MORGAN: ASPECTS OF LARVAL ECOLOGY OF SQUILLA EMPUSA 



Table l. — Larval abundance ofSquilla empusa with mean temperatures and salinities for each 

 subarea (Figure 1) of the lower Chesapeake Bay for August and September 1971 and 1972. 



(Table 1). Larvae were also more abundant in the 

 lower regions of the sampling area than in the 

 upper (subareas G and H). 



Squilla empusa larvae occur in the Chesapeake 

 Bay when the mean temperatures are the highest 

 of the year. The first larvae were encountered in 

 July for both 1972 and 1973 when mean tempera- 

 tures were 25.2° and 24.5° C. The larvae were most 

 abundant in August when the mean temperatures 

 were 24.9° and 24.2° C in 1971 and 1972. The mean 

 temperatures declined in September along with 

 the abundance of larvae until larvae were rarely 

 found or not found in October when temperatures 

 were 19.7° and 19.4° C in 1971 and 1972. The mean 

 salinity during the seasonal occurrence of the lar- 

 vae in 1971 and 1973 fluctuated between 21.5 and 

 23.1%o, while in 1972 it was much lower as a result 

 of Tropical Storm Agnes. In July 1972 the mean 

 salinity was 16.5%© and it increased to 21.2%o in 

 October when larvae no longer occurred in the 

 plankton. 



Temperature and Salinity Tolerance 



Although none of the 576 larvae reared at the 16 

 different temperature and salinity combinations 

 was reared through the entire pelagic develop- 

 ment to metamorphosis, larvae survived well and 

 molted frequently at 2 of the test combinations. At 

 20° C-25%0 and 25° C-25%o, A19c of the larvae 

 molted three or more times, 24*7^ underwent at 

 least five ecdyses, and 3% molted seven times over 

 a 6-wk period. Metamorphosis to postlarva oc- 

 curred 34 times and was not a problem in the 

 rearing process. 



In general, larvae fared best at higher tempera- 

 tures and salinities (20°, 25° C, 25, 35%o) and 

 were least successful at the lower temperatures 

 and salinities (10°, 15° C, 10, 15%o). Excluding lar- 



vae reared at 10° C, the longest survival and 

 greatest number of molts occurred at salinities of 

 25%o followed by 35, 15, and 10%o in order of de- 

 creasing length of survival and number of molts 

 (Figures 5, 6). Length of survival at 25°, 20°, and 

 15° C was similar but at 25° and 20° C the mean 

 number of molts was much higher. At 10° C larvae 



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 TEMPERATURE (°C) 



Figure 5. — Average survival, in days, for all larval stages of 

 Squilla empusa, grouped by 16 temperature-salinity combina- 

 tions according to salinity. 



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