SOME EFFECTS OF DREDGING ON POPULATIONS 

 OF MACROBENTHIC ORGANISMS 



Eugene H. Kaplan/ J. R. Welker,^ and M. Gayle Kraus^ 



ABSTRACT 



Populations of epi- and infauna were studied from 10 mo before to 11 mo after a navigation channel 

 was dredged through a small, shallow lagoon. A new sampler which jjenetrated 20-30 cm into the 

 substratum was used. 



Current velocities and sedimentation patterns were changed due to an altered distribution of tidal 

 currents, although flushing time was not appreciably altered. 



Values of certain particulate and dissolved nutrients changed after dredging, but no correlation 

 was observed between animal populations and fluctuations in nutrients. 



Significant reductions in standing crop figures and species and specimen numbers occurred in both 

 the bay and the dredged channel. Mercenaria mercenaria populations were reduced, but there was 

 no evidence of mass mortality. Recovery of biomass in the channel was affected by sediment 

 composition, but seasonal and sediment type variations were not significant in the bay as a whole. 



Goose Creek had a high predredging epi- and infaunal standing crop estimated at 36.83 g/m^, but 

 the number of organisms/m^ was relatively low, indicating a preponderance of large forms. 



Productivity of Goose Creek was calculated at 89.87 g/m^/yr before dredging and 31.18 g/m*/yr after 

 dredging. Productivity figures for the mixed peripheral marsh were calculated and the annual loss 

 due to replacement of 10.87 ha of marsh by spoil areas was estimated at 49,487 kg. Altered 

 land usage patterns tended to fix this loss on a permanent basis. 



The unusually profound effects of dredging reported for Goose Creek are attributed to its small 

 size and shallowness. 



In 1965, Suffolk County, N. Y., obtained the 

 services of a consortium of universities to study 

 the characteristics of a small embayment before 

 and after a channel 22.8 m wide x 2.1 m deep x 

 1,037 m long was dredged from the narrow inlet 

 through most of the bay. The investigations re- 

 ported in this paper are confined to the population 

 dynamics and ecology of the macrobenthic 

 organisms. Reference will be made to the other 

 areas of investigation only as they affect the 

 macrobenthos. 



The following phenomena will be considered in 

 relation to their effects on epi- and infaunal 

 population dynamics: 



1. Changes in the hydrodynamics of Goose 

 Creek as the result of the introduction of the newly 

 dredged channel. 



2. Changes in the morphology of the sediment 

 effected by the dredging process. 



'Biology Department, Hofstra University, Hempstead, NY 

 11550. 



^Institute of Marine Sciences, Southampton College, South- 

 ampton, NY 12837. 



^Zoology Department, University of Rhode Island, Kingston, 

 RI 02881. 



3. Changes in physical and chemical char- 

 acteristics of the water associated with the dredg- 

 ing process. 



4. Changes in populations of macrobenthic 

 organisms which occurred during 1966 and 1967. 



The Study Area 



Goose Creek is a small, shallow lagoon located 

 on the north fork of Long Island in the town of 

 Southold, N. Y. (lat. 41°03'00"N, long. 72°25'23" 

 W). Its dimensions are 1,464 m east-west by 533 m 

 north-south, a total area of about 0.32 km^. A 

 channel approximately 30.5 m wide at the east- 

 ern end opens into Southold Bay, thence into 

 Shelter Island Sound, an arm of Little Peconic 

 Bay (see Figure 1). 



The mean high water depth before dredging was 

 1.7 m, but much of the bay was extremely shallow 

 and at low water it was impossible to navigate 

 even a small boat in the western half of the bay. 

 Mean tidal range was 68.5 cm, and the mean depth 

 at mean low water was 1.0 m. 



The prevailing wind is from the southwest in 



Manuscript accepted September 1973. 

 FISHERY BULLETIN: VOL. 72, NO. 2, 1974. 



445 



