Biota 



We recorded 145 invertebrate species represent- 

 ing nine phyla in the study area (Appendix Table 3). 

 Our preliminary analysis of the species composition 

 at all stations (Appendix Table 4) indicates that the 

 benthic fauna in the survey area can be separated 

 into at least two distinct assemblages. Two of these 

 assemblages show a strong association with sedi- 

 ment types (medium to coarse sand and fine sand 

 mixed with silt) as well as with depth. A third as- 

 semblage dominated by apparently unattached 

 clumps of the blue mussel, Mytilus edulis, was col- 

 lected on both mud and hard sand sediments and 

 showed no particular association with sediment 

 type. 



The medium sand assemblage. — This assem- 

 blage was found at all stations except B6 and B7. 

 The dominant organisms were the bivalve, Tellina 

 agilis; the burrowing amphipod, Protohaustorius 

 deichmannae; the sand dollar, Echinarachius 

 parma; the tube-dwelling amphipod, Unciola ir- 

 rorata; and the surf clam, Spisula solidissima. 

 Other invertebrates commonly collected as part of 

 this assemblage were the cumacean, Leptocuma 

 minor; the amphipods, Acanthohaustorius millsi, 

 Trichophoxus epistomus, and Monoculodes ed- 

 wardsi; and the polychaetes, Sthenelais limicola, 

 Lumbrineris fragilis, and Spiophanes bombyx. 



The mean number of organisms collected from the 

 medium sand sediment ranged from 49 animals/m 2 , 

 Station El, to 2,030 animals/m 2 , Station E3 (Appen- 

 dix Table 5). The total number of species generally 

 increased with depth from a low of 1 1 at Station El to 

 a high of 54 at Station D5 (Appendix Table 5). 



The fine silty sand assemblage. — This assem- 

 blage was evident offshore mainly at Stations B6 

 and B7 and occasionally at the offshore stations of 

 the D, E, and G transects. The dominant or- 

 ganisms were the bivalve, Nucula proximo, and 

 the polychaete, Nephtys incisa, with other 

 polychaetes, Pherusa affinis and Clymenella tor- 

 quata, and the amphipod, Leptocheirus pinguis, 

 also abundant. The average density at Station B7, 

 the only station not transitional with the medium 

 sand assemblage, was 1,440 animals/m 2 (Appendix 

 Table 5). A total of 50 species were collected from 

 this station (Appendix Table 5). 



Aggregations of Mytilus edulis. — Clumps of 

 blue mussels unattached to a substratum, were 

 found on Stations Al, A2, and A5 during June 

 through September (Appendix Table 4). These 

 clumps consisted of variable size mussels from 1 to 

 5 cm in length; the 1 -cm-size group included ap- 

 proximately 95% of all individuals. These clumps 

 were situated on a medium to coarse sand bottom; a 

 solid substrate, usually necessary for Mytilus 

 attachment and development, was absent. Com- 

 monly found within the Mytilus clumps were the 

 polychaetes, Harmothoe extenuata, H. imbricata, 

 Nereis succinea, and Lepidonatus squamatus. The 

 brachyuran crab, Neopanope texana, and the 

 anemone, Metridium senile, were also abundant. 

 The fauna in the sand underlying the clumps was 

 typical of the Tellina-Protohaustorius-Echinar- 

 achnius medium-sand assemblage. Where these 

 clumps originated is unknown. They may have been 

 broken away by storm surges from mussel beds that 

 are known to be nearby. It is possible that our sam- 

 pling in the spring and fall missed the clumps which 

 are present throughout the year. 



DISCUSSION 



It is apparent from Appendix Tables 4 and 5 that 

 the relative abundance and diversity of species vary. 

 In general, an increase in total numbers of species 

 collected per station is directly related to an increase 

 in water depth. For example, the average total 

 number of species collected on the 11 stations in less 

 than 10 m in depth was 20.8 species, on the 21 sta- 

 tions between 10 and 20 m. the average total was 

 27.9 species, and on the 7 stations in water greater 

 than 20 m the average total was 45.7 species. No 

 correlation between total number of organisms col- 

 lected and depth could be detected. Many of the 

 most abundant species appear to be distributed con- 

 tagiously (Fager, 1966) on the bottom, especially: 

 Unciola irrorata, Echinarachnius parma, 

 Spiophanes bombyx, and Spisula solidissima. It is 

 possible that this contagion is the result of inade- 

 quate sampling. 



The fine silty sand assemblage, dominated by 

 Nucula proximo and Nephtys incisa, is similar to the 

 soft bottom community in Buzzards Bay, Mass., 

 and Long Island Sound (Sanders, 1956, 1958). San- 

 ders reported that Nucula proximo and Nephtys in- 

 cisa made up 57% and 17% respectively of the total 

 number of organisms collected in Buzzards Bay. At 



