NATURE ADRIFT 



Salps, too, can be used in this way oft the east coast of Austraha, arrow- 

 worms can be used off^ Peru and in the North Pacific, and oft the Atlantic 

 coasts of America and Africa. Oceanic hsh arc used to determine the pene- 

 tration of water into the Strait of Georgia between Vancouver Island and the 

 coast of Canada. 



Some of the sea shore-animals like barnacles and limpets, and bottom- 

 living animals too, can be used in a similar way. As their distributions are 

 usually less transient than in the plankton they can be used in determining 

 the long-term trends associated with climatic changes rather than the more 

 immediate changes. A warning, however, needs to be given, as some bottom- 

 living animals have been transported by man to new surroundings and 

 have managed to survive there. The Chinese mitten crab is an example; 

 it became established, as an adult, in the German rivers like the Elbe from 

 which it has gradually dispersed, causing worry because of the damage it does 

 by burrowing into the soft banks of river estuaries. This artificial introduction 

 rarely happens to plankton organisms but it has occurred, for example with 

 the diatom Biddttlphia sinensis (p. 36). 



Although only a few species have been named in this chapter the list 

 could be very greatly extended, and indeed many of the microscopic forms 

 found in the phytoplankton could also be included. Ease of identification on 

 the spot has, however, such an advantage that those species that require 

 specialist techniques are not so readily accepted as practical indicators. 



hidicators are used not only for labelling water masses to trace the move- 

 ment of the currents but, as shown in the previous chapter, these labels also 

 indicate the boundaries of the various water masses and the mixtures of these 

 that have difterent fertilities. Even more importantly they indicate the 

 biological changes occurring en route. It should be emphasized that those 

 indicator organisms may play only an insignificant part in the whole 

 plankton community; it is their value as labels that is important. We need 

 the labels because the different water masses have different abilities to support 

 production of plankton, of fish food and so of the fish themselves. 



Some fish arc also drifted out of their normal range and fishermen often 

 come across such strangers. The fishery laboratories are glad to receive these 

 unusual specimens as the records help them to understand the ever-changing 

 conditions at sea. In return for the help given they will identify the fish, 

 or whatever it is, and send the hndcr a short comment about it. 



152 



