Asexual reproduction of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

Abstract

The goal of this research is to enhance our knowledge of the contributions of doliolids to the planktonic community as consumers and secondary producers. The objectives are to quantify asexual reproduction and carbon release rates of Dolioletta gegenbauri phorozooids at four food concentrations and four temperatures in order to determine their impact as producers throughout the water column. Although doliolids are abundant in numerous regions of the coastal ocean, and are considered to be major planktonic grazers, data on rates of asexual reproduction are scarce. Laboratory experiments were conducted at 20°C at food concentrations of 7, 20, 60 and 160 μg C l-1 of Thalassiosira weissflogii and Rhodomonas sp., and at 60 μg C l-1 at 16.5, 20, 23.5 and 26.5°C, to quantify the phorozooid release rates of gonozooids, and the amount of carbon released. Results from these experiments suggest that release rates increased at 20°C as concentration increases from 7 to 16o μg C l-1. Release rates remained similar as the temperature increased from 16.5 to 26.5°C at a phytoplankton concentration of 60 μg C l-1. Food concentration and temperature has an effect on phorozooid reproductive longevity, size of gonozooids released, and the amount of carbon released asexually. Doliolid reproduction rates are a function of environmental food concentrations and temperatures, and the results imply that doliolids can be important secondary producers in the neritic environment.