234 Papers from the Department of Marine Biology. 



on shore. There is an abundant growth of eel-grass in shallow water 

 around Marquesas and in the lagoon where the water is not extremely 

 shallow or perhaps disappears at low tide. 



In the shallow pool between Bush Key and Long Key, Tortugas, 

 blocked off from the sea except at extreme high tide by sand-bars 

 thrown up in a recent hurricane, there is a dense growth of seaweed, 

 which probably gets its fixed nitrogen from the adjacent shores. It 

 seems probable that the fixed nitrogen formed by electric discharges, 

 decomposition of organisms, and nitrifying bacteria that finds its way 

 to Tortugas is so reduced by the action of Drew's bacilli as to be the 

 limiting factor for the growth of seaweed. At any rate, the amount of 

 phytoplankton per unit volume of sea-water is much smaller than in 

 cold seas. Only on the bottom, and especially along shores where the 

 plants may have access to fixed nitrogen (from the decay of organisms) 

 before Drew's bacilli have had time to decompose it, do we find an 

 abundant plant growth. 



The limiting factor for animals seems to be food, but under some 

 unusual conditions oxygen might become the limiting factor. Fish in 

 an aquarium open to the air, and with a constant stream of oxygenated 

 sea-water flowing in, suffocate if the stream of water is not sufficiently 

 rapid. The same is true of sponges and other animals. If we take 

 the lowest oxygen concentration found right at the sea surface, 1 kg. of 

 fish would use all of the oxygen in 4,300 liters of sea-water in 24 hours 

 and would show symptoms of altered metabolism before it was used up. 

 Oxygen diffuses into the water from the air very slowly, and the fact 

 that fish can come to the surface does not help them much. It seems 

 improbable that fish would congregate in such numbers as to suffocate. 

 On the other hand, dinoflagellates sometimes multiply or congregate 

 in such numbers as to die and make the water foul. In the summer of 

 1907 I observed such swarms of Gonyaulax polyedra in the Pacific Ocean 

 off La Jolla, California, that the water was red by day and turned to 

 fire at night. The infected water welled up in spots which grew larger 

 until nearly all of the water was infected. In about 3 days the water 

 stunk and some dead fish were cast on shore by the waves. The death 

 of large numbers of fish from unknown causes are reported by Taylor. 

 It is not intended to imply that these were due to lack of oxygen, but 

 the oxygen content of the water was not investigated and no satisfac- 

 tory explanation was found. 



No direct determinations showing absence of oxygen in sea-water 

 have come to my notice, but II2S in the water is destroyed by oxygen 

 and the presence of H2S indicates oxygen-lack. In some Scandinavian 

 fjords II2S sometimes rises to within 4 feet of the surface and kills the 

 oysters in ^'oyster polls." In the Black Sea H2S appears at a depth of 

 180 meters, according to Palitzsch. 



