infauna may be greater inside of marine grass beds 

 because the grass itself provides a qualitatively 

 different and new habitat which permits the add- 

 ition of new infaunal species that are dependent 

 in some way on the presence of the seagrass. The 

 third hypothesis suggested to explain why infaunal 

 densities are higher in vegetated areas can be called 

 the predation hypothesis. Predators may be less 

 effective in grass beds because the rhizome and 

 root mats of the grasses may inhibit their foraging 

 and thus provide a refuge from predation for 

 many infauna. 



Although each of these three explanations 

 may contribute somewhat to the pattern of lower 

 infaunal density in imvegetated sediments, most 

 authors seem to think that the predation hypoth- 

 esis is the single most important (Heck and Wet- 

 stone 1977, Orth 1977, Reise 1977a). In North 

 Carolina, experimental removal of shoalgrass 

 {Halodule) resulted in 100% mortality of all size 

 classes of the hard clam {Mercenaria mercenaria) 

 on intertidal flats that also contained whelks 

 {Busycon spp.) (C. H. Peterson, unpub. data). 

 Reise (1977a, b, 1978) built cages on intertidal 

 flats in the North Sea to exclude predators. Some 

 cages were constructed on unvegetated flats, while 

 others were located in adjacent grass beds. Caging 

 and the resultant exclusion of large predators had 

 no effect on the infauna of the grass bed, whereas 

 infaunal densities outside of the vegetated area 

 increased by 4 to 20 fold. This result, too, suggests 

 that large predators control the abundance of in- 

 fauna on unvegetated intertidal flats, but not in 

 vegetated areas, where infaunal densities are ac- 

 cordingly far greater. Young et al. (1976) per- 

 formed a similar set of caging experiments in grass 

 beds in the Indian River estuary of Florida, where 

 they, too, found that infaunal densities did not 

 consistently increase following the exclusion of 

 predators from the vegetated bottom. 



While the results of these experiments seem to 

 indicate that large mobile predators, such as are 

 excluded by building a cage over the bottom sedi- 

 ments, often control the densities of infauna on 

 intertidal flats, the experiments done in North 

 Carolina have produced ambiguous results. 

 Commito (1976) demonstrated a higher density 

 of benthic infauna inside cages on a mud flat in 

 the Newport River estuary. However, this higher 

 abundance (three times the infaunal density on 

 the uncaged flat) only existed during the March- 



April season of heavy infaunal recruitment. By 

 summertime, density of the infauna had declined 

 inside the predator-exclusion cages as well as out- 

 side where predators had continuous access. 

 Commito's results suggest that large mobile preda- 

 tors may not be very significant in controlling 

 densities on North Carolina mud flats. However, 

 these experiments did not test the impact of the 

 major sediment processors, the funnel feeders, 

 which are probably of great significance. 



Other caging experiments done on intertidal 

 and shallow subtidal sand flats in Bogue and Back 

 Sounds in North Carolina (H. Stuart, North Caro- 

 lina State Univ., Raleigh, unpub. data; H. C. Sum- 

 merson, Univ. North Carolina, Chapel Hill, un- 

 pub. data) provide strong support for the conten- 

 tion that larger predators are important in con- 

 trolling infaunal abundances on unvegetated flats 

 in North Carolina. Since Woodin (1978, in pre- 

 paration), working farther north on intertidal 

 muddy sand flats off Assateague Island, x\Id., has 

 convincingly shown that larger predators do help 

 to control infaunal abundances in that environ- 

 ment, it is reasonable to expect that larger mobile 

 predators in combination with large-scale sedi- 

 ment processors may be important determinants 

 of infaunal densities on North Carolina flats also. 



Because the intauna of North Carolina's soft 

 sediments are controlled by predation and biolo- 

 gical disturbance in general, the vast majority of 

 infaunal species tend to be small, short-lived 

 opportunistic species. Polychaetcs in the families 

 Spionidae, Capitellidae, and Nereidae, and ampeli- 

 scid and corophiid amphipods tend to dominate 

 the fauna of intertidal flats. In the face of heavy 

 predation pressure, the evolution of short-lived 

 ojiportunists would be expected because these are 

 the species which can live long enough to reach 

 reproductive maturity, reproduce, and thereby 

 persist. 



As a consequence of these high rates of pre- 

 dation, which are most intense in the warmer 

 summer months, the abundance ot infauna on 

 intertidal flats in North Carolina shows a dis- 

 tinct pattern of seasonal change. Densities are 

 high in spring, which is the peak period of repro- 

 ductive activity for the North Carolina infauna 

 (Commito 1976). Infaunal abundance declines 

 steadily through the summer and shows a second 

 lower peak of abundance in the fall when preda- 



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