| Field and laboratory studies were carried out to define the roles of Thalia democratica Forskal and Dolioletta gegenbauri Uljanin in neritic ecosystems. Methods are described for collecting and culturing live thaliaceans. Laboratory studies with offspring from net-collected zooids are reported. Salps and doliolids were maintained, at 20(DEGREES)C, for up to three weeks, with daily mortality rates of less than 15%. Fecundity and growth investigations show that doliolids have greater asexual reproduction capabilities than do salps and that both salps and doliolids have similar, substantial growth rates (k = 0.15 x 24h('-1)) at low food concentrations ( 500 zooids x m('-3)) of D. gegenbauri was conducted to determine why they are persistent each year only between February and May. Swarms seem to occur in response to high primary productivity along mid-shelf temperature and salinity fronts in the Georgia Bight. Swarms are a result of asexual reproduction and are not due to advective import of a concentrated population into coastal waters. Doliolids have a significant impact on particulate food of less than 60 (mu)m equivalent spherical diameter and are associated with lower than normal concentrations of other zooplankton. When mid-shelf waters are warmed in the summer, temperature fronts move further offshore, and intrusions occur along the bottom. Thus, there is little primary production in mid-shelf surface waters and no doliolid swarms. Laboratory clearance rates indicate that swarm populations clear their resident water volume in about 24 h. |
