10 



primarily with the environments of the Gulf of California are located on 

 figure 2 a, while the stations taken primarily on the continental slope from 

 California to Guatemala are shown on figure 3. As in the previous studies 

 in the Gulf of Mexico, many kinds of sampling devices were used (fig. 2b). 

 A series of Petersen and Van Veen grab samples were taken which could 

 be compared with grab samples from other regions, although the total 

 area covered by these samples (2.8 m^) is so small that no direct comparison 

 can be made between the Gulf of California region and other regions where 

 more intensive bottom studies have been carried out using quantitative 

 gear. The majority of shallow-water samples were taken with a small 

 shell dredge, towed for five to ten minutes, or otter trawls. All sizes of 

 trawls, the large beam trawl and the deep-diving dredge had inner net 

 liners constructed of the same size mesh, about 1 cm. in diameter. The 

 deeper stations were all taken with large beam and otter trawls or the 

 high-speed, deep-diving dredge (Isaacs and Kidd, 1953). 



Although physical and chemical measurements were not taken with 

 every station, a large body of environmental data already existed from 

 this and other investigations of the Gulf of California. Nearly every 

 biological station had a sediment analysis made specifically for that station, 

 or an excellent sediment map existed for the region where the stations 

 were taken (see van Andel, et. al., 1964, in press). Depths, bottom-water 

 temperatures, bottom-oxygen values, and, in some cases, salinities were 

 also taken with the biological stations, or else the necessary data for the 

 specific areas sampled were available from other sources. The principal 

 physical factors considered in explaining the distribution of invertebrates 

 in the Gulf of California are, therefore, depth, sediment, bottom-water 

 temperature, salinity, turbulence or upwelling and oxygen. 



There are also many biological factors which may be important in 

 limiting the distribution of benthic faunas. For this reason, some of the 

 research has been carried out at the Zoological Museum and Marine Bio- 

 logical Laboratory of the University of Copenhagen, Denmark, where a 

 great accumulation of knowledge on the life processes of benthic marine 

 invertebrates is to be found. The combination of associated physical factors, 

 relation to marine geomorphological features, and dependence upon 

 biological factors among the organisms themselves, should describe these 

 sedimentary environments (on a faunal basis) in such a way that the 

 interpretation of depositional environments of more ancient basins may 

 be made a little easier. 



