ASPECTS OF LARVAL ECOLOGY OF SQUILLA EMPUSA 

 (CRUSTACEA, STOMATOPODA) IN CHESAPEAKE BAY 



Steven G. Morgan' 



ABSTRACT 



Larvae ofSquilla empusa were collected from the plankton and were laboratory-reared in 16 combina- 

 tions of temperature and salinity to determine their tolerances. Larvae survived longer and molted 

 more frequently when reared at 25%o and 20° or 25° C, which corresponds to the natural conditions of 

 Chesapeake Bay when the larvae were collected. 



A 2-yr planktonic survey conducted in the lower region of the bay by the Virginia Institute of Marine 

 Sciences was compared with a survey made at the bay mouth in 1976. The seasonal occurrence of 

 Squilla empusa larvae extended from the last week of July until the first week of October with a peak 

 abundance occurring about the first week of September The peak abundance in the lower region of the 

 bay was 0.37 larva/m^ in 1971 and 0.59 larva/m^ in 1972. Four of the nine stages were not captured. 

 Collections taken at the bay mouth in 1976 with a % m net captured all stages and the peak abundance 

 was determined to be 0.27 larva/m^. The larvae were more abundant in the higher salinity waters of the 

 channel areas and eastern portion of lower Chesapeake Bay. A large-mouth plankton net with rela- 

 tively coarse mesh should be towed at night to ensure the collection of all larval stages since the larger 

 larvae are apparently able to avoid small nets. 



The Order Stomatopoda is a small group of primi- 

 tive, specialized crustaceans which reside primar- 

 ily in shallow tropical marine waters. Of the 350 

 species (Caldwell and Dingle 1976) only a few ex- 

 tend into temperate waters, Squilla empusa 

 among them. This mantis shrimp, which attains a 

 length of 20 cm, is found from Massachusetts to 

 northern South America and is quite abundant 

 throughout its range, including Chesapeake Bay 

 (Brooks 1878; Cowles 1930; Wass 1972). 



Stomatopod larvae are often found in great 

 swarms, particularly in tropical waters where 

 adults are most abundant. The planktonic larval 

 stages compose a substantial portion of the neritic 

 plankton and constitute a considerable part of the 

 diet of reef fishes, jacks, scads, herrings, snappers, 

 and commercially important pelagic fishes such as 

 tunas and mackerel (Sunier 1917; Fish 1925; 

 Reintjes and King 1953; Randall 1967; Dragovich 

 1970). 



Squilla empusa larvae are large crustacean lar- 

 vae, attaining 17.5 mm long. The larvae undergo 

 nine pelagic stages before settling to the bottom as 

 postlarvae (Morgan and Provenzano 1979). Brooks 

 (1878) found stomatopod larvae he assumed were 



'Institute of Oceanography, Old Dominion University, Norfolk, 

 Va.; present address: Duke University Marine Laboratory, Pivers 

 Island, Beaufort, NC 28516. 



those of S. empusa present in Chesapeake Bay 

 from early July to the middle of August in the 

 greatest abundance, but he discontinued the study 

 before the larvae had completed their metamor- 

 phosis. No other data on larvae of this species have 

 been added to the literature since. 



Due to the paucity of ecological information on 

 the larvae of this prevalent crustacean, an inves- 

 tigation was undertaken to determine their sea- 

 sonal occurrence, distribution, and abundance in 

 Chesapeake Bay. The abundance and duration of 

 the larvae as part of the plankton may be impor- 

 tant factors in the ecology of the bay, since the 

 larvae not only serve as food for a variety of or- 

 ganisms, including commercially important 

 fishes, but are also rapacious predators them- 

 selves, thriving on other members of the 

 planktonic community. 



In recent years the effects of temperature and 

 salinity on the larval development of decapod 

 crustaceans have been studied, but no studies 

 have been made on the temperature and salinity 

 tolerance for the larvae of any species within the 

 Order Stomatopoda. Temperature and salinity are 

 critical factors affecting the survival of marine 

 and estuarine organisms, especially during the 

 sensitive developmental stages upon which the 

 success of the species relies. Thus, a qualitative 

 determination of the temperature and salinity tol- 



Manuscript accepted February 1980. 

 FISHERY BULLETIN: VOL. 78, NO. 



3. 1980. 



693 



