SCIENCE AND THE SEA 



COMMON TYPES OF PLANKTON AFFECTING COLOR CHANGES IN SEA WATER 



CERATIUM 



POUCHETIA 



GYMNODINIUM 



PERIDINIUM 



NOCTIIUCA 



water enters the ocean, can often be recognized by the differ- 

 ences in their color. 



The discolorations discussed in this article however, are 

 largely caused by living organisms. These plants and animals, 

 floating at and near the surface of the water, depending almost 

 entirely on water currents for their transportation, are known 

 collectively as Plankton. The organisms range in size from 

 microscopic bacteria to forms as large as jellyfish and carry 

 colored granules, (most frequently red), in their bodies. These 

 colored organisms are distributed throughout the world from the 



polar waters to the tropics. Although they occur in almost all 

 waters in large numbers, their color does not become noticeable 

 until they exceed their normal abundance. Millions of organisms 

 in a small volume of water are required for definite dis- 

 coloration. 



When the necessary combination of factors is just right, the 

 PlajJcton reproduces at a great rate and the tremendously 

 increased population is called a ** bloom". If these organisms 

 contain pigments, the bloom is visible as discoloration. Some 

 of these causative factors are increased food material, more 

 favorable temperature or salinity, etc. 



The bloom, however, is usually short Lived. This tremendous 

 population begins to compete with itself for food which is fast 

 being consumed. Also the waste products which may have been 

 caused by killing off enemy forms now begins to pollute the 

 water to the point where it kills off the bloom itself. The 

 original situation which made conditions right may now have 

 changed, the temperature may have dropped or risen to an un- 

 favorable point, oxygen may have become scarce, etc. A change 

 in wind or tide may often be sufficient to dispel the bloom. 



As is the case in all living forms, the basic foods are 

 nutrient chemicals, (nitrates, phosphates, dissolved organic 

 matter etc.) and the energy from the sun. The plant Plankton 

 makes use of these and the animal Planktonlives on the plants. 



Coastal waters provide these nutrients in greater abundance 

 than do the open seas because decomposing matter which 

 supplies these chemicals, settles to the bottom, but in the 

 shallow coastal water, remains within reach of the Plankton 

 near the surface. Also, the population of these waters is 

 greater than that of the open sea, accounting for the large 

 supplies of decomposing material. Organic material washed 

 from the land is another important source of food for the life 

 of the coastal waters. Where the shore is steep-to and the 

 water deep, upwelling may occur, bringing bottom materials to 

 the surface. Such regions are often rich in Plankton. 



Polar waters are also rich, but mainly during the spring 

 season when the products of decomposition, accumulating 

 during the long dark winter, are released by the turbulence of 

 the warming water for the use of the Plankton which is coming 

 out of a sort of hibernation under the influence of the sun. 



Thus while coastal waters are characterized by a variability 

 of conditions frequently favorable for Plankton blooms, the open 

 ocean is stable and rarely changing even from place to place. 

 Plankton and food are generally scarce. Nevertheless, unusual 

 effects of wind or weather or unusual current movements may 

 occasionally lead to discoloration. 



DISTRIBUTION 



The phenomenon of discolored water is almost cosmopolitan 

 in distribution, although individual species causing discolor- 

 ation may have a relatively localized range. There are reports 

 of it from the antarctic seas, the temperate seas, the tropical 

 seas and the arctic. 



Although records included on the accompanying chart are 

 mainly those submitted by the merchant marine, and are there- 

 fore restricted to commercial ship lanes, other data obtained 

 by scientific expeditions and coastwise vessels corroborate the 

 theory that discolored water is primarily a coastal phenomenon. 



The areas best known for discoloration are areas of up- 

 welling. Here, at seasons when the current regime is proper 

 for the phenomenon, the cold deep waters are brought up to 

 the surface, carrying with them nitrogen and phosphates from 

 decomposition products. This suddenly abundant supply of 

 nutrients is often a "trigger mechanism" for the Plankton 

 bloom. Upwelling is common off the coasts of Peru and Chile, 

 the coast of Latin America, Mexico and California, the Florida 

 Keys, the Malabar and South Kanara coasts in southwest India 

 at certain seasons, the Madras coast in southeast India, Walvis 

 Bay and elsewhere in southwest Africa, the Arabian coast 

 between Aden and Perim, the east Japan coast and the East 

 Australian coast. In many of these areas, the discoloration 

 is an annual occurrence and may be seasonal. 



As in upwelling, a general change of water mass may also 



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