3. Trophic Structure of Invertebrate Coitimunities . 



The trophic structure o£ the major terrestrial and aquatic marsh 

 communities is presented in Figures 13 to 18. Data from large en- 

 closure and aquatic sweep net collections have been omitted because 

 these collections include both submerged terrestrial and aquatic 

 species. An analysis of the trophic structure of such assemblages 

 would be misleading, since they do not represent communities as such. 



The major feature of these figures is the predominance of de- 

 tritivores and scavengers in most of the communities. Oligochaetes, 

 amphipods (Corophium) , and Acarina were the principal detritivores 

 of the soil communities; Acarina were the most abundant detriti- 

 vores in low vegetation, high vegetation, and debris line communities. 

 Herbivore populations (mostly homopterans) were abundant in the high 

 vegetation especially in high marshes, where their densities exceeded 

 those of the detritivores. Scavengers were numerous in the soil marsh 

 (ceratopogonid and chironomid larvae) , in the low vegetation of the 

 low marsh (isopods, amphipods, limnebiid beetles), and in the debris 

 line (amphipods, limnebiids) . 



Carnivores generally comprised a small fraction of the animal 

 life in soil and low vegetation habitats. However, dolichopodid 

 (Diptera) larvae were abundant in high marsh soils, and also occurred 

 in low marsh soils. The carnivore populations of low vegetation were 

 composed primarily of Araneae and staphylinid beetles. High vegetation 

 carnivores tended to be more numerous, and included several types of 

 dipterous adults (Dolichopodidae, Ceratopogonidae and Muscidae) and 

 Araneae. The debris line carnivores were A.raneae and Saldidae (Hemip- 

 tera) which occurred in moderate abundance. 



The trophic structure of infaunal communities of the tidal creeks 

 and tidal flats was heavily weighted to the detritivorous components (Figs. 

 17 and 18). In all creek and tidal flat communities, oligochaetes 

 and capitellid polychaetes were among the dominant detritivores. 

 Other detritivores were Haplosaoloplos (Polychaeta) and Corophium 

 (Amphipoda) . Common carnivores were the Polychaete Eteone and a 

 small cnidarian polyp. Although algae covered much of the sedge 

 creek and tidal flat substrate surface at the time of sampling, 

 macrofaunal herbivores were rare. 



4. Composition of Fish Communities. 



Of 26 species of fish captured in seine and trawls, 2 species 

 (staghorn sculpin, Leptooottus avmatus, and the threespine stickle- 

 back, Gasterosteus aouleatus) dominated the catches in both high and 

 low marshes (Table 4). The two species were common in creeks, pans, 

 and submerged vegetation at the marsh edge, as well as in nonmarsh 

 habitats. However, staghorn sculpin were not captured in low marsh 

 pans. Threespine stickleback captured in marsh habitats were juveniles 



32 



