## LSU Historical Dissertations and Theses

1998

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Thomas B. Lawson

Kelly A. Rusch

#### Abstract

Computer-control, recirculation, and fluidized-bed technologies were utilized in the integration of a land-based seed clam nursery system with an algae production system to improve northern quahog seed production (6-10 mm). The components of the integrated system included: a seawater treatment system; an algae production system; a seed clam nursery system; and a computer-control system. Treatment of the incoming seawater for the integrated system included filtration (20, 1, and 0.5 micron), chlorination, UV sterilization, and ozonation. During the summer months a chiller was used to maintain the treated seawater at approximately $\rm 20\sp\circ C.$ The diatom, Chaetoceros muelleri, was cultured in an algae production system which consisted of two 550 L tanks, covered with clear lexan to prevent the entrance of airborne contaminants. An air pump aerated and mixed the cultures and $\rm CO\sb2$ was injected into the airline to maintain pH. The biomass of the algal cultures was estimated using a HACH 1720C turbidimeter. Cultures were harvested when the estimated biomass concentration was greater than the control program set point. Harvest volume was set at 90% tank volume (450 L). After harvesting, the tanks were refilled with the treated seawater and resupplied with nutrients. The harvested algae was the food source for the land-based nursery seed clam system. The nursery system consists of six clear cylindrical upweller units (5 cm diameter, 76 cm in height); a 400 L feed reservoir, a solids separator, a bead filter $\rm (0.03\ m\sp3)$ and a chiller. A high water flow velocity was maintained in the upweller units to fluidize the seed mass. Fluidizing the seed mass allows for the high density culture of seed by providing a more uniform distribution of food, and transporting waste material away from the seed mass. Individual upweller units obtained a biomass density of approximately 5.5 g whole wet weight clam per $\rm cm\sp2$ and greatest growth rates were observed when provided an effective daily algal ration of approximately 2% g dry weight algae per g whole wet weight clam.

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