THE GROWTH CYCLE OF SPARTINA AND ITS RELATION 

 TO THE INSECT POPULATIONS IN THE MARSH ^) 



by 



Alfred E. Smalley 

 University of Georgia 



Spartina alterniflora Loisel is the dominant spermatophyte of the marshes 

 around Sapelo Island, Georgia, usually occurring in pure stands of varying 

 height and density. Clip samples were taken at frequent intervals throughout 

 the year by R, A. Ragotzkie in streamside marshes, the area of highest pro- 

 duction, and by the author in the relatively 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 pro- 

 viding 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 occu- 

 pied by each as determined from aerial photos. 



The seasonal pattern of dead grass which remains in the marsh shows 

 that the marshes of higher altitude contain large amounts of dead standing grass 

 the year around, while most of the grass growing along tidal creeks either 

 washes out while still growing or after dying in the winter and fall. Decompo- 

 sition of the grass on the high marsh takes place largely in situ; that of the 

 streamside marsh largely in the waters of the creeks and sounds. The weight 

 ratio, roots and rhizomes /living leaves, is approximately 1.0. Much of the 

 below -ground material is dead. Below -ground production is not considered 

 here. 



The pattern of Spartina distribution revealed by standing crop measure - 

 ments suggests that the organisms which depend on the grass as a nutrient 

 source fall into two categories. The first are those which feed on the living, 

 growing grass. The second are those which 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 com- 

 plex 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 consist of two species of insects. One 

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

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



1) lam indebted to E. P. Odum and J. M. Teal for help in this research, 

 which was aided by a grant from the National Science Foundation to E. P. Odum, 



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