Reference: Biol. Bull. 168: 147-160. (February, 1985) THE EFFECTS OF FACTORS IMPORTANT IN SEMI-ARID ENVIRONMENTS ON THE EARLY DEVELOPMENT OF UCA SUBCYLINDRICA 1 NANCY N. RABALAIS 2 AND JAMES N. CAMERON The University of Texas at Austin, Port Aransas Marine Laboratory. Port Aransas. Texas 78373 ABSTRACT Lack of food and salinity extremes are conditions encountered by the early life stages of Uca subcylindrica in their semi-arid habitats, where nursery areas are tem-porary rainfall puddles. Several characteristics of the larvae and early postlarvae pro-mote high survivorship in these extreme environments. When starved, yolk reserves in the two zoeal stages lasted through metamorphosis to the megalopal stage and allowed >50% survival for 1 1 days after that. Food was required by the megalopae, however, before molt to crab I occurred. Larvae and early postlarvae survived and developed in a wide range of salinities under laboratory conditions 0.08 to ~50%o. The ability to hyperosmotically regulate the blood was present at hatch. Tolerance to higher salinities increased with successive stages as the ability to hypo-osmotically regulate improved. The early stages of other fiddler crab species are unlikely to survive and develop in the conditions experienced by the zoeae, megalopae, and early crabs of U. subcylindrica in their unusual habitats. INTRODUCTION Early development of Uca subcylindrica is unique among the Ocypodidae in that larval development is completed with only two brief, maturationally advanced zoeal stages. Metamorphosis occurs within 2 to 3 days of hatch, producing morphologically and behaviorally advanced megalopae. First crabs may appear within 4.5 days of hatch but average 8 days. This abbreviated development is critical since the early stages develop in temporary rainfall puddles which last only a few days (Rabalais and Cameron, 1983). Besides a restricted time for development, the early stages of U. subcylindrica also face salinity extremes due to high evaporation and sporadic heavy rainfall in their semi-arid habitats. Larval and early postlarval stages have been collected in the field from water ranging from fresh up to 65%o salinity (Rabalais, 1983). Finally, suitable food is limited in these temporary puddles. The effects of salinity and nutrition have been studied in the early life stages of several decapod crustaceans but seldom in species with abbreviated development. Rabalais and Gore (1985) compared closely related species with different developmental sequences and found that those with abbreviated development benefited from higher survival rates than those with more prolonged planktonic existence. Most authors point to degrees of lecithotrophism as the overriding advantage of abbreviated de-velopment. Several characteristics, including stored food reserves, appear to be im-Received 29 March 1984; accepted 19 November 1984. ' University of Texas Marine Science Institute Contribution Number 650. 2 Present address: Louisiana Universities Marine Consortium, Star Route Box 541, Chauvin, Louisiana 70344. 147
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