PLANKTON OF THE GULP OF MAINE 479 



entlv req ires " some specific substance present in minute quantity in the natural 

 sea water'" (E.J. Allen, 1914, p. 430), but not in the artificial. 



Fritz (1921a), experimenting in the culture of diatoms at St. Andrews, New 

 Brunswick, found that Melosira In/perborea not only made considerable growth in 

 artificii 1 sea water but continued to multiply rapidly in cultures in natural sea water 

 long after Tlxilassiosira nordenskioldi, Cltsttoceras debile, and SJceletonema costatum 

 became exhausted. Her conclusion that the persistence of Melosira is permitted 

 by its independence of some substances whicb the other forms required but soon 

 exhausted seems justified. 



Suggestive, ;dso, in this connection is Crawshay's (1915) observation tbat the 

 excretory products of the copepod Calanns jlnmarcliicus (apparently not, however, 

 of Pseudoc Linus or Acartia) exert a strong fertilizing action on the diatom genus 

 Nitschia; but no such effect followed E. J. Allen's (1914, p. 429) introduction of 

 the crustacean genus Iiemimysis, with its fteces, into artificial sea water, which 

 proved as barren for diatom growth with as without them. 



Nathansohn (1906) has suggested that the supply of carbonic acid (CO?) may 

 temporarily f. 11 below the minimum required for active growth of the phytoplankton, 

 a possibility also accepted by Gran (1912, p. 380); and Moore's calculation 88 that 

 20,000 to 30,000 tons of carbon are annually converted from inorganic to organic 

 form per cubic mile of water in the Irish Sea emphasizes the vast amount which the 

 flowerings of diatoms and peridinians utilize. More recent experimentation on the 

 dynamics of photosynthesis 89 have shown that when the total available C0 3 has 

 been withdrawn from the bicarbonates present in sea water the latter becomes fatally 

 alk; line, and since sea water has never been found in this state or even approxi- 

 mating it, although many determinations of alkalinity have been made, it is safe to 

 conclude that the growth of marine phytoplankton is never prevented by a shortage 

 of carbon dioxide. 



The facts outlined above show that the coastal waters of the Gulf of Maine are 

 probably more fertile for diatoms in spring than at any other time of year with 

 respect to dissolved silica; likewise in nitrogen, one of the other nutrients on which 

 this particular group of planktonic plants chieily depends. The density and state 

 of vertical circulation of the water also influence their abundance, both by governing 

 the availability of the phosphoric acid and compounds of nitrogen that go into solu- 

 tion on the bottom of the sea and by influencing the flotation of the diatoms them- 

 selves. 



The influence which the state of circulation of the water exerts on the seasonal 

 abundance of diatoms seems first to have been fully appreciated by Whipple (1905, 

 p". 103) for fresh water, for which it is now accepted generally. Briefly it is as follows: 

 During periods of stagnation (that is, when there is no vertical circulation) the 

 bottom waters of lakes are the seat of active decomposition of organic matter, with 

 consequent increase of ammonia and solution of inorganic substances. When 

 vertical circulation recommences this "foul" w r ater is brought to the surface, where, 



" Quoted from Ilerdman (1920 and 1923). 



!! Especially Osterhout and Uaas (191S;; Moore, Prideaux, and Ilerdman (1915); Moore. Whitley, and Webster (1921). 



75S98— 26 31 



