Composition and Distribution of Macrobenthic Invertebrate Fauna 



71 



(gravel, till, and shell) than in those composed 

 of fine particles (Tables 16-20; Fig. 30). Also, 

 the proportion of samples containing Porifera 

 was higher for the coarse than the fine sub- 

 strates. Till contained the highest density of 

 specimens, the greatest weight, and highest fre- 

 quency of occurrence. Gravel ranked second 

 in number and shell ranked second in weight. 

 Sand contained intermediate quantities, and 

 sand-silt and silt-clay contained the smallest 

 quantities. 



Relation to Water Temperature 

 Porifera were generally most numerous in ar- 

 eas where the annual range in bottom water 

 temperature was moderate — 4° to 12°C (Tables 

 21-25; Fig. 31 ). Where the annual temperature 

 excursions were less than 4° or greater than 

 12°C the average biomass was markedly lower 

 than at midrange. The frequency of occurrence 

 was highest (15%) in those samples from lo- 

 calities in which the seasonal changes in tem- 

 perature were between 4° and 8°C. 



Two other aspects of the relative density of 

 Porifera and bottom water temperature th.it 

 were examined, but not tabulated or illustrated 

 here, concern annual maximum and annual 

 minimum temperature. Sponges were more 

 plentiful (2 to 7 g/m 2 ) in areas where the maxi- 

 mum temperature was moderate, between 6° 

 and 12°C; they were scarce (<1 g/m-') where 

 the maximum temperature remained below 6° 

 or rose above 12°C. Porifera were abundant 

 (>4 g/m 2 ) where the minimum temperature 

 was low (0° to 3.9°C) and scarce (<1 g/m 2 ) 

 where the minimum temperature was high. 



Relation to Sediment Organic Carbon 

 Porifera were found only where sediments con- 

 tained low to moderate (0.01 to 1.99%) amounts 

 of organic carbon (Tables 26-30; Fig. 32). Both 

 mean density and biomass diminished with in- 

 creasing organic carbon content. Density 

 ranged from 3 to 0.2/m 2 , and biomass from 5 

 to <0.01 g/m 2 . 



Ui IE 3 



CD < 



z => 



Z CO 



□ NUMBER 

 ■ WEIGHT 



I 



n n 



I~L 



n- 



I" 



? (E 



bj O 



GEORGES SOUTHERN GEORGES SOUTHERN 

 BAN" NEW ENGLAND SLOPE NEW ENGLAND 

 SHELF SLOPE 



GEOGRAPHIC AREA 



Figure 28 



Density and biomass of Porifera in each of the six geographic 

 areas. 



Coelenterata 



The macrobenthic coelenterate fauna of the New En- 

 gland region is composed of members of two classes: 

 Hvdrozoa and Anthozoa. Hydrozoa are treated at the 

 class level, whereas Anthozoa. composed of members 

 from seven orders contained in two subclasses, are dis- 

 cussed at the subclass levels: Alcvonaria and Zoantharia. 



No discussions are included at the taxonomic levels 

 Coelenterata or Anthozoa; however, the interested 

 reader will find summary data, for all treated para- 

 meters, for those taxonomic levels in Tables 5-30. 



Hydrozoa — Hydrozoans were common in parts of the 

 New England region, but their limited occurrence and 

 moderately small size severely restricted their contribu- 

 tion to the total biomass. They made up less than 1% of 



