Growth and Survival of Cultured Ribbed Mussel (Geukensia demissa) Larvae and Juveniles Fed Two Microalgal Diets

The ribbed mussel (Geukensia demissa) is a bivalve species that plays a critical role in US East Coast salt marsh ecosystems. Although ribbed mussels are in high demand for numerous ecological engineering applications, aquaculture techniques for this species are understudied and underdeveloped. The purpose of this study was to improve ribbed mussel aquaculture protocols by comparing two microalgal diets to rear larvae and juveniles. Because ribbed mussels are capable of feeding on picoplankton (0.2–2 µm), it was hypothesized that Nannochloropsis oceanica (NANNO), a relatively small green microalga with high lipid content, would be a beneficial supplement to a standard bivalve diet of Tisochrysis lutea (TISO) by improving survival and growth. Two feeding experiments were conducted to evaluate the performance of ribbed mussel larvae and juveniles fed a diet of 100% TISO or a diet consisting of N. oceanica and T. lutea in a 2:1 ratio (NANNO/TISO mix) by biomass. Diet did not significantly influence the survival of larval ribbed mussels, but did influence larval growth, with larvae fed the NANNO/ TISO mix treatment growing significantly slower. Larvae fed the TISO diet exhibited a normal distribution of final shell lengths, whereas those fed the NANNO/TISO mix diet exhibited a bimodal distribution with a noticeable overlap between its left-skewed peak and the unimodal distribution of the TISO-fed larvae. In contrast to the larval experiment, juveniles fed the NANNO/TISO mixed diet demonstrated statistically higher survival than juveniles that were fed solely TISO, yet diet did not have a significant influence on juvenile growth. Unlike the larval experiment, juveniles fed the two diet treatments exhibited broadly overlapping final shell length distributions. The difference in performance between larvae and juveniles suggests ontogenetic differences in feeding behavior and/or nutritional requirements. This study also suggests that incorporating N. oceanica into the diets of juvenile ribbed mussel aquaculture can benefit seed production.