LANGTON and UZMANN: GULF OF MAINE MEGAFAUNA 



categories of megafauna, representing a variety 

 of taxonomic levels, that could be resolved in 

 the photogi'aphs are listed in Appendix Table 2. 

 From one to seven sediment samples, collected 

 on each dive, w^ere analyzed by the U.S. Geo- 

 logical Survey for surficial grain size analysis. 

 The statistical parameters for this analysis were 

 calculated by the method of moments (Krum- 

 bein and Pettijohn 1938), while the average 

 sediment types for each dive were classified and 

 are described using the terminology of Folk 

 (1980). 



RESULTS 



Sediment types are shown in Figure 1 at the 

 29 dive locations. The general sediment pattern, 

 from south to north, is a gradation of coarse to 

 fine sediments. Georges Basin is, generally, 

 sandy along its midsection, changing into a 

 gravelly area towards Truxton Swell. Jordan 

 Basin, which is north of Georges Basin, is domi- 

 nated by finer silts and clays. 



A total of 5,714 color photographs (35 mm 

 slides) were examined from the 29 submersible 

 dives. Over 27,000 individual organisms were 

 counted. The overall taxonomic ranking, based 

 on the percentage of total numbers observed for 

 the top 18 taxonomically distinct groups, is 

 shown in Figin-e 2. These 18 groups represent 

 96% of all the organisms counted. From the 

 figure, it is clear that there are only five nu- 



merically dominant taxa representing two 

 phyla, the Echinodermata and the Cnidaria. 

 Ophiuroidea and Asteroidea are the dominant 

 echinoderms, while ceriantharian anemones, sea 

 pens of the genus Pennatula, and rock (Bolo- 

 cera) anemones account for the dominant 

 cnidarians. 



If the same data are examined on a year and 

 location basis, there are, again, very few domi- 

 nant gi'oups. In addition to the echinoderms and 

 cnidarians observed in all three years, arthro- 

 pods (pandalid shrimp) were reasonably abun- 

 dant in 1984 in the middle Gulf and southern 

 Jordan Basin area, while invertebrate tubes 

 (polychaetes or amphipods) occurred at the sta- 

 tions, visited in 1985, in central Jordan Basin 

 and to the northeast (Table 1). The year and 

 area breakdown, Hke the overall ranking, dem- 

 onstrates a simple picture for the softer sedi- 

 ment megafaunal communities in the Gulf of 

 Maine. Seven taxonomically distinct groups ac- 

 count for 97 to 99% of all the biota observed. 



The relation between sediment type and 

 animal abundance is shown in Figure 3 and de- 

 tailed in Appendix Table 1. Of interest is the 

 substrate specificity of the various gi'oups. Sea 

 pens, Pennatula (most likely P. aculeata, 

 Langton, pers. obs.), occurred in clay and silts 

 as well as gravel. They were, however, most 

 common in silt reaching a maximum density of 

 1.20 animals m ". They occurred in gravel 

 at only 2 stations compared to 10 stations with 



(13 



50 

 40 

 30 

 20 

 10 



# # d-" '^^ 



Overall Taxonomic Ranking 

 N= 27,276 



,5' <? 5 



5* 



<? i" #■' i? ^ ^ 



^"^ # ^ ,.? ^"^ .S' ^ ^ #' # ^- 







„"?• if 



Figure 2. — Overall ta.xonomic ranking, expressed as percentage of the total number 

 of organisms observed (N = 27,276), for 29 submersible dives in the Gulf of Maine 

 from 1983 through 1985. 



947 



