Grover: Feeding habits of pelagic summer flounder larvae 
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0000 0400 0800 1200 1600 2000 
0200 0600 1000 1400 1800 2200 
Onset of time block 
Figure 3 
Gut fullness (F) of pelagic larval summer flounder P. dentatus, in the NW 
Atlantic Ocean, as a function of time of day (EST), where 0 = empty, 1 = 1— 
25%, 2 = 26-50%, 3 = 51-75%, and 4 = 76-100% full. 
24 h (Table 1) revealed that pelagic 
larvae began feeding near sunrise in 
oceanic habitats. The presence of prey 
in larval guts reached its lowest point, 
8.3%, at 0400-0559 hours, then dra- 
matically increased to 54.5% at 0600- 
0759 hours, the time block of sunrise 
for all collections. The only time dur- 
ing which incidence of feeding was 
100% was 0800-0959. Throughout 
hours of full daylight, incidence of feed- 
ing remained high, >70%. Late after- 
noon or early-evening feeding may 
have buoyed the feeding incidence at 
2000-2159, but evidence of recent 
feeding decreased sharply from 
2000-2159 to 2200-2359 hours. Dur- 
ing late night hours, the percentage 
of larvae that had prey in their guts 
gradually decreased from 22.0% at 
2200-2359 to 8.3% at 0400-0559. 
Gut fullness 
Because incidence of feeding data 
were generated from gut-fullness data (i.e. F>0), they 
provide a qualitative measure of gut fullness; how- 
ever, gut-fullness data also provide direct estimates 
of the volume of prey in the gut over the course of 24 
h (Fig. 3). Although larvae appeared to begin feeding 
at 0600-0759, full guts were not observed until 1200- 
1359. Maximum gut fullness (F=A) was only seen at 
1200-1559 and 2000-2159. The only time block dur- 
ing which all larvae contained prey in their guts was 
0800-0959. 
Diet of metamorphic (JV1EJ larvae in estuaries 
The estuarine portion of this study was based on 119 
metamorphic larvae (ME), representing metamorphic 
stages G through I (Keefe and Able, 1993) (with n - 47 
at stage G, n - 34 at stage H-, n = 35 at stage H, n=l 
at stage H+, and n = 2 at stage I, Table 1). The guts of 
15 (12.6%) ME larvae contained recognizable prey, 
and 87.4% had empty guts. At the time of examina- 
tion, larval lengths ranged from 8.1 to 14.6 mm SL. 
Pelagic feeding was clearly demonstrated by > 85% 
of ME larvae. The primary prey of pelagic ME larvae 
was the calanoid copepod Temora longicornis, regard- 
less of the method of analysis (Table 5). 
The mean number of prey found in the guts of ME 
larvae was 2.1 (SD=0.99, range=l-4). The relatively 
good condition of some prey items in the guts of fish 
collected late at night suggests that some prey were 
likely ingested after dark. 
Table 5 
Diet of metamorphic (ME) summer flounder, P. dentatus, 
larvae collected from a New Jersey estuary, in terms of 
numerical percentage composition (%N), volumetric per- 
centage composition (%Vol), percentage frequency of occur- 
rence (%FO), and percentage index of relative importance 
(IRI = (%N + %Vol)x %FO). All values are based on a sample 
size, with prey, of 15 larvae. Prey were pelagic unless oth- 
erwise indicated. 
Prey 
%N 
%Vol 
%FO 
%IRI 
Polychaete larvae 
3.1 
0.7 
6.7 
0.4 
Polychaete tentacles 
(benthic) 
3.1 
12.0 
6.7 
1.6 
Cirripede larvae 
3.1 
0.2 
6.7 
0.3 
Paracalanus parvus 
3.1 
2.0 
6.7 
0.5 
Centropages typicus 
6.3 
13.6 
6.7 
2.1 
Temora longicornis 
46.8 
55.3 
53.3 
86.2 
Acartia sp. 
3.1 
2.9 
6.7 
0.6 
Unidentified calanoids 
6.3 
3.7 
13.3 
2.1 
Harpacticoids (benthic) 
6.3 
1.5 
6.7 
0.8 
Mysids (diurnal migrants) 
9.4 
6.1 
13.3 
3.3 
Oikopleura sp. 
6.3 
1.8 
13.3 
1.7 
Unidentified prey 
remnants 
3.1 
0.2 
6.7 
0.4 
Evidence of benthic feeding was observed only in 
late-stage metamorphic larvae (H+ and I). Of two 
late-stage larvae that had prey in their guts, one 
