Utilising mixotrophically cultured “designer algae” as blue mussel larval feed

The production of blue mussels is currently reliant upon supply of wild larvae, which is a limiting factor to upscaling production. A potential solution to address this limiting factor is to develop a larval hatchery; however, costs associated with microalgal cultivation to feed the larvae account for around 30% of total costs. Microalgae are classically considered to be photoautotrophic and are cultured under light, in seawater with additional nitrate and phosphate. Many microalgae can be cultured mixotrophically, or heterotrophically, on an organic carbon source which results in an enhanced cell density and altered biochemical profile. Over the course of two feeding trials this study compares larval growth and survival employing current “industry standard” and mixotrophic “designer” microalgal feeds as diets. The “designer” feed employed proved to be as effective as the standard feed and subsequent optimisation demonstrated that a diet tailored towards the development of the larvae performs the most effectively in terms of larval growth. A sequential diet of mixotrophically cultured microalgae, where the primary component of the diet changed as the larvae increased in size, resulted in the greatest larval growth (174.35 μm) and total fatty acid content (7.20% dry weight). First-order modelling indicates that approximately ten times lower volume of mixotrophically cultivated microalgae was required to produce sufficient larval feed. Thus, mixotrophic culture has the potential to reduce the costs of microalgal cultivation and increase the profitability of a mussel larval hatchery.