Composition and Distribution of Macrobenthic Invertebrate Fauna 



91 



biomass (0.44 g/irr) occurred where organic 

 carbon ranged from 1.5 to 2%, declined at 

 higher and moderately lower levels, and 

 showed another somewhat lower peak (0.8 g/ 

 m 2 ) at levels between 0.01 and 1%. Intermedi- 

 ate biomass occurred where carbon was absent. 

 Frequency of occurrence of nemertines in 

 samples also exhibited a generally negative 

 correlation with organic carbon content 

 (Table 30). In areas with measurable amounts 

 of carbon (between 0.01 and 3%), occurrence 

 diminished from 46 to 15%. In areas with no 

 measurable amounts, occurrence was moder- 

 ately high (40%). 



Aschelminthes 



Nematoda — Free-living nematodes, members 

 of the phvlum Aschelminthes, are one of the 

 most numerous animal groups inhabiting the 

 bottom sediments of the northeastern coast 

 of the United States. Previous studies con- 

 ducted by Wieser (1960) in shallow coastal 

 habitats off southeastern Massachusetts re- 

 vealed nematode densities of nearly 800.000 

 individuals/m 2 . Farther offshore, on the 

 southeastern coast of Massachusetts at a depth 

 of 58 m, Wigley and Mclntyre (1964) encoun- 

 tered nematodes in densities of nearly 1 mil- 

 lion individuals/m , and this measure did not 

 include the young stages of numerous spe- 

 cies. The vast majority of free-living nema- 

 todes are very small, less than 1 or 2 mm in 

 length; consequently only a small portion (the 

 large specimens) of the total population was 

 recovered and treated in the present study. 

 The bulk of the captured specimens were 

 between 0.5 and 2 cm long; however, a small 

 proportion of both larger and smaller speci- 

 mens was represented. In addition to their 

 great numerical density, this group of ani- 

 mals is also exceedingly profuse in species 

 composition. 



Three types of feeding habits are commonly 

 found among free-living nematodes. Some 

 are saprophagous, feeding on detritus and 

 dead and decaying animal material; others 

 are herbivorous, feeding on green plants, par- 

 ticularly diatoms; still others are carnivorous, 

 ingesting rotifers, tardigrades, small annelids, 

 other nematodes, and bryozoans. 



Because of the incomplete representation 

 group, the quantitative distribution discussed 

 refers only to the exceptionally large species. 



00 .1 



5 3 



3 O 



Z CO 



* cr 

 < 



h- 3 



GRAVEL TILL SMELL SAND SAND SILT- 



SILT CLAY 



BOTTOM SEDIMENTS 



Figure 60 



Density and biomass <>1 Nemertea in relation to bottom 

 sediments. 



cr lu 



u a 



00 < 



Z 3 



3 O 



z en 



O O NUMBER 



• • WEIGHT 



0-39 3-79 e-119 12-159 16 199 20-239 



ANNUAL RANGE IN BOTTOM WATER TEMPERATURE 



IN DEGREES CELSIUS 



Figure 61 



Density and biomass of Nemertea in relation to the annual range 

 of bottom water temperature. 



of this We found nematodes in 98 samples (9% of total); 



herein their density averaged 2.8/m 2 , and the biomass aver- 



aged 0.01 g/irr (Table 5). 



