing variety of shapes， sizes， and cok~r~ m<br >his plankton soup as a reliable food supply， creates a coral head. The base of any stony-coral -<br > structures they form.<br > structure is composed of ancestral skeletons， with the There are vast castles of tan Montastrea ~avcr~:o.<br >rest be stirred. The motion of the earth<br > CUrrent generation of live polyps inhabiting their cups corals; tortured edifices of fire coral (milleporal;<br >tis activity through wind and water Currents on the surface of the structure~ When you think of the dainty pink or purple Acropo，u with their delicate<br > e the plankton in endless cycles about the masszve size of many Coral heads， you begin to antler-like branches; and the soaring stonehcnges<br >basins. Plankton and ocean currents are the appreciate both the numbers and the crucial building formed by huge beds of elkhorn coral.<br > ival for ~he stationary creatures of the coral role of corals on a reef~ Vast accumulations of coral Then there are the gorgonians. Those ~ hich h~e<br >~ft， radially symmetrical ey inder containing heads form the world s coral reefs. Whole tropical the shallows， where the wave-surge is their trequem<br > the basic body plan of a coral polyp. The islands are composed of immense coral reefs rudely companion， have a flexible skeleton of wiry gor~oni<br >tad digestive tissues， plus reproductive " thrust above the water s surface by the forces of plate which can withstand countless Wave-surg~:s without<br >p this cylinder is mounted a central mouth. .~，~ ~!:: teCtomcs or glaciation~ ~<br >mouth on the upper surface (or at least You Soon begin to appreciate the astronomical breaking. Other gorgonian corms are limited to rock<br >O.u_ter edge) of the cylinder is a ring of<br > 2.~，~ numbers of coral polyps nvolved in these dry canyons in vast reef structures， canyons through wh~<br > {" recitations of fact. Spend a montent on a snorkel or environment can produce fans of brilliant vdlow，<br >u~g tentacles. -~ ~?; -， tidal currents flow. In the South Pacific th s<br > scuba dive and try to count the coral polvos on a<br >y，h~ ~ght or a multiple of eight tentacles single coral head. There will be at least hundreds and current flow. A third type hidcs its brilliant reds， its<br > IrLsome corals these tentacles arc smooth ， .<br >~! il~gs the ten tacles of rep tst held testg tion in a his to ry 150 feet.<br > fagt ones 7::， n thehu~~reds ~r Thoroyalty of ~rotbe<br > ~ a n!illion polyp the l~d，_ o，，，:c immense soft corals of<br >