Composition and Distribution of Macrobenthic Invertebrate Fauna 



165 



en o 



z CD 



u. UJ 

 O 5 



or u 

 uj or 



CD <j 



1° 



2 en 



with density, the disparity between the high- 

 est and lowest biomass values was quite large. 

 Average biomass (0.44 to 0.04 g/rrr) in the 

 other five sediment types was nearly 3 to 30 

 times smaller than in till. 



Frequency of occurrence of isopods in 

 samples from the various sediment tvpes re- 

 flected about the same quantitative distribu- 

 tion exhibited by density and biomass com- 

 bined. Fifty percent or more of the samples 

 from both till and sand contained isopods, 

 whereas only 16 to 32% of the samples from 

 the other sediment types vielded specimens 

 (Table 20). 



Relation to Water Temperature 

 Among the six temperature range classes two 

 major concentrations of isopod density were 

 detected (Table 21; Fig. 170). One concentra- 

 tion occurred in the broadest (20— 23.9°C) 

 temperature range class, which contained tin- 

 highest density (67 individuals/ m 2 ) . The sec- 

 ond concentration occurred where the tem- 

 perature range was from 8 to 15.9°C. Isopod 

 densities in this zone averaged 16 to 25/m . 

 Over the remaining temperature ranges, average iso- 

 pod densities were from 3 to 7/irr. 



Although the biomass of isopods was small in all 

 temperature range classes, the quantities varied in ap- 

 proximately direct proportion to their density (Table 

 23; Fig. 170). Relatively large biomasses (0.34 to 0.42 g/ 

 m 2 ) occurred in the same temperature range classes as 

 those for high density. Smaller quantities were present 

 where the density was low. 



Frequency of occurrence in each of the temperature 

 range classes was moderate to moderately low. The 

 occurrence rates varied directly with density and biom- 

 ass values. Relatively high percentages of samples (43 to 

 61%) contained isopods in the intermediate and broad- 

 est temperature range classes. Relatively low occurrence 

 rates (20 to 31%) percent) were found in the other 

 classes (Table 25). 



Relation to Sediment Organic Carbon 



Isopod density in the various organic carbon content 

 classes exhibited a trend similar to that in relation to 

 water temperature in that two major concentrations 

 were detectable (Table 26; Fig. 171). The highest con- 

 centration (18 individuals/m 2 ) occurred in the next to 

 highest content class (3.00-4.99% organic carbon); 

 whereas, the second highest concentration (13/m ) 

 was in the class containing the lowest amounts of or- 

 ganic carbon detected (0.02-0.49%). Interestingly, a 

 moderate density (9/trr) of isopods occurred in areas 

 of undetectable organic carbon. Lowest density (<l/rrr) 



O O NUMBER 



• • WEIGHT 



O 60 — 



u. 50 — 



40 



50 



20 — 



s& 



04 * <r 



UJ o 



Densit) 



bottom 



0-3.9 4-79 8-119 12-159 16-199 20-239 



ANNUAL RANGE IN BOTTOM WATER TEMPERATURE 



IN DEGREES CELSIUS 



Figure 170 



and biomass of Isopoda in relation to the annual range of 

 water temperature. 



occurred in the lower middle range (1.5-1.99%) of 

 carbon content. 



Biomass of isopods was negatively correlated to or- 

 ganic carbon content, tending to decrease as organic 

 content increased (Table 28; Fig. 171). On the whole, 

 biomass was relatively low, ranging from 0.27 to 0.03 g/ 

 m 2 . Notable anomalies in the general trend occurred in 

 the absence of measurable carbon (0.19 g/m L ) and in a 

 comparatively sizeable (0.14 g/m 2 ) biomass in the con- 

 tent class that contained the lowest density ( 1.5-1.99%). 



Frequency of occurrence of isopods in the samples in 

 the organic carbon content classes was moderately high 

 (47 and 25%) at the extreme ends of the range and 

 intermediate (5 to 15%) in the intervening content 

 classes (Table 30). 



Amphipoda — Am phi pods were exceedingly numer- 

 ous and widely distributed throughout New England 

 marine waters. They were the most abundant taxo- 

 nomic group encountered in this study, forming 43% 

 of the total number of individuals in the macrobenthos. 

 Because of their small size, however, they did not con- 

 tribute a correspondingly large share (2.3%) of the 

 total standing crop (Table 3). 



The amphipods collected included a wide variety of 

 taxonomicallv diverse kinds (Dickinson et al., 1980; 

 Dickinson and Wiglev, 1981 ). We estimate that between 

 100 and 150 different species are represented in the 

 samples. Four new genera and eight new species of 

 amphipods were described, at least in part, from speci- 

 mens collected during the present study. The following 



