SEA-WATER SYSTEMS AT FRIDAY HARBOR LABORATORIES 



135 



Figure 4. — Insulated glass line from cantilever pier to receiving tanks. 



Polyethylene of virgin grade and highest 

 quality, while sometimes varying from one 

 production lot to another, proved superior 

 to other commonly recommended plastics. 

 While many of these plastics are adver- 

 tised as "nontoxic to humans" and appear 

 to have no obviously deleterious effect on 

 many adult marine invertebrates, they 

 may block developmental stages or cause 

 serious abnormalities of differentiation. 



Developing eggs and embryos of the 

 purple sea urchin, Stronglyocentrotus pur- 

 puratus^ have been used to real advantage 

 as test subjects to determine the toxicity 

 of various possible materials for use in sea- 

 water systems. Since they have been used 

 extensively as experimental material in 

 this laboratory, their development is very 

 well known and any variation from the 

 normal in rate or kind of development can 



be readily detected. In addition they are 

 quite sensitive to heavy metals and other 

 toxic agents and the presence of minute 

 quantities of such is usually reflected in 

 dramatic change in the normal pattern of 

 development. 



As will have been noted, there is no 

 filtering of the sea water pumped through 

 our systems. The water arrives at the 

 tanks with the usual complement of plank- 

 tonic organisms, and plankton feeders 

 thrive in the tanks and aquariums. In ad- 

 dition, since the system is essentially free 

 from toxic agents, the walls of the pipes 

 provide settling space for larvae of many 

 sessile forms and other animals taken in 

 at the intake. Thus the system supports 

 a considerable growth of barnacles, mus- 

 sels, limpets, etc., as operation continues. 



