KAPLAN, WELKER, and KRAUS: EFFECTS OF DREDGING 



Table 15. — Number of species found at stations 2-12, 14-19, 

 22, 23 on June 1967 and June 1968. 



June 1968 



5 



5 



17 



3 (4/68) 



13 

 13 



5 

 5 



6 



4 (4/68) 

 



3 

 1 

 7 

 3 

 1 



Table 16.— Chi-square analysis of the number of species before 

 and after dredging, as a function of sediment type. Stations 

 2-25; 2-25 and A-J, M; channel stations A-J, M. 



Table 17.— Chi-square analyses of number of organisms before 

 and after dredging, stations 2-21, 23; 2-21, 23 plus A-J, M; 

 stations A-J, M only. 



Table 18. — Chi-square analysis of the number of organisms 

 before and after dredging as a function of sediment type, 

 stations 2-25; 2-25 plus A-J, M; stations A-J, M. 



Similar chi-square analyses were performed 

 using number of individuals at all stations. Here 



results were even more positive. For example, 

 the pre-dredging number of specimens at station 

 2 was 6,682; the post-dredging number was 27. 

 Five out of 30 stations, or 16.6%, showed post- 

 dredging increases in population; the others 

 experienced drastic decreases. 



Table 17 is a summary of the chi-square 

 analysis of the number of individuals before and 

 after dredging. The difference in specimen num- 

 bers was highly significant in both the bay as a 

 whole and in the channel. 



Chi-square analyses were made on the number 

 of specimens before and after dredging as a func- 

 tion of sediment type. In both the bay as a whole 

 and the channel the number of specimens was 

 significantly different (0.005) in the post-dredging 

 samples, according to sediment types (Table 18). 



In summary, the numbers of species and 

 organisms differed significantly before and after 

 dredging, in the bay as a whole, as well as in 

 the channel. Additional data show that this 

 difference was in the direction of a post-dredging 

 reduction in both species diversity and number of 

 individuals found at each station. A few stations 

 showed apparent recovery by June 1968, 11 mo 

 after dredging. These were invariably low-popula- 

 tion stations in the mud-silt region of the bay, 

 where a few influents could appreciably change 

 the population size. Stations 2-11, the sand, 

 muddy sand, sandy mud stations, had drastic 

 reductions in both parameters. Table 19 provides 

 further substantiation for this conclusion. 



Standing Crop Estimates 



A total of 137 species was taken from the sedi- 

 ment of Goose Creek during the 22 mo of the 

 study. Maximum wet weight at any one sta- 

 tion was 2,581.4 g/m^, with a corresponding dry 

 weight of 355.6 g/m^. Mean dry weight before 

 dredging (excluding the channel) was 36.8 g/m^ 

 (49.6 g/m^ including the channel) while the cor- 

 responding weight after dredging was 12.7 g/m^ 

 (10.1 g/m^ including the channel), a loss of 

 63% of dry weight. The loss, including the channel, 

 was 79%. (Pfitzenmeyer, 1970, reported a loss of 

 64% in his spoil deposition area and 72% in 

 the channel.) 



The mean number of species per station (sta- 

 tions 2-24 minus the four intertidal stations) was 

 5.47 (54.7/m2) before dredging and 4.02 (40.20/m2) 

 after dredging, a reduction of 26%. 



463 



