LIFE-HISTORY CHARACTERISTICS OF THE FLORIDA LANCELET, BRANCHIOSTOMA-FLORIDAE - SOME FACTORS AFFECTING POPULATION-DYNAMICS IN TAMPA-BAY

The influence of biotic and abiotic factors on population dynamics was studied for Branchiostoma floridae in Tampa Bay, Florida, USA. As lan celets grow from 4 mm (newly settled) to 58 mm (maximum size), their n umbers decline steadily. A conspicuous cause of mortality of large lan celets is predation by stingrays. During the late spring and summer re productive period, individual females probably spawn repeatedly at wee kly to fortnightly intervals. The number of oocytes shed per spawning female increases geometrically with body size. For example, females of 23 mm and 50 mm typically spawn about 500 and 11,000 oocytes, respect ively. Settled juvenile and adult lancelets survive temperatures from 3 to 37 degrees C and salinities down to 6 parts per thousand; however , early developmental stages are less tolerant. Small lancelets are un common very close to shore where water temperature and salinity will f luctuate widely. Also, in comparison to the sand plain nearby, the sub strate beneath seagrass beds contained relatively few small lancelets, evidently because many of them are eaten by predators (chiefly small crustaceans) associated with the seagrass.