February 15-18, 2009 Washington State Convention Center Seattle ...

10
LABORATORY CULTURE OF THE DIATOM Chaetoceros gracilis USING EFFLUENT FROM
AN INTENSIVE MARINE RECIRCULATING AQUACULTURE SYSTEM FOR BLACK SEA
BASS Centropristis striatus
Dustin M. Allen* and Wade O. Watanabe
University of North Carolina Wilmington
Center for Marine Science
601 S. College Rd.
Wilmington, NC 28403-5927 USA
DMA5903@uncw.edu
Concerns of effluent management, land availability and access to water resources for marine finfish production have increased
attention to recirculating aquaculture systems (RAS), which conserve water by reusing greater than 90% of its total daily water
volume, but produce an effluent that is highly concentrated. The objective of this study was to evaluate the effluent from a
marine RAS for black sea bass (BSB, Centropristis striatus) as a nutritive base for production of the marine diatom, Chaetoceros
gracilis, a valuable species that is commonly used for the culture of marine bivalves. An experiment was conducted to
evaluate growth of C. gracilis on RAS effluent in 2-L flasks under controlled laboratory conditions (26.3 ± 1.5 ◦ C and 24 L :
0 D). Four treatment media were compared: RAS effluent with silica added, RAS effluent without silica, Guillards f/2 media,
and a seawater control (32 g/L). Media was filtered, sterilized, and then inoculated with C. gracilis at 1 x 10 6 cells/mL. RAS
effluent was filtered (0.45 μm) before use in the experiment to simulate the incorporation of geotube technology in the water
renovation process. Geotubes are used in wastewater treatment to remove solids by passing the effluent through a geotextile
fabric bag containing a polymer to accelerate flocculation.
Cell density (cells/mL) in the control treatment remained near initial levels, fluctuating between 7.11 x 10 5 and 1.21 x 10 6 from
d 0 to d 9. The f/2 media produced better growth, with cell densities increasing steadily to a plateau of 3.42 x 10 6 by d 7. The
effluent without silica produced faster growth than the f/2, with cell densities reaching 4.42 x 10 6 by d 6. The effluent with
silica added produced similar growth to effluent without silica through d 6, but cell densities plateaued at a higher level of 4.98
x 10 6 by d 7. Increasing cell densities were associated with a reduction in nitrogen (N) levels in the culture media. In the effluent
plus silica treatment, mean (sd) nutrient concentrations (mg/L) of TN, NO 3 /NO 2 , PO 4 and TP declined from initial levels
of 14.1 (0.59), 7.43 (0.22), 0.47 (0.03), and 0.81 (0.08), respectively, to 8.13 (0.48), 0.13 (0.08), 0.00 (0.00) and 0.00 (0.00)
by d 8. NH 4 oscillated between 0.61 (0.15) and 1.03 (0.12). Nondetectable levels of phosphorus in the media by d 3 strongly
suggested a phosphate-based limitation to cell growth. These results showed that effluent from an intensive marine RAS for
BSB was an effective nutrient base for growth of C. gracilis under laboratory conditions. These data will be used to scale up
C. gracilis culture to larger bioreactors and to develop techniques for integrated marine finfish-microalgae-shellfish polyculture
as a means of reducing the nutrient loading associated with fish culture and of producing bivalves for habitat restoration and
mitigation projects.