LAROCHE: TROPHIC PATTERNS AMONO LARVAE OF SCULPINS (COTTIDAE) 



Table 4. — Summary of the food habits of 31 Myoxocephalus octoiiecemsfjinoxus 

 larvae captured on 22 January and 6 February 1973. %FO = percent frequency 

 of occurrence (FO) among larvae containing food; %7V = percent of the total num- 

 ber (JV) of food items ingested by larvae in that size group. 



both M. aenaeus and M. octodecemspinosus was 

 Microsetella norvegica, while Coscinodiscus sp. 

 dominated the diet of Myoxocephalus scorpius 

 larvae. Coscinodiscus sp. cells are bright green 

 in color and the digestive tracts of M. scorpius 

 larvae observed in the field before preservation 

 appeared to be this same color. Unlike similar- 

 sized M. octodecemspinosus and M. scorpius, 

 Triglops murrayi larvae fed primarily on adult 

 Pseudocalanus mi nut us and calanoid copepod- 

 ites. which were largely digested but most re- 

 sembled, and probably were, immature Pseudo- 

 calanus. There appeared to be no distinct change 

 in dominant prey types as larvae grew within the 

 size ranges examined. The largest M. octodecem- 

 spinosus and M. scorpius larvae ingested more 

 kinds of prey than smaller larvae, but the reverse 

 was true for T. murrayi. 



In March, the overwhelmingly dominant prey 

 of all three species of Myoxocephalus were Ba- 

 lanus nauplii. Microsetella ranked second in 

 importance among 7.5-9.5 (9.4) mm SL Myoxo- 

 cephalus aenaeus and M. octodecemspinosus lar- 

 vae, but was replaced by adult Temora longi- 

 comis in 9.5-12.4 mm SL M. octodecemspinosus. 

 No other prey of M. scorpius larvae at any size 

 approached the importance of Balanus nauplii 

 which were nearly the exclusive prey of this spe- 

 cies in March. Mean number of nauplii per M. 

 scorpius larva ranged from 12 to 16 depending 

 on larval size, whereas the range in mean num- 

 ber for the other two species of Myoxocephalus 

 was only 3-8 nauplii/larva. As in January and 



February, Pseudocalanus dominated the diet of 

 T. murrayi larvae in four of six size groups. 

 Balanus nauplii ranked second in importance in 

 four size groups, and ranked first in the largest 

 size group. Other fish larvae, primarily M. aenae- 

 us, were nearly the exclusive prey of all H. amer- 

 icanus larvae examined. Up to four prey larvae 

 were found in the gut of a single H. americanus 

 larva, and a 13 mm SL rockgunnel, Pholis gun- 

 nellus, larva was found coiled up inside the gut of 

 a 13 mm SL specimen. There was no dramatic 

 change in prey types ingested among the five 

 species with increasing larval size. Only the 

 change in the second-ranked prey of M. octo- 

 decemspinosus larvae from Microsetella to 

 Temora may have been related to increased size. 

 The most important seasonal change in diet 

 among cottid larvae was replacement of Coscino- 

 discus sp. and, to a lesser extent, Microsetella by 

 Balanus nauplii. Barnacle nauplii also became a 

 relatively important component of the diet of T. 

 murrayi larvae in March but Pseudocalanus 

 continued to dominate the diet of larvae in most 

 size groups. 



Diet Overlap 



Diet overlap was measured among larvae of 

 four species of cottids (H. americanus excluded 

 because of its obviously unique diet), using the 

 Schoener index (1970) which describes the rela- 

 tive amount of dietary overlap between species 

 pairs on a scale of = no overlap to 100 = com- 



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