particles adhering to the exterior of an amphipod, Acan- 

 thohaustorius intermedius, from sample 7-1 and missing but healed 

 appendages in other amphipods. 



Benthk assemblages present at the site.— It is useful to group 

 samples according to their faunal composition to aid in recognizing 

 deviations from the norm and in interpreting the effects of the 

 physical environment or fauna. 



The most striking fauna! assemblage in these samples is that 

 associated with mussel beds (5-1, 5-2, 5-3, 7-2). This includes two 

 species of scale worms, epifaunal amphipods, and a number of 

 deposit-feeding polychaetes (species of Tharyx, Polycirrus, 

 Aricidea, Capitelia). Capitella capitata is often used on an indicator 

 of organic pollution. I find it present in mussel biodeposits in 

 Rhode Island in the winter, presumably responding to the presence 

 of organic sediments rather than pollutants. 



Stations outside Watch Hill Reef (2, 8, 17) were characterized 

 by species adapted for unstable sandy bottoms. These species which 

 are widespread in Block Island Sound and the nearshore con- 

 tinental shelf included shallow-burrowing bivalves, free-burrowing 

 amphipods (haustorids and phoxocephalids), a tube-dwelling 

 amphipod (Byblis sp.), and free-burrowing nepthid polychaetes and 

 nemertine worms. 



The most numerous species in the coarse sand and gravel at 

 station 7 were interstitial sillid polychaetes. 



Station 6 had such low numbers of species and individuals that 

 dominants cannot be identified. This poverty of fauna can be con- 

 trasted with the abundant fauna at station 5 which is at similar 

 depths 0.8 km to the west, but which was colonized by blue 

 mussels. 



Some background data on benthic fauna exists for areas adja- 

 cent to the spill site. Biembaum (1975) examined amphipods at sta- 

 tions off Napatree Point and south of Fishers Island East Point. His 

 samples were large, and he recovered a total of 28 amphipod species 

 from these stations. These appear to be distinct seasonal groups in 

 his collections. Epifaunal and free-burrowing species were found in 

 the winter, and tube builders were found in the summer. This sug- 

 gests a response to sediment stability. The amphipods found in the 

 spill samples are the same species found in Biernbaum's winter 

 samples. 



East Hole, a depression southeast of Fishers Island 37-55 m 

 deep, was studied in detail by Steimle et al. (1976)." The presence 

 of a diverse and productive assemblage of tube-dwelling amphipods 

 there illustrates the negative effects of wave exposure on the level 

 bottom benthos in the spill area. It is assumed that depth provides 

 some protection from spills such as this because of the greater 

 volume of water with which water soluble components have to mix 

 and the greater distance that buoyant droplets would have to be 

 vertically advected. 



With the exception of blue mussels, the amphipod Byblis sp., 

 and a number of small bivalves, most of the dominant infaunal 

 species in the spill area are deposit feeders. Since all feeding types 

 are exposed to water soluble gasoline fractions through respiratory 

 currents, there may be no reason to expect differential effects from 

 a spill of this type. 



Very few predators or scavengers were recovered in these 

 samples and so no projections of food web effects can be made. 



The northward range of the polychaete Pisone remota has 

 been extended from Delaware Bay to Rhode Island by its occur- 

 rence at station 17. 



Condition of benthic assemblages. — In studies of stressed en- 

 vironments it has been found that there are changes in the density 

 and diversity of benthic fauna and that sensitive species are replaced 

 by more resistant ones. This type of change was not expected at the 

 Watch Hill Reef site because of the limited duration of gasoline ex- 

 posure. It is possible, however, that a study of infauna data would 

 show that one or more species was absent where expected either due 

 to mortality or escape to the surface. 



No examples of such defaunation are detectable from the data 

 of this study. Where species were abundant enough to be sampled 

 adequately, densities are similar in samples from similar habitats. 

 The samples with very low numbers of animals were small in 

 volume and came from areas of sediment instability. 



Crustaceans have been identified as especially sensitive to 

 hydrocarbon toxicity, but there are no samples in which this group 

 is obviously reduced. 



Adequacy of study. — The samples from shallow areas sur- 

 rounding the spill site appear adequate to detect any mass mortality 

 of benthic fauna. Either presence of recently dead fauna or absence 

 of fauna from assemblages could have been identified. I consider 

 the time spent separating and identifying infauna worthwhile 

 because it assured that all individuals were examined for visible ab- 

 normalities and gave information on the fauna at risk and on the 

 probable physical environment at the site. 



Emphasis on immediate mortality rather than long-term 

 biological "imbalances" seems justified in this area. Since the fauna 

 is controlled by substrate instability, it is unlikely that long-term 

 changes due to the relative sensitivity of predators or competitors 

 would be detectable. There may be some species or groups which 

 are sensitive to gasoline fractions and could be rapidly identified 

 and examined. No such animals were identified in this study, 

 however. 



It seems likely that the greatest exposure to gasoline must have 

 been on the rocks on which the barge was grounded. However, 

 logistic problems prevented sampling of the epifauna in that area, 

 so an opportunity was lost to leam about the resistance of epifauna 

 to an acute exposure to gasoline in a natural setting. It is possible 

 that in this situation motile epifauna such as amphipods may have 

 left the substrate and indicate gasoline exposure by their absence. 



Acknowledgments. — This work was supported by NOAA 

 PO 01 1-8D04-O0063 through the NMFS, Narragansett Laboratory. 

 Carolyn Griswold (NMFS, Narragansett Laboratory) coordinated 

 field collections. Andrea Knapp and Carol Price (URI) sorted, 

 identified and measured animals and seived sediments. 



3.3 Zooplankton Community Structure in the Area of 

 Ocean 250 Gasoline Spill 



This section was prepared by Jerome Preaoso''' and Carolyn 

 A. Griswold." 



"Steimle, F. W., C. J. Byrne, R. N. Reid, and T. R. Azarovitz. 1976. 

 Hydrology, sediments, benthic macrofauna and demersal ftnfish of an alternative 

 disposal site (East Hole in Block Island Sound) for the Thames River (Connecticut) 

 dredging project. Final Report. Northeast Fisheries Center Sandy Hook 

 Laboratory, NMFS, NOAA, Highlands, N.J., Informal Report 110, 61 p. 



Sampling procedure. — Paired 61 cm aluminum bongo frames 

 fitted with 0.333 and 0.505 mm mesh nets were towed in continuous 



"Northeast Fisheries Center Narragansett Laboratory, National Marine 

 Fisheries Service. NOAA, South Ferry Road, Narragansett, RI 02882. 



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