lacustris , and Mel ita spp. are known to be 

 leaf ThreddeFs [i.e., herbivores), 

 although other amphipods are predaceous, 

 feeding on hydroids, bryozoans, and 

 (possibly) zooplankton. Crustaceans such 

 as the tanaid Hargeria rapax are generally 

 omnivores, but some are shredders or 

 parasites. Mysid shrimp generally feed on 

 fine detritus and diatoms. Decapod 

 crustaceans found in the litter 

 associations are largely omnivores and 

 detritus feeders, although certain 

 dominants, such as penaeid shrimp and blue 

 crabs, are predominately carnivorous 

 during certain life stages. 



During the spring months, river flow 

 discharge decreases, salinity increases, 

 and the water clears. These conditions 

 trigger the late spring phvtoplankton 

 blooms and associated zooplankton 

 increases. The spring plankton peaks are 

 concurrent with increased relative 

 abundances of plankti vorous fishes such as 

 anchovies and menhaden. As the 

 temperature increases and river flow 

 falls, the high numbers of infaunal 

 macroinvertebrates fall precipitously. As 

 a result, by the end of spring there are 

 few spot and Atlantic croaker in the bay, 

 and the sand seatrout, feeding on 

 anchovies, becomes the dominant scianid. 

 Sheridan (1978) postulated that the summer 

 anchovy peaks are truncated bv sand 

 seatrout. There is little trophic 

 Interaction of the sand seatrout with 

 other dominant fish predators; likewise, 

 there is little dietary overlap of these 

 species during their concurrent periods in 

 the estuary (May-August). During such 

 periods, predation pressure on penaeid 

 shrimp and crabs is low. Ry fall, most of 

 the sand seatrout have moved out of the 

 estuary and anchovies become dominant. 



As temperature peaks during the 

 summer, the numbers of invertebrates 

 (penaeid shrimp, blue crabs) increase 

 (Figure 27). During this time, local 

 rainfall reaches seasonally hiqh levels. 

 Benthic macrophytes attain peak 

 productivity and standing crop. Ry the 

 end of summer, macrophytes start to die 

 off, and estuarine detritus levels 

 increase as the temperature begins to 

 decline and salinity increases throughout 

 the estuary. By early fall, the numbers 

 of species of fishes and invertebrate 



species reach high levels. One possible 

 explanation for this situation is that 

 those species limited by low salinity 

 during most of the year are able to enter 

 the shallow portions of the estuary at 

 this time. Other factors that could 

 enhance the observed high numbers of 

 species during the fall could be falling 

 temperatures (to optimal levels) and the 

 availability of detritus and/or 

 detriti vorous invertebrates as food. 



An overwhelming majority of the 

 estuarine nekton is omnivorous at some 

 life-history stage, and detritus forms an 

 important component of stomach contents at 

 any given time (Sheridan 1978; Sheridan 

 and Livingston 1979; Livingston 1982b). 

 Of the seven dominant macroinvertebrates, 

 representing over 90% of the trawl- 

 susceptible catch, five ( Peaneus 

 setiferus , Palaemonetes pugio , Callinect es 

 sapid us, Penaeus azte cus and Loll iguncula 

 brevisT are omnivore/carni vore types; 

 Ner i ti na reel i vata is an herbivore, and 

 Lolliguncula brevis is a zooplankti vore. 

 While the nutritional importance of the 

 detritus remains in doubt, omnivory 

 appears to be an important characteristic 

 of the predominant feeding patterns at 

 intermediate levels of the estuarine food 

 webs. 



Top predators, feeding largely on 

 decapod crustaceans and fishes during the 

 fall, include spotted seatrout ( Cynoscion 

 nebulosu s), flatfishes ( Paral ichthys 

 spp. ), adult silver perch ~ T"Bairdiel1a" 

 chrysoura ), searobins ( PrionotTTs spp. ), 

 and various shark types. 



During November, as the temperature 

 drops rapidly, epibenthic organisms 

 decrease and various migratory species 

 leave the estuary for nearshore gulf 

 waters as part of their annual migration. 

 Penaeid shrimp are an example of this type 

 of population behavior. River flow starts 

 to increase during the early winter, and 

 salinity goes down. Benthic infaunal 

 species richness and abundance increase as 

 winter progresses (Figure 27). 



The seasonal succession of habitat 

 change, energy distribution, soecies- 

 specific recruitment patterns, predator- 

 prey relationships, and the resulting food 

 web configurations contribute to the 



87 



