World Aquacluture Magazine - September 2020

58 SEP TEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG requirements, and metamorphosis cues must be understood. Sea urchin larvae, as with other marine invertebrates, make an active decision on where to settle, guided by searching behavior (Cameron and Hinegardner 1974, Pearce and Scheibling 1991, Rahim et al. 2004). They are prompted by suitable environmental cues, including temperature, marine biofilms, macroalgae and various others (Pawlik 1992). Once metamorphosed, the ideal location with suitable food is necessary to prolong life and sustain growth (Grosjean et al . 1998). Recruitment of competent larvae is crucial in sea urchin seed production, with growth and survival relying heavily on settlement success and grazing. The objective of this study was to evaluate a local pennate diatom Nitzschia laevis , offered as a microphytobenthic biofilm, as an initial grazing substrate for cost- effective production. Purple sea urchin metamorphosis induction, growth, and post-larval survival was evaluated. Experimental Treatments Five treatments were used, each with five replicates (Fig. 2): Nitzschia laevis biofilm(NIT). Biofilms of N. laevis were grown for seven days in 100 mL of F/2 media and an initial inoculation with 50,000 cells/mL under the conditions of 15 C, a 14 h light, 10 h dark cycle, and a light intensity of approximately 100 μmol/m 2 sec. Nitzschia laevis with added antibiotic (NIT+A). Replicates were prepared in the same manner as the NIT treatment, with the addition of 4 mL of antibiotic-antimycotic solution at the start of the culture (Jauffrais et al . 2017). Before the larvae assay commenced, the F/2 media from treatments NIT and NIT+A were gently removed and replaced with 100 mL of FSW (5-μm filtered and T he purple sea urchin Paracentrotus lividus (Lamarck 1816; Fig. 1) is found in sublittoral waters of about 20 m depth among seagrass meadows and on rocky substrate (Boudouresque and Verlaque 2013). This moderately fast-growing species can reach 4 cm test diameter in about 4 to 5 years and individuals 12 years or older can measure 7 cm or more (Boudouresque and Verlaque 2013). Purple sea urchins are found in the Mediterranean Sea and northeast Atlantic Ocean and are considered a culinary delicacy throughout Europe and Asia (Boudouresque and Verlaque 2013). The marketing of purple sea urchin gonad (roe) is extremely profitable, with an estimated production of about 70,000 t per year at a market value ranging from 60 €/kg to 221 €/kg in the Japanese market (Sonu 1995, Stefansson et al . 2017). Unfortunately, this has caused the sea urchin to fall subject to overexploitation (Carboni et al . 2012). Development Purple sea urchins gather in large groups to spawn. Females release orange eggs, triggering males to release a cloud of white sperm. Newly fertilized eggs float freely for up to eight weeks and then become pluteus larvae that feed on microalgae and undergo a series of metamorphic stages from two- to eight-armed. When eight- armed competent larvae have a fully developed rudiment, they pick up cues from the surrounding environment, triggering them sink to the bottom and metamorphose. Juvenile sea urchins feed on benthic diatoms for about one year until they are fully developed and then shift to larger algae, reaching sexual maturity at 4 to 5 years old (Harrold and Reed 1985, Hinegardner 1969, Huggett et al. 2005, Kelly 2005). In sea urchin aquaculture, their life cycle, nutritional The Effects of Microphytobenthic Biofilms on Purple Sea Urchin Recruitment Janel McNab FIGURE 1. Purple sea urchin Paracentrotus lividus . FIGURE 2. Treatments with 30 purple sea urchin larvae in each replicate. From left to right: NIT, NIT + A, NBIO, BOS, NBIO and FWS.