CHAPTER 4: THE FISHES 



4.1 TROPHIC ROLES 



Because tidal clianges would leave them 

 stranded during a portion of each day, few fishes 

 are permanent residents of intertidal flats. Only in 

 areas where relatively large burrows are common 

 in the intertidal sediments or where tide pools are 

 present can one find fishes which reside in the 

 intertidal zone. In the intertidal sand flats of 

 southern California lagoons, the ghost shrimp {Cal- 

 lianassa californiensis) can be extremely abundant. 

 Its burrows extend up to 1 m beneath the sediment 

 surface and remain filled with seawater even at 

 low tide. Consequently, fishes (like the arrow 

 goby, Clevlandia ios) survive this period by living 

 inside the burrows. Other fishes, such as various 

 blennies and gobies, are common tide pool resi- 

 dents along coasts with rocky shorelines. In North 

 Carolina, gobies, blennies, and cling fish occur as 

 permanent residents of the intertidal zone, but 

 they are usually found in association with hard 

 substrates and are not abundant on intertidal sand 

 and mud flats. 



.Although those fishes which are permanent 

 residents of intertidal flats are not important in 

 North Carolina's estuaries, the unvegetated inter- 

 tidal zone of sounds, lagoons, river mouths, and 

 estuaries is an important environment for many 

 coastal and marine fishes. Intertidal flats are im- 

 portant to these fishes in two major ways. First, 

 numerous fishes live and feed on intertidal flats 

 during high tide at some stage in their life cycles. 

 Second, many other fishes are, at least in part, 

 trophically dependent upon prey which have lived 

 and foraged on intertidal sand and mud flats. 

 Table 2 presents a list of those fishes which are 

 direct utilizers of North Carolina's intertidal flats. 

 In Table 3 appears a list of those fishes in North 

 Carolina which depend indirectly upon intertidal 

 flats because a substantial proportion of their 

 prey feed there. Distinctions necessary to con- 

 struct these tables required several rather arbitrary 

 decisions, but an attempt has been made to 

 include all of the major species in either Table 2 

 or 3. Rare and occasional species have been speci- 

 fically excluded. Although Tables 2 and 3 include 

 several species, this does not imply that intertidal 

 flats are a critical habitat for all of them. As a 

 general rule, the fishes and shorebirds have 

 complementary distributions in estuarine systems, 



with fishes foraging mostly in subtidal habitats 

 and shorebirds in the intertidal zone. Because 

 fishes have access to subtidal habitats, the elimi- 

 nation of intertidal flats would probably cause 

 few fish extinctions in North Carolina, but it 

 would result in drastic declines both in the popu- 

 lations of several fishes and in the total fish pro- 

 duction of estuarine systems. 



The fishes which forage on intertidal flats and 

 th(jse partially dependent upon prey that feed on 

 intertidal flats can be subdivided into four broad 

 trophic types: (1) planktivores, (2) detritivores, 

 (3) predators on benthic infauna, epifauna and 

 small mobile epibenthos, and (4) predators on 

 fish and larger mobile epibcnthic species. These 

 categories are artificial in that species in the same 

 category do not share exactly the same diet and 

 in that several species take prey in multiple cate- 

 gories. For instance, planktivores will often ingest 

 suspended detritus. Likewise, detritivores will 

 often consume small benthic animals as well as 

 detritus when they ingest bottom sediments. 

 Furthermore, as will be described later in detail, 

 virtually all fishes undergo major changes in their 

 food habits as they grow, moving from one trophic 

 category to another with age. 



4.2 PLANKTIVORES AND DETRITIVORES 



Of several common marine fishes in North 

 Carolina that are partially dependent upon the 

 production of intertidal flats, perhaps the most 

 abundant are planktivores, including the ancho- 

 vies [Anchoa spp.), menhaden [Brevoortia tyran- 

 nus), and other clupeids (such as Opisthonema 

 oglinuni). Menhaden filter the water column and 

 consume mainly phytoplankton. Because they 

 feed so low on the food chain, it is not surprising 

 that menhaden are extremely abundant and form 

 a higher percentage of the total poundage of 

 commercial fish landings in North Carolina than 

 any other single species. Although juvenile men- 

 haden grow up in rivers and sounds, they often 

 are found directly over intertidal flats. Production 

 of their food, phytoplankton, is greatly en- 

 hanced by the increased euphotic zone avail- 

 able over intertidal flats at high tide (see Chap- 

 ter 2). Two species of anchovies (Anchoa hep- 

 setus and A. mitchilli) are also common plank- 

 tivores found over tidal flats at high tide. Both 

 feed largely on zooplankton, although they also 



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