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

ABSTRACT

The influence of biotic and abiotic factors on population dynamics was studied for Branchiostoma floridae in Tampa Bay, Florida, USA. As lancelets grow from 4 mm (newly settled) to 58 mm (maximum size), their numbers decline steadily. A conspicuous cause of mortality of large lancelets is predation by stingrays. During the late spring and summer reproductive period, individual females probably spawn repeatedly at weekly 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, respectively. Settled juvenile and adult lancelets survive temperatures from 3 to 37 °C and salinities down to 6%c; however, early developmental stages are less tolerant. Small lancelets are uncommon very close to shore where water temperature and salinity will fluctuate widely. Also, in comparison to the sand plain nearby, the substrate beneath seagrass beds contained relatively few small lancelets, evidently because many of them are eaten by predators (chiefly small crustaceans) associated with the seagrass.