Table 4. — Average deniiilieii/in- (x), coefTicienlii of variation (CV), and rrequencies of occurrence (f) of 

 s|H'. Ii". iiimmonly found in muddy, deep-water sediments in Long Island Sound, 1972-7.1. 



Means for entire samples, including rarer species. 



finer-sediment assemblage. Mean species richness, 

 diversity, and equitability were almost identical be- 

 tween the two samplings. Mean faunal density did show 

 a large drop in 1973; however, the high 1972 mean den- 

 sity had been due mostly to a large population of a small 

 bivalve. Gemma gemma, at a single station (37). If this 

 population is excluded from the calculations, faunal den- 

 sity is actually greater in 1973 (x = 3,703 vs. 3,041 indi- 

 viduals/m-). Major changes in densities of individual 

 species included decreases in Ensis and Spisula and in- 

 creases in Tellina and the polychaete Spiophanes bom- 

 byx. 



A third faunal group (Table 6), occurring at 21 sta- 

 tions (Fig. 40) with faunal similarity >41%, was transi- 

 tional between the extremes of shallow sandy and deep 

 muddy habitats. This group contained Ensis directus, 

 Tellina agilis, Ampharete arctica, Ampelisca vadorum, 

 and Unciota irrorata from the sand assemblage. Also 

 common were Folydora ligni. Pherusa af finis, and Ampe- 

 lisca abdita from the mud group, and the ubiquitous 

 Nassarius trivittatus and Oxyurostylis smithi. The over- 

 lap between the three assemblages indicates that distri- 

 butions of LIS macrofauna represent a faunal continuum 

 rather than discrete, well-defined communities. 



Populations in transitional sediments underwent 

 faunal decline between 1972 and 1973 (Table 6) which 

 was nearly as .severe as that seen in the mud assemblage. 

 Mean number of individuals dropped from 14,037 to 

 2,362/m'^; much of the decrease was due to a large reduc- 



tion in densities of four polychaetes, Polydora, Ampha- 

 rete, Streblospio benedicti, and Tharyx acutus, and to a 

 lesser extent the bivalves Ensis and Tellina. -Mean 

 number of species was also substantially reduced, falling 

 from 34.3 to 23.8 per sample. Diversity and equitability 

 increased due to the lowered polychaete dominance. 

 Only one species, the amphipod Ampelisca abdita, 

 showed a major population increase. 



While the "population crash" between 1972 and 1973 

 has also been reported elsewhere for portions of LIS (Mc- 

 Call, 1977; Rhoads and Michael'), no obvious causes of 

 the decline have been uncovered. Rhoads and Michael 

 theorized that a major erosion event in the spring of 1973 

 may have led to widespread recruitment failure. We are 

 continuing to explore possible causes of the decline, and 

 longer term fluctuations in the mud-bottom assem- 

 blage. Frequency, severity, and causes of these fluctua- 

 tions in the benthic macrofauna must be better under- 

 stood if the fauna are to be of value in environmental 

 monitoring and impact assessment. Moreover, future 

 management of resource finfish and crustaceans re- 

 quires a thorough understanding of changes in benthic 

 populations which serve as forage for these species. 



'Rhoads. D. C. and A. Michael. 1974. Sumraar.' of benthic bio- 

 logic sampling in central Long Lsland Sound and New Haven Harbor 

 prior to dredging and dumping. .July 1972-August 1973. Unpubl. manu- 

 scr.. 15 p. Report to U.S. Corps of Engineers, by Yale University. 



