FISHERY BULLETIN: VOL. 72, NO. 2 



The most numerous instances of high infaunal 

 standing-crop production were in areas which cor- 

 respond to the general classification proposed by 

 Sanders (1956), of a relatively high silt-clay 

 composition, although the stations with the 

 highest animal biomass were either somewhat 

 above the 13-25'7c silt-clay level reported as most 

 highly productive, or toward the lower end of 

 the spectrum. Suspension feeders, with the excep- 

 tion of station 2, were not the dominant forms in 

 the sandy sediments of Goose Creek, except in the 

 littoral. Instead, deposit feeding polychaetes were 

 numerically dominant and often constituted the 

 major weight factor in the biomass. Further- 

 more, if Mercenaria andSclerodactyla are grouped 

 together (Sanders, 1956), the biomass of suspen- 

 sion feeders predominates in high silt-clay regions. 

 An important Ampelisca community was not 

 found. 



The Effects of Dredging on the 

 Substratum and Its Fauna 



Three major categories of environmental dis- 

 turbance brought about by dredging are: 



1. Immediate effects, during and directly after 

 the dredging, including suffocation of benthic ani- 

 mals by siltation; flocculation and removal from 

 the water column of planktonic organisms (which 

 affects benthic filter feeders by removing their 

 source of food); and changes in water chemistry, 

 as substances are released from the substratum 

 and dissolved. Large quantities of bottom mater- 

 ials placed in suspension by the dredging process 

 decrease light penetration, change the propor- 

 tion of wavelengths of light reaching the plants 

 and interfere with the food-getting processes of 

 filter feeders by inundating them with wrong size 

 or nonnutritive particles. 



On the other hand, the release of nutrients into 

 the water profoundly affects the composition of 

 the plankton by favoring the growth of some 

 species. This effect could be beneficial or harmful 

 depending on whether or not the plankton bloom 

 is utilized by the filter feeders. If nannoplankton 

 like Nannochloris and Stichococcus, which have 

 been incriminated in mass mortalities of Mer- 

 cenaria, are the dominant forms in the bloom, 

 selective removal of certain species of filter- 

 feeders could be expected. 



2. Transitory or semipermanent effects such 

 as the mechanical removal of the benthos from the 



dredged area and a change in the nature of the 

 substratum by the deposition of spoil. These 

 changes may be temporary, as the dredged area 

 is recolonized or tidal currents reestablish the 

 original substratum composition by scouring 

 away fine particles and reestablishing old chan- 

 nels, or depositing fine sediment over exposed, 

 sandy areas. 



Recolonization of areas denuded of organisms 

 has been studied under either artificially induced 

 conditions or as the result of major disturbances 

 such as oil spillage. Reestablishment of the 

 original fauna is estimated to take at least 

 8 yr in the intertidal zone, as reported by 

 Castenholz (1967) and by North (1967). Clarke 

 and Neushul ( 1967:47) give some insight into the 

 complexity of the recolonization process when 

 they report: "Apparently a barnacle stage had to 

 be established before the surface of the rock was 

 suitable for the larval stages ofMytilus to become 

 established." In their study it took 4 yr for the 

 reestablishment of small Mytilus californianus 

 colonies. 



In the aforementioned works the environment 

 was not fundamentally changed by the conditions 

 leading to defaunation, namely, storms, oil spil- 

 lage, or artificial removal of the organisms from 

 the substratum. 



If a rock has been manually denuded of 

 organisms, natural succession can begin imme- 

 diately. In the case of dredging, however, the 

 substratum may remain unstable for a con- 

 siderable time and final recolonization cannot 

 begin until the climax substratum is reestab- 

 lished. 



3. Permanent changes in the ecology brought 

 about by dredging occur if the ambient flow of 

 water and current distribution patterns are dis- 

 rupted. One of the results of dredging was the 

 reapportionment of maximum water transport 

 into Goose Creek from channel A to channel B. 

 Furthermore, the current velocity in all three 

 channels dropped because of the enlarged capacity 

 of the dredged channel for containing water, 

 since it was approximately three times deeper 

 than the channel it replaced. A different dis- 

 tribution pattern of silt and other fine particles 

 occurred as the result of lowered current veloci- 

 ties which resulted in sediment changes in a sub- 

 stantial portion of the bay. 



Spoil deposition on the surrounding marshes 

 has a profound effect on the species composition 



472 



