Feeding growth and reproduction rates of the doliolid dolioletta gegenbauri uljanin (tunicata, thaliacea)
Gibson, Deidre Michelle
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The objectives were to quantify feeding and growth of Dolioletta gegenbauri gonozooids and reproduction rates of Dolioletta gegenbauri phorozooids at 4 food concentrations, 3 food sizes, and 4 temperatures in order to determine their impact as grazers throughout the water column. Laboratory experiments were conducted at 16.5, 20, 23.5, and 26.5ºC quantifying removal of a 50:50 volumetric concentration of Thalassiosira weissflogii and Rhodomonas sp. at four different food concentrations of 7 20, 60, 160, and 390 µg C · l -1. Gonozooid clearance rates are similar at concentrations from 20 to 60 µg C · l -1, and decrease as the food concentrations increase to 160, and 390 µg C · l –1. The ingestion rates increase over a range of phytoplankton concentrations from 20 to 160 µg C · l -1, then decrease when abnormally high concentrations of 390 µg C · l -1 are offered. Clearance and ingestion rates increase as temperature increases from 16.5 to 26.5º C. The exponential growth rates range from k = 0.2 - 0.7 with the lowest rates occurring at the highest food concentration. Growth rates increase with increasing temperature from K = 0.1-0.3/day at 16.5º C to 0.45-0.7 at 26.5º C. Phorozooid release rates increased at 20 oC as concentration increases from 7 to 160 µg C/l. Release rates remained similar as the temperature increased from 16.5 to 26.5 oC at a phytoplankton concentration of 60 µg C/l. Food concentration and temperature has an affect on phorozooid reproductive longevity, size of gonozooids released, and the amount of carbon released asexually. As Dolioletta gegenbauri gonozooids increased from 3.5 to 5.5 mm, their ability to ingest R. alata increased. Small and medium sized gonozooids can ingest large and small cells at similar rates at all concentrations, while at highest concentration of R. alata the larger gonozooid's clearance rates on the large diatom, reduced the grazing pressure on smaller cells. Doliolid feeding, growth and reproduction rates are a function of environmental food size and concentrations and temperatures, and imply that they can be important consumers in a changing neritic environment.