136 



DEPARTMENT OF THE NATAL SERVICE 



6 GEORGE V, A. 1916 



The folio-wing figures slio-vv that for these -waters, at any rate, values of density 

 •and salinity content can be regarded as parallel. The salinity has been assumed to 

 be proportional to the halide content, and this, estimated as chloride by Mohr's 

 method (with silver nitrate, using chromate as indicator). The samples of -water 

 ■were taken from Departure bay and points -within 10 miles of it. In the fifth column, 

 P represents the percentage of sodium chloride, and E the percentage excess of the 

 density observed over that of -water. 



So far -we have been able to work out accurately only one example of the rela- 

 tionship between salinity and distribution, namely, in connection with the Pacific 

 coast kelps. The results, which -will be published fully elsewhere, show definitely that 

 for the species Nereocystis lutkeana (hull-kelp), other factors being constant, with 

 increased salinity is concomitant increased growth, both as to weight and length of 

 individual plants and size of beds, while a second species, Macrocystis pyrifera (sea 

 vine) will not grow in such a low mean salinity as is found in area (ii) above defined, 

 i.e., where the salinity falls below c mean value of 1-019 to 1020, but is always found 

 in waters where the salinity reaches a slightly higher mean value (density 1-021 to 

 1-022). The surface values of density are fully applicable here, since these kelps 

 grow chiefly at depths of from 4 to 6 fathoms in British Columbia coast waters, while 

 the greater part of each plant remains near the surface continually; hence their 

 conditions of growth are primarily subject to changes in the surface waters. 



According to Thompson (British Columbia Fisheries Report, 1914, p. R. 126- 

 R. 130), the abalone, Haliotis gigantea, has a similar range to that which we have 

 found to exist for Macrocystis. This also is found within the same limits of depth, 

 and probably illustrates a case from the animal kingdom in which the distribution 

 is conditioned by salinity. 



We consider that the results so far obtained indicate that further, exact observa- 

 tions should be made over a longer period with a view to determining: (i) to what 

 depth the sudden fluctuations observed in Departure bay and its neighbourhood 

 extend; and (ii) the relative effect of such sudden fluctuations on marine plant and 

 animal life compared with those more regular changes to be observed in the estuary 

 of such a river as the St. Croix (cf. Copeland, Contributions to Canadian Biology, 

 1906-1910, p. 281). 



Such an inquiry would probably be of special importance in relation to proposals 

 to transfer species with sedentary habits such as the lobster and the oyster to a new 

 habitat, and we hope that provision will be made to carry out such observations with 

 a view to solving these and similar questions. 



