The abundance and distribution of heterotrophic and autotrophic nanoflagellates in the NE Subarctic Pacific

• Main Author: Doherty, Sean Patrick
• Format: Thesis
• Language: English
• Published: 1995
• Subjects: Pacific; Subarctic
• Online Access: http://hdl.handle.net/2429/3555

In the NE subarctic Pacific, the marine microbial food web, specifically the heterotrophic and autotrophic nanoflagellates (HNF and ANF), and cyanobacteria and heterotrophic bacteria, is not well understood. Further, studies of these populations have almost been exclusively done at Station P (50°N, 145°W) only in the spring and summer. The abundance and distribution of the above micro-organisms was investigated along Line P (between 48°N, 126°W, and 50°N, 145°W) in May, 1993, and February and May, 1994. This is the first study to examine their horizontal distribution, and obtain winter data on their abundance and distribution in this region. HNF, ANF, cyanobacteria and heterotrophic bacteria were identified, enumerated and biomass was estimated by epifluorescence microscopy. In May 1993, ANF and HNF biomass and abundance was an order of magnitude higher at most stations, compared to 1994 cruises, and May 1993 vertical profiles averaged 5.7* 106 cells L"1 at Station P. In February and May 1994, ANF and HNF population abundance and biomass was separated into three size fractions; the 2 to 5 um size group dominated. During both May cruises, a mirdmum in abundance and biomass of HNF, ANF and cyanobacteria was observed at Stations P12 and P16, which is ascribed to water mass changes along Line P. Winter abundance and biomass estimates of ANF, HNF, cyanobacteria and heterotrophic bacteria populations were comparable to those in May 1994, indicating that predator prey relationships remain functional at this time of year. Carbon budgets of winter and late spring HNF and their prey populations indicated that prey (cyanobacteria and heterotrophic bacteria) population biomass was sufficient to support the carbon requirement of the HNF in February and May 1994. In February 1994, at station P4 the combined biomass of cyanobacteria and heterotrophic bacteria was five times the requirement of the HNF, and 1.4 times this amount at Station P, further demonstrating the maintanence of predator/prey trophodynamics during the winter. Science, Faculty of Zoology, Department of Graduate