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Aquacu l tu ra l Eng ineer ing 2 (1983) 27-47

La r g e - sc a le Mic r o a lg a e P r o d u c t io n fo r Nu r se r y R e a r in go f M a r in e B iv a lv e s

Niels D e Pau w* , Jan Verboven t and Christine Claus**Laboratory for Mariculture, State University of Ghent, J. Plateaustraat 22,B-9000 Ghent, Belgiumtlnstitute for Marine Scientific Research (IZWO), Prinses Elisabettdaan 69,B-8401 Bredene, Belgium

A B S T R A C TThe f eas ib i l i t y o f l arge -sca le b lo om induc t ion o f nu t r i t i ona l l y su i t ed na tura lph y to p la nk ton spec ie s , t o f e e d a semi - indus t ria l nur se ry o f ed ib le she ll -f i sh , bu i l t on the Belg ian coas t , was tes ted .T h e o u t d o o r m i c ro a lg a l p r o d u c t i o n u n i t c o n s i s te d o f f o u r t a n k s o f1 0 0 m 2 s u r fa c e e ac h ( tw o o f l m d e p t h a n d t w o o f O .5 m d e p t h ) , e q u i p p e dw i t h d i f f e r e n t m i x i n g d e v ic e s.

The cu l t u re s were run a s chemo s ta t s in wh ich s eawa te r was enr i chedwi th com me rc ia l i norgan ic N , P , and S i f e r t il i z e r s . De pend ing on t hes e as o n , b e t w e e n 5 - 1 0 a n d 8 0 % o f t h e c u l tu r e v o l u m e c o u l d b e h a r v e s t edda i ly , w i th a lga l dens i t i e s rang ing f ro m 50 000 t o 5 00 00 0 ce l ls pe r mL

B y m a n i p u l a ti o n o f o p e r a ti o n a l p a r a m e t e r s su c h a s d e t e n t i o n t im e ,nu t r i en t l e ve l s and nu t r i en t ra t io s ( N : S i : P ), u nsu i t ed o r l e s s su i t ed spec i e sof algae (e .g. Chlorella a n d Phaeodactylum) c o u l d b e r e p l a c e d b y m o r edesirable species (e .g. Skeletonema, Nitzschia, Chaetoceros).

Various b io log i ca l and t e chno log i ca l p rob l em s enco un te red dur ing yea rrou nd opera t i on , i nc lud ing co l l apsing o f the cu l tu re , s eawa te r enr i chm en t ,w a t e r q u a li ty , f o u f n g a n d w a t e r tr e a tm e n t , a re c o m m e n t e d .

INTRODUCTIONNursery r e a r i n g of edible bivalve molluscs means the controlled cultur-ing of postlarvae (i.e. spat), from a few millimeters in length up to a few27Aquacu l tu ra l Eng ineer ing 0144-8609/83/0002-0027/$03.00 - Applied SciencePublishers Ltd, England, 1983. Printed in Great Britain

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28 N. De Pauw , J . Verb oven, C. Clausc e n t i m e t e r s ( B a y e s , 1 9 7 9 ) . T h e h i g h m o r t a l i t y w i t h i n t h i s siz e c la ss ,w h e n t r a n s f e r r e d d i r e c t l y f r o m t h e h a t c h e r y t o t h e n a t u r a l e n v i r o n -m e n t , c a n be s e r i ou s ly r e d u c e d w h e n t h e s p a t is r e a re d u n d e r c o n t r o l l e dc o n d i t i o n s ( C O S T , 1 9 7 8 ; P e r s o o n e a n d C l a us , 1 9 8 0 ; C l a u s, 1 98 1 ; C l a u se t a l . , 1 9 8 1 ) .

A m a j o r b o t t l e - n e c k i n h i g h - d e n s i t y n u r s e r y re a r in g is t h e n e e d f o rl a r g e q u a n t i t i e s o f l i v e u n i c e l l u l a r a l g a e a s f o o d f o r t h e m o l l u s c s ,b e c a u s e n o a l t e rn a t i v e i n e r t f e e d s ar e p r e s e n t l y av a il a bl e ( P e r s o o n ea n d C l a u s , 1 9 8 0 ; D e P a u w , 1 9 8 1 ) .

T h e w e l l - e st a b li s h e d , b u t e x p e n s i v e i n d o o r t e c h n i q u e s u s e d f o rm o n o s p e c i f i c a lg al p r o d u c t i o n i n h a t c h e ri e s , c a n n o t , f o r e c o n o m i cr e a s o n s , b e s c a le d u p t o t h e l ar g e v o l u m e s n e e d e d f o r f e e d i n g n u r s e r yb i v a lv e s ( D e P a u w , 1 9 8 1 ).

A s a r e s u l t, n e a r l y a ll c o m m e r c i a l e n t e r p r i s e s i n v o l v e d i n n u r s e r yr e a r i n g o f b i v a l v e m o l l u s c s u t i l i z e n a t u r a l p h y t o p l a n k t o n p r e s e n t i nt h e s e a w a t e r a s f o o d . C u l t u r i n g o f t h e p o s t l a r v a e is p e r f o r m e d e i th e ri n s i t u ( in t h e s e a) , o r in o n s h o r e c o n s t r u c t i o n s w i t h f lo w th r o u g hp u m p i n g o f s e a w a t e r ( C l a u s, 1 98 1 ; D e P a u w , 1 98 1 ) .

T h o u g h s a t i s f a c t o r y i n s o m e c a s e s , r e s u l t s a r e o f t e n i n c o n s i s t e n td u e t o f o o d s h o r ta g e o r t h e d e v e l o p m e n t o f u n d e si r a b le s p e c ie s .

T h e r e f o r e , t h e a l t e rn a t i v e f o r t h e n u r s e r y r e a r in g o f j u v e n i l e b iv a lv e sm a y b e t h e l ar g e- sc a le p r o d u c t i o n o f m i c r o a l g a e r e ly i n g o n s p e ci e s-c o n t r o ll e d i n d u c e d b l o o m in g s o f n a tu r a l p h y t o p l a n k t o n (D e P a u w ,1 9 8 1 ) .H o w e v e r , a s G o l d m a n ( 1 9 7 9 ) v e r y p r o p e r l y o b s er v e d , t h e c o n t r o la n d m a n i p u l a t i o n o f p h y t o p l a n k t o n s p e ci es i n la rg e -s ca le o u t d o o rc u l t u r e s , i s p e r h a p s t h e m a j o r u n r e s o l v e d p r o b l e m i n m a s s - c u l t u r et e c h n o l o g y .

I n o r d e r t o c o n t r i b u t e t o t h e s o l u t io n o f t h is p r o b l e m , a n d a f t e re x p e r i m e n t i n g s ev e ra l y e a r s w i t h s m a ll -s c a le (1 m 2 ) o u t d o o r c u l t u r eu n i t s ( D e P a u w a n d D e L e e n h e e r , 1 9 7 9 ; D e P a u w e t a l . , 1 9 8 0 ) ,e x p e r i e n c e i s p r e s e n t l y b e i n g g a i n e d o n t h e B e l g i a n c o a s t w i t h l a r g eo u t d o o r p r o d u c t i o n u n i ts f o r th e c o n t i n u o u s c u l tu r in g o f n a tu r a lp h y t o p l a n k t o n t o f e e d a s e m i - i n d u s tr i a l n u r s e r y ( c f. C l a us e t a l . , 1 9 8 2 ) .

I n a d d i t i o n t o a c q u i r in g a n in s i g h t i n t h e b i o lo g i c a l a n d t e c h n o l o g i c a lp r o b l e m s r e s u l t i n g f r o m t h e s c a l e - u p o f t h e s e c u l t u r e s t o t h e s e m i -i n d u s t r i a l l e v e l , o u r m a j o r o b j e c t i v e i s t o g a i n c o n t r o l o v e r t h e s p e c i e sc o m p o s i t i o n o f th e s e in d u c e d b l o o m s o f m a r in e p h y t o p l a n k t o n .

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Mieroalgae for nursery marine bivalves 29T h i s p a p e r a i m s a t re v i e w i n g t h e r e s u l ts o b t a i n e d s o f a r w i t h f o u r

o u t d o o r a lg a e t a n k s o f 1 0 0 m 2 e a c h , a f t e r o n e f u ll y e a r o f o p e r a t i o n .

M A T E R I A L S A N D M E T H O D SPlant descriptionA s c h e m e o f t h e a lg al p r o d u c t i o n p l a n t l o c a t e d a t B r e d e n e , B e l g iu m( 5 1 N ) , i s p r e s e n t e d i n F i g . 1 .

T h e p l a n t c o n s i s ts o f o n e s e a w a t e r s t o c k i n g t a n k ( 3 2 m 3 c a p a c i t y ,1 m d e p t h ) a n d f o u r r e c t a n g u la r a lg a e p r o d u c t i o n t a n k s ( 1 0 0 0 m 2s u r f a c e , t w o t a n k s o f 1 m d e p t h a n d t w o o f 0. 5 m d e p t h ) , b u i l t o na c o n c r e t e f lo o r . T h e 1 m d e e p t a n k s a re m a d e o f w o o d e n p a n e lss u p p o r t e d b y i r o n f r a m e w o r k s ; t h e 0 . 5 m d e e p t a n k s a r e m a d e o f l ar geh o l l o w c e m e n t b r i c k s, r e i n f o r c e d i n s id e w i t h i r o n b a r s f i x e d i n t h ec o n c r e t e f o u n d a t i o n . A l l t a n k s a r e w a t e r p r o o f e d w i t h a n o n - t o x i c0 .5 m m t h i c k p l a s ti c P V C l in e r, w h i c h is p r o t e c t e d a t t h e b o t t o m , b ya 1 0 c m t h i c k l a y e r o f fi n e s a n d .

T h r e e o f t h e f o u r p r o d u c t i o n t a n k s a re e q u i p p e d w i t h d i f f e re n tm i x i n g d e v i c e s i n o r d e r t o e v a l u a t e t h e m i x i n g y i e l d o f t h e s e s y s t e m s :( 1 ) a n e i g h t - b l a d e d p a d d l e - w h e e l , c o n n e c t e d t o a 1.5 k W e l e c t r i c m o t o rp r o v i d e d w i t h r e d u c t o r p e r m i t t i n g r o t a t i o n s b e t w e e n 0 a n d 2 6 r p m ;( 2 ) 2 2 a i r- li f t p u m p s o f 1 m l e n g t h a n d 5 c m i n d i a m e t e r , f i x e d a l o n gt h e s id e w a l ls o f t h e t a n k ; a n d ( 3 ) 1 1 p e r f o r a t e d ( 3 m m ) a i r - b u b b l in gt u b e s ( 3 c m i n d i a m e t e r ) f i x e d a t t h e b o t t o m . T h e a i r i s p r o v i d e d b yt w o 1-5 k W c y c l o b l o w e r s (0 -1 b a r ( 3 - 5 m a m i n - l ) ) . T h e p a d d l e - w h e e lm o t o r a s w e l l a s t h e c y c l o b l o w e r s , a r e c o n n e c t e d w i t h t i m e - s w i t ch e s , ino r d e r t o r e g u l a t e t h e m i x i n g t i m e . T h e f o u r t h t a n k h a s n o m i x i n g d e v i c e( 0 . 5 m d e p t h ) a n d s e r v e s a s a c o n t r o l .Culture procedureT h e c u l t u r e p r o c e d u r e i s r e p r e s e n t e d i n F ig . 2.

S e a w a t e r is p u m p e d u p f r o m t h e n e a r b y S l ui ce D o c k la g o o n (8 2 h a )i n t o a re s e r v o ir t o a l l o w p r e - s e d i m e n t a t i o n o f l a rg e r p a rt i c le s .

B y m e a n s o f a c o n s t a n t h e a d s y s t e m ( 3 m h ig h , 3 1- 5 c m i n d i a m e t e r ,0 - 2 3 m 3 c a p a c i t y ) , s e a w a t e r i s d i s t r i b u t e d w i t h c o n s t a n t p r e s s u re f r o m

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