Measuring the Effects of Recycled Water on the Growth of Three Algal Species: Tisochrysis lutea, Chaetcoeros calcitrans, and C. muelleri in a Commercial-Scale Oyster Hatchery

Abstract

Algal production is often the limiting factor in large-scale oyster hatcheries, and constant, reliable production is required to grow enough algae to support all oyster larvae and broodstock grown and conditioned in a hatchery. The algal rooms in the Michael C. Voisin Oyster Hatchery at Grand Isle, LA are temperature-controlled to maintain consistent temperature, but this hatchery is also unique in its ability to recycle natural seawater pumped from the northern Gulf of Mexico. Effects of recycling seawater on algal production in an oyster hatchery, however, are undocumented. In this study, Tisochrysis lutea, Chaetoceros calcitrans and C. muelleri were grown in different water sources to determine if productivity would be affected by water source. Algae were grown in ambient filtered seawater, recycled filtered seawater, and artificial seawater for a period of 10 days. To evaluate algal production, cell concentrations were measured every other day and dry biomass and growth rate were calculated. Water chemistry (nitrate, phosphate, and silicate concentrations) was measured initially and at ten days. Dry weights and growth were significantly different between species (p=0.0475, p<0.0001), but not water sources. C. muelleri grew the greatest in biomass and the slowest growth rate , followed by C. calcitrans, and T. lutea. Nitrate and phosphates had no significant effects on growth between species, although silicate content was significantly higher in T. lutea. Overall there were no statistically significant effects for the interaction of the three water sources on the growth of these algal species over time (p=0.2882). Although there were no significant differences, algae grown in ambient bay water grew denser and greater biomass than those in recycled bay water or artificial seawater.