The effects of tank system, water velocity and water movement on survival, somatic and gonad growth of juvenile and adult green sea urchin,Strongylocentrotus droebachiensis

Abstract

AbstractThe effects of water velocity and tipping frequency(water movement) on survival, somatic and gonadgrowth of juvenile and adult green sea urchin,Strongylocentrotus droebachiensis were investigated.Juvenile and adult urchins were held in ‘laminar’or ‘tipper’ tanks. Both were supplied with threeinlet water flows (1.5, 3.0 and 7.5 L min 1 )which converted to water velocities of 0.28, 0.57and 1.43 cm s 1 in the ‘laminar’ tanks and tip-ping frequencies of 30, 10 and 5 s in the ‘tipper’tanks. Juvenile sea urchins had significantly lowermortality and greater somatic growth when heldin ‘laminar’ flow tanks compared with ‘tipper’tanks. The varying water velocities tested in the‘laminar’ flow treatment had no effect on thegrowth of juvenile sea urchins. The juvenile seaurchins in the ‘tipping’ treatment held at high tip-ping frequency had significantly slower growththan those in the medium and low tippingfrequency treatments. There were no differences inmortality or gonad growth in the adult seaurchins regardless of treatment. The ‘laminar’ flowtanks retained significantly more organic materialcompared with the ‘tipper’ tanks. The authors dis-cuss the effects of water velocity and tipping fre-quencies in system design for aquaculture of seaurchins.Keywords: Strongylocentrotus droebachiensis,‘laminar’ and ‘tipper’ systems, water velocity, tip-ping frequency, somatic and gonad growthIntroductionThe aquaculture of sea urchins can be dividedinto two forms. The first is gonad enhancement ofwild-caught adults fed prepared diets in captivityfor a short period of time (Lawrence, Olave,Otaiza, Lawrence & Bustos 1997; Kelly, Brodie M Siikavuopio, Christiansen & Dale2006; James 2007). The second is closed cycleculture which involves spawning of adult broodstock then rearing larvae and juveniles through tomarket size (Grosjean, Spirlet, Gosselin, Va€italin-gon & Jangoux 1998; Lawrence 2007; Siikavuo-pio & James 2011). Both forms require suitableholding systems (Lesser & Walker 1998) and yetthere is a paucity of research regarding systemdesigns and the key factors that should be consid-ered in such systems, particularly for growingjuvenile urchins (Pearce, Williams, Yuan, Castell& Robinson 2005; Daggett, Pearce & Robinson2006; James 2007).The few studies that have investigated sea urchinholding systems have found little differences ingonad characteristics between holding types, butsignificant differences in tank cleaning times andurchin survival (Motnikar, Marson & Tetreault1998; Daggett et al. 2006). Daggett, et al. (2006)suggested that ‘the actual movement of water ortank volume replacement time was the most impor-tant factor in urchin mortality’ in their study. Theanatomy of sea urchins makes them particularlysusceptible to the effects of water movement due tothe rudimentary nature of their circulatory and