Vecchione: Paralarval ecology of Lolliguncula brevis 



517 



mation on the abiotic dimensions of the paralarval 

 niche. 



For the second category, I wanted to determine 

 average abundance within the water masses in which 

 paralarval L. brevis were found, rather than average 

 abundance throughout the entire geographic area. 

 Because the paralarvae are planktonic and presumably 

 stay within the water masses into which they hatch, 

 average abundance would be artificially depressed if 

 stations from other water masses (i.e., outside of the 

 small-scale paralarval range) were included in calcula- 

 tions. For instance, physical conditions were sometimes 

 very different at one or more stations because a coastal 

 front divided the stations, so that L. brevis was col- 

 lected in one group of stations but not in the other. 

 Under those circumstances, including the water filtered 

 at stations where the species was absent in the calcula- 

 tion of the number of L. brevis per m 3 of coastal water 

 that month would not be an accurate representation 

 of small-scale abundance. Descriptive statistics pre- 

 sented below are therefore based only on stations that 

 collected L. brevis. For example, mean abundance for 

 a month is the average of all samples, including nega- 

 tive ones, at all stations from which L. brevis were 

 collected, but does not include negative stations. The 

 statistical tests of hypotheses presented below were 

 likewise based on the assumption that, if all twelve 

 samples at a station failed to collect L. brevis, that sta- 

 tion was extralimital for the paralarvae. For all tests 

 of hypotheses, statistical significance was defined 

 a priori as o = 0.05. 



Fifty digestive tracts were examined. Specimens 

 were selected arbitrarily to be representative of the 

 paralarval size range. Specimens were cleared with 

 trypsin and then transferred to glycerol, allowing direct 

 examination of the intact esophagus, stomach, caecum, 

 and intestine for food remains (Vecchione In press a). 



Results 



In all, 3159 zooplankton samples were collected. Two 

 hundred seventy cephalopod paralarvae were collected 

 in 164 samples. These included two Loligo sp., one Illex 

 sp., and 267 Lolliguncula brevis. The L. brevis came 

 from 161 samples and ranged in length from 1.1 to 

 13.6mm DML. 



Coastal distribution 



Mesh comparisons Paralarval L. brevis were col- 

 lected with 505 (im mesh in 75 samples and with 333 \xm 

 mesh in 77 samples. The Wilcoxon paired-sample, 

 signed-rank test was used to compare both abundance 

 and size of paralarval L. brevis in the two mesh sizes 



OCCURRENCE 



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Lolli g uncula brevis 



Figure 2 



Seasonal distribution of paralarval Lolliguncula brevis in 

 coastal Louisiana waters. (Top) Number of positive samples 

 (out of 108 samples/month); (bottom) mean number of para- 

 larval Lolliguncula brevis collected per 100 m 3 of water 

 filtered at positive stations. The 108 samples collected per 

 month filtered ~2000m 3 . 



of the bongo samples. Neither abundance nor size of 

 the paralarvae differed significantly between mesh 

 sizes. Therefore, in the following analyses the bongo 

 samples are considered as a single data set regardless 

 of mesh size. 



Seasonal patterns Paralarval L. brevis were col- 

 lected from April through January (Fig. 2). Both the 

 highest average abundance (mean iV/lOOm 3 ) and the 

 highest frequency of occurrence (number of samples 

 that collected L. brevis) were found to occur in the 

 spring (April-June) of both years. There appeared to 

 be a slight tendency toward a bimodal seasonal distribu- 

 tion with a late-summer abundance minimum, similar 

 to what I have found in many species of ichthyoplank- 

 ton collected in these samples (unpubl. data). 



Hydrographic relationships During the months in 

 which L. brevis were collected, they were found 



