THE EFFECT OF PLANT MATERIAL ON A BENTHIC COMMUNITY OF THE 



BERMUDA CONTINENTAL SLOPE 



J. Frederick Grassle 1 , Paul V. R. Snelgrove 1 , 

 James R. Weinberg , and Robert B. Whitlatch^ 



1 - Woods Hole Oceanographic Institution 

 2 - University of Connecticut 



ABSTRACT 



Aggregations of organic material have been shown to be 

 important in determining the composition of deep-sea benthic 

 communities on the continental margin. Using the submersible 

 Pisces , a bottom station was established on the continental 

 slope northwest of Bermuda. Sargassum seaweed collected from 

 surface waters near Bermuda was placed in the sediments to 

 determine the effect of this organic addition on the bottom 

 community. In a period of 37 days the addition of Sargassum 

 resulted in sharp population increases of several relatively 

 opportunistic benthic species. 



INTRODUCTION 



The small invertebrate fauna of the deep-sea floor rivals 

 rain forest insect faunas in the number of species found in each 

 local collection (Grassle and Maciolek in prep.). The complex 

 patterns of biogenic structures (such as burrows, stalks and 

 tubes) and uneven distribution of organic material settling from 

 the water column introduce the temporal and spatial 

 heterogeneities required to maintain a large number of species. 

 The surface of deep-sea sediments is uneven ( from activities of 

 organisms as well as geologic processes) and the flow of water 

 over shallow depressions and burrows ensures a patchy 

 distribution of organic particles settling to the bottom. In 

 contrast to continental shelves and coastal embayments, the 

 bottom sediments are not homogenized by storm waves or intense 

 currents in most deep-sea areas. In these circumstances sediment 

 structures can last for more than a single generation of even the 

 most long-lived deep-sea species. 



Despite the complexity of seafloor habitats, it is a 

 relatively easy environment in which to conduct experiments in 

 situ. This is because each treatment is a single event, unlikely 

 to be confounded by fluctuations in the physical environment. 

 Dead carcasses of nektonic organisms, clumps of Sargassum weed, 

 and gelatinous clumps of salp bodies from surface blooms produce 

 sharp changes in the abundance of benthic organisms (Grassle and 

 Morse-Porteous 1987). Because of the need for precise placement 

 of samples within and outside experimental treatments, the 



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