far 



they 



Cod. 



north as Massachusetts Bay though 

 are usually seen only south of Cape 



Littorina 1 ittorea , the common 

 periwinkle, is a common marsh resident in 

 New England, but in Maryland marshes it is 

 replaced by L. irrorata (gulf periwinkle). 

 Littorina obtusata occurs near the lower 

 edge of the marsh among the rockweeds with 

 which it is commonly associated. 

 Melampus bidentatus (salt marsh snail) is 

 a pulmonate snail on the marsh. All these 

 snails feed by scraping off the surface 

 layer of algae and detritus from the 

 surface of the mud and from the lower 

 parts of the grass. The tiny snail 

 Hydrobia totteni , which feeds by digesting 

 organic matter and microbes from ingested 

 sediment (Newell 1965), may be very 

 abundant. Mud snails ( Ilyanassa 

 obsoletus ) are more typical of intertidal 

 mudflats, but they do occur in the marshes 

 as well, where they feed mostly on benthic 

 algae (Connor 1980). 



Ribbed mussels, Geukensia (= Modiolus ) 

 demissa , often live in clusters throughout 

 the marsh and serve as hard substrate for 

 other organisms such as barnacles and 



■n 



Figure 13. Male fiddler crab (Uca pugnax ) 

 on salt marsh. This crab has been 

 cornered by the plastic pipe. The male's 

 large claw is used for defending its 

 territory and signaling females. The 

 small claw is used in feeding. Photo by 

 J.M. Teal, Woods Hole Oceanographic 

 Institution. 



hydroids. Barnacles may also sometimes be 

 found on the bases of Spartina growing at 

 the lowest elevations. Amphipods and 

 isopods are common on the mud surface 

 between the grass stems and are especially 

 abundant under any accumulations of wrack. 

 Several kinds of small shrimps, including 

 the sand shrimp ( Crangon septemspinosus ) 

 and the grass shrimp ( Palaemonetes pugio ) , 

 are often very abundant. They can be seen 

 drifting up even the smallest marsh creeks 

 as the tide rises. 



Although the above organisms are all 

 epi fauna, many more organisms are found 

 among the infauna in this same environ- 

 ment. The marsh infauna includes a 

 variety of polychaetes, ol igochaetes , 

 insects (especially as larvae), and 

 crustaceans, but little is known about 

 most of these. As one moves south of New 

 England, other species join or replace the 

 marsh fauna. Among these are the marsh 

 clam ( Polymesoda carol iniana ) , the wharf 

 crab ( Sesarma cinereum ) , the brown shrimp 

 ( Penaeus aztecus ) , arid the white shrimp 

 (P. setiferus ) , all of which use the 

 shallow waters of the marshes and 

 estuaries. Other species, such as the 

 blue crab, become more abundant south of 

 New England; the blue crab can support an 

 intense fishery in the marsh creeks along 

 the southern Atlantic coast. 



Macrobenthic organisms play a number 

 of important roles in the functioning of 

 the salt marsh. They churn up the surface 

 layers of the sediment in their search for 

 food and in their burrowing. Katz (1980) 

 found that the burrowing of Uca pugnax at 

 a density of 42 animals/m 2 turned over 18% 

 of the upper 15 cm of sediment per year. 

 Their burrows increased the surface area 

 of the marsh by 59%. Cammen et al. (1980) 

 showed that the epifaunal fiddler crabs 

 and marsh periwinkles in a North Carolina 

 marsh consumed an amount of organic matter 

 equivalent to about one-third of the net 

 production of S. al ternif lora and benthic 

 algae. 



The infauna may have an even more 

 significant impact on the marsh than do 

 the epifauna. A population of the 

 polychaete worm Nereis succinea "ingested 

 four times as much sediment and detritus" 

 as the fiddler crabs and snails (Cammen 

 1979). All these animals grind up the 



22 



