II-B-13 



Smalley, A.E. 1959. The growth cycle of Spartina and its relation to 



the insect populations in the marsh. Pages 96-100 i_n_ Proceedings of the 

 salt marsh conference, Sapelo Island, Georgia. University of Georgia, Athens, 



Spartina alterniflora Loisel is the dominant spermatophyte of the 

 marshes around Sapelo Island, Georgia, usually occurring in pure stands 

 of varying height and density. A previous study took clip samples at 

 frequent intervals throughout the year in streamside marshes (the area 

 of highest production). This study used the same technique in the rel- 

 atively low production areas of high marshes. Net production was computed 

 from the between-sample increases in the living, standing crops and changes 

 in dead standing crops (the latter providing a partial estimate of grass 

 which died in the interval between samples). The estimate of the average 

 annual net production of the entire marsh was 973 grams dry matter per 

 square meter or 4248 kilogram calories/m^ based on estimates of production 

 of each marsh type in proportion to the area occupied by each as determined 

 from aerial photos. 



The pattern of Spartina distribution revealed by standing crop meas- 

 urements suggests that the organisms that depend on the grass as a 

 nutrient source fall into two categories. The first are those that feed 

 on the living, growing grass. The second are those that utilize the 

 grass after it has died, whether it remains in the marsh or is washed out 

 into the surrounding waters. The latter group must consist largely of 

 microorganisms. The decomposed and fragmented grass forms part of the 

 detritus of the marsh-estuarine complex and in this form may enter the 

 marsh again when the marsh is flooded by the surrounding waters. 



Observations and collections on the marsh show that the most important 

 herbivores feeding on living Spartina are two species of insects. One 

 is a grasshopper, Orchelimum fidicinium Rehn and Hebard (Orthoptera: 

 Tettigoniidae) , occurring from May to September; the other, a leafhopper, 

 Prokelesia marginata Van Duzee (Homoptera: Fulgoridae), which occurs 

 the year round, but is most common in winter. These two major herbivores 

 were found to assimilate only 7 percent of the annual net production of 

 grass. In comparison, the "utilization efficiency" of herbivores was 

 shown to be 38 percent in a spring community and as high as 81 percent 

 in a marine zooplankton-phytoplankton system in the English Channel. 

 It is suggested that a tidal marsh is similar to a forest in its trophic 

 structure at the herbivore level, since in either case immediate consumption 

 of the primary photosynthetic product is of less importance than its 

 subsequent utilization and decomposition by detritus feeders and microor- 

 ganisms. Discussion appears following presentation of the paper. (G.S.) 



Keywords: Spartina , salt marsh, primary production, Georgia 



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