10 



Occ(in()(!^rapJuj 1951 



correlated over a long period. Phosphate- 

 rich water from the Atlantic is associated 

 with one species of glass worm and a good 

 herring year, but phosphate-poor water 

 from the Channel with another species and 

 failure of the herring fishery. As a result 

 of these and other observations during the 

 last twenty-five years, both in the United 

 States and elsewhere, it is obvious that 

 certain species are indicative of one water 

 mass, others of another. 



Thus, water movements affect the pro- 

 ductivity of fishing banks. Eddies exist 

 over Georges Bank, for example, in which 

 young fish thrive and grow, but at times 

 conditions occur which sweep the young 

 larvae off the bank into deep water to 

 the south, where they die. Following such 

 a disaster, a poor haddock fishery is to be 

 predicted in New England waters. Pre- 

 cise evidence that water movements may 

 determine the productivity of an area could 

 not be obtained until recently, however, 

 as sufficient information of the character 

 of the water movements involved was 

 lacking. 



Reactions of the organisms to environ- 

 mental conditions, on the other hand, may 

 in part control their distribution. Many 

 zooplankton organisms migrate vertically 

 in shallow waters — away from the sur- 

 face as the light intensity increases each 

 day, toward the surface at night. This pro- 

 vides a mechanism for transferring organ- 

 isms from one body of water to another, 

 perhaps to be dispersed in quite the oppo- 

 site direction by counter-currents at vari- 

 ous depths. More recently, a so-called 

 "scattering layer" has been detected at con- 

 siderable depths with echo-sounding gear. 

 Like the layers found earlier in shallower 

 water, this layer also moves toward the 

 surface at night. Presumably it is due to 

 planktonic organisms or other animals prey- 

 ing upon them. 



Plankton studies are only one aspect of 

 marine biology; fisheries biology has been 

 studied chiefly in the areas where the fish- 

 eries are economically important. Fishery 

 statistics, like plankton studies, show that 

 the populations of many marine fishes fluc- 



tuate from year to year. For some species 

 these fluctuations depend on the success 

 or failure of spawning. Variations in the 

 ocean circulation may be the cause of this 

 success or failure. Fluctuations may also 

 arise from predator-prey relations, the pre- 

 dator checking the increase of the prey and 

 then, in turn, declining in numbers for lack 

 of food. Changes in abundance of useful 

 fishes are often attributable to such mys- 

 terious cycles rather than to overfishing or 

 to conservation measures. Studies must be 

 made of food, enemies, and of the physical 

 conditions under which each species lives 

 to reach an understanding of these prob- 

 lems. 



Marine organisms are subject to cataclys- 

 mic disasters and to severe epidemics whose 

 nature and cause are unknown. The classic 

 case is the tile fish, which was formerly 

 abundant at the edge of the continental 

 shelf off New York. In 1882 it was ob- 

 served floating dead on the surface in 

 countless millions. Subsequently, not one 

 commercial catch of tile fish was landed 

 until 1892. Since then it has slowly re- 

 gained its former abundance and again 

 forms the basis of a practical fishery. 

 Twenty years ago the eel grass along the 

 shores of the entire North Atlantic was 

 blighted by an epidemic protozoan para- 

 site. Within a year the whole shore-line 

 ecology had changed, and only now are 

 there signs of recovery. Recently a mass 

 destruction of fish occurred on the west 

 coast of Florida, in the so-called "red tide." 

 This was caused by a sudden "blooming" of 

 poisonous microscopic plants. Epidemic 

 diseases are also known to destroy oysters, 

 clams, herring, and many other useful or- 

 ganisms. 



The major part of the work in marine 

 biology has been accounted for above, but 

 several minor, although important, aspects 

 are yet to be mentioned. Twenty years 

 ago the role of bacteria in the sea was 

 scarcely known, but today, largely through 

 the leadership of Dr. Selman A. Waksman 

 at Woods Hole and Dr. Claude Zobell at 

 La Jolla, it fills a substantial textbook. Like- 

 wise, physiological investigations, often a 



