The sea urchin, Lytechinus variegatus, inhabits the eastern coast of the United States, ranging through the Gulf of Mexico from NC, USA to the northern coast of Brazil. L. variegatus are one of the most widely used model systems and have been cultured for aquaculture production. The Algal Turf Scrubber (ATS) uses attached algae to efficiently remove inorganic nutrients from water, producing harvestable algal biomass. ATS biomass typically has a high ash content, which has been difficult to utilize in fish and crustacean aquaculture feeds. However, the high ash content present in many sea urchin diets allows ATS biomass to be utilized as a potential option in sustainable feed for L. variegatus. The present study was conducted to assess ATS biomass as a fishmeal and ash replacement in nutritionally complete diets. The biomass was harvested from two ATS systems, one receiving treated wastewater effluent and the other incorporated into a hydroponics system. Successful incorporation of this biomass into L. variegatus diets improves the sustainability of the feed by using a biomass grown solely on waste inorganic nutrients (i.e. nitrogen and phosphorus).
Juvenile L. variegatus were collected from Port St. Joe (29.8119° N, 85.3030° W), FL and transported to Aquaponics Research Laboratory in Savann ah, Georgia USA. The closed recirculating aquaculture system used in this study consisted of thirty-two 0.6-liter polyethylene tanks. One hundred and twenty L. variegatus were randomly distributed and initial weights and diameters were recorded. Initial average weight (g) was 23.96 and diameter (mm) was 59.94. Thirty tanks contained four individuals per tank and six dietary treatments (n=5) were assigned. Six nutritionally complete diets were formulated as follows: (I) full fish meal control, (II) te n percent Fish Meal Replacement (FMR) with Wastewater Treatment Algae (WWTP), (III) twenty percent FMR WWTP, (IV) ten percent FMR Aquaponics Algae (AP), (V) twenty percent FMR AP, and (VI) fifty percent FMR AP. L. variegatus were fed to slight excess daily. Water quality was checked for nitrate and ammonia levels once every four weeks. A one-way ANOVA was performed based on dietary treatments .
After twelve weeks there were no significant differences between final weights of the different treatments . One-hundred percent survival occurred across all individuals. Final average weight (g) was 31.92 and diameter (mm) was 67.76. We saw an average of 7.96 (g) increase across individuals during the twelve weeks.
Subsequent to receiving samples back for analysis, additional data will be presented on: final test weight (g), lantern weight (g), and proximate composition of the gonad.
Results indicate that fishmeal protein and ash can be replaced by ATS algae for both WWTP and aquaponics algae in L. variegatus diets.