WEINSTEIN SHALLOW MARSH HABITATS AS PRIMARY NURSERIES 



recorded from low salinity sites with the exception 

 of the two very small, unidentified species from 

 Walden Creek in August (salinity 18.3"/(iu). Also 

 absent from low salinity rotenone collections were 

 S. aquDnufi. E. (.-rossotug, and P. clentatiis; on the 

 other hand, the southern flounder, P. lethostigma , 

 was common at low salinity stations and was the 

 14th most abundant species at Barnards Creek, 

 composing 1.2'7f of the total captured. A winter 

 visitor to the estuary, striped cusk-eel, Rissula 

 niarginata , was present in Baldhead Creek 

 rotenone collections; a total of 1.5 specimens were 

 captured during February-April, and a single 

 specimen was also captured at the seine site. At 

 least three estuarine species with a previously 

 reported preference for higher salinities were col- 

 lected in larger numbers at Baldhead Island sta- 

 tions, the Atlantic silverside (Johnson 1975). 

 striped killifish (Griffith 1974), and blackcheek 

 tonguefish, Symphurus plagiusa (Gunter 1945; 

 Reid 1954), which also was taken in substantial 

 numbers in Dutchman Creek. 



The affiliation of Dutchman Creek presents an 

 interesting case among marshes. Recent construc- 

 tion activities nearby have effectively reduced the 

 input of freshwater to this orginally brackish 

 water creek (Birkhead"). Thus, apparently in the 

 process of change, Dutchman Creek retains both 

 original similarities to Walden Creek, and "new- 

 er" associations with higher salinity marshes 

 (e.g., for the Atlantic silverside and white mullet). 



DISCUSSION 



Tidal Creeks as Nurseries 



Due partly to sampling difficulties, the nursery 

 role of tidal salt marshes, especially the shallow 

 upper reaches of tidal creeks, has seldom been 

 investigated (Herke 1971; Copeland and Bechtel 

 1974; Cain and Dean 1976). Nevertheless, it is this 

 very habitat that has been defined by Purvis (see 

 footnote 2) and others (Kilby 1955; Herke 1971; 

 Dahlberg 1972) as one of the primary nursery 

 zones where initial postlarval development takes 

 place. Populations of marine-spawned species in 

 the areas Purvis studied in Pamlico Sound, N.C., 

 (low salinity, shallow tributaries with mud or 

 mud-grass bottoms) were uniformly of very early 



'W, Birkhead. Associate, Cape Fear Estuarine Laboratory, 

 North Carolina State University, Southport, N.C., pers. com- 

 mun, Apnl 1978. 



juveniles. In the past, several investigators have 

 pointed to the relationship between the size of 

 organisms in an area and salinity as an indicator 

 of the primary nursery grounds (Gunter 1945, 

 1961, 1967; Herke 1971; Dahlberg 1972; Copeland 

 and Bechtel 1974). Others, however, have noted 

 that the size-salinity relationship is not a simple 

 one, and that interactions with food supplies, sub- 

 stratum characteristics, and other physicochemi- 

 cal factors dictate preferred zones for nursery 

 utilization (Kilby 1955; Reid 1957; Simmons 1957; 

 Dawson 1958; Reid and Hoese 1958; McHugh 

 1967; Parker 1971). 



Results of my study demonstrate that shallow 

 tidal creeks and marsh shoals of the Cape Fear 

 River estuary harbor dense populations of post- 

 larvae of several marine-spawned species. Field 

 observations showed that young fishes and shell- 

 fish were actively seeking the creek headwaters, 

 that in effect, the marshes fill up backwards dur- 

 ing recruitment. Postlarval spot, Mugil spp., 

 Paralichthys spp., red drum, and other species ac- 

 cumulated in great numbers in the upper reaches 

 of the creeks and gi'adually decreased in densities 

 downstream. Ichthyoplankton tows in the mouths 

 and a short distance upstream in these same 

 creeks yielded much lower concentrations of post- 

 larvae than collections closer to the headwaters 

 (Hodson see footnote 6). Although the gear de- 

 ployed in these surveys differed, recent studies of 

 gear efficiency indicated that the methods are 

 reasonably similar ( Weinstein and Davis in prep. ). 

 The period of residency in these habitats is appar- 

 ently lengthy; winter recruits of several species 

 were abundant throughout the summer (Figure 

 3); and a mass exodus did not seem to take place 

 until the following fall. Other studies have shown, 

 however, that larger members of the population 

 tend to move downstream as they grow, leaving 

 behind slower growing individuals and newer re- 

 cruits (Herke 1971; Dunham 1972; Purvis see 

 footnote 2). 



Parallel conclusions on the comparative rich- 

 ness of shallow marsh habitats were reached by 

 Marshall (1976). Employing similar sampling 

 techniques, including the use of 1 mm mesh 

 seines, he reported densities of spot, Mugil spp., 

 Atlantic menhaden, and brown shrimp in two 

 marsh areas altered by ditching for mosquito con- 

 trol to exceed 0.1/m-. Standing crops of most 

 species in the natural creeks and ditches he 

 studied were among the highest ever reported for 

 small estuarine nekton. A survev of the literature 



351 



