NATURE ADRIFT 



deposited as a slime on the beach, and in July 1958 it was severe enough to 

 adhere to bathing suits at the Danish resort of Fan^^. Luckily such occurrences 

 are very rare. 



One feature of the phytoplankton, of whatever type, is that so long as 

 conditions suit it perfectly, it can reproduce extremely rapidly to form denser 

 and denser masses. The denser the mass, the more nutrient required so that the 

 limit is reached very suddenly and the patch disintegrates even faster than it 

 formed. Such patches, which occur in fresh water as well as in the sea, are 

 called 'blooms', referring to the sudden burst of activity, and not to any 

 analogy with the flowers of the higher plants. These blooms have their impor- 

 tance in the economy of the sea (Chapter 10) and may also show interesting 

 side effects. One of the Blue-green threads called TricliodcsDiiiiiii crythractiin has 

 a red colouring matter as well as the green. It lives in warm waters and on 

 blooming forms mucilaginous balls of about i 32 inch in diameter, which 

 give the whole water a red appearance. It is responsible for the name of the 

 Red Sea. Similar red-coloured plants, of various species, bloom suddenly and 

 give rise to the stories of converting water into blood, and another is re- 

 sponsible for the colour of 'pink icebergs'. Such blooms depend on the 

 simultaneous presence of several factors of which an abundant supply of 

 nutrients is one. This supply can come from the upwelling of nutrient-rich 

 deep water, drainage from richly fertilized land, mining operations or decay 

 of a patch of other organisms which may themselves have taken a long time 

 to concentrate the nutrients from a wide area. Sometimes a bloom occurs of a 

 toxin-producing species forming a 'red tide', and although these occur mostly 

 in warm water they can occur locally in cooler areas, but mostly in brackish 

 waters where there is little tidal mixing. Red tides are mostly associated with 

 dinoflagcllates, such as Gyiiiiiodiiiiiiiii hrevis and Goiiiaiilax tiionilata; about a 

 dozen are known. In a bloom sufficient toxin can be produced to kill off" 

 large numbers of fish within the affected area, and the poison carried ashore 

 in wind-blown spray, can cause irritation to the people living there. Some- 

 times fish are killed merely by lack of oxygen when the bloom decays, 

 the bacterial process of decay having used up the available oxygen. Red 

 tides in New Zealand have been found to be due to minute animals called 

 rotifers which have a bright red eye spot, but these are non-poisonous. 



A poisonous dinoflagellate lives in British waters; it is Gymuodiiihiui 

 vciicficiiiiii, which has been grown in culture at the Marine Biological Station 

 at Plymouth (Fig. 10). It has never been known to 'bloom' here and is so 

 unlikely to, that any danger of large-scale destruction of fish from this 

 cause is quite remote. Nevertheless, a reporter got hold of the story and in a 

 short article headed Deadly plant found in the sea he said 'Marine biologists have 

 discovered a particularly deadly sea plant in Plymouth Sound. If the plant 



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