IDENTIFICATION OF MARINE GROWTHS. 3 



purely economic aspect, the problem is one of vital national import- 

 ance in war-time from an operational point of view. The outcome 

 of a naval engagement might well depend on the increased endurance 

 and higher maximum speed that would result from a reduction of 

 fouling. 



(3) The Growth of Fouling. 



When a plate painted with a non-poisonous paint is immersed in 

 the sea at certain times of the year, a community of organisms 

 rapidly settles upon it. Included among these organisms are : 



(i) Marine bacteria, some types of which secrete a coherenu 

 slimy film over the surface. 



(ii) The young stages (spores) of seaweeds, microscopic in 

 size, but many of them rapidly developing into typical seaA^eed 

 form. 



(iii) Diatoms, which are minute plant cells Occurring singly, 

 in chains or in masses. These may form a brown slimy layer 

 over the surface or long trailing brown threads similar in 

 appearance to certain seaweeds. 



(iv) The larval forms of many sessile marine animals. 

 These are all microscopic free-swimming organisms capable, at 

 a certain sharply defined stage in their development, of settling 

 on a suitable surface, to which they attach themselves by a 

 cementing organ. Attachment precedes a metamorphosis pro- 

 ducing the adult organism. As the animal grows, more cement- 

 ing material is laid down, ever increasing the security of attach- 

 ment. This sequence occurs with the common animal fouling 

 organisms such as barnacles, calcareous tubeworms, ascidians 

 (sea-squirts) and polyzoa. The attachment and growth of 

 hydroids (which belong to the animal kingdom) follo^^ a more 

 plant-like pattern; the larva settles and grows out over the 

 substratum as a series of branching tubes, from which at intervals 

 arise the stalks bearing the main body and feeding organs of the 

 animal. 



A heavily fouled surface may show a basal " carpet '' of bacterial 

 and diatom sHme from which project the " stalks ",of hydroids a.- 

 well as diverse seaweeds, and sometimes the trailing brown filaments 

 of certain diatoms. Barnacles, tubeworms and many other animal 

 forms attach themselves very firmly to the paint surface, for this 

 purpose penetrating the slime, and often the surface layers of j'aint, 

 if this is fairly soft. 



A very heavy growth of one type of organism is fre(}U<ntly 

 accompanied by the more or less complete absence of rival forms 

 both plant and animal, so that a badly fouled surface can usually be 

 described in terms of a very few animal or plant types, fhis 

 phenomenon is known as biological exclusion. 



