KAPLAN, WELKER, and KRAUS: EFFECTS OF DREDGING 



For data reported on the basis of the 0.2 g 

 dry weight cut-off point, it is sufficient, in many 

 cases, to add the factor suggested by Holme when 

 he points out that 64.4% of the dry weight of his 

 samples was excluded by the 0.2 g point, in order 

 to bring the data to comparable levels. 



Factors relevant in an explanation of the 

 relatively high standing crop in Goose Creek are: 



1. None of the studies referred to sampled to a 

 depth beyond 22 cm, and most examined only 

 the top 6-10 cm of sediment. Deeper-dwelling, 

 large forms were excluded. 



2. Virtually all of the investigations previously 

 referred to examined relatively large, slow cur- 

 rent velocity, deep bodies of water with relatively 

 unvarying bottom sediments, such as Chesapeake 

 Bay. Often the populations described comprise 

 mud-silt or silt-clay communities, such as the 

 Ampelisca community described by Stickney and 

 Stringer (1957). It is well known that this 

 sediment is not highly productive of biomass 

 since most organisms are relegated to the upper 

 few centimeters where gaseous exchange is most 

 rapid (cf Raymont, 1950; Sanders, 1956; Holme, 

 1953; Pfitzenmeyer, 1970). In Goose Creek the 

 high current velocity over a substantial portion of 

 the bay and the diversity of sediment types sup- 

 ported sizeable populations of large organisms, 

 such as the 3,470 C. fornicata found in one 

 dredge haul at station 2. 



3. Phytoplankton production is high. Cassin 

 (1968) studied the phytoplankton cycle in Goose 

 Creek during the year before dredging, and found 

 a mean standing crop of 1.64 x 10^ cells/liter. 

 This was lower than that for Long Island Sound 

 (2.38 X 106 cells/liter; Conover, 1952), but 

 considerably higher than those for Block Island 

 Sound and Vineyard Sound. According to Riley 

 (1955), the mean standing crop of phytoplankton 

 in the English Channel is one-quarter that of 

 Long Island Sound; while Flemer (1970) makes a 

 primary production estimate for Upper Chesa- 

 peake Bay at one-fifth of that estimated by Riley 

 for Long Island Sound. Phytoplankton population 

 size appears to vary with benthic standing crop 

 in the studies mentioned above. 



Population Dynamics and Distribution 

 of Organisms 



Most of the dominant and subdominant organ- 

 isms found in the channel before dredging were 



present in greatly reduced numbers after dredg- 

 ing (Kaplan, Welker, and Kraus, in press-b). 

 Three species of mollusc increased in numbers 

 after dredging. Tellina agilis and Lyonsia hyalina 

 increased in sandy sediments while Mulinia 

 lateralis became more abundant in the finer 

 substrata. Two polychaetes, Notomastus later- 

 iceus and Clymenella torquata, abundant before 

 dredging, virtually disappeared afterwards. 

 O'Connor (1972) noted an increase in popula- 

 tions of Mulinia lateralis and Tellina agilis in 

 his study of Moriches Bay. He suggests that 

 M. lateralis is a fast-growing, short-lived species 

 that is more successful in silt. If this is so, it 

 may be suited as an indicator organism which 

 would rapidly increase in numbers in areas where 

 dredged channels cause decreased current veloc- 

 ity and, consequently, invasion of sandy areas 

 by softer sediments. 



The channel data were not duplicated in the 

 bay as a whole. The most fundamental difference 

 between the two areas was the fact that the 

 substratum and all its infauna were removed in 

 the channel study, while only stations 2 and 3 

 in the bay study were directly in the path of the 

 dredge. Consequently, the drastic effects of the 

 removal of the habitat were limited, and the 

 reduced population size throughout the bay must 

 be a concomitant of other long-term variables, 

 such as changes in current velocity and anoxia 

 resulting from siltation. Stations 22, 23, and 5 

 were particularly susceptible to this latter in- 

 fluence, being near spoil areas. Portions of Thyone 

 Cove were inundated when the spoil gate broke 

 during the dredging operation. In addition, sta- 

 tion 23 was in the path of the 1968 dredging of 

 an extension of the navigation channel through 

 Thyone Cove. 



Most stations, even those in the farthest 

 reaches of the bay, showed reductions in benthic 

 populations; however, no station was farther than 

 500 m from the dredge at some time during the 

 operation, except for station 25. Figure 12 depicts 

 the changes in population densities of 13 domi- 

 nant and subdominant benthic organisms before 

 and after dredging. In addition, the abscissa of 

 each histogram represents the sediment type, 

 from the gravel of station 2 to the silt of station 23. 



Clymenella torquata, the nearly ubiquitous 

 bamboo worm, was the numerical dominant in 

 the sandy substrata, forming dense colonies. 

 Notomastus latericeus shared this habitat, though 

 in reduced numbers. Both species of worm 



465 



