TROPHIC PATTERNS AMONG LARVAE OF FIVE SPECIES OF 

 SCULPINS (FAMILY: COTTIDAE) IN A MAINE ESTUARY 



Joanne Lyczkowski Laroche 1 



ABSTRACT 



The food habits and trophic relationships of larvae of five species of marine cottids — Myoxocephalus 

 aenaeus, M. octodecemspinosus, M. scorpius, Triglops murrayi, and Hemitripterns americanus — 

 were examined and compared during winter and early spring when they cooccur at peak abundance 

 in the Damariscotta River estuary, Maine. Overall feeding incidence was high with <14% of the 

 larvae in any species having empty guts. Larvae of all five species began to feed before yolk absorp- 

 tion was complete. 



Among the five species, M. aenaeus and M. octodecemspinosus were most similar in mouth size, 

 prey size, and dominant prey— adult Microsetella norvegica in January and February (winter) and 

 Balanus nauplii in March (early spring). Mouth size, prey size, and dominant prey in early spring 

 (Bal aim* nauplii) of Myoxocephalus scorpius were similar to the other species of Myoxocephalus, but 

 the most frequently ingested prey in winter was the centric diatom, Coscinodiscus sp. Triglops 

 murrayi larvae had relatively larger mouths and ingested somewhat larger prey than similar-sized 

 Myoxocephalus larvae, feeding primarily on adult Pseudocalanus minutus in both winter and early 

 spring. Although mouth sizes of//, americanus and T. murrayi larvae were similar, the diet of H. 

 americanus was composed almost exclusively of fish larvae, primarily other cottids. 



The high incidence of ingestion of Balanus nauplii by Myoxocephalus and T. murrayi in early 

 spring may indicate some degree of density-dependent food utilization by those larvae. Yet other 

 prey, adult Temora longicumis and epibenthicharpacticoidcopepods, appeared to be preferred over 

 other presumably more abundant zooplankton. 



Percent diet overlap was greatest among the three species of Myoxocephalus and, except between 

 M. aenaeus and M. octodecemspinosus, was lower in winter when mean plankton volume (an ap- 

 proximate measure of food supply) was low. Observed differences in vertical distribution resulting 

 in partial spatial segregation of M. aenaeus and M. octodecemspinosus larvae may reduce competi- 

 tion for food between the two species, thus allowing the consistently high degree of dietary overlap 

 between them. 



Prey size (maximum carapace width) at first feeding ranged from 100 to 375 /im among the three 

 species of Myoxocephalus and >800 /xm for H. americanus. There was no dramatic change in prey 

 types or sizes with increasing larval size. Larvae of the five species of cottids were found to most 

 closely resemble hake (genus Merluccius) in prey size relationships. 



There have been relatively few detailed descrip- 

 tions of the food habits of marine fish larvae de- 

 spite the reputed importance of starvation as a 

 primary cause of mortality in the sea (Hunter 

 1976). Our generalized concept of early feeding 

 ecology in marine fishes is based mostly on 

 highly fecund species whose larvae hatch from 

 small planktonic eggs at 2-3 mm in length with 

 undeveloped eyes and mouths( Arthur 1976; Last 

 1978a, b; Sumida and Moser 1980). Little is 

 known of trophic relations among larvae of fishes 

 such as the cottids which deposit relatively few, 

 large, demersal eggs and whose planktonic lar- 

 vae hatch at sizes ^5 mm, in a relatively ad- 

 vanced stage of development with pigmented 



'Gulf Coast Research Laboratory, East Beach Drive, Ocean 

 Springs, MS 39564. 



Manuscript accepted June 1982. 

 FISHERY BULLETIN: VOL. 80, NO. 4. 



1982. 



eyes and functional mouths (Laroche 1980). 

 Fishes with widely divergent ontogenies would 

 be expected to also have different early trophic 

 relations, whose comparisons may yield further 

 insights into processes controlling survival in the 

 sea. 



The kinds of food used in most laboratory 

 studies of foraging behavior, feeding efficien- 

 cies, and growth of fish larvae are usually organ- 

 isms which are easily cultured in quantity but 

 are not natural larval fish prey, or which are 

 known size fractions of wild plankton whose spe- 

 cies composition is only approximately known. 

 Laboratory results, based solely on unnatural 

 and/or single prey, or prey described by size 

 only, may have little relevance to the real situa- 

 tion in the sea. It is not unreasonable to suspect 

 that different kinds (and sizes) of prey may sig- 



827 



