236 Gordon A. Riley 



achieves great dominance only in waters that are sufficiently brackish to exclude the 

 more efficient oceanic forms. 



The estimate of zooplankion respiration is based on Conover's work, and the 

 phytoplankton respiratory rate is a compilation of field and laboratory data by 

 Riley, Stommel, and Bumpus (1949). When these items are subtracted from the total 

 estimated respiration in the water column, the remainder, representing 0-46 g of 

 organic matter consumed per day, is ascribed in Table II to bacteria and the fraction 

 of small zooplankton that is not captured by the Number 10 net. While both of these 

 elements of the population appear to be important, it is apparent that the method of 

 calculation allows a wide margin of possible error in the estimate. 



Consumption on the bottom in Long Island Sound appears to be about the same 

 as Harvey's total, although collections of benthic invertebrates in the Sound (Sanders, 

 in preparation) are larger. Later work in the English Channel by Holme (1953) 

 tends to reduce Harvey's estimate, so there is little doubt that the Sound has a larger 

 total biomass. The number of animals is enormous, and the mean size of the 

 individual is small compared with the English Channel. 



Wheatland (1955) has demonstrated that the Sound is an important spawning 

 and nursery ground for several species of fish. Little work has been done on adult 

 fishes, but the commercial catch is small, and Wheatland's examination of catch 

 statistics indicated that the catch per unit effort is smaller than in the adjacent Block 

 Island Sound. 



In short, the high basic production in Long Island Sound is utilized by great numbers 

 of small animals. Conversion to high-level food chain carnivores appears to be 

 relatively inefficient. 



GENERAL DISCUSSION OF FOOD CHAIN EFFICIENCY 

 Block Island Sound has a net production (excess of photosynthesis over respiration 

 of the phytoplankton) estimated by Riley (1952 b) at 285 grams of carbon per square 

 metre of sea surface in a year, as compared with 205 grams in Long Island Sound. 

 However, a considerable fraction of phytoplankton appeared to be lost by horizontal 

 dispersal into the outer coastal region and the amount utilized in situ by the biological 

 association was estimated to be only 150 grams. The annual fish production in Block 

 Island Sound is about 50 to 100 lb. per acre wet weight (estimated from data in 

 Merriman and Warfel, 1947). In terms of carbon content, this amounts to between 

 0-4 and 0-8% of the net phytoplankton production. From Table II it may be seen 

 that Harvey's estimate of the combined pelagic and demersal fish production in the 

 English Channel is 0-52 to 0-65 % of the phytoplankton production. Hence both areas 

 have about the same level of efficiency in food chain conversion, although Block 

 Island Sound is more productive in the absolute sense. 



Phytoplankton production on Georges Bank also nets about 150 grams of carbon 

 per year (Riley, 1944). Commercial fish catches have ranged from 7 to 33 lb. per 

 acre, according to Clarke (1946). Total production is probably more than twice 

 the landings of table fish, so that the efficiency level is not very different from the 

 figures listed for Block Island Sound and the English Channel. 



A very different situation is found in such areas as the Sargasso Sea. Here the level 

 of net production is uncertain, recent estimates var>ing from 30 g carbon per m^ per 

 year (Steemann Nielsen, 1952) to 1 10 g (Riley, 1953). According to Riley, Stommel 



