Composition and Distribution of Macrobenthic Invertebrate Fauna 



19 



Faunal Composition 



The macrobenthic invertebrate fauna of the 

 New England region is moderate in variety. 

 A modest number of species (567 in the 

 present study) , in combination with a graded 

 abundance of individuals composed of a va- 

 rietv of dominants and codominants, is char- 

 acteristic of the fauna, and is generally typi- 

 cal of Boreal-Temperate faunal assemblages. 



Taxa reported on in this study represent 13 

 phyla and 28 lesser groups such as subphyla, 

 classes, subclasses, and orders. The majority of 

 species are Boreal forms, followed closely in 

 abundance by Virginian (or warm-temperate) 

 forms. Additionally, there is a small contingent of 

 Arctic and Subarctic species, particularly in 

 the Gulf of Maine. Also, a few tropical and 

 subtropical species occur chiefly in the South- 

 ern New England and Georges Bank areas. 



The ecological importance of these 

 groups, judged primarily from their numeri- 

 cal abundance and biomass, ranges from 

 minor (components that account for less 

 than 0.1% in number of individuals and bio- 

 mass) to dominant components that make 

 up 20% or more in number of individuals or 

 biomass. The 44 major taxonomic groups, 

 with the percentage of total number of indi- 

 viduals and percentage of total biomass for 

 each, are listed in Table 3. Also, they are classi- 

 fied into four dominance categories, I to IV. 



Over 80% of both the biomass and num- 

 ber of individuals in the macrobenthos is 

 formed by only five taxonomic groups. These 

 are classified in dominance category I in 

 Table 3. Bivalvia is the dominant contribu- 

 tor (44.1%) to the biomass and is also a 

 major component (10.8%) in terms of num- 

 bers of individuals. Amphipoda, on the other 

 hand, is numerically dominant (43.4%) but 

 contributes only 2.3% of the biomass. Con- 

 versely, Echinoidea and Holothuroidea are 

 important components of the biomass, but 

 are numerically sparse. Annelida is a major 

 contributor in both measures of quantity. 



Category II, in Table 3, consists of eight 

 taxa that contribute moderate biomass (1.2 

 to 2.3% of the total fauna) and number of individuals 

 ( 1.0 to 2.9% of the total fauna). Categories III and IV 

 contain those taxa that contribute small to very small 

 quantities to the total biomass and density. 



The New r England region macrobenthos is dominated 

 by members of four phyla: Annelida, Mollusca, Arthro- 

 poda, and Echinodermata. These groups will be dis- 



cussed in more detail in the following sections. Table 4 

 lists the components of the macrobenthic invertebrate 

 fauna inhabiting the New England region, and Table 5 

 lists the quantitative measures of abundance (mean 

 and total weights and numbers per square meter), num- 

 ber of samples, and frequency of occurrence for each 

 taxonomic group considered in this report. 



