KAPLAN, WELKER, and KRAUS: EFFECTS OF DREDGING 



showed substantial reductions in density in the 

 post-dredging samples. Spio setosa, another 

 inhabitant of sandy substrata, seems to have 

 maintained its population size, with 50% of the 

 stations recording increases in the number of 

 specimens.'^ 



Capitella capitata and Polydora ligni, inhabi- 

 tants of sandy mud, also decreased in number. 

 Nereis areonodacea was found in muddy sand in 

 small numbers, whileNereis succinea was present 

 in densities up to 42/in^ in the sandy mud and 

 silt stations, which were also frequented by 

 Mercenaria mercenaria. Modest reductions in the 

 Nereis and Mercenaria populations occurred after 

 dredging. 



Mya arenaria was found in sand and muddy 

 sand. Certain areas experienced drastic reduc- 

 tions in the densities of these organisms, but since 

 most of the Mya recorded were juveniles, popula- 

 tion fluctuations independent of dredging may 

 have been an important factor. Factors favorable 

 to larval settling and the growth of juveniles 

 may have been unsuited to their sustenance as 

 adults, resulting in mass mortality of juveniles at 

 critical points in their development. 



Of the epifauna, Neopanope texana sayi was 

 found in greatest abundance in the high current 

 velocity, stony gravel of station 2. It was also 

 abundant in the muddy sand of station 8 and the 

 silt of stations 16, 18 and 22. It was recovered in 

 five of the samples at station 16 and four at station 

 18, so it is unlikely that the presence of this crab 

 in the silt regions was accidental. Neopanope 

 texana sayi experienced a reduction in population 

 density after dredging. 



Crepidulafornicata was found in large numbers 

 (3,470 in one haul) at station 2 before dredging,- 

 but since this station was in the channel, it was 

 decimated by the dredge and no recovery was 

 noted in the 11 mo period after dredging. Crepi- 

 dula broods its young; recovery would be expected 

 to be relatively slow in a decimated area as 

 dispersal is not accomplished by free-swimming 

 larvae. 



Four species of Caridean shrimp were abundant 

 on the silt substratum of Goose Creek. These were 



■'The reader should be cautioned in interpreting the fluctua- 

 tions in population densities on these graphs. Although each 

 column represents six pre-dredging or six post-dredging 

 samples, the distribution of organisms was so patchy that 

 accumulating the data and recording means still does not 

 compensate for possible sampling error as the corer penetrated 

 a worm colony one month and sampled a relatively sterile 

 area 1 m away from it the next. Trends, however, are apparent. 



Hippolyte pleurancanthus , Crangon septimspino- 

 sus, Palaemonetes vulgaris, and P. pugio. Their 

 numbers fluctuated seasonally and from station to 

 station, possibly reflecting sampling error in- 

 herent in using the cumbersome corers to capture 

 these relatively rapidly moving organisms. There 

 were population decreases at most stations. 



The snail, Hydrobia totteni, was most common 

 in the sandier sediments, especially at stations 

 3 and 7 which had substantial current velocities. 

 Its post-dredging density was considerably re- 

 duced from pre-dredging levels. 



Mulinia lateralis was found to be more abun- 

 dant in the channel after dredging than before. 

 Too few were encountered in the bay study 

 to corroborate this finding. 



The polychaete Maldanopsis elongata was 

 found only at station 11 in virtually all samples, 

 reaching a density of 60/m2. Its population size 

 was maintained after dredging. 



The holothurian Sclerodactyla ( = Thyone) 

 hriaerius was common in the silt stations 12-22, 

 reaching a density of QOIva^ in the deep silt of 

 station 22. The mean numbers at station 22 were 

 33/m2 before dredging and 2lxn^ after 

 dredging, reflecting, perhaps, the close proximity 

 of this station to the spoil gate of spoil area C. 

 Sclerodactyla briaerius experienced declines at 

 five of the six stations at which it was recorded 

 in substantial numbers. 



The tunicate, Molgula manhattanensis , was 

 common on the Enterornorpha which covered the 

 silt at stations 22, 23, and 24, reaching a con- 

 centration of 590/m2 in December 1966 at station 

 23 and declining in numbers after dredging at 

 all three stations. 



An amphipod community, similar to those 

 described by Stickney and Stringer (1957) and 

 Rhoades and Young (1970), occurred in the silt 

 west of station 12. The most abundant species 

 were identified as Ampelisca macrocephala and A. 

 spinipes. Maximum abundance recorded for sta- 

 tions 16, 17, and 18 was 310, 490, and 190/m2, 

 considerably lower than the level of 10,000 m^ 

 mentioned by Stickney and Stringer for Green- 

 wich Bay. The 1.4 mm sieve size used in this 

 study contrasts with the practice used by Stickney 

 and Stringer of examining the fine sediments 

 completely, using no sieve. However, it seems 

 unlikely that population densities would be 

 comparable, since there was no massive concen- 

 tration of amphipod tubes in the Goose Creek 



467 



