1 70 NOAA Technical Report NMFS 140 



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SILT CLAY 



BOTTOM SEDIMENTS 



Figure 175 

 Density and biomass of Amphipoda in relation to bottom sediments. 



tremes. Lowest density occurred in the absence of mea- 

 surable organic carbon. 



Biomass followed the pattern established by density 

 (Table 28; Fig. 177). Biomass was high (8.3 to 5.3 g/m 2 ) 

 at high and low carbon concentrations, fell to much 

 lower levels (0.2 to 1.8 g/m'-') in intermediate levels, 

 and was lower still where carbon was absent or at the 

 highest levels measured. 



Frequency of occurrence was high (93 to 100% of the 

 samples) in the organic carbon content classes contain- 

 ing the lowest and highest concentrations measured 

 but dropped to moderate levels (49 to 72%) in all other 

 classes (Table 30). 



Mysidacea — Mysids constituted a minor portion of 

 the total benthos, 0.2% of the number of individuals 

 and less than 0.1% of the biomass (Table 3). They were 

 small in size, their geographic distribution was limited, 



and their numerical density was generally low. The 

 average number of specimens usually was less than 5/ 

 m 2 and average biomass less than 0.01 g/m . Some 

 species of mysids characteristically make diurnal excur- 

 sions from the sea bottom to the upper water layers, at 

 which time they become members of the plankton com- 

 munitv; however, when they retreat to the ocean floor 

 to feed or to excavate in the bottom sediments, they are 

 considered an integral part of the benthos. Since bot- 

 tom grabs do not sample mysids well, our data should not 

 be taken as indicative of actual distribution or abundance. 



Individual specimens in our collections ranged in 

 body length from 3 to 12 mm. The large inshore species 

 Mysis stenolepis and Praunusflexuosuswere not present in 

 our quantitative samples. 



The color of the majority of specimens was white or 

 translucent with small areas of brownish to nearly black 



