NOTES 



LABORATORY STUDIES OF 



THE PATTERN OF REPRODUCTION OF 



THE ISOPOD CRUSTACEAN IDOTEA BALTICA 



The isopod Idotea baltica is a cosmopolitan species 

 that can be an important component of fishes' diets 

 in the field (summarized in Sywula 1964 and Strong 

 and Daborn 1979). Tinturier-Hamelin (1963) reported 

 that /. baltica extends along all European coasts, 

 from Finland to Gibraltar, including Great Britain; 

 it is present in the Baltic, the Mediterranean, and 

 the Black and Caspian Seas. In North America it 

 is present from Nova Scotia to North Carolina. In 

 addition, Sywula (1964) reported that it is also found 

 in South America, Bermuda and Barbados, the Red 

 Sea, Australia, New Zealand, and Java. 



Investigators who have observed I. baltica in the 

 field have reported the species' association with the 

 dominant plants of the community. Interestingly, 

 the type of associated plant varies with geographic 

 locality. In Nova Scotia it is found on Ascophyllum 

 nodosum (Strong 1978), in the Baltic on Fucus vesi- 

 culosus (Salemaa 1979), in Poland on Zostera 

 (Mobius 1873, as reported in Sywula 1964), and on 

 Ulva lactuca in Jamaica Bay, NY (present study). 

 Generally, the animals' principal food is the plant 

 on which they are found, and this species is often 

 the principal primary consumer of its community 

 (Strong and Daborn 1979), occupying a critical link 

 in local fish food chains. 



The present study was undertaken to provide in- 

 formation about /. baltica' s reproductive behavior 

 and physiology under laboratory conditions in order 

 to determine the feasibility of developing it as a fish 

 food for mariculture systems. 



Materials and Methods 



All animals were collected in July and August 

 1985, by removing attached Ulva lactuca thalli from 

 the fouling community attached to submerged piers 

 at the Barrens Island Marina, Jamaica Bay. The ani- 

 mals were sorted from these collections in the labor- 

 atory, and placed in individual 22.5 cm diameter 

 glass culture dishes of ambient seawater (29 ppt) 

 either in heterosexual pairs (30 pairs), or in isosexual 

 pairs (20 male and 20 female isosexual pairs). The 

 pairs were maintained at room temperature (x - 

 24.3 ± 2°C SD), with a light cycle of 15:9 L:D. They 



were fed Viva lactuca thalli ad libitum. These pairs 

 were observed 2 times a day, 12 hours apart, in the 

 light, and maintained until one of the members of 

 the pair died. Observations consisted of noting the 

 occurrence of molts and ovulations, as well as any 

 reproductive behaviors exhibited. 



Intermolt periods were calculated by counting the 

 number of days between the first and second molts 

 only of animals maintained in heterosexual pairs. 

 This was done to minimize any artifacts of culture 

 conditions. 



In addition to the pairs, 60 females were isolated 

 in individual 10 cm diameter culture dishes. These 

 females were used to determine the variability in 

 timing of molts, ovulations, and expression of repro- 

 ductive behavior. Females were observed at 12-h 

 intervals, and the dates and times of their molts 

 noted. Males were introduced either on the day the 

 females molted, on day 1 or day 2 after the molts, 

 or no males were introduced at all (12, 19, 13, and 

 16 different females observed, respectively). The oc- 

 currence and timing of copulations, ovulations, and 

 subsequent brood developments were noted for all 

 four groups of females. 



Finally, to determine the timing of copulation with 

 respect to the sequence of the shedding of the two 

 parts (see following section) of the female's exo- 

 skeleton, males were introduced to five females 

 between the first and second partial molts and the 

 males' responses noted. 



Results 



Molts 



Intermolt />eWo</5,— Individuals of both sexes 

 molted repeatedly until they died. Some females 

 molted four times in succession. The average inter- 

 molt period of the females was 13.4 ± 0.8 SD days 

 (n = 17, range = 12-15 days); for the males it was 

 13.0 ± 4.4 days (n = 15, range = 7.5-23.0 days). 

 There was no significant difference between the 

 sexes (Student's ^test; t = 0.24, df = 30, P > 0.05). 



Nature of the molts.— The exoskeleta of both sexes 

 were cast off the same way. First the posterior half 

 of the exoskeleton (from the fifth segment back) was 

 shed, then the remaining anterior portion was cast 

 off. The anterior part included the first four pairs 



FISHERY BULLETIN: VOL. 85. NO. 2, 1987. 



377 



