BIGFORD: EFFECT OF DIETS ON SPIDER CRAB LARVAE 



juveniles, diet ABD (replicates I and II) often re- 

 sulted in the largest measurements. 



DISCUSSION 



Survival 



Based on survival, laboratory diets that in- 

 cluded Artemia salina nauplii were better than 

 diets consisting solely of rotifers, algae, ciliates, or 

 copepod nauplii. However, when offered in combi- 

 nation with brine shrimp nauplii, rotifers and 

 copepods may provide some nutritional value to 

 the larvae. Survival percentages to zoeal stage II 

 were very high with diet ABDE: diet ABD pro- 

 duced the best survival to the first stage juvenile. 

 Johns and Lang (1977; unpubl. data), using an 

 excess diet of A. salina and a compartmented box 

 culture system, got 20% survival to first stage 

 crab. 



The success oi Artemia nauplii as a laboratory 

 diet is well documented (e.g.. Brick 1974; Sulkin et 

 al. 1976). Studies by Brick ( 1974) also showed that 

 survival ofScylla serrata to megalopae increased 

 as the concentration of Artemia nauplii was in- 

 creased. Results showed a 25% survival to 

 megalopae at concentrations of 5 nauplii/ml and 

 44% at 16 nauplii/ml. 



Differences in survival on various diets is com- 

 monly observed in laboratory studies. Diets that 

 permit partial development, e.g., diet BD in this 

 study, normally yield correspondingly lower sur- 

 vival. This trend has also been observed in diet 

 studies on larvae of the sand shrimp, Crangon 

 septemspinosa (Bigford^). 



Division of molt times into three subsets during 

 zoeal development infers thatL. emarginata may 

 prefer certain food types or sizes at different 

 stages. Diets including Artemta also consisted of 

 the largest size food particles, with copepods, roti- 

 fers, ciliates, and algae being smaller. This possi- 

 ble discriminate particle selection was not ob- 

 served in megalopae; all diets were consumed 

 equally and development times were similar. All 

 larvae surviving to first stage crabs were reared on 

 Artemia, alone or in combination, during stage II 

 and megalopae. 



The lack of development observed in diets D, 

 EED, and S, plus the partial development in BD, is 

 supported by the literature. Studies by Sulkin 

 (1975) have shown that algae and ciliates do not 

 satisfy the nutritional requirements of 

 brachyuran zoeae. Broad (1957) concluded that 

 various algal diets were similar to starved con- 

 trols, with the addition of animal matter required 

 for metamorphosis in grass shrimp, PaZaemone^es, 

 larvae. Particle size and biochemical composition, 

 among other factors, may limit development and 

 survival. Conversely, rotifers have been found to 

 enhance survival and development of several 

 other decapod larvae, most notably the blue crab, 

 Callinectes sapidus (Sulkin and Epifanio 1975). 

 Food size appears to be the controlling factor in 

 selection of the rotifer as food for early stage zoeae 

 of the blue crab. 



Although ABDE was a successful diet in the 

 zoeal stages, it did not sustain metamorphosis to 

 the crab stage in this study. Perhaps at differing 

 concentrations of Artemia and Eurytemora the 

 diet would prove more successful for megalopae. 



Development Times 



The diets resulting in the shortest development 

 times closely parallel those yielding the highest 

 survival percentages. These diets all include Ar- 

 temia nauplii (Tables 3, 4). 



For the molt from zoeal stage I to stage II the 

 shortest development times were recorded for 

 diets ABDE and A2, which also are the diets yield- 

 ing maximum survival to stage II. These same 

 diets continue to rate high in terms of survival and 

 molt time for the second molt also. 



^Bigford, T. E. 1975, The effects of diet on larval development 

 of the early stages of the sand shrimp Crangon septemspinosa 

 Say. Unpubl. manuscr. U.S. Environmental I^search Lab., Nar- 

 ragansett, R.I. 



Carapace Measurements 



There does not appear to be a significant differ- 

 ence in carapace size between the diets studied. 

 Instead, the effects of diets were manifested in 

 terms of development rate. Larvae apparently 

 molt upon reaching a certain biomass, with the 

 postmolt sizes similar in most cases. 



Carapace length measurements for second stage 

 zoeae and megalopae (Table 5) for diets Aj and Ag 

 compare favorably with the values reported by 

 Johns and Lang (1977) in their description of the 

 larvae reared on excess concentrations of Artemia. 

 Their mean measurements of 0.94 mm and 1.21 

 mm, respectively, were only slightly below the 

 values reported here. Differences in measuring 



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