124 



NOAA Technical Report NMFS 140 



Both measures indicated a trend of increasing 

 abundance with increased range in tempera- 

 ture. Quantitative values for density were pro- 

 portionally higher than those for biomass, but 

 the percentage composition of the total fauna 

 for both measures was moderately low (Tables 

 22, 24). With the exception of die two broadest 

 temperature range classes (16°-19.9° and 20°- 

 23.9°C), where relatively high densities (85 

 and 47 individuals/m 2 , respectively) occurred, 

 gastropod density was fairly uniform at a mod- 

 erate level of about 10 to 15 individuals/m 2 . 



Gastropod biomass values generally paral- 

 leled those of density, but the trend of in- 

 creased biomass with increased temperature 

 range was more pronounced. The two larg- 

 est biomasses (4.96 and 4.09 g/m ) occurred 

 in the two broadest temperature range 

 classes. In all other temperature range classes 

 the biomass was moderate (0.26 to 3.75 g/ 

 m 2 ) and fairly stable. 



Frequency of occurrence of these organisms 

 was moderately high and stable in all tempera- 

 ture range classes (Table 25 ). They varied only 

 from 38 to 57%, with no obvious trends. 



Relation to Sediment Organic Carbon 

 Gastropods displaved a generally bimodal 

 trend of increasing numerical abundance 

 and biomass with increasing (to moderate 

 levels) organic carbon content in the sedi- 

 ments (Tables 26, 28; Fig. 116). Average den- 

 sity ranged from a low of 2 individuals/m in 

 areas with no measurable organic carbon to 

 a high of 45/m- in 1.5 to 1.9% organic car- 

 bon. The first peak (20/m 2 ) occurred in 

 levels of 0.01 to 0.49% and the second in the 

 1.5 to 1.9%; class. No gastropods were found 

 where carbon content was greater than 3%. 



Biomass values ranged from a low of 0.02/ 

 m- in the absence of organic carbon to a 

 high of 10.42 g in- in the 2.00-2.99%, con- 

 tent class. The first peak in moderate biom- 

 ass (3.8 g/m'-') occurred at levels of 0.01- 

 0.49%. Biomass decreased significantly be- 

 tween 0.50 to 1.99% levels and rose dramati- 

 cally to highest recorded biomass in the high- 

 est levels in which they were found. 



Frequency of occurrence ranged from 20 to 61% of the 

 samples (Table 30). Lowest occurrence occurred at both 

 extremes of carbon content, whereas fairly uniform occur- 

 rence occurred in the other content classes. 



Bivalvia — Bivalvia were inordinately dominant in terms 

 of wet weight, contributing 44.1% of the total biomass 



of the New England marine benthic fauna. In terms of 

 number of individuals they provided 10.8% of the total 

 (Table 3). Weight determinations included shells (see 

 "Material and Methods"), but even if shells were ex- 

 cluded from weight measurements, the Bivalvia would 

 still rank first in biomass. In number of individuals they 

 rank third, after Amphipoda and Annelida. 



