RHYTHM OF THE SEA lOi 



of their life near the surface, and as a rule it is the larval sta^rcs 

 which exist in countless quantities at and just below The 

 sea-level. We can trace a distinct rhythm in this part of the 

 ocean. It has a regular succession of organisms during (he 

 twelve months, and the skilled zoologist could make a"vcry 

 shrewd guess at the time of year at which a collection of 

 floating organisms was captured. At the end of winter and 

 the beginning of spring in our seas there is a great outbreak 

 of diatoms, those unicellular algae which form the ultimate 

 food of fishes. As the sunlight increases and the amoimt of 

 food in solution becomes larger, diatoms multiply and in- 

 crease greatly. A little later the fish begin to spawn, and 

 copepods and other small Crustacea increase greatly in numbers. 

 Soon the larvae of many deep-sea and middle-sea forms begin 

 to appear in the tow-net. The larvae of barnacles come to the 

 surface in enormous numbers as spring sets in. These may 

 linger as late as April or May and some even until the end of 

 summer. In March we find the crab spawning, and its larvae 

 soon become prominent. By May the number of diatoms 

 begins to decrease, and this decrease lasts for some few months. 

 Soon the summer-spawning fish produce their surface larvae, 

 and so do the sea-urchins and starfish. The phosphorescence 

 is perhaps at its height in July, and during the summer 

 months swarms of jellyfish stain square miles of the sea a 

 uniform reddish colour. In the late autumn and winter 

 months the diatoms begin to reappear and reach the second 

 peak of their curve in November, after which month they 

 die down again. As winter advances, the surface fauna and flora 

 fall away both in quantity and in variety; still some animals 

 and plants are persistent the whole year round, and take no 

 part in this cycle. 



There is thus a regular succession of organisms in the sur- 

 face waters, and it has been pointed out that the main features 

 of this succession are: (1) the relative scarcity at the beginning 

 of the year; (2) an outburst of diatom life in the late winter 

 and early spring; (3) the appearance of countless myriads 

 of fish and invertebrate eggs and larvae in the spring and 

 early summer; (4) a decrease in the abundance of the diatoms, 

 and the gradual disappearance from the plankton —the drifting. 



